sudo_plugin - Sudo Plugin API
Please see following description for synopsis
SUDO_PLUGIN(5) File Formats Manual SUDO_PLUGIN(5)
NAME
sudo_plugin - Sudo Plugin API
DESCRIPTION
Starting with version 1.8, sudo supports a plugin API for policy and
session logging. Plugins may be compiled as dynamic shared objects
(the default on systems that support them) or compiled statically into
the sudo binary itself. By default, the sudoers 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(4) 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(4) 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(4), if there
is one. The flags are passed to the plugin exactly
as they appear in sudo.conf(4). 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(4) 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(4).
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.
Additional settings may be added in the future so the
plugin should silently ignore settings that it does not
recognize.
user_info
A vector of information about the user running the command
in the form of name=value strings. The vector is
terminated by a NULL pointer.
When parsing user_info, the plugin should split on the
first equal sign (`=') since the name field will never
include one itself but the value might.
cols=int
The number of columns the user's terminal supports.
If there is no terminal device available, a default
value of 80 is used.
cwd=string
The user's current working directory.
egid=gid_t
The effective group ID of the user invoking sudo.
euid=uid_t
The effective user ID of the user invoking sudo.
gid=gid_t
The real group ID of the user invoking sudo.
groups=list
The user's supplementary group list formatted as a
string of comma-separated group IDs.
host=string
The local machine's hostname as returned by the
gethostname(2) system call.
lines=int
The number of lines the user's terminal supports. If
there is no terminal device available, a default
value of 24 is used.
pgid=int
The ID of the process group that the running sudo
process is a member of. Only available starting with
API version 1.2.
pid=int
The process ID of the running sudo process. Only
available starting with API version 1.2.
plugin_options
Any (non-comment) strings immediately after the
plugin path are passed as arguments to the plugin.
These arguments are split on a white space boundary
and are passed to the plugin in the form of a NULL-
terminated array of strings. If no arguments were
specified, plugin_options will be the NULL pointer.
NOTE: the plugin_options parameter is only available
starting with API version 1.2. A plugin must check
the API version specified by the sudo front end
before using plugin_options. Failure to do so may
result in a crash.
ppid=int
The parent process ID of the running sudo process.
Only available starting with API version 1.2.
sid=int
The session ID of the running sudo process or 0 if
sudo is not part of a POSIX job control session.
Only available starting with API version 1.2.
tcpgid=int
The ID of the foreground process group associated
with the terminal device associated with the sudo
process or -1 if there is no terminal present. Only
available starting with API version 1.2.
tty=string
The path to the user's terminal device. If the user
has no terminal device associated with the session,
the value will be empty, as in tty=.
uid=uid_t
The real user ID of the user invoking sudo.
user=string
The name of the user invoking sudo.
user_env
The user's environment in the form of a NULL-terminated
vector of name=value strings.
When parsing user_env, the plugin should split on the first
equal sign (`=') since the name field will never include
one itself but the value might.
close
void (*close)(int exit_status, int error);
The close() function is called when the command being run by sudo
finishes.
The function arguments are as follows:
exit_status
The command's exit status, as returned by the wait(2)
system call. The value of exit_status is undefined if
error is non-zero.
error
If the command could not be executed, this is set to the
value of errno set by the execve(2) system call. The
plugin is responsible for displaying error information via
the conversation() or plugin_printf() function. If the
command was successfully executed, the value of error is 0.
If no close() function is defined, no I/O logging plugins are
loaded, and neither the timeout not use_pty options are set in
the command_info list, the sudo front end may execute the command
directly instead of running it as a child process.
show_version
int (*show_version)(int verbose);
The show_version() function is called by sudo when the user
specifies the -V option. The plugin may display its version
information to the user via the conversation() or plugin_printf()
function using SUDO_CONV_INFO_MSG. If the user requests detailed
version information, the verbose flag will be set.
check_policy
int (*check_policy)(int argc, char * const argv[]
char *env_add[], char **command_info[],
char **argv_out[], char **user_env_out[]);
The check_policy() function is called by sudo to determine
whether the user is allowed to run the specified commands.
If the sudoedit option was enabled in the settings array passed
to the open() function, the user has requested sudoedit mode.
sudoedit is a mechanism for editing one or more files where an
editor is run with the user's credentials instead of with
elevated privileges. sudo achieves this by creating user-
writable temporary copies of the files to be edited and then
overwriting the originals with the temporary copies after editing
is complete. If the plugin supports sudoedit, it should choose
the editor to be used, potentially from a variable in the user's
environment, such as EDITOR, and include it in argv_out (note
that environment variables may include command line flags). The
files to be edited should be copied from argv into argv_out,
separated from the editor and its arguments by a -- element. The
-- will be removed by sudo before the editor is executed. The
plugin should also set sudoedit=true in the command_info list.
The check_policy() function returns 1 if the command is allowed,
0 if not allowed, -1 for a general error, or -2 for a usage error
or if sudoedit was specified but is unsupported by the plugin.
In the latter case, sudo will print a usage message before it
exits. If an error occurs, the plugin may optionally call the
conversation() or plugin_printf() function with
SUDO_CONF_ERROR_MSG to present additional error information to
the user.
The function arguments are as follows:
argc The number of elements in argv, not counting the final NULL
pointer.
argv The argument vector describing the command the user wishes
to run, in the same form as what would be passed to the
execve(2) system call. The vector is terminated by a NULL
pointer.
env_add
Additional environment variables specified by the user on
the command line in the form of a NULL-terminated vector of
name=value strings. The plugin may reject the command if
one or more variables are not allowed to be set, or it may
silently ignore such variables.
When parsing env_add, the plugin should split on the first
equal sign (`=') since the name field will never include
one itself but the value might.
command_info
Information about the command being run in the form of
name=value strings. These values are used by sudo to set
the execution environment when running a command. The
plugin is responsible for creating and populating the
vector, which must be terminated with a NULL pointer. The
following values are recognized by sudo:
chroot=string
The root directory to use when running the command.
closefrom=number
If specified, sudo will close all files descriptors
with a value of number or higher.
command=string
Fully qualified path to the command to be executed.
cwd=string
The current working directory to change to when
executing the command.
exec_background=bool
By default, sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When exec_background is enabled and the
command is being run in a pty (due to I/O logging or
the use_pty setting), the command will be run as a
background process. Attempts to read from the
controlling terminal (or to change terminal settings)
will result in the command being suspended with the
SIGTTIN signal (or SIGTTOU in the case of terminal
settings). If this happens when sudo is a foreground
process, the command will be granted the controlling
terminal and resumed in the foreground with no user
intervention required. The advantage of initially
running the command in the background is that sudo
need not read from the terminal unless the command
explicitly requests it. Otherwise, any terminal
input must be passed to the command, whether it has
required it or not (the kernel buffers terminals so
it is not possible to tell whether the command really
wants the input). This is different from historic
sudo behavior or when the command is not being run in
a pty.
For this to work seamlessly, the operating system
must support the automatic restarting of system
calls. Unfortunately, not all operating systems do
this by default, and even those that do may have
bugs. For example, Mac OS X fails to restart the
tcgetattr() and tcsetattr() system calls (this is a
bug in Mac OS X). Furthermore, because this behavior
depends on the command stopping with the SIGTTIN or
SIGTTOU signals, programs that catch these signals
and suspend themselves with a different signal
(usually SIGTOP) will not be automatically
foregrounded. Some versions of the linux su(1)
command behave this way. Because of this, a plugin
should not set exec_background unless it is
explicitly enabled by the administrator and there
should be a way to enabled or disable it on a per-
command basis.
This setting has no effect unless I/O logging is
enabled or use_pty is enabled.
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_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));
};
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.
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:
o SIGALRM
o SIGHUP
o SIGINT
o SIGPIPE
o SIGQUIT
o SIGTERM
o SIGTSTP
o SIGUSR1
o 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(4).
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(4).
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(4) 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.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | security/sudo |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
sudo.conf(4), sudoers(4), sudo(1m)
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.
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original community
source was downloaded from
http://www.sudo.ws/sudo/dist/sudo-1.8.18p1.tar.gz
Further information about this software can be found on the open source
community website at http://www.sudo.ws/.
Sudo 1.8.18p1 January 20, 2016 SUDO_PLUGIN(5)