Provided by: sudo-ldap_1.8.21p2-3ubuntu1.6_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 debug file path name followed by a space and a comma-separated list of
debug flags that correspond to the plugin's Debug entry in sudo.conf(5),
if there is one. The flags are passed to the plugin exactly as they
appear in sudo.conf(5). The syntax used by sudo and the sudoers plugin is
subsystem@priority but a plugin is free to use a different format so long
as it does not include a comma (‘,’). Prior to sudo 1.8.12, there was no
way to specify plugin-specific debug_flags so the value was always the
same as that used by the sudo front end and did not include a path name,
only the flags themselves. As of version 1.7 of the plugin interface,
sudo will only pass debug_flags if sudo.conf(5) contains a plugin-specific
Debug entry.
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.
plugin_path=string
The path name of plugin loaded by the sudo front end. The path name will
be a fully-qualified unless the plugin was statically compiled into sudo.
preserve_environment=bool
Set to true if the user specified the -E 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.
timeout=string
User-specified command timeout. Not all plugins support command timeouts
and the ability for the user to set a timeout may be restricted by policy.
The format of the timeout string is plugin-specific.
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.
umask=octal
The invoking user's file creation mask. Only available starting with API
version 1.10.
user=string
The name of the user invoking sudo.
user_env
The user's environment in the form of a NULL-terminated vector of “name=value”
strings.
When parsing user_env, the plugin should split on the first equal sign (‘=’)
since the name field will never include one itself but the value might.
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, macOS fails to restart the tcgetattr() and tcsetattr() system
calls (this is a bug in macOS). Furthermore, because this behavior
depends on the command stopping with the SIGTTIN or SIGTTOU signals,
programs that catch these signals and suspend themselves with a different
signal (usually SIGTOP) will not be automatically foregrounded. Some
versions of the linux su(1) command behave this way. Because of this, a
plugin should not set exec_background unless it is explicitly enabled by
the administrator and there should be a way to enabled or disable it on a
per-command basis.
This setting has no effect unless I/O logging is enabled or use_pty is
enabled.
execfd=number
If specified, sudo will use the fexecve(2) system call to execute the
command instead of execve(2). The specified number must refer to an open
file descriptor.
iolog_compress=bool
Set to true if the I/O logging plugins, if any, should compress the log
data. This is a hint to the I/O logging plugin which may choose to ignore
it.
iolog_group=string
The group that will own newly created I/O log files and directories. This
is a hint to the I/O logging plugin which may choose to ignore it.
iolog_mode=octal
The file permision mode to use when creating I/O log files and
directories. This is a hint to the I/O logging plugin which may choose to
ignore it.
iolog_user=string
The user that will own newly created I/O log files and directories. This
is a hint to the I/O logging plugin which may choose to ignore it.
iolog_path=string
Fully qualified path to the file or directory in which I/O log is to be
stored. This is a hint to the I/O logging plugin which may choose to
ignore it. If no I/O logging plugin is loaded, this setting has no
effect.
iolog_stdin=bool
Set to true if the I/O logging plugins, if any, should log the standard
input if it is not connected to a terminal device. This is a hint to the
I/O 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.
sudoedit_checkdir=bool
Set to false to disable directory writability checks in sudoedit. By
default, sudoedit 1.8.16 and higher will check all directory components of
the path to be edited for writability by the invoking user. Symbolic
links will not be followed in writable directories and sudoedit will
refuse to edit a file located in a writable directory. These restrictions
are not enforced when sudoedit is run by root. The sudoedit_follow option
can be set to false to disable this check. Only available starting with
API version 1.8.
sudoedit_follow=bool
Set to true to allow sudoedit to edit files that are symbolic links. By
default, sudoedit 1.8.15 and higher will refuse to open a symbolic link.
The sudoedit_follow option can be used to restore the older behavior and
allow sudoedit to open symbolic links. Only available starting with API
version 1.8.
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_API_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
I/O plugin API
struct io_plugin {
#define SUDO_IO_PLUGIN 2
unsigned int type; /* always SUDO_IO_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t plugin_printf, char * const settings[],
char * const user_info[], char * const command_info[],
int argc, char * const argv[], char * const user_env[],
char * const plugin_options[]);
void (*close)(int exit_status, int error); /* wait status or error */
int (*show_version)(int verbose);
int (*log_ttyin)(const char *buf, unsigned int len);
int (*log_ttyout)(const char *buf, unsigned int len);
int (*log_stdin)(const char *buf, unsigned int len);
int (*log_stdout)(const char *buf, unsigned int len);
int (*log_stderr)(const char *buf, unsigned int len);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
int (*change_winsize)(unsigned int lines, unsigned int cols);
};
When an I/O plugin is loaded, sudo runs the command in a pseudo-tty. This makes it possible
to log the input and output from the user's session. If any of the standard input, standard
output or standard error do not correspond to a tty, sudo will open a pipe to capture the
I/O for logging before passing it on.
The log_ttyin function receives the raw user input from the terminal device (note that this
will include input even when echo is disabled, such as when a password is read). The
log_ttyout function receives output from the pseudo-tty that is suitable for replaying the
user's session at a later time. The log_stdin(), log_stdout() and log_stderr() functions
are only called if the standard input, standard output or standard error respectively
correspond to something other than a tty.
Any of the logging functions may be set to the NULL pointer if no logging is to be
performed. If the open function returns 0, no I/O will be sent to the plugin.
If a logging function returns an error (-1), the running command will be terminated and all
of the plugin's logging functions will be disabled. Other I/O logging plugins will still
receive any remaining input or output that has not yet been processed.
If an input logging function rejects the data by returning 0, the command will be terminated
and the data will not be passed to the command, though it will still be sent to any other
I/O logging plugins. If an output logging function rejects the data by returning 0, the
command will be terminated and the data will not be written to the terminal, though it will
still be sent to any other I/O logging plugins.
The io_plugin struct has the following fields:
type 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_ttyin(), log_ttyout(), log_stdin(),
log_stdout(), log_stderr(), or show_version() functions are called. It is only called
if the version is being requested or if the policy plugin's check_policy() function
has returned successfully. It returns 1 on success, 0 on failure, -1 if a general
error occurred, or -2 if there was a usage error. In the latter case, sudo will print
a usage message before it exits. If an error occurs, the plugin may optionally call
the conversation() or plugin_printf() function with SUDO_CONF_ERROR_MSG to present
additional error information to the user.
The function arguments are as follows:
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
running command) or -1 if an error occurred.
The function arguments are as follows:
buf The buffer containing user input.
len The length of buf in bytes.
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
running command) or -1 if an error occurred.
The function arguments are as follows:
buf The buffer containing command output.
len The length of buf in bytes.
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
running command) or -1 if an error occurred.
The function arguments are as follows:
buf The buffer containing user input.
len The length of buf in bytes.
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 running
command) or -1 if an error occurred.
The function arguments are as follows:
buf The buffer containing command output.
len The length of buf in bytes.
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 running
command) or -1 if an error occurred.
The function arguments are as follows:
buf The buffer containing command output.
len The length of buf in bytes.
register_hooks
See the Policy plugin API section for a description of register_hooks.
deregister_hooks
See the Policy plugin API section for a description of deregister_hooks.
change_winsize
int (*change_winsize)(unsigned int lines, unsigned int cols);
The change_winsize() function is called whenever the window size of the terminal
changes from the initial values specified in the user_info list. It returns 1 on
success, 0 on failure, -1 if an error occurred (which will terminate the running
command).
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
• SIGPIPE
• SIGQUIT
• SIGTERM
• SIGTSTP
• SIGUSR1
• SIGUSR2
If a fatal signal is received before the command is executed, sudo will call the plugin's
close() function with an exit status of 128 plus the value of the signal that was received.
This allows for consistent logging of commands killed by a signal for plugins that log such
information in their close() function. An exception to this is SIGPIPE, which is ignored
until the command is executed.
A plugin may temporarily install its own signal handlers but must restore the original
handler before the plugin function returns.
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 {
unsigned int hook_version;
unsigned int hook_type;
sudo_hook_fn_t hook_fn;
void *closure;
};
The sudo_hook structure has the following fields:
hook_version
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_VERSION SUDO_API_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\
SUDO_HOOK_VERSION_MINOR)
For getters and setters see the Policy plugin API.
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.
Conversation function structures
The conversation function takes as arguments pointers to the following structures:
struct sudo_conv_message {
#define SUDO_CONV_PROMPT_ECHO_OFF 0x0001 /* do not echo user input */
#define SUDO_CONV_PROMPT_ECHO_ON 0x0002 /* echo user input */
#define SUDO_CONV_ERROR_MSG 0x0003 /* error message */
#define SUDO_CONV_INFO_MSG 0x0004 /* informational message */
#define SUDO_CONV_PROMPT_MASK 0x0005 /* mask user input */
#define SUDO_CONV_PROMPT_ECHO_OK 0x1000 /* flag: allow echo if no tty */
int msg_type;
int timeout;
const char *msg;
};
#define SUDO_CONV_REPL_MAX 255
struct sudo_conv_reply {
char *reply;
};
typedef int (*sudo_conv_callback_fn_t)(int signo, void *closure);
struct sudo_conv_callback {
unsigned int version;
void *closure;
sudo_conv_callback_fn_t on_suspend;
sudo_conv_callback_fn_t on_resume;
};
Pointers to the conversation() and printf()-style functions are passed in to the plugin's
open() function when the plugin is initialized. The following type definitions can be used
in the declaration of the open() function:
typedef int (*sudo_conv_t)(int num_msgs,
const struct sudo_conv_message msgs[],
struct sudo_conv_reply replies[],
struct sudo_conv_callback *callback);
typedef int (*sudo_printf_t)(int msg_type, const char *fmt, ...);
To use the conversation() function, the plugin must pass an array of sudo_conv_message and
sudo_conv_reply structures. There must be a struct sudo_conv_message and struct
sudo_conv_reply for each message in the conversation. The struct sudo_conv_callback
pointer, if not NULL, should contain function pointers to be called when the sudo process is
suspended and/or resumed during conversation input. The on_suspend and on_resume functions
are called with the signal that caused sudo to be suspended and the closure pointer from the
struct sudo_conv_callback. These functions should return 0 on success and -1 on error. On
error, the conversation will end and the conversation function will return a value of -1.
The intended use is to allow the plugin to release resources, such as locks, that should not
be held indefinitely while suspended and then reacquire them when the process is resumed.
Note that the functions are not actually invoked from within a signal handler.
The plugin is responsible for freeing the reply buffer located in each struct
sudo_conv_reply, if it is not NULL. SUDO_CONV_REPL_MAX represents the maximum length of the
reply buffer (not including the trailing NUL character). In practical terms, this is the
longest password sudo will support. It is also useful as a maximum value for the memset_s()
function when clearing passwords filled in by the conversation function.
The printf()-style function uses the same underlying mechanism as the conversation()
function but only supports SUDO_CONV_INFO_MSG and SUDO_CONV_ERROR_MSG for the msg_type
parameter. It can be more convenient than using the conversation() function if no user
reply is needed and supports standard printf() escape sequences.
See the sample plugin for an example of the conversation() function usage.
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)
For getters and setters see the Policy plugin API.
PLUGIN API CHANGELOG
The following revisions have been made to the Sudo Plugin API.
Version 1.0
Initial API version.
Version 1.1 (sudo 1.8.0)
The I/O logging plugin's open() function was modified to take the command_info list as
an argument.
Version 1.2 (sudo 1.8.5)
The Policy and I/O logging plugins' open() functions are now passed a list of plugin
parameters if any are specified in sudo.conf(5).
A simple hooks API has been introduced to allow plugins to hook in to the system's
environment handling functions.
The init_session Policy plugin function is now passed a pointer to the user
environment which can be updated as needed. This can be used to merge in environment
variables stored in the PAM 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)
The preserve_fds entry was added to the command_info list.
Version 1.6 (sudo 1.8.11)
The behavior when an I/O logging plugin returns an error (-1) has changed.
Previously, the sudo front end took no action when the log_ttyin(), log_ttyout(),
log_stdin(), log_stdout(), or log_stderr() function returned an error.
The behavior when an I/O logging plugin returns 0 has changed. Previously, output
from the command would be displayed to the terminal even if an output logging function
returned 0.
Version 1.7 (sudo 1.8.12)
The plugin_path entry was added to the settings list.
The debug_flags entry now starts with a debug file path name and may occur multiple
times if there are multiple plugin-specific Debug lines in the sudo.conf(5) file.
Version 1.8 (sudo 1.8.15)
The sudoedit_checkdir and sudoedit_follow entries were added to the command_info list.
The default value of sudoedit_checkdir was changed to true in sudo 1.8.16.
The sudo conversation function now takes a pointer to a struct sudo_conv_callback as
its fourth argument. The sudo_conv_t definition has been updated to match. The
plugin must specify that it supports plugin API version 1.8 or higher to receive a
conversation function pointer that supports this argument.
Version 1.9 (sudo 1.8.16)
The execfd entry was added to the command_info list.
Version 1.10 (sudo 1.8.19)
The umask entry was added to the user_info list. The iolog_group, iolog_mode, and
iolog_user entries were added to the command_info list.
Version 1.11 (sudo 1.8.20)
The timeout entry was added to the settings list.
Version 1.12 (sudo 1.8.21)
The change_winsize field was added to the io_plugin struct.
SEE ALSO
sudo.conf(5), sudoers(5), sudo(8)
AUTHORS
Many people have worked on sudo over the years; this version consists of code written
primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the sudo distribution (https://www.sudo.ws/contributors.html)
for an exhaustive list of people who have contributed to sudo.
BUGS
If you feel you have found a bug in sudo, please submit a bug report at
https://bugzilla.sudo.ws/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties, including, but not limited
to, the implied warranties of merchantability and fitness for a particular purpose are
disclaimed. See the LICENSE file distributed with sudo or https://www.sudo.ws/license.html
for complete details.