SUDO_PLUGIN(5) BSD File Formats Manual SUDO_PLUGIN(5)NAMEsudo_plugin — Sudo Plugin API
DESCRIPTION
Starting with version 1.8, sudo supports a plugin API for policy and ses‐
sion 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 associ‐
ated I/O logging plugin are used. Via the plugin API, sudo can be con‐
figured 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 spec‐
ified 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 sup‐
ported 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 fail‐
ure.
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 speci‐
fied 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 argu‐
ments 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, indicat‐
ing 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 net‐
masks 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, indicat‐
ing 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, indicat‐
ing that the user wishes to preserve the environment.
preserve_groups=bool
Set to true if the user specified the -P flag, indicat‐
ing 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 speci‐
fied 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 avail‐
able starting with API version 1.4.
run_shell=bool
Set to true if the user specified the -s flag, indicat‐
ing that the user wishes to run a shell.
runas_group=string
The group name or gid to run the command as, if speci‐
fied via the -g flag.
runas_user=string
The user name or uid to run the command as, if speci‐
fied 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 speci‐
fies 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 edi‐
tor 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, poten‐
tially 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 execut‐
ing the command.
exec_background=bool
By default, sudo runs a command as the foreground
process as long as sudo itself is running in the fore‐
ground. When exec_background is enabled and the com‐
mand is being run in a pty (due to I/O logging or the
use_pty setting), the command will be run as a back‐
ground 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 back‐
ground 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 com‐
mand stopping with the SIGTTIN or SIGTTOU signals, pro‐
grams 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-com‐
mand 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 log‐
ging 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 ter‐
minal 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 ter‐
minal 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 sys‐
tems that support login classes.
nice=int
Nice value (priority) to use when executing the com‐
mand. The nice value, if specified, overrides the pri‐
ority associated with the login_class on BSD systems.
noexec=bool
If set, prevent the command from executing other pro‐
grams.
preserve_fds=list
A comma-separated list of file descriptors that should
be preserved, regardless of the value of the closefrom
setting. Only available starting with API version 1.5.
preserve_groups=bool
If set, sudo will preserve the user's group vector
instead of initializing the group vector based on
runas_user.
runas_egid=gid
Effective group ID to run the command as. If not spec‐
ified, the value of runas_gid is used.
runas_euid=uid
Effective user ID to run the command as. If not speci‐
fied, 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 com‐
mand.
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 invok‐
ing 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 suc‐
cess, 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 privi‐
leges 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 argu‐
ments.
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 sup‐
port 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 authen‐
tication credentials, this function will invalidate the creden‐
tials. If the remove flag is set, the plugin may remove the cre‐
dentials 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 exe‐
cution 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 speci‐
fied 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 sup‐
port hooks, register_hooks should be set to the NULL pointer.
The version argument describes the version of the hooks API sup‐
ported by the sudo front end.
The register_hook() function should be used to register any sup‐
ported hooks the plugin needs. It returns 0 on success, 1 if the
hook type is not supported and -1 if the major version in struct
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 sup‐
ported by the sudo front end.
The deregister_hook() function should be used to deregister any
hooks that were put in place by the register_hook() function. If
the plugin tries to deregister a hook that the front end does not
support, deregister_hook will return an error.
See the Hook function API section below for more information about
hooks.
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 ses‐
sion. 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 out‐
put 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() func‐
tions 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 ver‐
sion is being requested or the check_policy() function has returned
successfully. It returns 1 on success, 0 on failure, -1 if a gen‐
eral error occurred, or -2 if there was a usage error. In the lat‐
ter 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 addi‐
tional 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 sup‐
ported 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 speci‐
fied 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 vec‐
tor 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 com‐
mand 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 speci‐
fies 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 termi‐
nate 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 out‐
put. 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 sig‐
nals 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 log‐
ging 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 type‐
def:
typedef int (*sudo_hook_fn_unsetenv_t)(const char *name,
void *closure);
SUDO_HOOK_GETENV
The C library getenv(3) function. Any registered hooks will
run before the C library implementation. The hook_fn field
should be a function that matches the following 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 implementa‐
tion. The actual function arguments will vary depending on the
hook_type (see hook_type above). In all cases, the closure field
of struct sudo_hook is passed as the last function parameter. This
can be used to pass arbitrary data to the plugin's hook implementa‐
tion.
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 com‐
mands. 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 com‐
mand.
For example, the policy plugin could utilize ssh to perform remote com‐
mand execution. The helper program would be responsible for running ssh
with the proper options to use a private key or certificate that the
remote host will accept and run a program on the remote host that would
setup the execution environment accordingly.
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 guaran‐
teed 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 conve‐
nient 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 con‐
versation. 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 con‐
versation 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 Soft‐
ware.
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() func‐
tion with SUDO_CONF_ERROR_MSG to present additional error informa‐
tion to the user.
The function arguments are as follows:
version
The version passed in by sudoers allows the plugin to deter‐
mine 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 fail‐
ure.
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)
