sudo_plugin — Sudo
Plugin API
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 policy plugin and an associated
I/O logging plugin are used. Via the plugin API,
sudo can be configured to use alternate policy
and/or I/O logging 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 incremented 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.
A policy plugin must declare and populate a
policy_plugin struct 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 plugin_printf, char * const settings[],
char * const user_info[], char * const user_env[],
char * const plugin_options[]);
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[]);
int (*list)(int argc, char * const argv[], int verbose,
const char *list_user);
int (*validate)(void);
void (*invalidate)(int remove);
int (*init_session)(struct passwd *pwd, char **user_env[]);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
};
The policy_plugin struct has the following fields:
type field should always be set to
SUDO_POLICY_PLUGIN.version field should be set to
SUDO_API_VERSION.
This allows sudo to determine the API
version the plugin was built against.
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t plugin_printf, char * const settings[],
char * const user_info[], char * const user_env[],
char * const plugin_options[]);
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 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:
sudo allows the
plugin to determine the major and minor version number of the plugin
API supported by sudo.conversation()
function that can be used by the plugin to interact with the user (see
below). Returns 0 on success and -1 on failure.printf()-style function that
may be used to display informational or error messages (see below).
Returns the number of characters printed on success and -1 on
failure.sudo settings in the
form of “name=value” strings. The vector is terminated
by a NULL pointer. These settings correspond
to flags the user specified when running sudo.
As such, they will only be present when the corresponding flag 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.
-a flag, to use on systems where BSD
authentication is supported.-C flag 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.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-specific Debug
entry.-k
flag along with a command, indicating that the user wishes to
ignore any cached authentication credentials.
implied_shell
to true. This allows sudo with no
arguments 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.sudo will pass the plugin the path to the
user's shell and set-c flag.-i
flag, indicating that the user wishes to run a login shell.:’), it is an IPv6
address, else it is IPv4.-n
flag, indicating that sudo should operate
in non-interactive mode. The plugin may reject a command run in
non-interactive mode if user interaction is required.sudo front end. This is the default
directory set at compile time and may not correspond to the
directory the running plugin was loaded from. It may be used by a
plugin to locate support files.sudo
front end. The path name will be a fully-qualified unless the
plugin was statically compiled into
sudo.-E
flag, indicating that the user wishes to preserve the
environment.-P
flag, indicating that the user wishes to preserve the group vector
instead of setting it based on the runas user.-p flag.-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.-s
flag, indicating that the user wishes to run a shell.-g flag.-u flag.-r flag.-t flag.-H
flag. If true, set the HOME environment
variable to the target user's home directory.-e flag is is
specified or if invoked 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.Additional settings may be added in the future so the plugin should silently ignore settings that it does not recognize.
NULL pointer.
When parsing user_info, the plugin
should split on the first equal sign
(‘=’) since the
name field will never include one itself but the
value might.
sudo.sudo.sudo.sudo process is a member of. Only
available starting with API version 1.2.sudo
process. Only available starting with API version 1.2.NULL-terminated array of strings. If no
arguments were specified, plugin_options will be
the NULL pointer.
NOTE: 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.
sudo
process. Only available starting with API version 1.2.sudo process
or 0 if sudo is not part of a POSIX job
control session. Only available starting with API version
1.2.sudo
process or -1 if there is no terminal present. Only available
starting with API version 1.2.tty=”.sudo.sudo.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.
void (*close)(int exit_status, int error);
The
close()
function is called when the command being run by
sudo finishes.
The function arguments are as follows:
exit_status is undefined if
error is non-zero.errno set by the execve(2)
system call. The plugin is responsible for displaying error
information via the
conversation()
or
plugin_printf()
function. If the command was successfully executed, the value of
error is 0.If no
close()
function is defined, no I/O logging plugins are loaded, and neither the
timeout not 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.
int (*show_version)(int verbose);
The
show_version()
function is called by sudo when the user
specifies the -V option. The plugin may display
its version information to the user via the
conversation() or
plugin_printf() function using
SUDO_CONV_INFO_MSG. If the user requests
detailed version information, the verbose flag will be set.
int (*check_policy)(int argc, char * const argv[]
char *env_add[], char **command_info[],
char **argv_out[], char **user_env_out[]);
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
elevated 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 complete. If the plugin supports sudoedit, it
should choose the editor to be used, potentially from a variable in the
user's environment, such as EDITOR, and include
it in argv_out (note that environment variables may
include command line flags). The files to be edited should be copied
from argv into 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
should also set
sudoedit=true
in the command_info list.
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 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:
NULL pointer.NULL pointer.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.
sudo to set the execution environment when
running a command. The plugin is responsible for creating and
populating the vector, which must be terminated with a
NULL pointer. The following values are
recognized by sudo:
sudo will close all files
descriptors with a value of number or
higher.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 pty (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 settings) 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 terminal
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 really wants the input). This is different
from historic
sudo
behavior or when the command is not being run in a pty.
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
(usually 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 enabled or disable it on a per-command
basis.
This setting has no effect unless I/O logging is enabled or use_pty is enabled.
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
descriptor.sudo will preserve the user's
group vector instead of initializing the group vector based on
runas_user.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. 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. Symbolic links will not be followed in writable
directories 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_follow option can be set to
false to disable this check. Only available starting with API
version 1.8.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.sudo will only run the command in a pty
when an I/O log plugin is loaded.sudo will base
the new entry on the invoking user's existing entry.Unsupported values will be ignored.
NULL-terminated argument vector to pass to
the execve(2) system call when executing the
command. The plugin is responsible for allocating and populating the
vector.NULL-terminated environment vector to use
when executing the command. The plugin is responsible for allocating
and populating the vector.int (*list)(int verbose, const char *list_user,
int argc, char * const argv[]);
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
plugin_printf()
function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
Privileges should be output via the
conversation()
or
plugin_printf()
function using SUDO_CONV_INFO_MSG,
NULL, the plugin should list the
privileges of the invoking user.NULL pointer.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 command line arguments.int (*validate)(void);
The
validate()
function is called when sudo is run with the
-v flag. For policy plugins such as
sudoers that cache authentication 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
plugin_printf()
function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
void (*invalidate)(int remove);
The
invalidate()
function is called when sudo is called with the
-k or -K flag. For
policy plugins such as sudoers that cache
authentication credentials, this function will invalidate the
credentials. If the
remove
flag is set, 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.
int (*init_session)(struct passwd *pwd, char **user_envp[);
The
init_session()
function is called before sudo sets up the
execution environment for the command. It is run in the parent
sudo process and before any uid or gid changes.
This can be used to perform session setup that is not supported by
command_info, such as opening the PAM session. The
close() function can be used to tear down the
session that was opened by init_session.
The pwd argument points to a passwd struct
for the user the command will be run as if the uid the command will run
as was found in the password database, otherwise it will be
NULL.
The user_env argument
points to the environment the command will run in, in the form of a
NULL-terminated vector of
“name=value” strings. This is the same string passed back
to the front end via the Policy Plugin's
user_env_out
parameter. If the
init_session()
function needs to modify the user environment, it should update the
pointer stored in user_env. The expected use case is
to merge the contents of the PAM environment (if any) with the contents
of user_env. NOTE: the user_env
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. Failure to do so may result in a crash.
Returns 1 on success, 0 on failure and -1
on error. On error, the plugin may optionally call the
conversation()
or
plugin_printf()
function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
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 support hooks,
register_hooks should be set to the
NULL pointer.
The version argument describes the version
of the hooks API supported by the sudo front
end.
The
register_hook()
function should be used to register any supported 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 hook does not
match the front end's major hook API version.
See the Hook function API section below for more information about hooks.
NOTE: 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.
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 supported 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.
NOTE: the
deregister_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, deregister_hooks will not be
called.
/* Plugin API version major/minor. */
#define SUDO_API_VERSION_MAJOR 1
#define SUDO_API_VERSION_MINOR 2
#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)
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 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[]);
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);
int (*log_ttyout)(const char *buf, unsigned int len);
int (*log_stdin)(const char *buf, unsigned int len);
int (*log_stdout)(const char *buf, unsigned int len);
int (*log_stderr)(const char *buf, unsigned int len);
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);
};
When an I/O plugin is loaded, sudo runs
the command in a pseudo-tty. 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 (note that 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-tty that is suitable for replaying the
user's session 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 logging 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 disabled. Other I/O logging plugins will still receive any remaining input or output that has not yet been processed.
If an input logging function rejects the data by returning 0, the command 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.
The io_plugin struct has the following fields:
type field should always be set to
SUDO_IO_PLUGIN.version field should be set to
SUDO_API_VERSION.
This allows sudo to determine the API
version the plugin was built against.
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t plugin_printf, char * const settings[],
char * const user_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(), 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 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
information to the user.
The function arguments are as follows:
sudo allows the
plugin to determine the major and minor version number of the plugin
API supported by sudo.conversation()
function that may be used by the
show_version() function to display version
information (see show_version() below). The
conversation() function may also be used to
display additional error message to the user. The
conversation() function returns 0 on success
and -1 on failure.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
characters printed on success and -1 on failure.sudo settings in the
form of “name=value” strings. The vector is terminated
by a NULL pointer. These settings correspond
to flags the user specified when running sudo.
As such, they will only be present when the corresponding flag 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 possible settings.
NULL pointer.
When parsing user_info, 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 possible strings.
NULL pointer.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.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.
NULL-terminated array of strings. If no
arguments were specified, plugin_options will be the
NULL pointer.
NOTE: 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.
void (*close)(int exit_status, int error);
The
close()
function is called when the command being run by
sudo finishes.
The function arguments are as follows:
exit_status is undefined if
error is non-zero.errno set by the execve(2)
system call. If the command was successfully executed, the value of
error is 0.int (*show_version)(int verbose);
The
show_version()
function is called by sudo when the user
specifies the -V option. The plugin may display
its version information to the user via the
conversation() or
plugin_printf() function using
SUDO_CONV_INFO_MSG. If the user requests
detailed version information, the verbose flag will be set.
int (*log_ttyin)(const char *buf, unsigned int len);
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:
int (*log_ttyout)(const char *buf, unsigned int len);
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 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:
int (*log_stdin)(const char *buf, unsigned int len);
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:
int (*log_stdout)(const char *buf, unsigned int len);
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:
int (*log_stderr)(const char *buf, unsigned int len);
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 rejected (which will terminate the running command) or -1 if an
error occurred.
The function arguments are as follows:
register_hooks.deregister_hooks.int (*change_winsize)(unsigned int lines, unsigned int cols);
The
change_winsize()
function is called whenever the window size of the terminal changes from
the initial values specified in the user_info
list. It returns 1 on success, 0 on failure, -1 if an error occurred
(which will terminate the running command).
Same as for the Policy plugin API.
The sudo front end installs default signal
handlers to trap common signals while the plugin functions are run. The
following signals are trapped by default before the command is executed:
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 logging of commands killed by a signal
for plugins that log such information 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 restore the original handler before the plugin function returns.
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
environment 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;
};
The sudo_hook structure has the following
fields:
hook_version field should be set to
SUDO_HOOK_VERSION.hook_type field may be one of the following
supported hook types:
SUDO_HOOK_SETENVhook_fn field should be a function that
matches the following typedef:
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 results are unspecified.
SUDO_HOOK_UNSETENVhook_fn field should be a function that
matches the following typedef:
typedef int (*sudo_hook_fn_unsetenv_t)(const char *name, void *closure);
SUDO_HOOK_GETENVhook_fn field should be a function that
matches the following typedef:
typedef int (*sudo_hook_fn_getenv_t)(const char *name, char **value, void *closure);
If the registered hook does not match the typedef the results are unspecified.
SUDO_HOOK_PUTENVhook_fn field should be a function that
matches the following typedef:
typedef int (*sudo_hook_fn_putenv_t)(char *string, void *closure);
If the registered hook does not match the typedef the results are unspecified.
The hook_fn field should be set to the
plugin's hook implementation. 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 implementation.
The function return value may be one of the following:
SUDO_HOOK_RET_ERRORSUDO_HOOK_RET_NEXTSUDO_HOOK_RET_NEXT if the specified variable
was not found in the private copy of the environment.SUDO_HOOK_RET_STOPsetenv hook that operates on a
private copy of the environment but leaves
environ unchanged.Note that it is very easy to create an infinite loop when hooking C library functions. For example, a getenv(3) hook that calls the snprintf(3) function may create a loop if the snprintf(3) implementation 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.
The sudo front end does not have native
support for 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 supported 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 command.
For example, the policy plugin could utilize
ssh to perform remote command 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.
Note that 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 plugin 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 tty (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 convenient 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 */
int msg_type;
int timeout;
const char *msg;
};
#define SUDO_CONV_REPL_MAX 255
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 *fmt, ...);
To use the
conversation()
function, the plugin must pass an array of
sudo_conv_message and
sudo_conv_reply structures. There must be a
struct sudo_conv_message and struct
sudo_conv_reply for each message in the conversation. 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 resources, such as locks, that should not be held indefinitely while
suspended and then reacquire them when the process is resumed. Note that the
functions are not actually invoked from within a signal handler.
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 represents the maximum length of
the reply buffer (not including the trailing NUL character). In practical
terms, this is the longest password sudo will
support. It is also useful as a maximum value for the
memset_s()
function when clearing passwords filled in by the conversation function.
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 convenient 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 usage.
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
sudoers_group_plugin struct 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_printf,
char *const argv[]);
void (*cleanup)(void);
int (*query)(const char *user, const char *group,
const struct passwd *pwd);
};
The sudoers_group_plugin struct has the
following fields:
version field should be set to
GROUP_API_VERSION.
This allows sudoers to determine the
API version the group plugin was built against.
int (*init)(int version, sudo_printf_t 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()
function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
The function arguments are as follows:
sudoers allows the
plugin to determine the major and minor version number of the group
plugin API supported by sudoers.printf()-style
function that may be used to display informational or error message to
the user. Returns the number of characters printed on success and -1
on failure.NULL-terminated array of arguments generated
from the
group_plugin
option in sudoers. If no arguments were given,
argv will be NULL.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.
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:
NULL./* 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)
The following revisions have been made to the Sudo Plugin API.
open()
function was modified to take the command_info
list as an argument.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 handle before a command is run.
command_info list.
The
max_groups
and
plugin_dir
entries were added to the settings list.
The
version()
and close() functions are now optional.
Previously, a missing version() or
close() function would result in a crash. If no
policy plugin close() function is defined, a
default 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.
settings list.command_info list.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.
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.
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 definition has
been updated to match. The plugin must specify that it supports plugin
API version 1.8 or higher to receive a conversation function pointer
that supports this argument.
command_info list.user_info list. The
iolog_group,
iolog_mode,
and
iolog_user
entries were added to the command_info list.settings list.change_winsize field was added to the
io_plugin struct.Many people have worked on sudo over the
years; this version consists of code written primarily by:
See the CONTRIBUTORS file in the sudo
distribution (https://www.sudo.ws/contributors.html) for an exhaustive list
of people who have contributed to sudo.
If you feel you have found a bug in sudo,
please submit a bug report at https://bugzilla.sudo.ws/
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.
sudo is provided “AS IS” and
any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose
are disclaimed. See the LICENSE file distributed with
sudo or https://www.sudo.ws/license.html for
complete details.