Provided by: sudo-ldap_1.8.9p5-1ubuntu1.4_amd64 
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 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.
Policy plugin API
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 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 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:
version
The version passed in by sudo allows the plugin to determine 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 below). 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 below). 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 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.
bsdauth_type=string
Authentication type, if specified by the -a flag, to use on systems where BSD
authentication is supported.
closefrom=number
If specified, the user has requested via the -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_flags=string
A comma-separated list of debug flags that correspond to sudo's Debug entry in
sudo.conf(5), if there is one. The flags are passed to the plugin as they appear in
sudo.conf(5). The syntax used by sudo and the sudoers plugin is subsystem@priority but
the plugin is free to use a different format so long as it does not include a comma
(‘,’). There is not currently a way to specify a set of debug flags specific to the
plugin--the flags are shared by sudo and the plugin.
debug_level=number
This setting has been deprecated in favor of debug_flags.
ignore_ticket=bool
Set to true if the user specified the -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.
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
login_class=string
BSD login class to use when setting resource limits and nice value, if specified by the
-c flag.
login_shell=bool
Set to true if the user specified the -i flag, indicating 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 contains a colon
(‘:’), it is an IPv6 address, else it is IPv4.
noninteractive=bool
Set to true if the user specified the -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.
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 running plugin was
loaded from. It may be used by a plugin to locate support files.
preserve_environment=bool
Set to true if the user specified the -E flag, indicating that the user wishes to
preserve the environment.
preserve_groups=bool
Set to true if the user specified the -P flag, indicating 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 flag.
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 flag, indicating that the user wishes to run a
shell.
runas_group=string
The group name or gid to run the command as, if specified via the -g flag.
runas_user=string
The user name or uid to run the command as, if specified via the -u flag.
selinux_role=string
SELinux role to use when executing the command, if specified by the -r flag.
selinux_type=string
SELinux type to use when executing the command, if specified by the -t flag.
set_home=bool
Set to true if the user specified the -H flag. If true, set the HOME environment
variable to the target user's home directory.
sudoedit=bool
Set to true when the -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.
user_info
A vector of information about the user running the command in the form of “name=value”
strings. The vector is terminated by a 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.
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.
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
plugin in the form of a 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.
ppid=int
The parent process ID of the running sudo process. Only available starting with API
version 1.2.
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 -1 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.
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.
close
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
The command's exit status, as returned by the wait(2) system call. 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 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.
show_version
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.
check_policy
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:
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 plugin is
responsible for creating and populating the vector, which must be terminated with a NULL
pointer. The following values are recognized by sudo:
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 executing the command.
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 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, Mac OS X fails to restart the tcgetattr()
and tcsetattr() system calls (this is a bug in Mac OS X). 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.
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_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 logging 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 logging 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 logging 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 redirected from a file.
This is a hint to the I/O logging 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 command. The nice value, if specified,
overrides the priority associated with the login_class on BSD systems.
noexec=bool
If set, prevent the command from executing other programs.
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.
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_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.
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-tty 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.
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 command.
use_pty=bool
Allocate a pseudo-tty to run the command in, regardless of whether or not I/O logging
is in use. By default, sudo will only run the command in a pty 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 invoking user. If not set, sudo will base the new
entry 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 plugin is responsible for allocating and populating the vector.
user_env_out
The NULL-terminated environment vector to use when executing the command. The plugin is
responsible for allocating and populating the vector.
list
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,
verbose
Flag indicating whether to list in verbose mode or not.
list_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.
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 command line arguments.
validate
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.
invalidate
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.
init_session
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.
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 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.
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 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.
Policy Plugin Version Macros
/* 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_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 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));
};
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.
The io_plugin struct 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 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_input(), log_output() or show_version() functions are
called. It is only called if the version is being requested or the 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:
version
The version passed in by sudo allows the plugin to determine 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 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.
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 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 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.
user_info
A vector of information about the user running the command in the form of “name=value”
strings. The vector is terminated by a 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.
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 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.
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.
close
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
The command's exit status, as returned by the wait(2) system call. 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 0.
show_version
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.
log_ttyin
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 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.
log_ttyout
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 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.
log_stdin
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 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.
log_stdout
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 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.
log_stderr
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 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.
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.
I/O Plugin Version Macros
Same as for the “Policy plugin API”.
Signal handlers
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:
• SIGALRM
• SIGHUP
• SIGINT
• 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 logging of commands killed by a signal for plugins that log such information in their close()
function.
A plugin may temporarily install its own signal handlers but must restore 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 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 {
int hook_version;
int hook_type;
sudo_hook_fn_t hook_fn;
void *closure;
};
The sudo_hook structure 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 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_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 typedef:
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 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_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 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.
hook_fn
sudo_hook_fn_t hook_fn;
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_ERROR
The hook function encountered an error.
SUDO_HOOK_RET_NEXT
The hook completed without error, go on to the next hook (including the native 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 native implementation. For example, a setenv 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_MKVERSION(x, y) ((x << 16) | y)
#define SUDO_HOOK_VERSION SUDO_HOOK_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\
SUDO_HOOK_VERSION_MINOR)
/* Getters and setters for hook API version */
#define SUDO_HOOK_VERSION_GET_MAJOR(v) ((v) >> 16)
#define SUDO_HOOK_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define SUDO_HOOK_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define SUDO_HOOK_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
Remote command execution
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.
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 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.
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_DEBUG_MSG 0x0006 /* debugging message */
#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_t)(int num_msgs,
const struct sudo_conv_message msgs[],
struct sudo_conv_reply replies[]);
typedef int (*sudo_printf_t)(int msg_type, const char *fmt, ...);
Pointers to the conversation() and printf()-style functions are passed in to the plugin's open() function
when the plugin is initialized.
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 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, SUDO_CONV_ERROR_MSG and SUDO_CONV_DEBUG_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.
Unlike, SUDO_CONV_INFO_MSG and Dv SUDO_CONV_ERROR_MSG , messages sent with the SUDO_CONV_DEBUG_MSG
msg_type are not directly user-visible. Instead, they are logged to the file specified in the Debug
statement (if any) in the sudo.conf(5). file. This allows a plugin to log debugging information and is
intended to be used in conjunction with the debug_flags setting.
See the sample plugin for an example of the conversation() function usage.
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 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
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 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:
version
The version passed in by sudoers allows the plugin to determine 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. Returns 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)
/* Getters and setters for group version */
#define GROUP_API_VERSION_GET_MAJOR(v) ((v) >> 16)
#define GROUP_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define GROUP_API_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define GROUP_API_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
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 handle
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. 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.
Version 1.4 (sudo 1.8.8)
The remote_host entry was added to the settings list.
Version 1.5 (sudo 1.8.9)