Policy plugin API¶

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:

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 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:

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 Conversation API for details). Returns 0 on success and -1 on failure.

sudo_plugin_printf

A pointer to a printf()-style function that may be used to display informational or error messages (see Conversation API for details). 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 options the user specified when running sudo. As such, they will only be present when the corresponding option 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.

The following values may be set by sudo:

bsdauth_type=string

Authentication type, if specified by the -a option, to use on systems where BSD authentication is supported.

closefrom=number

If specified, the user has requested via the -C option 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.

cmnd_chroot=string

The root directory (see chroot(2)) to run the command in, as specified by the user via the -R option. The plugin may ignore or restrict the user's ability to specify a new root directory. Only available starting with API version 1.16.

cmnd_cwd=string

The working directory to run the command in, as specified by the user via the -D option. The plugin may ignore or restrict the user's ability to specify a new working directory. Only available starting with API version 1.16.

debug_flags=string

A debug file path name followed by a space and a comma-separated list of debug flags that correspond to the plugin's Debug entry in sudo.conf(5), if there is one. The flags are passed to the plugin exactly as they appear in sudo.conf(5). The syntax used by sudo and the sudoers plugin is subsystem@priority but a plugin is free to use a different format so long as it does not include a comma (‘,’). Prior to sudo 1.8.12, there was no way to specify plugin-specific debug_flags so the value was always the same as that used by the sudo front-end and did not include a path name, only the flags themselves. As of version 1.7 of the plugin interface, sudo will only pass debug_flags if sudo.conf(5) contains a plugin-specific Debug entry.

ignore_ticket=bool

Set to true if the user specified the -k option 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 implied_shell.

intercept_ptrace=bool

Indicates whether or not the system supports intercept mode using ptrace(2). This is currently only true for Linux systems that support seccomp(2) filtering and the “trap” action. Other systems will use a dynamic shared object to implement intercept. Only available starting with API version 1.19.

intercept_setid=bool

Indicates whether or not the system supports running set-user-ID and set-group-ID binaries in intercept mode. This is currently only true for Linux systems that support seccomp(2) filtering and the “trap” action. On systems that use a dynamic shared object to implement intercept, the dynamic linker (ld.so or the equivalent) will disable preloading of shared objects when executing a set-user-ID or set-group-ID binary. This will disable intercept mode for that program and any other programs that it executes. The policy plugin may refuse to execute a set-user-ID or set-group-ID binary in intercept mode to avoid this. Only available starting with API version 1.19.

login_class=string

BSD login class to use when setting resource limits and nice value, if specified by the -c option.

login_shell=bool

Set to true if the user specified the -i option, indicating that the user wishes to run a login shell.

max_groups=int

The maximum number of groups a user may belong to. This will only be present if there is a corresponding setting in sudo.conf(5).

network_addrs=list

A space-separated list of IP network addresses and netmasks in the form “addr/netmask”, e.g., “192.168.1.2/255.255.255.0”. The address and netmask pairs may be either IPv4 or IPv6, depending on what the operating system supports. If the address contains a colon (‘:’), it is an IPv6 address, else it is IPv4.

noninteractive=bool

Set to true if the user specified the -n option, 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 option, indicating that the user wishes to preserve the environment.

preserve_groups=bool

Set to true if the user specified the -P option, 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 option.

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 option, indicating that the user wishes to run a shell.

runas_group=string

The group name or group-ID to run the command as, if specified via the -g option.

runas_user=string

The user name or user-ID to run the command as, if specified via the -u option.

selinux_role=string

SELinux role to use when executing the command, if specified by the -r option.

selinux_type=string

SELinux type to use when executing the command, if specified by the -t option.

set_home=bool

Set to true if the user specified the -H option. If true, set the HOME environment variable to the target user's home directory.

sudoedit=bool

Set to true when the -e option is specified or if invoked as sudoedit. The plugin shall substitute an editor into argv in the check_policy() function or return -2 with a usage error if the plugin does not support sudoedit. For more information, see the check_policy() section.

timeout=string

Command timeout specified by the user via the -T option. Not all plugins support command timeouts and the ability of the user to set a timeout may be restricted by policy. The format of the timeout string is plugin-specific.

update_ticket=bool

Set to false if the user specified the -N option, indicating that the user wishes to avoid updating any cached authentication credentials. Only available starting with API version 1.20.

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.

The following values may be set by sudo:

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.

ppid=int

The parent process ID of the running sudo process. Only available starting with API version 1.2.

rlimit_as=soft,hard

The maximum size to which the process's address space may grow (in bytes), if supported by the operating system. The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_core=soft,hard

The largest size core dump file that may be created (in bytes). The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_cpu=soft,hard

The maximum amount of CPU time that the process may use (in seconds). The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_data=soft,hard

The maximum size of the data segment for the process (in bytes). The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_fsize=soft,hard

The largest size file that the process may create (in bytes). The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_locks=soft,hard

The maximum number of locks that the process may establish, if supported by the operating system. The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_memlock=soft,hard

The maximum size that the process may lock in memory (in bytes), if supported by the operating system. The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_nofile=soft,hard

The maximum number of files that the process may have open. The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_nproc=soft,hard

The maximum number of processes that the user may run simultaneously. The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_rss=soft,hard

The maximum size to which the process's resident set size may grow (in bytes). The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

rlimit_stack=soft,hard

The maximum size to which the process's stack may grow (in bytes). The soft and hard limits are separated by a comma. A value of “infinity” indicates that there is no limit. Only available starting with API version 1.16.

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 0 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 one exists. This entry is only present if the user has a terminal device associated with the session.

ttydev=dev_t

The number of the user's terminal device, if one exists, formatted as a long long value. This entry is only present if the user has a terminal device associated with the session. Only available starting with API version 1.22.

uid=uid_t

The real user-ID of the user invoking sudo.

umask=octal

The invoking user's file creation mask. Only available starting with API version 1.10.

user=string

The name of the user invoking sudo.

user_env

The user's environment in the form of a NULL-terminated vector of “name=value” strings.

When parsing user_env, the plugin should split on the first equal sign (‘=’) since the name field will never include one itself but the value might.

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.

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.

errstr

If the open() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

close

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:

exit_status

The command's exit status, as returned by the wait(2) system call, or zero if no command was run. 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 sudo_plugin_printf() function. If the command was successfully executed, the value of error is zero.

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.

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 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.

check_policy

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:

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:

apparmor_profile=string

AppArmor profile to transition to when executing the command. Only available starting with API version 1.19.

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. If sudo is unable to change to the new working directory, the command will not be run unless cwd_optional is also set (see below).

cwd_optional=bool

If set, sudo will treat an inability to change to the new working directory as a non-fatal error. This setting has no effect unless cwd is also set.

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 pseudo-terminal (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 pseudo-terminal.

For this to work seamlessly, the operating system must support the automatic restarting of system calls. Unfortunately, not all operating systems do this by default, and even those that do may have bugs. For example, macOS fails to restart the tcgetattr() and tcsetattr() system calls (this is a bug in macOS). Furthermore, because this behavior depends on the command stopping with the SIGTTIN or SIGTTOU signals, programs that catch these signals and suspend themselves with a different signal (usually SIGTOP) will not be automatically foregrounded. Some versions of the linux su(1) command behave this way. Because of this, a plugin should not set exec_background unless it is explicitly enabled by the administrator and there should be a way to enabled or disable it on a per-command basis.

This setting has no effect unless I/O logging is enabled or use_pty is enabled.

execfd=number

If specified, sudo will use the fexecve(2) system call to execute the command instead of execve(2). The specified number must refer to an open file descriptor.

intercept=bool

If set, sudo will intercept attempts to execute a subsequent command and perform a policy check via the policy plugin's check_policy() function to determine whether or not the command is permitted. This can be used to prevent shell escapes on supported platforms but it has a number of limitations. See Preventing shell escapes in sudoers(5) for details. Only available starting with API version 1.18.

intercept_verify=bool

If set, sudo will attempt to verify that a command run in intercept mode has the expected path name, command line arguments and environment. This setting has no effect unless use_ptrace is also enabled. Only available starting with API version 1.20.

iolog_compress=bool

Set to true if the I/O logging plugins, if any, should compress the log data. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_group=string

The group that will own newly created I/O log files and directories. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_mode=octal

The file permission mode to use when creating I/O log files and directories. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_user=string

The user that will own newly created I/O log files and directories. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_path=string

Fully qualified path to the file or directory in which I/O log is to be stored. This is a hint to the I/O logging plugin which may choose to ignore it. If no I/O logging plugin is loaded, this setting has no effect.

iolog_stdin=bool

Set to true if the I/O logging plugins, if any, should log the standard input if it is not connected to a terminal device. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_stdout=bool

Set to true if the I/O logging plugins, if any, should log the standard output if it is not connected to a terminal device. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_stderr=bool

Set to true if the I/O logging plugins, if any, should log the standard error if it is not connected to a terminal device. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_ttyin=bool

Set to true if the I/O logging plugins, if any, should log all terminal input. This only includes input typed by the user and not from a pipe or redirected from a file. This is a hint to the I/O logging plugin which may choose to ignore it.

iolog_ttyout=bool

Set to true if the I/O logging plugins, if any, should log all terminal output. This only includes output to the screen, not output to a pipe or file. This is a hint to the I/O logging plugin which may choose to ignore it.

login_class=string

BSD login class to use when setting resource limits and nice value (optional). This option is only set on systems that support login classes.

nice=int

Nice value (priority) to use when executing the command. The nice value, if specified, overrides the priority associated with the login_class on BSD systems.

log_subcmds=bool

If set, sudo will call the audit plugin's accept() function to log when the command runs a subsequent command, if supported by the system. If intercept is also specified, log_subcmds will be ignored. See Preventing shell escapes in sudoers(5) for more information. Only available starting with API version 1.18.

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.

rlimit_as=soft,hard

The maximum size to which the process's address space may grow (in bytes), if supported by the operating system. The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_core=soft,hard

The largest size core dump file that may be created (in bytes). The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_cpu=soft,hard

The maximum amount of CPU time that the process may use (in seconds). The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_data=soft,hard

The maximum size of the data segment for the process (in bytes). The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_fsize=soft,hard

The largest size file that the process may create (in bytes). The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_locks=soft,hard

The maximum number of locks that the process may establish, if supported by the operating system. The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_memlock=soft,hard

The maximum size that the process may lock in memory (in bytes), if supported by the operating system. The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_nofile=soft,hard

The maximum number of files that the process may have open. The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_nproc=soft,hard

The maximum number of processes that the user may run simultaneously. The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_rss=soft,hard

The maximum size to which the process's resident set size may grow (in bytes). The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

rlimit_stack=soft,hard

The maximum size to which the process's stack may grow (in bytes). The soft and hard limits are separated by a comma. If only a single value is specified, both the hard and soft limits are set. A value of “infinity” indicates that there is no limit. A value of “user” will cause the invoking user's resource limit to be preserved. A value of “default” will cause the target user's default resource limit to be used on systems that allow per-user resource limits to be configured. Only available starting with API version 1.18.

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_group=string

The name of the group the command will run as, if it is different from the runas_user's default group. This value is provided for auditing purposes only, the sudo front-end uses runas_egid and runas_gid when executing the command.

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.

runas_user=string

The name of the user the command will run as, which should correspond to runas_euid (or runas_uid if runas_euid is not set). This value is provided for auditing purposes only, the sudo front-end uses runas_euid and runas_uid when executing the command.

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-terminal 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_checkdir 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.

sudoedit_nfiles=number

The number of files to be edited by the user. If present, this is will be used by the sudo front-end to determine which elements of the argv_out vector are files to be edited. The ‘--’ element must immediately precede the first file to be edited. If sudoedit_nfiles is not specified, the sudo front-end will use the position of the ‘--’ element to determine where the file list begins. Only available starting with API version 1.21.

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. This value may be overridden by PAM or login.conf on some systems unless the umask_override option is also set.

umask_override=bool

Force the value specified by the umask option to override any umask set by PAM or login.conf.

use_ptrace=bool

If set, sudo will use ptrace(2) to implement intercept mode if supported by the system. This setting has no effect unless intercept is also set. Only available starting with API version 1.19.

use_pty=bool

Allocate a pseudo-terminal 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 pseudo-terminal 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.

errstr

If the check_policy() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

list

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:

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.

verbose

Flag indicating whether to list in verbose mode or not.

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.

errstr

If the list() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

validate

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:

errstr

If the validate() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

invalidate

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.

init_session

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:

pwd

If the user-ID the command will run as was found in the password database, pwd will describe that user, otherwise it will be NULL.

user_env_out

The NULL-terminated environment vector to use when executing the command. 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_out. The expected use case is to merge the contents of the PAM environment (if any) with the contents of user_env_out. The user_env_out 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_out. Failure to do so may result in a crash.

errstr

If the init_session() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

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 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.

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.

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.

event_alloc

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)

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 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:

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 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:

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 Fa(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.

sudo_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 sudo_plugin_printf() function may also be used to display additional error message to the user. The sudo_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 options the user specified when running sudo. As such, they will only be present when the corresponding option 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.

command_info

A vector of information describing the command being run in the form of “name=value” strings. The vector is terminated by a NULL pointer.

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.

argc

The number of elements in argv, not counting the final NULL pointer. It can be zero, such as when sudo is called with the -V option.

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.

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.

errstr

If the open() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

close

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:

exit_status

The command's exit status, as returned by the wait(2) system call, or zero if no command was run. 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 zero.

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 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.

log_ttyin

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:

buf

The buffer containing user input.

len

The length of buf in bytes.

errstr

If the log_ttyin() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

log_ttyout

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:

buf

The buffer containing command output.

len

The length of buf in bytes.

errstr

If the log_ttyout() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

log_stdin

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:

buf

The buffer containing user input.

len

The length of buf in bytes.

errstr

If the log_stdin() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

log_stdout

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:

buf

The buffer containing command output.

len

The length of buf in bytes.

errstr

If the log_stdout() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

log_stderr

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:

buf

The buffer containing command output.

len

The length of buf in bytes.

errstr

If the log_stderr() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

register_hooks

See the Policy plugin API section for a description of register_hooks().

deregister_hooks

See the Policy plugin API section for a description of deregister_hooks().

change_winsize

int (*change_winsize)(unsigned int lines, unsigned int cols,
    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:

lines

The number of lines (rows) in the re-sized terminal.

cols

The number of columns in the re-sized terminal.

errstr

If the change_winsize() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

log_suspend

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:

signo

The signal that caused the command to be suspended, or SIGCONT if the command was resumed.

errstr

If the log_suspend() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

event_alloc

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 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:

type

The type field should always be set to SUDO_AUDIT_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 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:

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 options the user specified when running sudo. As such, they will only be present when the corresponding option 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.

submit_optind

The index into submit_argv that corresponds to the first entry that is not a command line option. If submit_argv only consists of options, which may be the case with the -l or -v options, submit_argv[submit_optind] will evaluate to the NULL pointer.

submit_argv

The argument vector sudo was invoked with, including all command line options. The submit_optind argument can be used to determine the end of the command line options.

submit_envp

The invoking user's environment in the form of a NULL-terminated vector of “name=value” 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.

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.

errstr

If the open() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

close

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:

status_type

The type of status being passed. One of SUDO_PLUGIN_NO_STATUS, SUDO_PLUGIN_WAIT_STATUS, SUDO_PLUGIN_EXEC_ERROR or SUDO_PLUGIN_SUDO_ERROR.

status

Depending on the value of status_type, this value is either ignored, the command's exit status as returned by the wait(2) system call, the value of errno set by the execve(2) system call, or the value of errno resulting from an error in the sudo front-end.

accept

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:

plugin_name

The name of the plugin that accepted the command or “sudo” for the sudo front-end.

plugin_type

The type of plugin that accepted the command, currently either SUDO_POLICY_PLUGIN, SUDO_POLICY_APPROVAL, or SUDO_FRONT_END. The accept() function is called multiple times--once for each policy or approval plugin that succeeds and once for the sudo front-end. When called on behalf of the sudo front-end, command_info may include information from an I/O logging plugin as well.

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.

command_info

An optional vector of information describing the command being run in the form of “name=value” strings. The vector is terminated by a NULL pointer.

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.

run_argv

A NULL-terminated argument vector describing a command that will be run in the same form as what would be passed to the execve(2) system call.

run_envp

The environment the command will be run with in the form of a NULL-terminated vector of “name=value” 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.

errstr

If the accept() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

reject

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:

plugin_name

The name of the plugin that rejected the command.

plugin_type

The type of plugin that rejected the command, currently either SUDO_POLICY_PLUGIN, SUDO_APPROVAL_PLUGIN, or SUDO_IO_PLUGIN.

Unlike the accept() function, the reject() function is not called on behalf of the sudo front-end.

audit_msg

An optional string describing the reason the command was rejected by the plugin. If the plugin did not provide a reason, audit_msg will be the NULL pointer.

command_info

An optional vector of information describing the command being run in the form of “name=value” strings. The vector is terminated by a NULL pointer.

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.

errstr

If the reject() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

error

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:

plugin_name

The name of the plugin that generated the error or “sudo” for the sudo front-end.

plugin_type

The type of plugin that generated the error, or SUDO_FRONT_END for the sudo front-end.

audit_msg

An optional string describing the plugin error. If the plugin did not provide a description, audit_msg will be the NULL pointer.

command_info

An optional vector of information describing the command being run in the form of “name=value” strings. The vector is terminated by a NULL pointer.

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.

errstr

If the error() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

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.

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().

event_alloc

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.

Approval plugin API¶

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:

type

The type field should always be set to SUDO_APPROVAL_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 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:

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 Conversation API for details). 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 Conversation API for details). 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 options the user specified when running sudo. As such, they will only be present when the corresponding option 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.

submit_optind

The index into submit_argv that corresponds to the first entry that is not a command line option. If submit_argv only consists of options, which may be the case with the -l or -v options, submit_argv[submit_optind] will evaluate to the NULL pointer.

submit_argv

The argument vector sudo was invoked with, including all command line options. The submit_optind argument can be used to determine the end of the command line options.

submit_envp

The invoking user's environment in the form of a NULL-terminated vector of “name=value” 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.

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.

errstr

If the open() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

close

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.

check

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:

command_info

A vector of information describing the command being run in the form of “name=value” strings. The vector is terminated by a NULL pointer.

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.

run_argv

A NULL-terminated argument vector describing a command that will be run in the same form as what would be passed to the execve(2) system call.

run_envp

The environment the command will be run with in the form of a NULL-terminated vector of “name=value” 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.

errstr

If the open() function returns a value other than 1, the plugin may store a message describing the failure or error in errstr. The sudo front-end will then pass this value to any registered audit plugins. The string stored in errstr must remain valid until the plugin's close() function is called.

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.

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.

Signal handlers¶

The sudo front-end installs default signal handlers to trap common signals while the plugin functions are run. The following signals are trapped by default before the command is executed:

• SIGALRM
• SIGHUP
• SIGINT
• SIGPIPE
• SIGQUIT
• SIGTERM
• SIGTSTP
• SIGUSR1
• SIGUSR2

If a fatal signal is received before the command is executed, sudo will call the plugin's close() function with an exit status of 128 plus the value of the signal that was received. This allows for consistent logging of commands killed by a signal for plugins that log such information in their close() function. An exception to this is SIGPIPE, which is ignored until the command is executed.

A plugin may temporarily install its own signal handlers but must restore the original handler before the plugin function returns.

Hook function API¶

Beginning with plugin API version 1.2, it is possible to install hooks for certain functions called by the sudo front-end.

Currently, the only supported hooks relate to the handling of environment variables. Hooks can be used to intercept attempts to get, set, or remove environment variables so that these changes can be reflected in the version of the environment that is used to execute a command. A future version of the API will support hooking internal sudo front-end functions as well.

Hook structure

Hooks in sudo are described by the following structure:

typedef int (*sudo_hook_fn_t)();

struct sudo_hook {
    unsigned int hook_version;
    unsigned int hook_type;
    sudo_hook_fn_t hook_fn;
    void *closure;
};

A struct sudo_hook 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 system 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 system implementation. For example, a setenv hook that operates on a private copy of the environment but leaves environ unchanged.

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.

Event 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:

set

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:

struct sudo_plugin_event *pev

A pointer to the struct sudo_plugin_event itself.

fd

The file or socket descriptor for I/O-based events or the signal number for signal events. For time-based events, fd must be -1.

events

The following values determine what will trigger the event callback:

SUDO_PLUGIN_EV_TIMEOUT

callback is run after the specified timeout expires

SUDO_PLUGIN_EV_READ

callback is run when the file descriptor is readable

SUDO_PLUGIN_EV_WRITE

callback is run when the file descriptor is writable

SUDO_PLUGIN_EV_PERSIST

event is persistent and remains enabled until explicitly deleted

SUDO_PLUGIN_EV_SIGNAL

callback is run when the specified signal is received

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.

sudo_plugin_ev_callback_t callback

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:

fd

The file or socket descriptor for I/O-based events or the signal number for signal events.

what

The event type that triggered that callback. For events that have multiple event types (for example SUDO_PLUGIN_EV_READ and SUDO_PLUGIN_EV_WRITE) or have an associated timeout, what can be used to determine why the callback was run.

closure

The generic pointer that was specified in the set() function.

closure

A generic pointer that will be passed to the callback function.

The set() function returns 1 on success, and -1 if a error occurred.

add

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.

del

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.

pending

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.

fd

int (*fd)(struct sudo_plugin_event *pev);

The fd() function returns the descriptor or signal number associated with the event pev.

setbase

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.

loopbreak

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.

free

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.

Remote command execution¶

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.

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 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 * restrict 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:

SUDO_CONV_PROMPT_ECHO_OFF

Prompt the user for input with echo disabled; this is generally used for passwords. The reply will be stored in the replies array, and it will never be NULL.

SUDO_CONV_PROMPT_ECHO_ON

Prompt the user for input with echo enabled. The reply will be stored in the replies array, and it will never be NULL.

SUDO_CONV_ERROR_MSG

Display an error message. The message is written to the standard error unless the SUDO_CONV_PREFER_TTY flag is set, in which case it is written to the user's terminal if possible.

SUDO_CONV_INFO_MSG

Display a message. The message is written to the standard output unless the SUDO_CONV_PREFER_TTY flag is set, in which case it is written to the user's terminal if possible.

SUDO_CONV_PROMPT_MASK

Prompt the user for input but echo an asterisk character for each character read. The reply will be stored in the replies array, and it will never be NULL. This can be used to provide visual feedback to the user while reading sensitive information that should not be displayed.

In addition to the above values, the following flag bits may also be set:

SUDO_CONV_PROMPT_ECHO_OK

Allow input to be read when echo cannot be disabled when the message type is SUDO_CONV_PROMPT_ECHO_OFF or SUDO_CONV_PROMPT_MASK. By default, sudo will refuse to read input if the echo cannot be disabled for those message types.

SUDO_CONV_PREFER_TTY

When displaying a message via SUDO_CONV_ERROR_MSG or SUDO_CONV_INFO_MSG, try to write the message to the user's terminal. If the terminal is unavailable, the standard error or standard output will be used, depending upon whether SUDO_CONV_ERROR_MSG or SUDO_CONV_INFO_MSG was used. The user's terminal is always used when possible for input, this flag is only used for output.

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.

Plugin invocation order¶

As of sudo 1.9.0, the plugin open() and close() functions are called in the following order:

1. audit open
2. policy open
3. approval open
4. approval close
5. I/O log open
6. command runs
7. command exits
8. I/O log close
9. policy close
10. audit close
11. sudo exits

Prior to sudo 1.9.0, the I/O log close() function was called after the policy close() function.

Sudoers group plugin API¶

The sudoers plugin supports its own plugin interface to allow non-Unix group lookups. This can be used to query a group source other than the standard Unix group database. Two sample group plugins are bundled with sudo, group_file, and system_group, are detailed in sudoers(5). Third party group plugins include a QAS AD plugin available from Quest Software.

A group plugin must declare and populate a 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:

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 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:

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)