SUDO_PLUGIN(5) File Formats Manual SUDO_PLUGIN(5)
NAME
sudo_plugin — Sudo Plugin API
DESCRIPTION
Starting with version 1.8, sudo supports a plugin API for policy and
session logging. Plugins may be compiled as dynamic shared objects
(the default on systems that support them) or compiled statically into
the sudo binary itself. By default, the sudoers plugin provides audit,
security policy and I/O logging capabilities. Via the plugin API, sudo
can be configured to use alternate plugins provided by third parties.
The plugins to be used are specified in the sudo.conf(5) file.
The API is versioned with a major and minor number. The minor version
number is incremented when additions are made. The major number is in-
cremented when incompatible changes are made. A plugin should be check
the version passed to it and make sure that the major version matches.
The plugin API is defined by the <sudo_plugin.h> header file.
Policy plugin API
A policy plugin must declare and populate a struct policy_plugin in the
global scope. This structure contains pointers to the functions that
implement the sudo policy checks. The name of the symbol should be
specified in sudo.conf(5) along with a path to the plugin so that sudo
can load it.
struct policy_plugin {
#define SUDO_POLICY_PLUGIN 1
unsigned int type; /* always SUDO_POLICY_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], char * const user_env[],
char * const plugin_options[], const char **errstr);
void (*close)(int exit_status, int error);
int (*show_version)(int verbose);
int (*check_policy)(int argc, char * const argv[],
char *env_add[], char **command_info[],
char **argv_out[], char **user_env_out[], const char **errstr);
int (*list)(int argc, char * const argv[], int verbose,
const char *user, const char **errstr);
int (*validate)(const char **errstr);
void (*invalidate)(int rmcred);
int (*init_session)(struct passwd *pwd, char **user_env[],
const char **errstr);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
struct sudo_plugin_event * (*event_alloc)(void);
};
A struct policy_plugin has the following fields:
type The type field should always be set to SUDO_POLICY_PLUGIN.
version
The version field should be set to SUDO_API_VERSION.
This allows sudo to determine the API version the plugin was
built against.
open
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], char * const user_env[],
char * const plugin_options[], const char **errstr);
Returns 1 on success, 0 on failure, -1 if a general error oc-
curred, or -2 if there was a usage error. In the latter case,
sudo will print a usage message before it exits. If an error oc-
curs, the plugin may optionally call the conversation() or
sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
The function arguments are as follows:
version
The version passed in by sudo allows the plugin to deter-
mine the major and minor version number of the plugin API
supported by sudo.
conversation
A pointer to the conversation() function that can be used
by the plugin to interact with the user (see “Conversation
API” for details). Returns 0 on success and -1 on failure.
sudo_plugin_printf
A pointer to a printf()-style function that may be used to
display informational or error messages (see “Conversation
API” for details). Returns the number of characters
printed on success and -1 on failure.
settings
A vector of user-supplied sudo settings in the form of
“name=value” strings. The vector is terminated by a NULL
pointer. These settings correspond to options the user
specified when running sudo. As such, they will only be
present when the corresponding option has been specified on
the command line.
When parsing settings, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
The following values may be set by sudo:
bsdauth_type=string
Authentication type, if specified by the -a option,
to use on systems where BSD authentication is sup-
ported.
closefrom=number
If specified, the user has requested via the -C op-
tion that sudo close all files descriptors with a
value of number or higher. The plugin may optionally
pass this, or another value, back in the command_info
list.
cmnd_chroot=string
The root directory (see chroot(2)) to run the command
in, as specified by the user via the -R option. The
plugin may ignore or restrict the user's ability to
specify a new root directory. Only available start-
ing with API version 1.16.
cmnd_cwd=string
The working directory to run the command in, as spec-
ified by the user via the -D option. The plugin may
ignore or restrict the user's ability to specify a
new working directory. Only available starting with
API version 1.16.
debug_flags=string
A debug file path name followed by a space and a
comma-separated list of debug flags that correspond
to the plugin's Debug entry in sudo.conf(5), if there
is one. The flags are passed to the plugin exactly
as they appear in sudo.conf(5). The syntax used by
sudo and the sudoers plugin is subsystem@priority but
a plugin is free to use a different format so long as
it does not include a comma (‘,’). Prior to sudo
1.8.12, there was no way to specify plugin-specific
debug_flags so the value was always the same as that
used by the sudo front-end and did not include a path
name, only the flags themselves. As of version 1.7
of the plugin interface, sudo will only pass
debug_flags if sudo.conf(5) contains a plugin-spe-
cific Debug entry.
ignore_ticket=bool
Set to true if the user specified the -k option along
with a command, indicating that the user wishes to
ignore any cached authentication credentials.
implied_shell to true. This allows sudo with no ar-
guments to be used similarly to su(1). If the plugin
does not to support this usage, it may return a value
of -2 from the check_policy() function, which will
cause sudo to print a usage message and exit.
implied_shell=bool
If the user does not specify a program on the command
line, sudo will pass the plugin the path to the
user's shell and set implied_shell.
intercept_ptrace=bool
Indicates whether or not the system supports inter-
cept mode using ptrace(2). This is currently only
true for Linux systems that support seccomp(2) fil-
tering and the “trap” action. Other systems will use
a dynamic shared object to implement intercept. Only
available starting with API version 1.19.
intercept_setid=bool
Indicates whether or not the system supports running
set-user-ID and set-group-ID binaries in intercept
mode. This is currently only true for Linux systems
that support seccomp(2) filtering and the “trap” ac-
tion. On systems that use a dynamic shared object to
implement intercept, the dynamic linker (ld.so or the
equivalent) will disable preloading of shared objects
when executing a set-user-ID or set-group-ID binary.
This will disable intercept mode for that program and
any other programs that it executes. The policy plu-
gin may refuse to execute a set-user-ID or set-group-
ID binary in intercept mode to avoid this. Only
available starting with API version 1.19.
login_class=string
BSD login class to use when setting resource limits
and nice value, if specified by the -c option.
login_shell=bool
Set to true if the user specified the -i option, in-
dicating that the user wishes to run a login shell.
max_groups=int
The maximum number of groups a user may belong to.
This will only be present if there is a corresponding
setting in sudo.conf(5).
network_addrs=list
A space-separated list of IP network addresses and
netmasks in the form “addr/netmask”, e.g.,
“192.168.1.2/255.255.255.0”. The address and netmask
pairs may be either IPv4 or IPv6, depending on what
the operating system supports. If the address con-
tains a colon (‘:’), it is an IPv6 address, else it
is IPv4.
noninteractive=bool
Set to true if the user specified the -n option, in-
dicating that sudo should operate in non-interactive
mode. The plugin may reject a command run in non-in-
teractive mode if user interaction is required.
plugin_dir=string
The default plugin directory used by the sudo front-
end. This is the default directory set at compile
time and may not correspond to the directory the run-
ning plugin was loaded from. It may be used by a
plugin to locate support files.
plugin_path=string
The path name of plugin loaded by the sudo front-end.
The path name will be a fully-qualified unless the
plugin was statically compiled into sudo.
preserve_environment=bool
Set to true if the user specified the -E option, in-
dicating that the user wishes to preserve the envi-
ronment.
preserve_groups=bool
Set to true if the user specified the -P option, in-
dicating that the user wishes to preserve the group
vector instead of setting it based on the runas user.
progname=string
The command name that sudo was run as, typically
“sudo” or “sudoedit”.
prompt=string
The prompt to use when requesting a password, if
specified via the -p option.
remote_host=string
The name of the remote host to run the command on, if
specified via the -h option. Support for running the
command on a remote host is meant to be implemented
via a helper program that is executed in place of the
user-specified command. The sudo front-end is only
capable of executing commands on the local host.
Only available starting with API version 1.4.
run_shell=bool
Set to true if the user specified the -s option, in-
dicating that the user wishes to run a shell.
runas_group=string
The group name or group-ID to run the command as, if
specified via the -g option.
runas_user=string
The user name or user-ID to run the command as, if
specified via the -u option.
selinux_role=string
SELinux role to use when executing the command, if
specified by the -r option.
selinux_type=string
SELinux type to use when executing the command, if
specified by the -t option.
set_home=bool
Set to true if the user specified the -H option. If
true, set the HOME environment variable to the target
user's home directory.
sudoedit=bool
Set to true when the -e option is specified or if in-
voked as sudoedit. The plugin shall substitute an
editor into argv in the check_policy() function or
return -2 with a usage error if the plugin does not
support sudoedit. For more information, see the
check_policy() section.
timeout=string
Command timeout specified by the user via the -T op-
tion. Not all plugins support command timeouts and
the ability of the user to set a timeout may be re-
stricted by policy. The format of the timeout string
is plugin-specific.
update_ticket=bool
Set to false if the user specified the -N option, in-
dicating that the user wishes to avoid updating any
cached authentication credentials. Only available
starting with API version 1.20.
Additional settings may be added in the future so the plu-
gin should silently ignore settings that it does not recog-
nize.
user_info
A vector of information about the user running the command
in the form of “name=value” strings. The vector is termi-
nated by a NULL pointer.
When parsing user_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
The following values may be set by sudo:
cols=int
The number of columns the user's terminal supports.
If there is no terminal device available, a default
value of 80 is used.
cwd=string
The user's current working directory.
egid=gid_t
The effective group-ID of the user invoking sudo.
euid=uid_t
The effective user-ID of the user invoking sudo.
gid=gid_t
The real group-ID of the user invoking sudo.
groups=list
The user's supplementary group list formatted as a
string of comma-separated group-IDs.
host=string
The local machine's hostname as returned by the
gethostname(2) system call.
lines=int
The number of lines the user's terminal supports. If
there is no terminal device available, a default
value of 24 is used.
pgid=int
The ID of the process group that the running sudo
process is a member of. Only available starting with
API version 1.2.
pid=int
The process ID of the running sudo process. Only
available starting with API version 1.2.
ppid=int
The parent process ID of the running sudo process.
Only available starting with API version 1.2.
rlimit_as=soft,hard
The maximum size to which the process's address space
may grow (in bytes), if supported by the operating
system. The soft and hard limits are separated by a
comma. A value of “infinity” indicates that there is
no limit. Only available starting with API version
1.16.
rlimit_core=soft,hard
The largest size core dump file that may be created
(in bytes). The soft and hard limits are separated
by a comma. A value of “infinity” indicates that
there is no limit. Only available starting with API
version 1.16.
rlimit_cpu=soft,hard
The maximum amount of CPU time that the process may
use (in seconds). The soft and hard limits are sepa-
rated by a comma. A value of “infinity” indicates
that there is no limit. Only available starting with
API version 1.16.
rlimit_data=soft,hard
The maximum size of the data segment for the process
(in bytes). The soft and hard limits are separated
by a comma. A value of “infinity” indicates that
there is no limit. Only available starting with API
version 1.16.
rlimit_fsize=soft,hard
The largest size file that the process may create (in
bytes). The soft and hard limits are separated by a
comma. A value of “infinity” indicates that there is
no limit. Only available starting with API version
1.16.
rlimit_locks=soft,hard
The maximum number of locks that the process may es-
tablish, if supported by the operating system. The
soft and hard limits are separated by a comma. A
value of “infinity” indicates that there is no limit.
Only available starting with API version 1.16.
rlimit_memlock=soft,hard
The maximum size that the process may lock in memory
(in bytes), if supported by the operating system.
The soft and hard limits are separated by a comma. A
value of “infinity” indicates that there is no limit.
Only available starting with API version 1.16.
rlimit_nofile=soft,hard
The maximum number of files that the process may have
open. The soft and hard limits are separated by a
comma. A value of “infinity” indicates that there is
no limit. Only available starting with API version
1.16.
rlimit_nproc=soft,hard
The maximum number of processes that the user may run
simultaneously. The soft and hard limits are sepa-
rated by a comma. A value of “infinity” indicates
that there is no limit. Only available starting with
API version 1.16.
rlimit_rss=soft,hard
The maximum size to which the process's resident set
size may grow (in bytes). The soft and hard limits
are separated by a comma. A value of “infinity” in-
dicates that there is no limit. Only available
starting with API version 1.16.
rlimit_stack=soft,hard
The maximum size to which the process's stack may
grow (in bytes). The soft and hard limits are sepa-
rated by a comma. A value of “infinity” indicates
that there is no limit. Only available starting with
API version 1.16.
sid=int
The session ID of the running sudo process or 0 if
sudo is not part of a POSIX job control session.
Only available starting with API version 1.2.
tcpgid=int
The ID of the foreground process group associated
with the terminal device associated with the sudo
process or 0 if there is no terminal present. Only
available starting with API version 1.2.
tty=string
The path to the user's terminal device. If the user
has no terminal device associated with the session,
the value will be empty, as in ‘tty=’.
uid=uid_t
The real user-ID of the user invoking sudo.
umask=octal
The invoking user's file creation mask. Only avail-
able starting with API version 1.10.
user=string
The name of the user invoking sudo.
user_env
The user's environment in the form of a NULL-terminated
vector of “name=value” strings.
When parsing user_env, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
plugin_options
Any (non-comment) strings immediately after the plugin path
are passed as arguments to the plugin. These arguments are
split on a white space boundary and are passed to the plu-
gin in the form of a NULL-terminated array of strings. If
no arguments were specified, plugin_options will be the
NULL pointer.
The plugin_options parameter is only available starting
with API version 1.2. A plugin must check the API version
specified by the sudo front-end before using
plugin_options. Failure to do so may result in a crash.
errstr
If the open() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
close
void (*close)(int exit_status, int error);
The close() function is called when sudo is finished, shortly be-
fore it exits. Starting with API version 1.15, close() is called
regardless of whether or not a command was actually executed.
This makes it possible for plugins to perform cleanup even when a
command was not run. It is not possible to tell whether a com-
mand was run based solely on the arguments passed to the close()
function. To determine if a command was actually run, the plugin
must keep track of whether or not the check_policy() function re-
turned successfully.
The function arguments are as follows:
exit_status
The command's exit status, as returned by the wait(2) sys-
tem call, or zero if no command was run. The value of
exit_status is undefined if error is non-zero.
error
If the command could not be executed, this is set to the
value of errno set by the execve(2) system call. The plu-
gin is responsible for displaying error information via the
conversation() or sudo_plugin_printf() function. If the
command was successfully executed, the value of error is
zero.
If no close() function is defined, no I/O logging plugins are
loaded, and neither the timeout nor use_pty options are set in
the command_info list, the sudo front-end may execute the command
directly instead of running it as a child process.
show_version
int (*show_version)(int verbose);
The show_version() function is called by sudo when the user spec-
ifies the -V option. The plugin may display its version informa-
tion to the user via the conversation() or sudo_plugin_printf()
function using SUDO_CONV_INFO_MSG. If the user requests detailed
version information, the verbose flag will be non-zero.
Returns 1 on success, 0 on failure, -1 if a general error oc-
curred, or -2 if there was a usage error, although the return
value is currently ignored.
check_policy
int (*check_policy)(int argc, char * const argv[], char *env_add[],
char **command_info[], char **argv_out[], char **user_env_out[],
const char **errstr);
The check_policy() function is called by sudo to determine
whether the user is allowed to run the specified commands.
If the sudoedit option was enabled in the settings array passed
to the open() function, the user has requested sudoedit mode.
sudoedit is a mechanism for editing one or more files where an
editor is run with the user's credentials instead of with ele-
vated privileges. sudo achieves this by creating user-writable
temporary copies of the files to be edited and then overwriting
the originals with the temporary copies after editing is com-
plete. If the plugin supports sudoedit, it must set
sudoedit=true in the command_info list. The plugin is responsi-
ble for choosing the editor to be used, potentially from a vari-
able in the user's environment, such as EDITOR, and should be
stored in argv_out (environment variables may include command
line options). The files to be edited should be copied from argv
to argv_out, separated from the editor and its arguments by a
‘--’ element. The ‘--’ will be removed by sudo before the editor
is executed. The plugin may also set sudoedit_nfiles to the num-
ber of files to be edited in the command_info list; this will
only be used by the sudo front-end starting with API version
1.21.
The check_policy() function returns 1 if the command is allowed,
0 if not allowed, -1 for a general error, or -2 for a usage error
or if sudoedit was specified but is unsupported by the plugin.
In the latter case, sudo will print a usage message before it ex-
its. If an error occurs, the plugin may optionally call the
conversation() or sudo_plugin_printf() function with
SUDO_CONF_ERROR_MSG to present additional error information to
the user.
The function arguments are as follows:
argc The number of elements in argv, not counting the final NULL
pointer.
argv The argument vector describing the command the user wishes
to run, in the same form as what would be passed to the
execve(2) system call. The vector is terminated by a NULL
pointer.
env_add
Additional environment variables specified by the user on
the command line in the form of a NULL-terminated vector of
“name=value” strings. The plugin may reject the command if
one or more variables are not allowed to be set, or it may
silently ignore such variables.
When parsing env_add, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
command_info
Information about the command being run in the form of
“name=value” strings. These values are used by sudo to set
the execution environment when running a command. The plu-
gin is responsible for creating and populating the vector,
which must be terminated with a NULL pointer. The follow-
ing values are recognized by sudo:
apparmor_profile=string
AppArmor profile to transition to when executing the
command. Only available starting with API version
1.19.
chroot=string
The root directory to use when running the command.
closefrom=number
If specified, sudo will close all files descriptors
with a value of number or higher.
command=string
Fully qualified path to the command to be executed.
cwd=string
The current working directory to change to when exe-
cuting the command. If sudo is unable to change to
the new working directory, the command will not be
run unless cwd_optional is also set (see below).
cwd_optional=bool
If set, sudo will treat an inability to change to the
new working directory as a non-fatal error. This
setting has no effect unless cwd is also set.
exec_background=bool
By default, sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When exec_background is enabled and the
command is being run in a pseudo-terminal (due to I/O
logging or the use_pty setting), the command will be
run as a background process. Attempts to read from
the controlling terminal (or to change terminal set-
tings) will result in the command being suspended
with the SIGTTIN signal (or SIGTTOU in the case of
terminal settings). If this happens when sudo is a
foreground process, the command will be granted the
controlling terminal and resumed in the foreground
with no user intervention required. The advantage of
initially running the command in the background is
that sudo need not read from the terminal unless the
command explicitly requests it. Otherwise, any ter-
minal input must be passed to the command, whether it
has required it or not (the kernel buffers terminals
so it is not possible to tell whether the command re-
ally wants the input). This is different from his-
toric sudo behavior or when the command is not being
run in a pseudo-terminal.
For this to work seamlessly, the operating system
must support the automatic restarting of system
calls. Unfortunately, not all operating systems do
this by default, and even those that do may have
bugs. For example, macOS fails to restart the
tcgetattr() and tcsetattr() system calls (this is a
bug in macOS). Furthermore, because this behavior
depends on the command stopping with the SIGTTIN or
SIGTTOU signals, programs that catch these signals
and suspend themselves with a different signal (usu-
ally SIGTOP) will not be automatically foregrounded.
Some versions of the linux su(1) command behave this
way. Because of this, a plugin should not set
exec_background unless it is explicitly enabled by
the administrator and there should be a way to en-
abled or disable it on a per-command basis.
This setting has no effect unless I/O logging is en-
abled or use_pty is enabled.
execfd=number
If specified, sudo will use the fexecve(2) system
call to execute the command instead of execve(2).
The specified number must refer to an open file de-
scriptor.
intercept=bool
If set, sudo will intercept attempts to execute a
subsequent command and perform a policy check via the
policy plugin's check_policy() function to determine
whether or not the command is permitted. This can be
used to prevent shell escapes on supported platforms
but it has a number of limitations. See Preventing
shell escapes in sudoers(5) for details. Only avail-
able starting with API version 1.18.
intercept_verify=bool
If set, sudo will attempt to verify that a command
run in intercept mode has the expected path name,
command line arguments and environment. This setting
has no effect unless use_ptrace is also enabled.
Only available starting with API version 1.20.
iolog_compress=bool
Set to true if the I/O logging plugins, if any,
should compress the log data. This is a hint to the
I/O logging plugin which may choose to ignore it.
iolog_group=string
The group that will own newly created I/O log files
and directories. This is a hint to the I/O logging
plugin which may choose to ignore it.
iolog_mode=octal
The file permission mode to use when creating I/O log
files and directories. This is a hint to the I/O
logging plugin which may choose to ignore it.
iolog_user=string
The user that will own newly created I/O log files
and directories. This is a hint to the I/O logging
plugin which may choose to ignore it.
iolog_path=string
Fully qualified path to the file or directory in
which I/O log is to be stored. This is a hint to the
I/O logging plugin which may choose to ignore it. If
no I/O logging plugin is loaded, this setting has no
effect.
iolog_stdin=bool
Set to true if the I/O logging plugins, if any,
should log the standard input if it is not connected
to a terminal device. This is a hint to the I/O log-
ging plugin which may choose to ignore it.
iolog_stdout=bool
Set to true if the I/O logging plugins, if any,
should log the standard output if it is not connected
to a terminal device. This is a hint to the I/O log-
ging plugin which may choose to ignore it.
iolog_stderr=bool
Set to true if the I/O logging plugins, if any,
should log the standard error if it is not connected
to a terminal device. This is a hint to the I/O log-
ging plugin which may choose to ignore it.
iolog_ttyin=bool
Set to true if the I/O logging plugins, if any,
should log all terminal input. This only includes
input typed by the user and not from a pipe or redi-
rected from a file. This is a hint to the I/O log-
ging plugin which may choose to ignore it.
iolog_ttyout=bool
Set to true if the I/O logging plugins, if any,
should log all terminal output. This only includes
output to the screen, not output to a pipe or file.
This is a hint to the I/O logging plugin which may
choose to ignore it.
login_class=string
BSD login class to use when setting resource limits
and nice value (optional). This option is only set
on systems that support login classes.
nice=int
Nice value (priority) to use when executing the com-
mand. The nice value, if specified, overrides the
priority associated with the login_class on BSD sys-
tems.
log_subcmds=bool
If set, sudo will call the audit plugin's accept()
function to log when the command runs a subsequent
command, if supported by the system. If intercept is
also specified, log_subcmds will be ignored. See
Preventing shell escapes in sudoers(5) for more in-
formation. Only available starting with API version
1.18.
noexec=bool
If set, prevent the command from executing other pro-
grams.
preserve_fds=list
A comma-separated list of file descriptors that
should be preserved, regardless of the value of the
closefrom setting. Only available starting with API
version 1.5.
preserve_groups=bool
If set, sudo will preserve the user's group vector
instead of initializing the group vector based on
runas_user.
rlimit_as=soft,hard
The maximum size to which the process's address space
may grow (in bytes), if supported by the operating
system. The soft and hard limits are separated by a
comma. If only a single value is specified, both the
hard and soft limits are set. A value of “infinity”
indicates that there is no limit. A value of “user”
will cause the invoking user's resource limit to be
preserved. A value of “default” will cause the tar-
get user's default resource limit to be used on sys-
tems that allow per-user resource limits to be con-
figured. Only available starting with API version
1.18.
rlimit_core=soft,hard
The largest size core dump file that may be created
(in bytes). The soft and hard limits are separated
by a comma. If only a single value is specified,
both the hard and soft limits are set. A value of
“infinity” indicates that there is no limit. A value
of “user” will cause the invoking user's resource
limit to be preserved. A value of “default” will
cause the target user's default resource limit to be
used on systems that allow per-user resource limits
to be configured. Only available starting with API
version 1.18.
rlimit_cpu=soft,hard
The maximum amount of CPU time that the process may
use (in seconds). The soft and hard limits are sepa-
rated by a comma. If only a single value is speci-
fied, both the hard and soft limits are set. A value
of “infinity” indicates that there is no limit. A
value of “user” will cause the invoking user's re-
source limit to be preserved. A value of “default”
will cause the target user's default resource limit
to be used on systems that allow per-user resource
limits to be configured. Only available starting
with API version 1.18.
rlimit_data=soft,hard
The maximum size of the data segment for the process
(in bytes). The soft and hard limits are separated
by a comma. If only a single value is specified,
both the hard and soft limits are set. A value of
“infinity” indicates that there is no limit. A value
of “user” will cause the invoking user's resource
limit to be preserved. A value of “default” will
cause the target user's default resource limit to be
used on systems that allow per-user resource limits
to be configured. Only available starting with API
version 1.18.
rlimit_fsize=soft,hard
The largest size file that the process may create (in
bytes). The soft and hard limits are separated by a
comma. If only a single value is specified, both the
hard and soft limits are set. A value of “infinity”
indicates that there is no limit. A value of “user”
will cause the invoking user's resource limit to be
preserved. A value of “default” will cause the tar-
get user's default resource limit to be used on sys-
tems that allow per-user resource limits to be con-
figured. Only available starting with API version
1.18.
rlimit_locks=soft,hard
The maximum number of locks that the process may es-
tablish, if supported by the operating system. The
soft and hard limits are separated by a comma. If
only a single value is specified, both the hard and
soft limits are set. A value of “infinity” indicates
that there is no limit. A value of “user” will cause
the invoking user's resource limit to be preserved.
A value of “default” will cause the target user's de-
fault resource limit to be used on systems that allow
per-user resource limits to be configured. Only
available starting with API version 1.18.
rlimit_memlock=soft,hard
The maximum size that the process may lock in memory
(in bytes), if supported by the operating system.
The soft and hard limits are separated by a comma.
If only a single value is specified, both the hard
and soft limits are set. A value of “infinity” indi-
cates that there is no limit. A value of “user” will
cause the invoking user's resource limit to be pre-
served. A value of “default” will cause the target
user's default resource limit to be used on systems
that allow per-user resource limits to be configured.
Only available starting with API version 1.18.
rlimit_nofile=soft,hard
The maximum number of files that the process may have
open. The soft and hard limits are separated by a
comma. If only a single value is specified, both the
hard and soft limits are set. A value of “infinity”
indicates that there is no limit. A value of “user”
will cause the invoking user's resource limit to be
preserved. A value of “default” will cause the tar-
get user's default resource limit to be used on sys-
tems that allow per-user resource limits to be con-
figured. Only available starting with API version
1.18.
rlimit_nproc=soft,hard
The maximum number of processes that the user may run
simultaneously. The soft and hard limits are sepa-
rated by a comma. If only a single value is speci-
fied, both the hard and soft limits are set. A value
of “infinity” indicates that there is no limit. A
value of “user” will cause the invoking user's re-
source limit to be preserved. A value of “default”
will cause the target user's default resource limit
to be used on systems that allow per-user resource
limits to be configured. Only available starting
with API version 1.18.
rlimit_rss=soft,hard
The maximum size to which the process's resident set
size may grow (in bytes). The soft and hard limits
are separated by a comma. If only a single value is
specified, both the hard and soft limits are set. A
value of “infinity” indicates that there is no limit.
A value of “user” will cause the invoking user's re-
source limit to be preserved. A value of “default”
will cause the target user's default resource limit
to be used on systems that allow per-user resource
limits to be configured. Only available starting
with API version 1.18.
rlimit_stack=soft,hard
The maximum size to which the process's stack may
grow (in bytes). The soft and hard limits are sepa-
rated by a comma. If only a single value is speci-
fied, both the hard and soft limits are set. A value
of “infinity” indicates that there is no limit. A
value of “user” will cause the invoking user's re-
source limit to be preserved. A value of “default”
will cause the target user's default resource limit
to be used on systems that allow per-user resource
limits to be configured. Only available starting
with API version 1.18.
runas_egid=gid
Effective group-ID to run the command as. If not
specified, the value of runas_gid is used.
runas_euid=uid
Effective user-ID to run the command as. If not
specified, the value of runas_uid is used.
runas_gid=gid
Group-ID to run the command as.
runas_group=string
The name of the group the command will run as, if it
is different from the runas_user's default group.
This value is provided for auditing purposes only,
the sudo front-end uses runas_egid and runas_gid when
executing the command.
runas_groups=list
The supplementary group vector to use for the command
in the form of a comma-separated list of group-IDs.
If preserve_groups is set, this option is ignored.
runas_uid=uid
User-ID to run the command as.
runas_user=string
The name of the user the command will run as, which
should correspond to runas_euid (or runas_uid if
runas_euid is not set). This value is provided for
auditing purposes only, the sudo front-end uses
runas_euid and runas_uid when executing the command.
selinux_role=string
SELinux role to use when executing the command.
selinux_type=string
SELinux type to use when executing the command.
set_utmp=bool
Create a utmp (or utmpx) entry when a pseudo-terminal
is allocated. By default, the new entry will be a
copy of the user's existing utmp entry (if any), with
the tty, time, type, and pid fields updated.
sudoedit=bool
Set to true when in sudoedit mode. The plugin may
enable sudoedit mode even if sudo was not invoked as
sudoedit. This allows the plugin to perform command
substitution and transparently enable sudoedit when
the user attempts to run an editor.
sudoedit_checkdir=bool
Set to false to disable directory writability checks
in sudoedit. By default, sudoedit 1.8.16 and higher
will check all directory components of the path to be
edited for writability by the invoking user. Sym-
bolic links will not be followed in writable directo-
ries and sudoedit will refuse to edit a file located
in a writable directory. These restrictions are not
enforced when sudoedit is run by root. The
sudoedit_checkdir option can be set to false to dis-
able this check. Only available starting with API
version 1.8.
sudoedit_follow=bool
Set to true to allow sudoedit to edit files that are
symbolic links. By default, sudoedit 1.8.15 and
higher will refuse to open a symbolic link. The
sudoedit_follow option can be used to restore the
older behavior and allow sudoedit to open symbolic
links. Only available starting with API version 1.8.
sudoedit_nfiles=number
The number of files to be edited by the user. If
present, this is will be used by the sudo front-end
to determine which elements of the argv_out vector
are files to be edited. The ‘--’ element must imme-
diately precede the first file to be editied. If
sudoedit_nfiles is not specified, the sudo front-end
will use the position of the ‘--’ element to deter-
mine where the file list begins. Only available
starting with API version 1.21.
timeout=int
Command timeout. If non-zero then when the timeout
expires the command will be killed.
umask=octal
The file creation mask to use when executing the com-
mand. This value may be overridden by PAM or lo-
gin.conf on some systems unless the umask_override
option is also set.
umask_override=bool
Force the value specified by the umask option to
override any umask set by PAM or login.conf.
use_ptrace=bool
If set, sudo will use ptrace(2) to implement inter-
cept mode if supported by the system. This setting
has no effect unless intercept is also set. Only
available starting with API version 1.19.
use_pty=bool
Allocate a pseudo-terminal to run the command in, re-
gardless of whether or not I/O logging is in use. By
default, sudo will only run the command in a pseudo-
terminal when an I/O log plugin is loaded.
utmp_user=string
User name to use when constructing a new utmp (or
utmpx) entry when set_utmp is enabled. This option
can be used to set the user field in the utmp entry
to the user the command runs as rather than the in-
voking user. If not set, sudo will base the new en-
try on the invoking user's existing entry.
Unsupported values will be ignored.
argv_out
The NULL-terminated argument vector to pass to the
execve(2) system call when executing the command. The plu-
gin is responsible for allocating and populating the vec-
tor.
user_env_out
The NULL-terminated environment vector to use when execut-
ing the command. The plugin is responsible for allocating
and populating the vector.
errstr
If the check_policy() function returns a value other than
1, the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
list
int (*list)(int argc, char * const argv[], int verbose,
const char *user, const char **errstr);
List available privileges for the invoking user. Returns 1 on
success, 0 on failure, and -1 on error. On error, the plugin may
optionally call the conversation() or sudo_plugin_printf() func-
tion with SUDO_CONF_ERROR_MSG to present additional error infor-
mation to the user.
Privileges should be output via the conversation() or
sudo_plugin_printf() function using SUDO_CONV_INFO_MSG.
The function arguments are as follows:
argc The number of elements in argv, not counting the final NULL
pointer.
argv If non-NULL, an argument vector describing a command the
user wishes to check against the policy in the same form as
what would be passed to the execve(2) system call. If the
command is permitted by the policy, the fully-qualified
path to the command should be displayed along with any com-
mand line arguments.
verbose
Flag indicating whether to list in verbose mode or not.
user The name of a different user to list privileges for if the
policy allows it. If NULL, the plugin should list the
privileges of the invoking user.
errstr
If the list() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
validate
int (*validate)(const char **errstr);
The validate() function is called when sudo is run with the -v
option. For policy plugins such as sudoers that cache authenti-
cation credentials, this function will validate and cache the
credentials.
The validate() function should be NULL if the plugin does not
support credential caching.
Returns 1 on success, 0 on failure, and -1 on error. On error,
the plugin may optionally call the conversation() or
sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
The function arguments are as follows:
errstr
If the validate() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
invalidate
void (*invalidate)(int rmcred);
The invalidate() function is called when sudo is run with the -k
or -K option. For policy plugins such as sudoers that cache au-
thentication credentials, this function will invalidate the cre-
dentials. If the rmcred flag is non-zero, the plugin may remove
the credentials instead of simply invalidating them.
The invalidate() function should be NULL if the plugin does not
support credential caching.
init_session
int (*init_session)(struct passwd *pwd, char **user_env[],
const char **errstr);
The init_session() function is called before sudo sets up the ex-
ecution environment for the command. It is run in the parent
sudo process before any user-ID or group-ID changes. This can be
used to perform session setup that is not supported by
command_info, such as opening the PAM session. The close() func-
tion can be used to tear down the session that was opened by
init_session().
Returns 1 on success, 0 on failure, and -1 on error. On error,
the plugin may optionally call the conversation() or
sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
The function arguments are as follows:
pwd If the user-ID the command will run as was found in the
password database, pwd will describe that user, otherwise
it will be NULL.
user_env_out
The NULL-terminated environment vector to use when execut-
ing the command. This is the same string passed back to
the front-end via the Policy Plugin's user_env_out parame-
ter. If the init_session() function needs to modify the
user environment, it should update the pointer stored in
user_env_out. The expected use case is to merge the con-
tents of the PAM environment (if any) with the contents of
user_env_out. The user_env_out parameter is only available
starting with API version 1.2. A plugin must check the API
version specified by the sudo front-end before using
user_env_out. Failure to do so may result in a crash.
errstr
If the init_session() function returns a value other than
1, the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
register_hooks
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
The register_hooks() function is called by the sudo front-end to
register any hooks the plugin needs. If the plugin does not sup-
port hooks, register_hooks should be set to the NULL pointer.
The version argument describes the version of the hooks API sup-
ported by the sudo front-end.
The register_hook() function should be used to register any sup-
ported hooks the plugin needs. It returns 0 on success, 1 if the
hook type is not supported, and -1 if the major version in struct
sudo_hook does not match the front-end's major hook API version.
See the “Hook function API” section below for more information
about hooks.
The register_hooks() function is only available starting with API
version 1.2. If the sudo front-end doesn't support API version
1.2 or higher, register_hooks() will not be called.
deregister_hooks
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
The deregister_hooks() function is called by the sudo front-end
to deregister any hooks the plugin has registered. If the plugin
does not support hooks, deregister_hooks should be set to the
NULL pointer.
The version argument describes the version of the hooks API sup-
ported by the sudo front-end.
The deregister_hook() function should be used to deregister any
hooks that were put in place by the register_hook() function. If
the plugin tries to deregister a hook that the front-end does not
support, deregister_hook() will return an error.
See the “Hook function API” section below for more information
about hooks.
The deregister_hooks() function is only available starting with
API version 1.2. If the sudo front-end doesn't support API ver-
sion 1.2 or higher, deregister_hooks() will not be called.
event_alloc
struct sudo_plugin_event * (*event_alloc)(void);
The event_alloc() function is used to allocate a struct
sudo_plugin_event which provides access to the main sudo event
loop. Unlike the other fields, the event_alloc pointer is filled
in by the sudo front-end, not by the plugin.
See the “Event API” section below for more information about
events.
The event_alloc() function is only available starting with API
version 1.15. If the sudo front-end doesn't support API version
1.15 or higher, event_alloc will not be set.
Policy Plugin Version Macros
/* Plugin API version major/minor. */
#define SUDO_API_VERSION_MAJOR 1
#define SUDO_API_VERSION_MINOR 13
#define SUDO_API_MKVERSION(x, y) ((x << 16) | y)
#define SUDO_API_VERSION SUDO_API_MKVERSION(SUDO_API_VERSION_MAJOR,\
SUDO_API_VERSION_MINOR)
/* Getters and setters for API version */
#define SUDO_API_VERSION_GET_MAJOR(v) ((v) >> 16)
#define SUDO_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define SUDO_API_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define SUDO_API_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
I/O plugin API
struct io_plugin {
#define SUDO_IO_PLUGIN 2
unsigned int type; /* always SUDO_IO_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], char * const command_info[],
int argc, char * const argv[], char * const user_env[],
char * const plugin_options[], const char **errstr);
void (*close)(int exit_status, int error); /* wait status or error */
int (*show_version)(int verbose);
int (*log_ttyin)(const char *buf, unsigned int len,
const char **errstr);
int (*log_ttyout)(const char *buf, unsigned int len,
const char **errstr);
int (*log_stdin)(const char *buf, unsigned int len,
const char **errstr);
int (*log_stdout)(const char *buf, unsigned int len,
const char **errstr);
int (*log_stderr)(const char *buf, unsigned int len,
const char **errstr);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
int (*change_winsize)(unsigned int lines, unsigned int cols,
const char **errstr);
int (*log_suspend)(int signo, const char **errstr);
struct sudo_plugin_event * (*event_alloc)(void);
};
When an I/O plugin is loaded, sudo runs the command in a pseudo-termi-
nal. This makes it possible to log the input and output from the
user's session. If any of the standard input, standard output, or
standard error do not correspond to a tty, sudo will open a pipe to
capture the I/O for logging before passing it on.
The log_ttyin() function receives the raw user input from the terminal
device (this will include input even when echo is disabled, such as
when a password is read). The log_ttyout() function receives output
from the pseudo-terminal that is suitable for replaying the user's ses-
sion at a later time. The log_stdin(), log_stdout(), and log_stderr()
functions are only called if the standard input, standard output, or
standard error respectively correspond to something other than a tty.
Any of the logging functions may be set to the NULL pointer if no log-
ging is to be performed. If the open function returns 0, no I/O will
be sent to the plugin.
If a logging function returns an error (-1), the running command will
be terminated and all of the plugin's logging functions will be dis-
abled. Other I/O logging plugins will still receive any remaining in-
put or output that has not yet been processed.
If an input logging function rejects the data by returning 0, the com-
mand will be terminated and the data will not be passed to the command,
though it will still be sent to any other I/O logging plugins. If an
output logging function rejects the data by returning 0, the command
will be terminated and the data will not be written to the terminal,
though it will still be sent to any other I/O logging plugins.
A struct audit_plugin has the following fields:
type The type field should always be set to SUDO_IO_PLUGIN.
version
The version field should be set to SUDO_API_VERSION.
This allows sudo to determine the API version the plugin was
built against.
open
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], char * const command_info[],
int argc, char * const argv[], char * const user_env[],
char * const plugin_options[]);
The open() function is run before the log_ttyin(), log_ttyout(),
log_stdin(), log_stdout(), log_stderr(), log_suspend(),
change_winsize(), or show_version() functions are called. It is
only called if the version is being requested or if the policy
plugin's check_policy() function has returned successfully. It
returns 1 on success, 0 on failure, -1 if a general error oc-
curred, or -2 if there was a usage error. In the latter case,
sudo will print a usage message before it exits. If an error oc-
curs, the plugin may optionally call the conversation() or
sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
The function arguments are as follows:
version
The version passed in by sudo allows the plugin to deter-
mine the major and minor version number of the plugin API
supported by sudo.
conversation
A pointer to the conversation() function that may be used
by the Fa(show_version) function to display version infor-
mation (see show_version() below). The conversation()
function may also be used to display additional error mes-
sage to the user. The conversation() function returns 0 on
success and -1 on failure.
sudo_plugin_printf
A pointer to a printf()-style function that may be used by
the show_version() function to display version information
(see show_version below). The sudo_plugin_printf() func-
tion may also be used to display additional error message
to the user. The sudo_plugin_printf() function returns
number of characters printed on success and -1 on failure.
settings
A vector of user-supplied sudo settings in the form of
“name=value” strings. The vector is terminated by a NULL
pointer. These settings correspond to options the user
specified when running sudo. As such, they will only be
present when the corresponding option has been specified on
the command line.
When parsing settings, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible settings.
user_info
A vector of information about the user running the command
in the form of “name=value” strings. The vector is termi-
nated by a NULL pointer.
When parsing user_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
command_info
A vector of information describing the command being run in
the form of “name=value” strings. The vector is terminated
by a NULL pointer.
When parsing command_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
argc The number of elements in argv, not counting the final NULL
pointer. It can be zero, such as when sudo is called with
the -V option.
argv If non-NULL, an argument vector describing a command the
user wishes to run in the same form as what would be passed
to the execve(2) system call.
user_env
The user's environment in the form of a NULL-terminated
vector of “name=value” strings.
When parsing user_env, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
plugin_options
Any (non-comment) strings immediately after the plugin path
are treated as arguments to the plugin. These arguments
are split on a white space boundary and are passed to the
plugin in the form of a NULL-terminated array of strings.
If no arguments were specified, plugin_options will be the
NULL pointer.
The plugin_options parameter is only available starting
with API version 1.2. A plugin must check the API version
specified by the sudo front-end before using
plugin_options. Failure to do so may result in a crash.
errstr
If the open() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
close
void (*close)(int exit_status, int error);
The close() function is called when sudo is finished, shortly be-
fore it exits.
The function arguments are as follows:
exit_status
The command's exit status, as returned by the wait(2) sys-
tem call, or zero if no command was run. The value of
exit_status is undefined if error is non-zero.
error
If the command could not be executed, this is set to the
value of errno set by the execve(2) system call. If the
command was successfully executed, the value of error is
zero.
show_version
int (*show_version)(int verbose);
The show_version() function is called by sudo when the user spec-
ifies the -V option. The plugin may display its version informa-
tion to the user via the conversation() or sudo_plugin_printf()
function using SUDO_CONV_INFO_MSG. If the user requests detailed
version information, the verbose flag will be non-zero.
Returns 1 on success, 0 on failure, -1 if a general error oc-
curred, or -2 if there was a usage error, although the return
value is currently ignored.
log_ttyin
int (*log_ttyin)(const char *buf, unsigned int len,
const char **errstr);
The log_ttyin() function is called whenever data can be read from
the user but before it is passed to the running command. This
allows the plugin to reject data if it chooses to (for instance
if the input contains banned content). Returns 1 if the data
should be passed to the command, 0 if the data is rejected (which
will terminate the running command), or -1 if an error occurred.
The function arguments are as follows:
buf The buffer containing user input.
len The length of buf in bytes.
errstr
If the log_ttyin() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
log_ttyout
int (*log_ttyout)(const char *buf, unsigned int len,
const char **errstr);
The log_ttyout() function is called whenever data can be read
from the command but before it is written to the user's terminal.
This allows the plugin to reject data if it chooses to (for in-
stance if the output contains banned content). Returns 1 if the
data should be passed to the user, 0 if the data is rejected
(which will terminate the running command), or -1 if an error oc-
curred.
The function arguments are as follows:
buf The buffer containing command output.
len The length of buf in bytes.
errstr
If the log_ttyout() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
log_stdin
int (*log_stdin)(const char *buf, unsigned int len,
const char **errstr);
The log_stdin() function is only used if the standard input does
not correspond to a tty device. It is called whenever data can
be read from the standard input but before it is passed to the
running command. This allows the plugin to reject data if it
chooses to (for instance if the input contains banned content).
Returns 1 if the data should be passed to the command, 0 if the
data is rejected (which will terminate the running command), or
-1 if an error occurred.
The function arguments are as follows:
buf The buffer containing user input.
len The length of buf in bytes.
errstr
If the log_stdin() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
log_stdout
int (*log_stdout)(const char *buf, unsigned int len,
const char **errstr);
The log_stdout() function is only used if the standard output
does not correspond to a tty device. It is called whenever data
can be read from the command but before it is written to the
standard output. This allows the plugin to reject data if it
chooses to (for instance if the output contains banned content).
Returns 1 if the data should be passed to the user, 0 if the data
is rejected (which will terminate the running command), or -1 if
an error occurred.
The function arguments are as follows:
buf The buffer containing command output.
len The length of buf in bytes.
errstr
If the log_stdout() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
log_stderr
int (*log_stderr)(const char *buf, unsigned int len,
const char **errstr);
The log_stderr() function is only used if the standard error does
not correspond to a tty device. It is called whenever data can
be read from the command but before it is written to the standard
error. This allows the plugin to reject data if it chooses to
(for instance if the output contains banned content). Returns 1
if the data should be passed to the user, 0 if the data is re-
jected (which will terminate the running command), or -1 if an
error occurred.
The function arguments are as follows:
buf The buffer containing command output.
len The length of buf in bytes.
errstr
If the log_stderr() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
register_hooks
See the “Policy plugin API” section for a description of
register_hooks().
deregister_hooks
See the “Policy plugin API” section for a description of
deregister_hooks().
change_winsize
int (*change_winsize)(unsigned int lines, unsigned int cols,
const char **errstr);
The change_winsize() function is called whenever the window size
of the terminal changes from the initial values specified in the
user_info list. Returns -1 if an error occurred, in which case
no further calls to change_winsize() will be made,
The function arguments are as follows:
lines
The number of lines (rows) in the re-sized terminal.
cols The number of columns in the re-sized terminal.
errstr
If the change_winsize() function returns a value other than
1, the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
log_suspend
int (*log_suspend)(int signo, const char **errstr);
The log_suspend() function is called whenever a command is sus-
pended or resumed. Logging this information makes it possible to
skip the period of time when the command was suspended during
playback of a session. Returns -1 if an error occurred, in which
case no further calls to log_suspend() will be made,
The function arguments are as follows:
signo
The signal that caused the command to be suspended, or
SIGCONT if the command was resumed.
errstr
If the log_suspend() function returns a value other than 1,
the plugin may store a message describing the failure or
error in errstr. The sudo front-end will then pass this
value to any registered audit plugins. The string stored
in errstr must remain valid until the plugin's close()
function is called.
The errstr parameter is only available starting with API
version 1.15. A plugin must check the API version speci-
fied by the sudo front-end before using errstr. Failure to
do so may result in a crash.
event_alloc
struct sudo_plugin_event * (*event_alloc)(void);
The event_alloc() function is used to allocate a struct
sudo_plugin_event which provides access to the main sudo
event loop. Unlike the other fields, the event_alloc()
pointer is filled in by the sudo front-end, not by the plu-
gin.
See the “Event API” section below for more information
about events.
The event_alloc() function is only available starting with
API version 1.15. If the sudo front-end doesn't support
API version 1.15 or higher, event_alloc() will not be set.
I/O Plugin Version Macros
Same as for the “Policy plugin API”.
Audit plugin API
/* Audit plugin close function status types. */
#define SUDO_PLUGIN_NO_STATUS 0
#define SUDO_PLUGIN_WAIT_STATUS 1
#define SUDO_PLUGIN_EXEC_ERROR 2
#define SUDO_PLUGIN_SUDO_ERROR 3
#define SUDO_AUDIT_PLUGIN 3
struct audit_plugin {
unsigned int type; /* always SUDO_AUDIT_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
void (*close)(int status_type, int status);
int (*accept)(const char *plugin_name,
unsigned int plugin_type, char * const command_info[],
char * const run_argv[], char * const run_envp[],
const char **errstr);
int (*reject)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
int (*error)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
int (*show_version)(int verbose);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
struct sudo_plugin_event * (*event_alloc)(void);
}
An audit plugin can be used to log successful and unsuccessful attempts
to run sudo independent of the policy or any I/O plugins. Multiple au-
dit plugins may be specified in sudo.conf(5).
A struct audit_plugin has the following fields:
type The type field should always be set to SUDO_AUDIT_PLUGIN.
version
The version field should be set to SUDO_API_VERSION.
This allows sudo to determine the API version the plugin was
built against.
open
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
The audit open() function is run before any other sudo plugin API
functions. This makes it possible to audit failures in the other
plugins. It returns 1 on success, 0 on failure, -1 if a general
error occurred, or -2 if there was a usage error. In the latter
case, sudo will print a usage message before it exits. If an er-
ror occurs, the plugin may optionally call the conversation() or
plugin_printf() function with SUDO_CONF_ERROR_MSG to present ad-
ditional error information to the user.
The function arguments are as follows:
version
The version passed in by sudo allows the plugin to deter-
mine the major and minor version number of the plugin API
supported by sudo.
conversation
A pointer to the conversation() function that may be used
by the show_version() function to display version informa-
tion (see show_version() below). The conversation() func-
tion may also be used to display additional error message
to the user. The conversation() function returns 0 on suc-
cess, and -1 on failure.
plugin_printf
A pointer to a printf()-style function that may be used by
the show_version() function to display version information
(see show_version below). The plugin_printf() function may
also be used to display additional error message to the
user. The plugin_printf() function returns number of char-
acters printed on success and -1 on failure.
settings
A vector of user-supplied sudo settings in the form of
“name=value” strings. The vector is terminated by a NULL
pointer. These settings correspond to options the user
specified when running sudo. As such, they will only be
present when the corresponding option has been specified on
the command line.
When parsing settings, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible settings.
user_info
A vector of information about the user running the command
in the form of “name=value” strings. The vector is termi-
nated by a NULL pointer.
When parsing user_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
submit_optind
The index into submit_argv that corresponds to the first
entry that is not a command line option. If submit_argv
only consists of options, which may be the case with the -l
or -v options, submit_argv[submit_optind] will evaluate to
the NULL pointer.
submit_argv
The argument vector sudo was invoked with, including all
command line options. The submit_optind argument can be
used to determine the end of the command line options.
submit_envp
The invoking user's environment in the form of a
NULL-terminated vector of “name=value” strings.
When parsing submit_envp, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
plugin_options
Any (non-comment) strings immediately after the plugin path
are treated as arguments to the plugin. These arguments
are split on a white space boundary and are passed to the
plugin in the form of a NULL-terminated array of strings.
If no arguments were specified, plugin_options will be the
NULL pointer.
errstr
If the open() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
close
void (*close)(int status_type, int status);
The close() function is called when sudo is finished, shortly be-
fore it exits.
The function arguments are as follows:
status_type
The type of status being passed. One of
SUDO_PLUGIN_NO_STATUS, SUDO_PLUGIN_WAIT_STATUS,
SUDO_PLUGIN_EXEC_ERROR or SUDO_PLUGIN_SUDO_ERROR.
status
Depending on the value of status_type, this value is either
ignored, the command's exit status as returned by the
wait(2) system call, the value of errno set by the
execve(2) system call, or the value of errno resulting from
an error in the sudo front-end.
accept
int (*accept)(const char *plugin_name, unsigned int plugin_type,
char * const command_info[], char * const run_argv[],
char * const run_envp[], const char **errstr);
The accept() function is called when a command or action is ac-
cepted by a policy or approval plugin. The function arguments
are as follows:
plugin_name
The name of the plugin that accepted the command or “sudo”
for the sudo front-end.
plugin_type
The type of plugin that accepted the command, currently ei-
ther SUDO_POLICY_PLUGIN, SUDO_POLICY_APPROVAL, or
SUDO_FRONT_END. The accept() function is called multiple
times--once for each policy or approval plugin that suc-
ceeds and once for the sudo front-end. When called on be-
half of the sudo front-end, command_info may include infor-
mation from an I/O logging plugin as well.
Typically, an audit plugin is interested in either the ac-
cept status from the sudo front-end or from the various
policy and approval plugins, but not both. It is possible
for the policy plugin to accept a command that is later re-
jected by an approval plugin, in which case the audit plu-
gin's accept() and reject() functions will both be called.
command_info
An optional vector of information describing the command
being run in the form of “name=value” strings. The vector
is terminated by a NULL pointer.
When parsing command_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
run_argv
A NULL-terminated argument vector describing a command that
will be run in the same form as what would be passed to the
execve(2) system call.
run_envp
The environment the command will be run with in the form of
a NULL-terminated vector of “name=value” strings.
When parsing run_envp, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
errstr
If the accept() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
reject
int (*reject)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
The reject() function is called when a command or action is re-
jected by a plugin. The function arguments are as follows:
plugin_name
The name of the plugin that rejected the command.
plugin_type
The type of plugin that rejected the command, currently ei-
ther SUDO_POLICY_PLUGIN, SUDO_APPROVAL_PLUGIN, or
SUDO_IO_PLUGIN.
Unlike the accept() function, the reject() function is not
called on behalf of the sudo front-end.
audit_msg
An optional string describing the reason the command was
rejected by the plugin. If the plugin did not provide a
reason, audit_msg will be the NULL pointer.
command_info
An optional vector of information describing the command
being run in the form of “name=value” strings. The vector
is terminated by a NULL pointer.
When parsing command_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
errstr
If the reject() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
error
int (*error)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
The error() function is called when a plugin or the sudo front-
end returns an error. The function arguments are as follows:
plugin_name
The name of the plugin that generated the error or “sudo”
for the sudo front-end.
plugin_type
The type of plugin that generated the error, or
SUDO_FRONT_END for the sudo front-end.
audit_msg
An optional string describing the plugin error. If the
plugin did not provide a description, audit_msg will be the
NULL pointer.
command_info
An optional vector of information describing the command
being run in the form of “name=value” strings. The vector
is terminated by a NULL pointer.
When parsing command_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
errstr
If the error() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
show_version
int (*show_version)(int verbose);
The show_version() function is called by sudo when the user spec-
ifies the -V option. The plugin may display its version informa-
tion to the user via the conversation() or plugin_printf() func-
tion using SUDO_CONV_INFO_MSG. If the user requests detailed
version information, the verbose flag will be set.
Returns 1 on success, 0 on failure, -1 if a general error oc-
curred, or -2 if there was a usage error, although the return
value is currently ignored.
register_hooks
See the “Policy plugin API” section for a description of
register_hooks().
deregister_hooks
See the “Policy plugin API” section for a description of
deregister_hooks().
event_alloc
struct sudo_plugin_event * (*event_alloc)(void);
The event_alloc() function is used to allocate a struct
sudo_plugin_event which provides access to the main sudo event
loop. Unlike the other fields, the event_alloc pointer is filled
in by the sudo front-end, not by the plugin.
See the “Event API” section below for more information about
events.
The event_alloc() function is only available starting with API
version 1.17. If the sudo front-end doesn't support API version
1.17 or higher, event_alloc() will not be set.
Approval plugin API
struct approval_plugin {
#define SUDO_APPROVAL_PLUGIN 4
unsigned int type; /* always SUDO_APPROVAL_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
void (*close)(void);
int (*check)(char * const command_info[], char * const run_argv[],
char * const run_envp[], const char **errstr);
int (*show_version)(int verbose);
};
An approval plugin can be used to apply extra constraints after a com-
mand has been accepted by the policy plugin. Unlike the other plugin
types, it does not remain open until the command completes. The plugin
is opened before a call to check() or show_version() and closed shortly
thereafter (audit plugin functions must be called before the plugin is
closed). Multiple approval plugins may be specified in sudo.conf(5).
A struct approval_plugin has the following fields:
type The type field should always be set to SUDO_APPROVAL_PLUGIN.
version
The version field should be set to SUDO_API_VERSION.
This allows sudo to determine the API version the plugin was
built against.
open
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
The approval open() function is run immediately before a call to
the plugin's check() or show_version() functions. It is only
called if the version is being requested or if the policy plu-
gin's check_policy() function has returned successfully. It re-
turns 1 on success, 0 on failure, -1 if a general error occurred,
or -2 if there was a usage error. In the latter case, sudo will
print a usage message before it exits. If an error occurs, the
plugin may optionally call the conversation() or plugin_printf()
function with SUDO_CONF_ERROR_MSG to present additional error in-
formation to the user.
The function arguments are as follows:
version
The version passed in by sudo allows the plugin to deter-
mine the major and minor version number of the plugin API
supported by sudo.
conversation
A pointer to the conversation() function that can be used
by the plugin to interact with the user (see “Conversation
API” for details). Returns 0 on success and -1 on failure.
plugin_printf
A pointer to a printf()-style function that may be used to
display informational or error messages (see “Conversation
API” for details). Returns the number of characters
printed on success and -1 on failure.
settings
A vector of user-supplied sudo settings in the form of
“name=value” strings. The vector is terminated by a NULL
pointer. These settings correspond to options the user
specified when running sudo. As such, they will only be
present when the corresponding option has been specified on
the command line.
When parsing settings, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible settings.
user_info
A vector of information about the user running the command
in the form of “name=value” strings. The vector is termi-
nated by a NULL pointer.
When parsing user_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
submit_optind
The index into submit_argv that corresponds to the first
entry that is not a command line option. If submit_argv
only consists of options, which may be the case with the -l
or -v options, submit_argv[submit_optind] will evaluate to
the NULL pointer.
submit_argv
The argument vector sudo was invoked with, including all
command line options. The submit_optind argument can be
used to determine the end of the command line options.
submit_envp
The invoking user's environment in the form of a
NULL-terminated vector of “name=value” strings.
When parsing submit_envp, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
plugin_options
Any (non-comment) strings immediately after the plugin path
are treated as arguments to the plugin. These arguments
are split on a white space boundary and are passed to the
plugin in the form of a NULL-terminated array of strings.
If no arguments were specified, plugin_options will be the
NULL pointer.
errstr
If the open() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
close
void (*close)(void);
The close() function is called after the approval plugin's
check() or show_version() functions have been called. It takes
no arguments. The close() function is typically used to perform
plugin-specific cleanup, such as the freeing of memory objects
allocated by the plugin. If the plugin does not need to perform
any cleanup, close() may be set to the NULL pointer.
check
int (*check)(char * const command_info[], char * const run_argv[],
char * const run_envp[], const char **errstr);
The approval check() function is run after the policy plugin
check_policy() function and before any I/O logging plugins. If
multiple approval plugins are loaded, they must all succeed for
the command to be allowed. It returns 1 on success, 0 on fail-
ure, -1 if a general error occurred, or -2 if there was a usage
error. In the latter case, sudo will print a usage message be-
fore it exits. If an error occurs, the plugin may optionally
call the conversation() or plugin_printf() function with
SUDO_CONF_ERROR_MSG to present additional error information to
the user.
The function arguments are as follows:
command_info
A vector of information describing the command being run in
the form of “name=value” strings. The vector is terminated
by a NULL pointer.
When parsing command_info, the plugin should split on the
first equal sign (‘=’) since the name field will never in-
clude one itself but the value might.
See the “Policy plugin API” section for a list of all pos-
sible strings.
run_argv
A NULL-terminated argument vector describing a command that
will be run in the same form as what would be passed to the
execve(2) system call.
run_envp
The environment the command will be run with in the form of
a NULL-terminated vector of “name=value” strings.
When parsing run_envp, the plugin should split on the first
equal sign (‘=’) since the name field will never include
one itself but the value might.
errstr
If the open() function returns a value other than 1, the
plugin may store a message describing the failure or error
in errstr. The sudo front-end will then pass this value to
any registered audit plugins. The string stored in errstr
must remain valid until the plugin's close() function is
called.
show_version
int (*show_version)(int verbose);
The show_version() function is called by sudo when the user spec-
ifies the -V option. The plugin may display its version informa-
tion to the user via the conversation() or plugin_printf() func-
tion using SUDO_CONV_INFO_MSG. If the user requests detailed
version information, the verbose flag will be set.
Returns 1 on success, 0 on failure, -1 if a general error oc-
curred, or -2 if there was a usage error, although the return
value is currently ignored.
Signal handlers
The sudo front-end installs default signal handlers to trap common sig-
nals while the plugin functions are run. The following signals are
trapped by default before the command is executed:
• SIGALRM
• SIGHUP
• SIGINT
• SIGPIPE
• SIGQUIT
• SIGTERM
• SIGTSTP
• SIGUSR1
• SIGUSR2
If a fatal signal is received before the command is executed, sudo will
call the plugin's close() function with an exit status of 128 plus the
value of the signal that was received. This allows for consistent log-
ging of commands killed by a signal for plugins that log such informa-
tion in their close() function. An exception to this is SIGPIPE, which
is ignored until the command is executed.
A plugin may temporarily install its own signal handlers but must re-
store the original handler before the plugin function returns.
Hook function API
Beginning with plugin API version 1.2, it is possible to install hooks
for certain functions called by the sudo front-end.
Currently, the only supported hooks relate to the handling of environ-
ment variables. Hooks can be used to intercept attempts to get, set,
or remove environment variables so that these changes can be reflected
in the version of the environment that is used to execute a command. A
future version of the API will support hooking internal sudo front-end
functions as well.
Hook structure
Hooks in sudo are described by the following structure:
typedef int (*sudo_hook_fn_t)();
struct sudo_hook {
unsigned int hook_version;
unsigned int hook_type;
sudo_hook_fn_t hook_fn;
void *closure;
};
A struct sudo_hook has the following fields:
hook_version
The hook_version field should be set to SUDO_HOOK_VERSION.
hook_type
The hook_type field may be one of the following supported hook
types:
SUDO_HOOK_SETENV
The C library setenv(3) function. Any registered hooks
will run before the C library implementation. The hook_fn
field should be a function that matches the following type-
def:
typedef int (*sudo_hook_fn_setenv_t)(const char *name,
const char *value, int overwrite, void *closure);
If the registered hook does not match the typedef the re-
sults are unspecified.
SUDO_HOOK_UNSETENV
The C library unsetenv(3) function. Any registered hooks
will run before the C library implementation. The hook_fn
field should be a function that matches the following type-
def:
typedef int (*sudo_hook_fn_unsetenv_t)(const char *name,
void *closure);
SUDO_HOOK_GETENV
The C library getenv(3) function. Any registered hooks
will run before the C library implementation. The hook_fn
field should be a function that matches the following type-
def:
typedef int (*sudo_hook_fn_getenv_t)(const char *name,
char **value, void *closure);
If the registered hook does not match the typedef the re-
sults are unspecified.
SUDO_HOOK_PUTENV
The C library putenv(3) function. Any registered hooks
will run before the C library implementation. The hook_fn
field should be a function that matches the following type-
def:
typedef int (*sudo_hook_fn_putenv_t)(char *string,
void *closure);
If the registered hook does not match the typedef the re-
sults are unspecified.
hook_fn
sudo_hook_fn_t hook_fn;
The hook_fn field should be set to the plugin's hook implementa-
tion. The actual function arguments will vary depending on the
hook_type (see hook_type above). In all cases, the closure field
of struct sudo_hook is passed as the last function parameter.
This can be used to pass arbitrary data to the plugin's hook im-
plementation.
The function return value may be one of the following:
SUDO_HOOK_RET_ERROR
The hook function encountered an error.
SUDO_HOOK_RET_NEXT
The hook completed without error, go on to the next hook
(including the system implementation if applicable). For
example, a getenv(3) hook might return SUDO_HOOK_RET_NEXT
if the specified variable was not found in the private copy
of the environment.
SUDO_HOOK_RET_STOP
The hook completed without error, stop processing hooks for
this invocation. This can be used to replace the system
implementation. For example, a setenv hook that operates
on a private copy of the environment but leaves environ un-
changed.
Care must be taken when hooking C library functions, it is very easy to
create an infinite loop. For example, a getenv(3) hook that calls the
snprintf(3) function may create a loop if the snprintf(3) implementa-
tion calls getenv(3) to check the locale. To prevent this, you may
wish to use a static variable in the hook function to guard against
nested calls. For example:
static int in_progress = 0; /* avoid recursion */
if (in_progress)
return SUDO_HOOK_RET_NEXT;
in_progress = 1;
...
in_progress = 0;
return SUDO_HOOK_RET_STOP;
Hook API Version Macros
/* Hook API version major/minor */
#define SUDO_HOOK_VERSION_MAJOR 1
#define SUDO_HOOK_VERSION_MINOR 0
#define SUDO_HOOK_VERSION SUDO_API_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\
SUDO_HOOK_VERSION_MINOR)
For getters and setters see the “Policy plugin API”.
Event API
When sudo runs a command, it uses an event loop to service signals and
I/O. Events may be triggered based on time, a file or socket descrip-
tor becoming ready, or due to receipt of a signal. Starting with API
version 1.15, it is possible for a plugin to participate in this event
loop by calling the event_alloc() function.
Event structure
Events are described by the following structure:
typedef void (*sudo_plugin_ev_callback_t)(int fd, int what, void *closure);
struct sudo_plugin_event {
int (*set)(struct sudo_plugin_event *pev, int fd, int events,
sudo_plugin_ev_callback_t callback, void *closure);
int (*add)(struct sudo_plugin_event *pev, struct timespec *timeout);
int (*del)(struct sudo_plugin_event *pev);
int (*pending)(struct sudo_plugin_event *pev, int events,
struct timespec *ts);
int (*fd)(struct sudo_plugin_event *pev);
void (*setbase)(struct sudo_plugin_event *pev, void *base);
void (*loopbreak)(struct sudo_plugin_event *pev);
void (*free)(struct sudo_plugin_event *pev);
};
A struct sudo_plugin_event contains the following function pointers:
set
int (*set)(struct sudo_plugin_event *pev, int fd, int events,
sudo_plugin_ev_callback_t callback, void *closure);
The set() function takes the following arguments:
struct sudo_plugin_event *pev
A pointer to the struct sudo_plugin_event itself.
fd The file or socket descriptor for I/O-based events or the
signal number for signal events. For time-based events, fd
must be -1.
events
The following values determine what will trigger the event
callback:
SUDO_PLUGIN_EV_TIMEOUT
callback is run after the specified timeout expires
SUDO_PLUGIN_EV_READ
callback is run when the file descriptor is readable
SUDO_PLUGIN_EV_WRITE
callback is run when the file descriptor is writable
SUDO_PLUGIN_EV_PERSIST
event is persistent and remains enabled until explic-
itly deleted
SUDO_PLUGIN_EV_SIGNAL
callback is run when the specified signal is received
The SUDO_PLUGIN_EV_PERSIST flag may be ORed with any of the
event types. It is also possible to OR SUDO_PLUGIN_EV_READ
and SUDO_PLUGIN_EV_WRITE together to run the callback when
a descriptor is ready to be either read from or written to.
All other event values are mutually exclusive.
sudo_plugin_ev_callback_t callback
typedef void (*sudo_plugin_ev_callback_t)(int fd, int what,
void *closure);
The function to call when an event is triggered. The
callback() function is run with the following arguments:
fd The file or socket descriptor for I/O-based events or
the signal number for signal events.
what The event type that triggered that callback. For
events that have multiple event types (for example
SUDO_PLUGIN_EV_READ and SUDO_PLUGIN_EV_WRITE) or have
an associated timeout, what can be used to determine
why the callback was run.
closure
The generic pointer that was specified in the set()
function.
closure
A generic pointer that will be passed to the callback func-
tion.
The set() function returns 1 on success, and -1 if a error oc-
curred.
add
int (*add)(struct sudo_plugin_event *pev, struct timespec *timeout);
The add() function adds the event pev to sudo's event loop. The
event must have previously been initialized via the set() func-
tion. If the timeout argument is not NULL, it should specify a
(relative) timeout after which the event will be triggered if the
main event criteria has not been met. This is often used to im-
plement an I/O timeout where the event will fire if a descriptor
is not ready within a certain time period. If the event is al-
ready present in the event loop, its timeout will be adjusted to
match the new value, if any.
The add() function returns 1 on success, and -1 if a error oc-
curred.
del
int (*del)(struct sudo_plugin_event *pev);
The del() function deletes the event pev from sudo's event loop.
Deleted events can be added back via the add() function.
The del() function returns 1 on success, and -1 if a error oc-
curred.
pending
int (*pending)(struct sudo_plugin_event *pev, int events,
struct timespec *ts);
The pending() function can be used to determine whether one or
more events is pending. The events argument specifies which
events to check for. See the set() function for a list of valid
event types. If SUDO_PLUGIN_EV_TIMEOUT is specified in events,
the event has an associated timeout and the ts pointer is non-
NULL, it will be filled in with the remaining time.
fd
int (*fd)(struct sudo_plugin_event *pev);
The fd() function returns the descriptor or signal number associ-
ated with the event pev.
setbase
void (*setbase)(struct sudo_plugin_event *pev, void *base);
The setbase() function sets the underlying event base for pev to
the specified value. This can be used to move an event created
via event_alloc() to a new event loop allocated by sudo's event
subsystem. If base is NULL, pev's event base is reset to the de-
fault value, which corresponds to sudo's main event loop. Using
this function requires linking the plugin with the sudo_util li-
brary. It is unlikely to be used outside of the sudoers plugin.
loopbreak
void (*loopbreak)(struct sudo_plugin_event *pev);
The loopbreak() function causes sudo's event loop to exit immedi-
ately and the running command to be terminated.
free
void (*free)(struct sudo_plugin_event *pev);
The free() function deletes the event pev from the event loop and
frees the memory associated with it.
Remote command execution
The sudo front-end does not support running remote commands. However,
starting with sudo 1.8.8, the -h option may be used to specify a remote
host that is passed to the policy plugin. A plugin may also accept a
runas_user in the form of “user@hostname” which will work with older
versions of sudo. It is anticipated that remote commands will be sup-
ported by executing a “helper” program. The policy plugin should setup
the execution environment such that the sudo front-end will run the
helper which, in turn, will connect to the remote host and run the com-
mand.
For example, the policy plugin could utilize ssh to perform remote com-
mand execution. The helper program would be responsible for running
ssh with the proper options to use a private key or certificate that
the remote host will accept and run a program on the remote host that
would setup the execution environment accordingly.
Remote sudoedit functionality must be handled by the policy plugin, not
sudo itself as the front-end has no knowledge that a remote command is
being executed. This may be addressed in a future revision of the plu-
gin API.
Conversation API
If the plugin needs to interact with the user, it may do so via the
conversation() function. A plugin should not attempt to read directly
from the standard input or the user's terminal (neither of which are
guaranteed to exist). The caller must include a trailing newline in
msg if one is to be printed.
A printf()-style function is also available that can be used to display
informational or error messages to the user, which is usually more con-
venient for simple messages where no use input is required.
Conversation function structures
The conversation function takes as arguments pointers to the following
structures:
struct sudo_conv_message {
#define SUDO_CONV_PROMPT_ECHO_OFF 0x0001 /* do not echo user input */
#define SUDO_CONV_PROMPT_ECHO_ON 0x0002 /* echo user input */
#define SUDO_CONV_ERROR_MSG 0x0003 /* error message */
#define SUDO_CONV_INFO_MSG 0x0004 /* informational message */
#define SUDO_CONV_PROMPT_MASK 0x0005 /* mask user input */
#define SUDO_CONV_PROMPT_ECHO_OK 0x1000 /* flag: allow echo if no tty */
#define SUDO_CONV_PREFER_TTY 0x2000 /* flag: use tty if possible */
int msg_type;
int timeout;
const char *msg;
};
#define SUDO_CONV_REPL_MAX 1023
struct sudo_conv_reply {
char *reply;
};
typedef int (*sudo_conv_callback_fn_t)(int signo, void *closure);
struct sudo_conv_callback {
unsigned int version;
void *closure;
sudo_conv_callback_fn_t on_suspend;
sudo_conv_callback_fn_t on_resume;
};
Pointers to the conversation() and printf()-style functions are passed
in to the plugin's open() function when the plugin is initialized. The
following type definitions can be used in the declaration of the open()
function:
typedef int (*sudo_conv_t)(int num_msgs,
const struct sudo_conv_message msgs[],
struct sudo_conv_reply replies[], struct sudo_conv_callback *callback);
typedef int (*sudo_printf_t)(int msg_type, const char * restrict fmt, ...);
To use the conversation() function, the plugin must pass an array of
struct sudo_conv_message and struct sudo_conv_reply. There must be a
struct sudo_conv_message and struct sudo_conv_reply for each message in
the conversation, that is, both arrays must have the same number of el-
ements. Each struct sudo_conv_reply must have its reply member ini-
tialized to NULL. The struct sudo_conv_callback pointer, if not NULL,
should contain function pointers to be called when the sudo process is
suspended and/or resumed during conversation input. The on_suspend and
on_resume functions are called with the signal that caused sudo to be
suspended and the closure pointer from the struct sudo_conv_callback.
These functions should return 0 on success and -1 on error. On error,
the conversation will end and the conversation function will return a
value of -1. The intended use is to allow the plugin to release re-
sources, such as locks, that should not be held indefinitely while sus-
pended and then reacquire them when the process is resumed. The func-
tions are not actually invoked from within a signal handler.
The msg_type must be set to one of the following values:
SUDO_CONV_PROMPT_ECHO_OFF
Prompt the user for input with echo disabled; this is generally
used for passwords. The reply will be stored in the replies ar-
ray, and it will never be NULL.
SUDO_CONV_PROMPT_ECHO_ON
Prompt the user for input with echo enabled. The reply will be
stored in the replies array, and it will never be NULL.
SUDO_CONV_ERROR_MSG
Display an error message. The message is written to the standard
error unless the SUDO_CONV_PREFER_TTY flag is set, in which case
it is written to the user's terminal if possible.
SUDO_CONV_INFO_MSG
Display a message. The message is written to the standard output
unless the SUDO_CONV_PREFER_TTY flag is set, in which case it is
written to the user's terminal if possible.
SUDO_CONV_PROMPT_MASK
Prompt the user for input but echo an asterisk character for each
character read. The reply will be stored in the replies array,
and it will never be NULL. This can be used to provide visual
feedback to the user while reading sensitive information that
should not be displayed.
In addition to the above values, the following flag bits may also be
set:
SUDO_CONV_PROMPT_ECHO_OK
Allow input to be read when echo cannot be disabled when the mes-
sage type is SUDO_CONV_PROMPT_ECHO_OFF or SUDO_CONV_PROMPT_MASK.
By default, sudo will refuse to read input if the echo cannot be
disabled for those message types.
SUDO_CONV_PREFER_TTY
When displaying a message via SUDO_CONV_ERROR_MSG or
SUDO_CONV_INFO_MSG, try to write the message to the user's termi-
nal. If the terminal is unavailable, the standard error or stan-
dard output will be used, depending upon whether
SUDO_CONV_ERROR_MSG or SUDO_CONV_INFO_MSG was used. The user's
terminal is always used when possible for input, this flag is
only used for output.
The timeout in seconds until the prompt will wait for no more input. A
zero value implies an infinite timeout.
The plugin is responsible for freeing the reply buffer located in each
struct sudo_conv_reply, if it is not NULL. SUDO_CONV_REPL_MAX repre-
sents the maximum length of the reply buffer (not including the trail-
ing NUL character). In practical terms, this is the longest password
sudo will support.
The printf()-style function uses the same underlying mechanism as the
conversation() function but only supports SUDO_CONV_INFO_MSG and
SUDO_CONV_ERROR_MSG for the msg_type parameter. It can be more conve-
nient than using the conversation() function if no user reply is needed
and supports standard printf() escape sequences.
See the sample plugin for an example of the conversation() function us-
age.
Plugin invocation order
As of sudo 1.9.0, the plugin open() and close() functions are called in
the following order:
1. audit open
2. policy open
3. approval open
4. approval close
5. I/O log open
6. command runs
7. command exits
8. I/O log close
9. policy close
10. audit close
11. sudo exits
Prior to sudo 1.9.0, the I/O log close() function was called after the
policy close() function.
Sudoers group plugin API
The sudoers plugin supports its own plugin interface to allow non-Unix
group lookups. This can be used to query a group source other than the
standard Unix group database. Two sample group plugins are bundled
with sudo, group_file, and system_group, are detailed in sudoers(5).
Third party group plugins include a QAS AD plugin available from Quest
Software.
A group plugin must declare and populate a struct sudoers_group_plugin
in the global scope. This structure contains pointers to the functions
that implement plugin initialization, cleanup, and group lookup.
struct sudoers_group_plugin {
unsigned int version;
int (*init)(int version, sudo_printf_t sudo_plugin_printf,
char *const argv[]);
void (*cleanup)(void);
int (*query)(const char *user, const char *group,
const struct passwd *pwd);
};
A struct sudoers_group_plugin has the following fields:
version
The version field should be set to GROUP_API_VERSION.
This allows sudoers to determine the API version the group plugin
was built against.
init
int (*init)(int version, sudo_printf_t sudo_plugin_printf,
char *const argv[]);
The init() function is called after sudoers has been parsed but
before any policy checks. It returns 1 on success, 0 on failure
(or if the plugin is not configured), and -1 if a error occurred.
If an error occurs, the plugin may call the plugin_printf() func-
tion with SUDO_CONF_ERROR_MSG to present additional error infor-
mation to the user.
The function arguments are as follows:
version
The version passed in by sudoers allows the plugin to de-
termine the major and minor version number of the group
plugin API supported by sudoers.
plugin_printf
A pointer to a printf()-style function that may be used to
display informational or error message to the user. Re-
turns the number of characters printed on success and -1 on
failure.
argv A NULL-terminated array of arguments generated from the
group_plugin option in sudoers. If no arguments were
given, argv will be NULL.
cleanup
void (*cleanup)();
The cleanup() function is called when sudoers has finished its
group checks. The plugin should free any memory it has allocated
and close open file handles.
query
int (*query)(const char *user, const char *group,
const struct passwd *pwd);
The query() function is used to ask the group plugin whether user
is a member of group.
The function arguments are as follows:
user The name of the user being looked up in the external group
database.
group
The name of the group being queried.
pwd The password database entry for user, if any. If user is
not present in the password database, pwd will be NULL.
Group API Version Macros
/* Sudoers group plugin version major/minor */
#define GROUP_API_VERSION_MAJOR 1
#define GROUP_API_VERSION_MINOR 0
#define GROUP_API_VERSION ((GROUP_API_VERSION_MAJOR << 16) | \
GROUP_API_VERSION_MINOR)
For getters and setters see the “Policy plugin API”.
PLUGIN API CHANGELOG
The following revisions have been made to the Sudo Plugin API.
Version 1.0
Initial API version.
Version 1.1 (sudo 1.8.0)
The I/O logging plugin's open() function was modified to take the
command_info list as an argument.
Version 1.2 (sudo 1.8.5)
The Policy and I/O logging plugins' open() functions are now
passed a list of plugin parameters if any are specified in
sudo.conf(5).
A simple hooks API has been introduced to allow plugins to hook
in to the system's environment handling functions.
The init_session() Policy plugin function is now passed a pointer
to the user environment which can be updated as needed. This can
be used to merge in environment variables stored in the PAM han-
dle before a command is run.
Version 1.3 (sudo 1.8.7)
Support for the exec_background entry has been added to the
command_info list.
The max_groups and plugin_dir entries were added to the settings
list.
The version() and close() functions are now optional. Previ-
ously, a missing version() or close() function would result in a
crash. If no policy plugin close() function is defined, a de-
fault close() function will be provided by the sudo front-end
that displays a warning if the command could not be executed.
The sudo front-end now installs default signal handlers to trap
common signals while the plugin functions are run.
Version 1.4 (sudo 1.8.8)
The remote_host entry was added to the settings list.
Version 1.5 (sudo 1.8.9)
The preserve_fds entry was added to the command_info list.
Version 1.6 (sudo 1.8.11)
The behavior when an I/O logging plugin returns an error (-1) has
changed. Previously, the sudo front-end took no action when the
log_ttyin(), log_ttyout(), log_stdin(), log_stdout(), or
log_stderr() function returned an error.
The behavior when an I/O logging plugin returns 0 has changed.
Previously, output from the command would be displayed to the
terminal even if an output logging function returned 0.
Version 1.7 (sudo 1.8.12)
The plugin_path entry was added to the settings list.
The debug_flags entry now starts with a debug file path name and
may occur multiple times if there are multiple plugin-specific
Debug lines in the sudo.conf(5) file.
Version 1.8 (sudo 1.8.15)
The sudoedit_checkdir and sudoedit_follow entries were added to
the command_info list. The default value of sudoedit_checkdir
was changed to true in sudo 1.8.16.
The sudo conversation() function now takes a pointer to a struct
sudo_conv_callback as its fourth argument. The sudo_conv_t defi-
nition has been updated to match. The plugin must specify that
it supports plugin API version 1.8 or higher to receive a conver-
sation function pointer that supports this argument.
Version 1.9 (sudo 1.8.16)
The execfd entry was added to the command_info list.
Version 1.10 (sudo 1.8.19)
The umask entry was added to the user_info list. The
iolog_group, iolog_mode, and iolog_user entries were added to the
command_info list.
Version 1.11 (sudo 1.8.20)
The timeout entry was added to the settings list.
Version 1.12 (sudo 1.8.21)
The change_winsize() function was added to struct io_plugin.
Version 1.13 (sudo 1.8.26)
The log_suspend() function was added to struct io_plugin.
Version 1.14 (sudo 1.8.29)
The umask_override entry was added to the command_info list.
Version 1.15 (sudo 1.9.0)
The cwd_optional entry was added to the command_info list.
The event_alloc() function was added to struct policy_plugin and
struct io_plugin.
The errstr argument was added to the policy and I/O plugin func-
tions which the plugin function can use to return an error
string. This string may be used by the audit plugin to report
failure or error conditions set by the other plugins.
The close() function is now is called regardless of whether or
not a command was actually executed. This makes it possible for
plugins to perform cleanup even when a command was not run.
SUDO_CONV_REPL_MAX has increased from 255 to 1023 bytes.
Support for audit and approval plugins was added.
Version 1.16 (sudo 1.9.3)
Initial resource limit values were added to the user_info list.
The cmnd_chroot and cmnd_cwd entries were added to the settings
list.
Version 1.17 (sudo 1.9.4)
The event_alloc() function was added to struct audit_plugin and
struct approval_plugin.
Version 1.18 (sudo 1.9.9)
The policy may now set resource limit values in the command_info
list. The intercept and log_subcmds entries were added to the
command_info list.
Version 1.19 (sudo 1.9.11)
The intercept_ptrace and intercept_setid entries were added to
the settings list. The apparmor_profile and use_ptrace entries
were added to the command_info list.
Version 1.20 (sudo 1.9.12)
The update_ticket entry was added to the settings list. The
intercept_verify entry was added to the command_info list.
Version 1.21 (sudo 1.9.13)
The sudoedit_nfiles entry was added to the command_info list.
SEE ALSO
sudo.conf(5), sudoers(5), sudo(8)
AUTHORS
Many people have worked on sudo over the years; this version consists
of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS.md file in the sudo distribution
(https://www.sudo.ws/about/contributors/) for an exhaustive list of
people who have contributed to sudo.
BUGS
If you believe you have found a bug in sudo, you can submit a bug re-
port at https://bugzilla.sudo.ws/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search
the archives.
DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties, includ-
ing, but not limited to, the implied warranties of merchantability and
fitness for a particular purpose are disclaimed. See the LICENSE.md
file distributed with sudo or https://www.sudo.ws/about/license/ for
complete details.
Sudo 1.9.15p5 July 10, 2023 SUDO_PLUGIN(5)
Generated by dwww version 1.16 on Tue Dec 16 14:32:48 CET 2025.