`sudo_plugin` ( 8 )

sudo Plugin API (Sudo Plugin API)

Name | Description | Plugin api changelog | See also |

Имя (Name)

sudo_plugin — Sudo Plugin API

Описание (Description)

Starting with version 1.8, sudo supports a plugin API for policy and session logging. Plugins may be compiled as dynamic shared objects (the default on systems that support them) or compiled statically into the sudo binary itself. By default, the sudoers policy plugin and an associated I/O logging plugin are used. Via the plugin API, sudo can be configured to use alternate policy and/or I/O logging plugins provided by third parties. The plugins to be used are specified in the sudo.conf(5) file.

The API is versioned with a major and minor number. The minor version number is incremented when additions are made. The major number is incremented when incompatible changes are made. A plugin should be check the version passed to it and make sure that the major version matches.

The plugin API is defined by the sudo_plugin.h header file.

Policy plugin API A policy plugin must declare and populate a policy_plugin struct in the global scope. This structure contains pointers to the functions that implement the sudo policy checks. The name of the symbol should be specified in sudo.conf(5) along with a path to the plugin so that sudo can load it.

struct policy_plugin { #define SUDO_POLICY_PLUGIN 1 unsigned int type; /* always SUDO_POLICY_PLUGIN */ unsigned int version; /* always SUDO_API_VERSION */ int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], char * const user_env[], char * const plugin_options[], 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 *list_user, const char **errstr); int (*validate)(const char **errstr); void (*invalidate)(int remove); 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); };

The policy_plugin struct has the following fields:

type The type field should always be set to SUDO_POLICY_PLUGIN.

version The version field should be set to SUDO_API_VERSION.

This allows sudo to determine the API version the plugin was built against.

open int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], char * const user_env[], char * const plugin_options[], 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 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.

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

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 gid to run the command as, if specified via the -g option.

runas_user=string The user name or uid 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.

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 the user has no terminal device associated with the session, the value will be empty, as in 'tty='.

uid=uid_t The real user-ID of the user invoking sudo.

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

user=string The name of the user invoking sudo.

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

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

plugin_options Any (non-comment) strings immediately after the plugin path are passed as arguments to the plugin. These arguments are split on a white space boundary and are passed to the plugin in the form of a NULL-terminated array of strings. If no arguments were specified, plugin_options will be the NULL pointer.

NOTE: the plugin_options parameter is only available starting with API version 1.2. A plugin must check the API version specified by the sudo front end before using plugin_options. Failure to do so may result in a crash.

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.

NOTE: 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 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 not use_pty options are set in the command_info list, the sudo front end may execute the command directly instead of running it as a child process.

show_version int (*show_version)(int verbose);

The show_version() function is called by sudo when the user specifies the -V option. The plugin may display its version information to the user via the conversation() or plugin_printf() function using SUDO_CONV_INFO_MSG. If the user requests detailed version information, the verbose flag will be set.

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 should choose the editor to be used, potentially from a variable in the user's environment, such as EDITOR, and include it in argv_out (note that environment variables may include command line options). The files to be edited should be copied from argv into argv_out, separated from the editor and its arguments by a '--' element. The '--' will be removed by sudo before the editor is executed. The plugin should also set sudoedit=true in the command_info list.

The check_policy() function returns 1 if the command is allowed, 0 if not allowed, -1 for a general error, or -2 for a usage error or if sudoedit was specified but is unsupported by the plugin. In the latter case, sudo will print a usage message before it exits. If an error occurs, the plugin may optionally call the conversation() or plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.

The function arguments are as follows:

argc The number of elements in argv, not counting the final NULL pointer.

argv The argument vector describing the command the user wishes to run, in the same form as what would be passed to the execve(2) system call. The vector is terminated by a NULL pointer.

env_add Additional environment variables specified by the user on the command line in the form of a NULL-terminated vector of 'name=value' strings. The plugin may reject the command if one or more variables are not allowed to be set, or it may silently ignore such variables.

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

command_info Information about the command being run in the form of 'name=value' strings. These values are used by sudo to set the execution environment when running a command. The plugin is responsible for creating and populating the vector, which must be terminated with a NULL pointer. The following values are recognized by sudo:

chroot=string The root directory to use when running the command.

closefrom=number If specified, sudo will close all files descriptors with a value of number or higher.

command=string Fully qualified path to the command to be executed.

cwd=string The current working directory to change to when executing the command. 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 enabled, 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.

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.

noexec=bool If set, prevent the command from executing other programs.

preserve_fds=list A comma-separated list of file descriptors that should be preserved, regardless of the value of the closefrom setting. Only available starting with API version 1.5.

preserve_groups=bool If set, sudo will preserve the user's group vector instead of initializing the group vector based on runas_user.

runas_egid=gid Effective group-ID to run the command as. If not specified, the value of runas_gid is used.

runas_euid=uid Effective user-ID to run the command as. If not specified, the value of runas_uid is used.

runas_gid=gid Group-ID to run the command as.

runas_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_follow option can be set to false to disable this check. Only available starting with API version 1.8.

sudoedit_follow=bool Set to true to allow sudoedit to edit files that are symbolic links. By default, sudoedit 1.8.15 and higher will refuse to open a symbolic link. The sudoedit_follow option can be used to restore the older behavior and allow sudoedit to open symbolic links. Only available starting with API version 1.8.

timeout=int Command timeout. If non-zero then when the timeout expires the command will be killed.

umask=octal The file creation mask to use when executing the command. 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_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.

list int (*list)(int argc, char * const argv[], int verbose, const char *list_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 plugin_printf() function with SUDO_CONF_ERROR_MSG to present additional error information to the user.

Privileges should be output via the conversation() or plugin_printf() function using SUDO_CONV_INFO_MSG.

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.

list_user The name of a different user to list privileges for if the policy allows it. If NULL, the plugin should list the privileges of the invoking user.

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.

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 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.

invalidate void (*invalidate)(int remove);

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 remove flag is set, the plugin may remove the credentials instead of simply invalidating them.

The invalidate() function should be NULL if the plugin does not support credential caching.

init_session int (*init_session)(struct passwd *pwd, char **user_env_out[]);

The init_session() function is called before sudo sets up the execution environment for the command. It is run in the parent sudo process and before any uid or gid changes. This can be used to perform session setup that is not supported by command_info, such as opening the PAM session. The close() function can be used to tear down the session that was opened by init_session.

The pwd argument points to a passwd struct for the user the command will be run as if the uid the command will run as was found in the password database, otherwise it will be NULL.

The user_env_out argument points to the environment the command will run in, in the form of a NULL-terminated vector of 'name=value' strings. This is the same string passed back to the front end via the Policy Plugin's user_env_out parameter. If the init_session() function needs to modify the user environment, it should update the pointer stored in user_env_out. The expected use case is to merge the contents of the PAM environment (if any) with the contents of user_env_out. NOTE: 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.

register_hooks void (*register_hooks)(int version, int (*register_hook)(struct sudo_hook *hook));

The register_hooks() function is called by the sudo front end to register any hooks the plugin needs. If the plugin does not support hooks, register_hooks should be set to the NULL pointer.

The version argument describes the version of the hooks API supported by the sudo front end.

The register_hook() function should be used to register any supported hooks the plugin needs. It returns 0 on success, 1 if the hook type is not supported and -1 if the major version in struct hook does not match the front end's major hook API version.

See the Hook function API section below for more information about hooks.

NOTE: the register_hooks() function is only available starting with API version 1.2. If the sudo front end doesn't support API version 1.2 or higher, register_hooks will not be called.

deregister_hooks void (*deregister_hooks)(int version, int (*deregister_hook)(struct sudo_hook *hook));

The deregister_hooks() function is called by the sudo front end to deregister any hooks the plugin has registered. If the plugin does not support hooks, deregister_hooks should be set to the NULL pointer.

The version argument describes the version of the hooks API supported by the sudo front end.

The deregister_hook() function should be used to deregister any hooks that were put in place by the register_hook() function. If the plugin tries to deregister a hook that the front end does not support, deregister_hook will return an error.

See the Hook function API section below for more information about hooks.

NOTE: the deregister_hooks() function is only available starting with API version 1.2. If the sudo front end doesn't support API version 1.2 or higher, deregister_hooks will not be called.

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.

NOTE: 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.

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.

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 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 (note that this will include input even when echo is disabled, such as when a password is read). The log_ttyout function receives output from the pseudo-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.

The audit_plugin struct has the following fields:

type The type field should always be set to SUDO_IO_PLUGIN.

version The version field should be set to SUDO_API_VERSION.

This allows sudo to determine the API version the plugin was built against.

open int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], 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 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.

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, when sudo is called with -V.

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.

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);

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.

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.

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.

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.

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.

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.

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.

event_alloc struct sudo_plugin_event * (*event_alloc)(void);

See the Event API section below for more information about events.

NOTE: 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_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).

The audit_plugin struct 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_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.

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.

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);

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);

See the Event API section below for more information about events.

NOTE: 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_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).

The approval_plugin struct 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.

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.