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.
Plugin directive, which causes a plugin to be loaded.
A Plugin line consists of the Plugin keyword, followed by the symbol_name and the path to the shared object containing the plugin. The symbol_name is the name of the struct policy_plugin or struct io_plugin in the plugin shared object. The path may be fully qualified or relative. If not fully qualified it is relative to the /usr/local/libexec directory. Any additional parameters after the path are passed as options to the plugin's open() function. Lines that don't begin with Plugin, Path, Debug or Set are silently ignored.
The same shared object may contain multiple plugins, each with a different symbol name. The shared object file must be owned by uid 0 and only writable by its owner. Because of ambiguities that arise from composite policies, only a single policy plugin may be specified. This limitation does not apply to I/O plugins.
# # Default /etc/sudo.conf file # # Format: # Plugin plugin_name plugin_path plugin_options ... # Path askpass /path/to/askpass # Path noexec /path/to/sudo_noexec.so # Debug sudo /var/log/sudo_debug all@warn # Set disable_coredump true # # The plugin_path is relative to /usr/local/libexec unless # fully qualified. # The plugin_name corresponds to a global symbol in the plugin # that contains the plugin interface structure. # The plugin_options are optional. # Plugin sudoers_policy sudoers.so Plugin sudoers_io sudoers.so
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 /etc/sudo.conf 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 field should always be set to SUDO_POLICY_PLUGIN.version field should be set to SUDO_API_VERSION.
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 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:
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.
Debug entry in /etc/sudo.conf, if there is one. The flags are passed to the plugin as they appear in /etc/sudo.conf. The syntax used by sudo and the sudoers plugin is subsystem@priority but the plugin is free to use a different format so long as it does not include a comma (‘,’).
For reference, the priorities supported by the sudo front end and sudoers are: crit, err, warn, notice, diag, info, trace and debug.
The following subsystems are defined: main, memory, args, exec, pty, utmp, conv, pcomm, util, list, netif, audit, edit, selinux, ldap, match, parser, alias, defaults, auth, env, logging, nss, rbtree, perms, plugin. The subsystem all includes every subsystem.
There is not currently a way to specify a set of debug flags specific to the plugin--the flags are shared by sudo and the plugin.
HOME environment variable to the target user's home directory.:’), it is an IPv6 address, else it is IPv4.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.
tty=”.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.
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.
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 is undefined if error is non-zero.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.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.
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:
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.
runas_user.Unsupported values will be ignored.
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,
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.
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.
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.
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.
void (*deregister_hooks)(int version, int (*deregister_hook)(struct sudo_hook *hook));
The deregister_hooks() function is called by the sudo front end to deregister any hooks the plugin has registered. If the plugin does not support hooks, deregister_hooks should be set to the NULL pointer.
The version argument describes the version of the hooks API supported by the sudo front end.
The deregister_hook() function should be used to deregister any hooks that were put in place by the register_hook() function. If the plugin tries to deregister a hook that the front end does not support, deregister_hook will return an error.
See the Hook function API section below for more information about hooks.
NOTE: the deregister_hooks() function is only available starting with API version 1.2. If the sudo front end doesn't support API version 1.2 or higher, deregister_hooks will not be called.
Policy Plugin Version Macros
/* Plugin API version major/minor. */
#define SUDO_API_VERSION_MAJOR 1
#define SUDO_API_VERSION_MINOR 2
#define SUDO_API_MKVERSION(x, y) ((x << 16) | y)
#define SUDO_API_VERSION SUDO_API_MKVERSION(SUDO_API_VERSION_MAJOR,\
SUDO_API_VERSION_MINOR)
/* Getters and setters for API version */
#define SUDO_API_VERSION_GET_MAJOR(v) ((v) >> 16)
#define SUDO_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define SUDO_API_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define SUDO_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
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[], int argc, char * const argv[],
char * const user_env[], char * const plugin_options[]);
void (*close)(int exit_status, int error); /* wait status or error */
int (*show_version)(int verbose);
int (*log_ttyin)(const char *buf, unsigned int len);
int (*log_ttyout)(const char *buf, unsigned int len);
int (*log_stdin)(const char *buf, unsigned int len);
int (*log_stdout)(const char *buf, unsigned int len);
int (*log_stderr)(const char *buf, unsigned int len);
void (*register_hooks)(int version,
int (*register_hook)(struct sudo_hook *hook));
void (*deregister_hooks)(int version,
int (*deregister_hook)(struct sudo_hook *hook));
};
When an I/O plugin is loaded, sudo runs the command in a pseudo-tty. This makes it possible to log the input and output from the user's session. If any of the standard input, standard output or standard error do not correspond to a tty, sudo will open a pipe to capture the I/O for logging before passing it on.
The log_ttyin function receives the raw user input from the terminal device (note that this will include input even when echo is disabled, such as when a password is read). The log_ttyout function receives output from the pseudo-tty that is suitable for replaying the user's session at a later time. The log_stdin(), log_stdout() and log_stderr() functions are only called if the standard input, standard output or standard error respectively correspond to something other than a tty.
Any of the logging functions may be set to the NULL pointer if no logging is to be performed. If the open function returns 0, no I/O will be sent to the plugin.
The io_plugin struct has the following fields:
type field should always be set to SUDO_IO_PLUGIN.version field should be set to SUDO_API_VERSION.
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 plugin_printf, char * const settings[],
char * const user_info[], int argc, char * const argv[],
char * const user_env[], char * const plugin_options[]);
The open() function is run before the log_input(), log_output() or show_version() functions are called. It is only called if the version is being requested or the check_policy() function has returned successfully. It returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error. In the latter case, sudo will print a usage message before it exits. If an error occurs, the plugin may optionally call the conversation() or plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.
The function arguments are as follows:
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 user_env, the plugin should split on the first equal sign (‘=’) since the name field will never include one itself but the value might.
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.
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 is undefined if error is non-zero.errno set by the execve(2) system call. If the command was successfully executed, the value of error is 0.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.
int (*log_ttyin)(const char *buf, unsigned int len);
The log_ttyin() function is called whenever data can be read from the user but before it is passed to the running command. This allows the plugin to reject data if it chooses to (for instance if the input contains banned content). Returns 1 if the data should be passed to the command, 0 if the data is rejected (which will terminate the command) or -1 if an error occurred.
The function arguments are as follows:
int (*log_ttyout)(const char *buf, unsigned int len);
The log_ttyout() function is called whenever data can be read from the command but before it is written to the user's terminal. This allows the plugin to reject data if it chooses to (for instance if the output contains banned content). Returns 1 if the data should be passed to the user, 0 if the data is rejected (which will terminate the command) or -1 if an error occurred.
The function arguments are as follows:
int (*log_stdin)(const char *buf, unsigned int len);
The log_stdin() function is only used if the standard input does not correspond to a tty device. It is called whenever data can be read from the standard input but before it is passed to the running command. This allows the plugin to reject data if it chooses to (for instance if the input contains banned content). Returns 1 if the data should be passed to the command, 0 if the data is rejected (which will terminate the command) or -1 if an error occurred.
The function arguments are as follows:
int (*log_stdout)(const char *buf, unsigned int len);
The log_stdout() function is only used if the standard output does not correspond to a tty device. It is called whenever data can be read from the command but before it is written to the standard output. This allows the plugin to reject data if it chooses to (for instance if the output contains banned content). Returns 1 if the data should be passed to the user, 0 if the data is rejected (which will terminate the command) or -1 if an error occurred.
The function arguments are as follows:
int (*log_stderr)(const char *buf, unsigned int len);
The log_stderr() function is only used if the standard error does not correspond to a tty device. It is called whenever data can be read from the command but before it is written to the standard error. This allows the plugin to reject data if it chooses to (for instance if the output contains banned content). Returns 1 if the data should be passed to the user, 0 if the data is rejected (which will terminate the command) or -1 if an error occurred.
The function arguments are as follows:
register_hooks.deregister_hooks.I/O Plugin Version Macros
Same as for the Policy plugin API.
Currently, the only supported hooks relate to the handling of environment variables. Hooks can be used to intercept attempts to get, set, or remove environment variables so that these changes can be reflected in the version of the environment that is used to execute a command. A future version of the API will support hooking internal sudo front end functions as well.
Hook structure
Hooks in sudo are described by the following structure:
typedef int (*sudo_hook_fn_t)();
struct sudo_hook {
int hook_version;
int hook_type;
sudo_hook_fn_t hook_fn;
void *closure;
};
The sudo_hook structure has the following fields:
hook_version field should be set to SUDO_HOOK_VERSION.hook_type field may be one of the following supported hook types:
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.
hook_fn field should be a function that matches the following typedef:
typedef int (*sudo_hook_fn_unsetenv_t)(const char *name, void *closure);
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.
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.
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:
setenv hook that operates on a private copy of the environment but leaves environ unchanged.Note that it is very easy to create an infinite loop when hooking C library functions. For example, a getenv(3) hook that calls the snprintf(3) function may create a loop if the snprintf(3) implementation calls getenv(3) to check the locale. To prevent this, you may wish to use a static variable in the hook function to guard against nested calls. For example:
static int in_progress = 0; /* avoid recursion */
if (in_progress)
return SUDO_HOOK_RET_NEXT;
in_progress = 1;
...
in_progress = 0;
return SUDO_HOOK_RET_STOP;
Hook API Version Macros
/* Hook API version major/minor */
#define SUDO_HOOK_VERSION_MAJOR 1
#define SUDO_HOOK_VERSION_MINOR 0
#define SUDO_HOOK_MKVERSION(x, y) ((x << 16) | y)
#define SUDO_HOOK_VERSION SUDO_HOOK_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\
SUDO_HOOK_VERSION_MINOR)
/* Getters and setters for hook API version */
#define SUDO_HOOK_VERSION_GET_MAJOR(v) ((v) >> 16)
#define SUDO_HOOK_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define SUDO_HOOK_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define SUDO_HOOK_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
msg if one is to be printed.
A printf()-style function is also available that can be used to display informational or error messages to the user, which is usually more convenient for simple messages where no use input is required.
struct sudo_conv_message {
#define SUDO_CONV_PROMPT_ECHO_OFF 0x0001 /* do not echo user input */
#define SUDO_CONV_PROMPT_ECHO_ON 0x0002 /* echo user input */
#define SUDO_CONV_ERROR_MSG 0x0003 /* error message */
#define SUDO_CONV_INFO_MSG 0x0004 /* informational message */
#define SUDO_CONV_PROMPT_MASK 0x0005 /* mask user input */
#define SUDO_CONV_DEBUG_MSG 0x0006 /* debugging message */
#define SUDO_CONV_PROMPT_ECHO_OK 0x1000 /* flag: allow echo if no tty */
int msg_type;
int timeout;
const char *msg;
};
struct sudo_conv_reply {
char *reply;
};
typedef int (*sudo_conv_t)(int num_msgs,
const struct sudo_conv_message msgs[],
struct sudo_conv_reply replies[]);
typedef int (*sudo_printf_t)(int msg_type, const char *fmt, ...);
Pointers to the conversation() and printf()-style functions are passed in to the plugin's open() function when the plugin is initialized.
To use the conversation() function, the plugin must pass an array of sudo_conv_message and sudo_conv_reply structures. There must be a struct sudo_conv_message and struct sudo_conv_reply for each message in the conversation. The plugin is responsible for freeing the reply buffer filled in to the struct sudo_conv_reply, if any.
The printf()-style function uses the same underlying mechanism as the conversation() function but only supports SUDO_CONV_INFO_MSG, SUDO_CONV_ERROR_MSG and SUDO_CONV_DEBUG_MSG for the msg_type parameter. It can be more convenient than using the conversation() function if no user reply is needed and supports standard printf() escape sequences.
Unlike, SUDO_CONV_INFO_MSG and Dv SUDO_CONV_ERROR_MSG , messages sent with the SUDO_CONV_DEBUG_MSG msg_type are not directly user-visible. Instead, they are logged to the file specified in the Debug statement (if any) in the /etc/sudo.conf
file. This allows a plugin to log debugging information and is intended to be used in conjunction with the debug_flags setting.
See the sample plugin for an example of the conversation() function usage.
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 field should be set to GROUP_API_VERSION.
This allows sudoers to determine the API version the group plugin was built against.
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:
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)
/* Getters and setters for group version */
#define GROUP_API_VERSION_GET_MAJOR(v) ((v) >> 16)
#define GROUP_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define GROUP_API_VERSION_SET_MAJOR(vp, n) do { \
*(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
} while(0)
#define GROUP_API_VERSION_SET_MINOR(vp, n) do { \
*(vp) = (*(vp) & 0xffff0000) | (n); \
} while(0)
command_info list as an argument.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.