| SUDO_PLUGIN(5) | File Formats Manual | SUDO_PLUGIN(5) |
sudo_plugin - Sudo Plugin API
Starting with version 1.8, sudo supports a plugin API for policy and session logging. Plugins may be compiled as dynamic shared objects (the default on systems that support them) or compiled statically into the sudo binary itself. By default, the sudoers plugin provides audit, security policy and I/O logging capabilities. Via the plugin API, sudo can be configured to use alternate plugins provided by third parties. The plugins to be used are specified in the sudo.conf(5) file.
The API is versioned with a major and minor number. The minor version number is incremented when additions are made. The major number is incremented when incompatible changes are made. A plugin should be check the version passed to it and make sure that the major version matches.
The plugin API is defined by the <sudo_plugin.h> header file.
A policy plugin must declare and populate a struct policy_plugin 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 sudo_plugin_printf, char * const settings[],
char * const user_info[], char * const user_env[],
char * const plugin_options[], const char **errstr);
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[], const char **errstr);
int (*list)(int argc, char * const argv[], int verbose,
const char *user, const char **errstr);
int (*validate)(const char **errstr);
void (*invalidate)(int rmcred);
int (*init_session)(struct passwd *pwd, char **user_env[],
const char **errstr);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
struct sudo_plugin_event * (*event_alloc)(void);
};
A struct policy_plugin has the following fields:
This allows sudo to determine the API version the plugin was built against.
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], char * const user_env[],
char * const plugin_options[], const char **errstr);
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 sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
The function arguments are as follows:
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.
The following values may be set by sudo:
Additional settings may be added in the future so the plugin should silently ignore settings that it does not recognize.
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.
The following values may be set by sudo:
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.
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.
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
void (*close)(int exit_status, int error);
The close() function is called when sudo is finished, shortly before it exits. Starting with API version 1.15, close() is called regardless of whether or not a command was actually executed. This makes it possible for plugins to perform cleanup even when a command was not run. It is not possible to tell whether a command was run based solely on the arguments passed to the close() function. To determine if a command was actually run, the plugin must keep track of whether or not the check_policy() function returned successfully.
The function arguments are as follows:
If no close() function is defined, no I/O logging plugins are loaded, and neither the timeout nor use_pty options are set in the command_info list, the sudo front-end may execute the command directly instead of running it as a child process.
int (*show_version)(int verbose);
The show_version() function is called by sudo when the user specifies the -V option. The plugin may display its version information to the user via the conversation() or sudo_plugin_printf() function using SUDO_CONV_INFO_MSG. If the user requests detailed version information, the verbose flag will be non-zero.
Returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error, although the return value is currently ignored.
int (*check_policy)(int argc, char * const argv[], char *env_add[],
char **command_info[], char **argv_out[], char **user_env_out[],
const char **errstr);
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 must set sudoedit=true in the command_info list. The plugin is responsible for choosing the editor to be used, potentially from a variable in the user's environment, such as EDITOR, and should be stored in argv_out (environment variables may include command line options). The files to be edited should be copied from argv to 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 may also set sudoedit_nfiles to the number of files to be edited in the command_info list; this will only be used by the sudo front-end starting with API version 1.21.
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 sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
The function arguments are as follows:
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.
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.
Unsupported values will be ignored.
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*list)(int argc, char * const argv[], int verbose,
const char *user, const char **errstr);
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 sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
Privileges should be output via the conversation() or sudo_plugin_printf() function using SUDO_CONV_INFO_MSG.
The function arguments are as follows:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*validate)(const char **errstr);
The validate() function is called when sudo is run with the -v option. 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 sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
The function arguments are as follows:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
void (*invalidate)(int rmcred);
The invalidate() function is called when sudo is run with the -k or -K option. For policy plugins such as sudoers that cache authentication credentials, this function will invalidate the credentials. If the rmcred flag is non-zero, the plugin may remove the credentials instead of simply invalidating them.
The invalidate() function should be NULL if the plugin does not support credential caching.
int (*init_session)(struct passwd *pwd, char **user_env[],
const char **errstr);
The init_session() function is called before sudo sets up the execution environment for the command. It is run in the parent sudo process before any user-ID or group-ID 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().
Returns 1 on success, 0 on failure, and -1 on error. On error, the plugin may optionally call the conversation() or sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
The function arguments are as follows:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
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 sudo_hook does not match the front-end's major hook API version.
See the Hook function API section below for more information about hooks.
The register_hooks() function is only available starting with API version 1.2. If the sudo front-end doesn't support API version 1.2 or higher, register_hooks() will not be called.
void (*deregister_hooks)(int version, int (*deregister_hook)(struct sudo_hook *hook));
The deregister_hooks() function is called by the sudo front-end to deregister any hooks the plugin has registered. If the plugin does not support hooks, deregister_hooks should be set to the NULL pointer.
The version argument describes the version of the hooks API supported by the sudo front-end.
The deregister_hook() function should be used to deregister any hooks that were put in place by the register_hook() function. If the plugin tries to deregister a hook that the front-end does not support, deregister_hook() will return an error.
See the Hook function API section below for more information about hooks.
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.
struct sudo_plugin_event * (*event_alloc)(void);
The event_alloc() function is used to allocate a struct sudo_plugin_event which provides access to the main sudo event loop. Unlike the other fields, the event_alloc pointer is filled in by the sudo front-end, not by the plugin.
See the Event API section below for more information about events.
The event_alloc() function is only available starting with API version 1.15. If the sudo front-end doesn't support API version 1.15 or higher, event_alloc will not be set.
Policy Plugin Version Macros
/* Plugin API version major/minor. */
#define SUDO_API_VERSION_MAJOR 1
#define SUDO_API_VERSION_MINOR 13
#define SUDO_API_MKVERSION(x, y) ((x << 16) | y)
#define SUDO_API_VERSION SUDO_API_MKVERSION(SUDO_API_VERSION_MAJOR,\
SUDO_API_VERSION_MINOR)
/* Getters and setters for API version */
#define SUDO_API_VERSION_GET_MAJOR(v) ((v) >> 16)
#define SUDO_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define SUDO_API_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define SUDO_API_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
struct io_plugin {
#define SUDO_IO_PLUGIN 2
unsigned int type; /* always SUDO_IO_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_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[], const char **errstr);
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,
const char **errstr);
int (*log_ttyout)(const char *buf, unsigned int len,
const char **errstr);
int (*log_stdin)(const char *buf, unsigned int len,
const char **errstr);
int (*log_stdout)(const char *buf, unsigned int len,
const char **errstr);
int (*log_stderr)(const char *buf, unsigned int len,
const char **errstr);
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,
const char **errstr);
int (*log_suspend)(int signo, const char **errstr);
struct sudo_plugin_event * (*event_alloc)(void);
};
When an I/O plugin is loaded, sudo runs the command in a pseudo-terminal. 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 (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-terminal 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.
A struct audit_plugin has the following fields:
This allows sudo to determine the API version the plugin was built against.
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_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[]);
The open() function is run before the log_ttyin(), log_ttyout(), log_stdin(), log_stdout(), log_stderr(), log_suspend(), change_winsize(), 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 sudo_plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
The function arguments are as follows:
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.
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.
When parsing command_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.
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.
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.
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
void (*close)(int exit_status, int error);
The close() function is called when sudo is finished, shortly before it exits.
The function arguments are as follows:
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 sudo_plugin_printf() function using SUDO_CONV_INFO_MSG. If the user requests detailed version information, the verbose flag will be non-zero.
Returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error, although the return value is currently ignored.
int (*log_ttyin)(const char *buf, unsigned int len,
const char **errstr);
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:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*log_ttyout)(const char *buf, unsigned int len,
const char **errstr);
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:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*log_stdin)(const char *buf, unsigned int len,
const char **errstr);
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:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*log_stdout)(const char *buf, unsigned int len,
const char **errstr);
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:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*log_stderr)(const char *buf, unsigned int len,
const char **errstr);
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:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*change_winsize)(unsigned int lines, unsigned int cols,
const char **errstr);
The change_winsize() function is called whenever the window size of the terminal changes from the initial values specified in the user_info list. Returns -1 if an error occurred, in which case no further calls to change_winsize() will be made,
The function arguments are as follows:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
int (*log_suspend)(int signo, const char **errstr);
The log_suspend() function is called whenever a command is suspended or resumed. Logging this information makes it possible to skip the period of time when the command was suspended during playback of a session. Returns -1 if an error occurred, in which case no further calls to log_suspend() will be made,
The function arguments are as follows:
The errstr parameter is only available starting with API version 1.15. A plugin must check the API version specified by the sudo front-end before using errstr. Failure to do so may result in a crash.
struct sudo_plugin_event * (*event_alloc)(void);
The event_alloc() function is used to allocate a struct sudo_plugin_event which provides access to the main sudo event loop. Unlike the other fields, the event_alloc() pointer is filled in by the sudo front-end, not by the plugin.
See the Event API section below for more information about events.
The event_alloc() function is only available starting with API version 1.15. If the sudo front-end doesn't support API version 1.15 or higher, event_alloc() will not be set.
I/O Plugin Version Macros
Same as for the Policy plugin API.
/* Audit plugin close function status types. */
#define SUDO_PLUGIN_NO_STATUS 0
#define SUDO_PLUGIN_WAIT_STATUS 1
#define SUDO_PLUGIN_EXEC_ERROR 2
#define SUDO_PLUGIN_SUDO_ERROR 3
#define SUDO_AUDIT_PLUGIN 3
struct audit_plugin {
unsigned int type; /* always SUDO_AUDIT_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
void (*close)(int status_type, int status);
int (*accept)(const char *plugin_name,
unsigned int plugin_type, char * const command_info[],
char * const run_argv[], char * const run_envp[],
const char **errstr);
int (*reject)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
int (*error)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
int (*show_version)(int verbose);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
struct sudo_plugin_event * (*event_alloc)(void);
}
An audit plugin can be used to log successful and unsuccessful attempts to run sudo independent of the policy or any I/O plugins. Multiple audit plugins may be specified in sudo.conf(5).
A struct audit_plugin has the following fields:
This allows sudo to determine the API version the plugin was built against.
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
The audit open() function is run before any other sudo plugin API functions. This makes it possible to audit failures in the other plugins. 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:
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.
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.
When parsing submit_envp, the plugin should split on the first equal sign (‘=’) since the name field will never include one itself but the value might.
void (*close)(int status_type, int status);
The close() function is called when sudo is finished, shortly before it exits.
The function arguments are as follows:
int (*accept)(const char *plugin_name, unsigned int plugin_type,
char * const command_info[], char * const run_argv[],
char * const run_envp[], const char **errstr);
The accept() function is called when a command or action is accepted by a policy or approval plugin. The function arguments are as follows:
Typically, an audit plugin is interested in either the accept status from the sudo front-end or from the various policy and approval plugins, but not both. It is possible for the policy plugin to accept a command that is later rejected by an approval plugin, in which case the audit plugin's accept() and reject() functions will both be called.
When parsing command_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.
When parsing run_envp, the plugin should split on the first equal sign (‘=’) since the name field will never include one itself but the value might.
int (*reject)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
The reject() function is called when a command or action is rejected by a plugin. The function arguments are as follows:
Unlike the accept() function, the reject() function is not called on behalf of the sudo front-end.
When parsing command_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.
int (*error)(const char *plugin_name, unsigned int plugin_type,
const char *audit_msg, char * const command_info[],
const char **errstr);
The error() function is called when a plugin or the sudo front-end returns an error. The function arguments are as follows:
When parsing command_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.
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.
Returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error, although the return value is currently ignored.
struct sudo_plugin_event * (*event_alloc)(void);
The event_alloc() function is used to allocate a struct sudo_plugin_event which provides access to the main sudo event loop. Unlike the other fields, the event_alloc pointer is filled in by the sudo front-end, not by the plugin.
See the Event API section below for more information about events.
The event_alloc() function is only available starting with API version 1.17. If the sudo front-end doesn't support API version 1.17 or higher, event_alloc() will not be set.
struct approval_plugin {
#define SUDO_APPROVAL_PLUGIN 4
unsigned int type; /* always SUDO_APPROVAL_PLUGIN */
unsigned int version; /* always SUDO_API_VERSION */
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
void (*close)(void);
int (*check)(char * const command_info[], char * const run_argv[],
char * const run_envp[], const char **errstr);
int (*show_version)(int verbose);
};
An approval plugin can be used to apply extra constraints after a command has been accepted by the policy plugin. Unlike the other plugin types, it does not remain open until the command completes. The plugin is opened before a call to check() or show_version() and closed shortly thereafter (audit plugin functions must be called before the plugin is closed). Multiple approval plugins may be specified in sudo.conf(5).
A struct approval_plugin has the following fields:
This allows sudo to determine the API version the plugin was built against.
int (*open)(unsigned int version, sudo_conv_t conversation,
sudo_printf_t sudo_plugin_printf, char * const settings[],
char * const user_info[], int submit_optind,
char * const submit_argv[], char * const submit_envp[],
char * const plugin_options[], const char **errstr);
The approval open() function is run immediately before a call to the plugin's check() or show_version() functions. 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:
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.
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.
When parsing submit_envp, the plugin should split on the first equal sign (‘=’) since the name field will never include one itself but the value might.
void (*close)(void);
The close() function is called after the approval plugin's check() or show_version() functions have been called. It takes no arguments. The close() function is typically used to perform plugin-specific cleanup, such as the freeing of memory objects allocated by the plugin. If the plugin does not need to perform any cleanup, close() may be set to the NULL pointer.
int (*check)(char * const command_info[], char * const run_argv[],
char * const run_envp[], const char **errstr);
The approval check() function is run after the policy plugin check_policy() function and before any I/O logging plugins. If multiple approval plugins are loaded, they must all succeed for the command to be allowed. 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:
When parsing command_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.
When parsing run_envp, the plugin should split on the first equal sign (‘=’) since the name field will never include one itself but the value might.
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.
Returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error, although the return value is currently ignored.
The sudo front-end installs default signal handlers to trap common signals while the plugin functions are run. The following signals are trapped by default before the command is executed:
If a fatal signal is received before the command is executed, sudo will call the plugin's close() function with an exit status of 128 plus the value of the signal that was received. This allows for consistent logging of commands killed by a signal for plugins that log such information in their close() function. An exception to this is SIGPIPE, which is ignored until the command is executed.
A plugin may temporarily install its own signal handlers but must restore the original handler before the plugin function returns.
Beginning with plugin API version 1.2, it is possible to install hooks for certain functions called by the sudo front-end.
Currently, the only supported hooks relate to the handling of environment variables. Hooks can be used to intercept attempts to get, set, or remove environment variables so that these changes can be reflected in the version of the environment that is used to execute a command. A future version of the API will support hooking internal sudo front-end functions as well.
Hook structure
Hooks in sudo are described by the following structure:
typedef int (*sudo_hook_fn_t)();
struct sudo_hook {
unsigned int hook_version;
unsigned int hook_type;
sudo_hook_fn_t hook_fn;
void *closure;
};
A struct sudo_hook has the following fields:
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.
typedef int (*sudo_hook_fn_unsetenv_t)(const char *name, void *closure);
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.
typedef int (*sudo_hook_fn_putenv_t)(char *string, void *closure);
If the registered hook does not match the typedef the results are unspecified.
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:
Care must be taken when hooking C library functions, it is very easy to create an infinite loop. 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.
When sudo runs a command, it uses an event loop to service signals and I/O. Events may be triggered based on time, a file or socket descriptor becoming ready, or due to receipt of a signal. Starting with API version 1.15, it is possible for a plugin to participate in this event loop by calling the event_alloc() function.
Event structure
Events are described by the following structure:
typedef void (*sudo_plugin_ev_callback_t)(int fd, int what, void *closure);
struct sudo_plugin_event {
int (*set)(struct sudo_plugin_event *pev, int fd, int events,
sudo_plugin_ev_callback_t callback, void *closure);
int (*add)(struct sudo_plugin_event *pev, struct timespec *timeout);
int (*del)(struct sudo_plugin_event *pev);
int (*pending)(struct sudo_plugin_event *pev, int events,
struct timespec *ts);
int (*fd)(struct sudo_plugin_event *pev);
void (*setbase)(struct sudo_plugin_event *pev, void *base);
void (*loopbreak)(struct sudo_plugin_event *pev);
void (*free)(struct sudo_plugin_event *pev);
};
A struct sudo_plugin_event contains the following function pointers:
int (*set)(struct sudo_plugin_event *pev, int fd, int events,
sudo_plugin_ev_callback_t callback, void *closure);
The set() function takes the following arguments:
The SUDO_PLUGIN_EV_PERSIST flag may be ORed with any of the event types. It is also possible to OR SUDO_PLUGIN_EV_READ and SUDO_PLUGIN_EV_WRITE together to run the callback when a descriptor is ready to be either read from or written to. All other event values are mutually exclusive.
typedef void (*sudo_plugin_ev_callback_t)(int fd, int what,
void *closure);
The function to call when an event is triggered. The callback() function is run with the following arguments:
The set() function returns 1 on success, and -1 if a error occurred.
int (*add)(struct sudo_plugin_event *pev, struct timespec *timeout);
The add() function adds the event pev to sudo's event loop. The event must have previously been initialized via the set() function. If the timeout argument is not NULL, it should specify a (relative) timeout after which the event will be triggered if the main event criteria has not been met. This is often used to implement an I/O timeout where the event will fire if a descriptor is not ready within a certain time period. If the event is already present in the event loop, its timeout will be adjusted to match the new value, if any.
The add() function returns 1 on success, and -1 if a error occurred.
int (*del)(struct sudo_plugin_event *pev);
The del() function deletes the event pev from sudo's event loop. Deleted events can be added back via the add() function.
The del() function returns 1 on success, and -1 if a error occurred.
int (*pending)(struct sudo_plugin_event *pev, int events,
struct timespec *ts);
The pending() function can be used to determine whether one or more events is pending. The events argument specifies which events to check for. See the set() function for a list of valid event types. If SUDO_PLUGIN_EV_TIMEOUT is specified in events, the event has an associated timeout and the ts pointer is non-NULL, it will be filled in with the remaining time.
int (*fd)(struct sudo_plugin_event *pev);
The fd() function returns the descriptor or signal number associated with the event pev.
void (*setbase)(struct sudo_plugin_event *pev, void *base);
The setbase() function sets the underlying event base for pev to the specified value. This can be used to move an event created via event_alloc() to a new event loop allocated by sudo's event subsystem. If base is NULL, pev's event base is reset to the default value, which corresponds to sudo's main event loop. Using this function requires linking the plugin with the sudo_util library. It is unlikely to be used outside of the sudoers plugin.
void (*loopbreak)(struct sudo_plugin_event *pev);
The loopbreak() function causes sudo's event loop to exit immediately and the running command to be terminated.
void (*free)(struct sudo_plugin_event *pev);
The free() function deletes the event pev from the event loop and frees the memory associated with it.
The sudo front-end does not support 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.
Remote sudoedit functionality must be handled by the policy plugin, not sudo itself as the front-end has no knowledge that a remote command is being executed. This may be addressed in a future revision of the plugin API.
If the plugin needs to interact with the user, it may do so via the conversation() function. A plugin should not attempt to read directly from the standard input or the user's terminal (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 */
#define SUDO_CONV_PREFER_TTY 0x2000 /* flag: use tty if possible */
int msg_type;
int timeout;
const char *msg;
};
#define SUDO_CONV_REPL_MAX 1023
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 struct sudo_conv_message and struct sudo_conv_reply. There must be a struct sudo_conv_message and struct sudo_conv_reply for each message in the conversation, that is, both arrays must have the same number of elements. Each struct sudo_conv_reply must have its reply member initialized to NULL. 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. The functions are not actually invoked from within a signal handler.
The msg_type must be set to one of the following values:
In addition to the above values, the following flag bits may also be set:
The timeout in seconds until the prompt will wait for no more input. A zero value implies an infinite timeout.
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.
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.
As of sudo 1.9.0, the plugin open() and close() functions are called in the following order:
Prior to sudo 1.9.0, the I/O log close() function was called after the policy close() function.
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 struct sudoers_group_plugin 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_plugin_printf,
char *const argv[]);
void (*cleanup)(void);
int (*query)(const char *user, const char *group,
const struct passwd *pwd);
};
A struct sudoers_group_plugin has the following fields:
This allows sudoers to determine the API version the group plugin was built against.
int (*init)(int version, sudo_printf_t sudo_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:
void (*cleanup)();
The cleanup() function is called when sudoers has finished its group checks. The plugin should free any memory it has allocated and close open file handles.
int (*query)(const char *user, const char *group,
const struct passwd *pwd);
The query() function is used to ask the group plugin whether user is a member of group.
The function arguments are as follows:
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.
The following revisions have been made to the Sudo Plugin API.
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.
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.
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.
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.
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.
The event_alloc() function was added to struct policy_plugin and struct io_plugin.
The errstr argument was added to the policy and I/O plugin functions which the plugin function can use to return an error string. This string may be used by the audit plugin to report failure or error conditions set by the other plugins.
The close() function is now is called regardless of whether or not a command was actually executed. This makes it possible for plugins to perform cleanup even when a command was not run.
SUDO_CONV_REPL_MAX has increased from 255 to 1023 bytes.
Support for audit and approval plugins was added.
The cmnd_chroot and cmnd_cwd entries were added to the settings list.
sudo.conf(5), sudoers(5), sudo(8)
Many people have worked on sudo over the years; this version consists of code written primarily by:
See the CONTRIBUTORS.md file in the sudo distribution (https://www.sudo.ws/about/contributors/) for an exhaustive list of people who have contributed to sudo.
If you believe you have found a bug in sudo, you can submit a bug report at https://bugzilla.sudo.ws/
Limited free support is available via the sudo-users mailing list, see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
sudo is provided “AS IS” and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE.md file distributed with sudo or https://www.sudo.ws/about/license/ for complete details.
| January 18, 2023 | Sudo 1.9.13p2 |