path: root/doc/sudo_plugin.cat

SUDO_PLUGIN(4)                Programmer's Manual               SUDO_PLUGIN(4)

NNAAMMEE
     ssuuddoo__pplluuggiinn - Sudo Plugin API

DDEESSCCRRIIPPTTIIOONN
     Starting with version 1.8, ssuuddoo 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
     ssuuddoo binary itself.  By default, the ssuuddooeerrss policy plugin and an
     associated I/O logging plugin are used.  Via the plugin API, ssuuddoo can be
     configured to use alternate policy and/or I/O logging plugins provided by
     third parties.  The plugins to be used are specified in the sudo.conf(4)
     file.

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

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

   PPoolliiccyy pplluuggiinn AAPPII
     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 ssuuddoo policy checks.  The name of the symbol should be
     specified in sudo.conf(4) along with a path to the plugin so that ssuuddoo
     can load it.

     struct policy_plugin {
     #define SUDO_POLICY_PLUGIN     1
         unsigned int type; /* always SUDO_POLICY_PLUGIN */
         unsigned int version; /* always SUDO_API_VERSION */
         int (*open)(unsigned int version, sudo_conv_t conversation,
                     sudo_printf_t plugin_printf, char * const settings[],
                     char * const user_info[], char * const user_env[],
                     char * const plugin_options[]);
         void (*close)(int exit_status, int error);
         int (*show_version)(int verbose);
         int (*check_policy)(int argc, char * const argv[],
                             char *env_add[], char **command_info[],
                             char **argv_out[], char **user_env_out[]);
         int (*list)(int argc, char * const argv[], int verbose,
                     const char *list_user);
         int (*validate)(void);
         void (*invalidate)(int remove);
         int (*init_session)(struct passwd *pwd, char **user_env[]);
         void (*register_hooks)(int version,
            int (*register_hook)(struct sudo_hook *hook));
         void (*deregister_hooks)(int version,
            int (*deregister_hook)(struct sudo_hook *hook));
     };

     The policy_plugin struct has the following fields:

     type  The type field should always be set to SUDO_POLICY_PLUGIN.

     version
           The version field should be set to SUDO_API_VERSION.

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

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

           Returns 1 on success, 0 on failure, -1 if a general error occurred,
           or -2 if there was a usage error.  In the latter case, ssuuddoo will
           print a usage message before it exits.  If an error occurs, the
           plugin may optionally call the ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff()
           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 ssuuddoo allows the plugin to determine
                 the major and minor version number of the plugin API
                 supported by ssuuddoo.

           conversation
                 A pointer to the ccoonnvveerrssaattiioonn() function that can be used by
                 the plugin to interact with the user (see below).  Returns 0
                 on success and -1 on failure.

           plugin_printf
                 A pointer to a pprriinnttff()-style function that may be used to
                 display informational or error messages (see below).  Returns
                 the number of characters printed on success and -1 on
                 failure.

           settings
                 A vector of user-supplied ssuuddoo settings in the form of
                 ``name=value'' strings.  The vector is terminated by a NULL
                 pointer.  These settings correspond to flags the user
                 specified when running ssuuddoo.  As such, they will only be
                 present when the corresponding flag has been specified on the
                 command line.

                 When parsing _s_e_t_t_i_n_g_s, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e might.

                 bsdauth_type=string
                       Authentication type, if specified by the --aa flag, to
                       use on systems where BSD authentication is supported.

                 closefrom=number
                       If specified, the user has requested via the --CC flag
                       that ssuuddoo close all files descriptors with a value of
                       _n_u_m_b_e_r or higher.  The plugin may optionally pass this,
                       or another value, back in the _c_o_m_m_a_n_d___i_n_f_o list.

                 debug_flags=string
                       A comma-separated list of debug flags that correspond
                       to ssuuddoo's Debug entry in sudo.conf(4), if there is one.
                       The flags are passed to the plugin as they appear in
                       sudo.conf(4).  The syntax used by ssuuddoo and the ssuuddooeerrss
                       plugin is _s_u_b_s_y_s_t_e_m@_p_r_i_o_r_i_t_y but the plugin is free to
                       use a different format so long as it does not include a
                       comma (`,').  There is not currently a way to specify a
                       set of debug flags specific to the plugin--the flags
                       are shared by ssuuddoo and the plugin.

                 debug_level=number
                       This setting has been deprecated in favor of
                       _d_e_b_u_g___f_l_a_g_s.

                 ignore_ticket=bool
                       Set to true if the user specified the --kk flag along
                       with a command, indicating that the user wishes to
                       ignore any cached authentication credentials.
                       _i_m_p_l_i_e_d___s_h_e_l_l to true.  This allows ssuuddoo 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 cchheecckk__ppoolliiccyy() function, which will
                       cause ssuuddoo to print a usage message and exit.

                 implied_shell=bool
                       If the user does not specify a program on the command
                       line, ssuuddoo 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 --cc flag.

                 login_shell=bool
                       Set to true if the user specified the --ii flag,
                       indicating that the user wishes to run a login shell.

                 max_groups=int
                       The maximum number of groups a user may belong to.
                       This will only be present if there is a corresponding
                       setting in sudo.conf(4).

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

                 noninteractive=bool
                       Set to true if the user specified the --nn flag,
                       indicating that ssuuddoo 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 ssuuddoo 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.

                 preserve_environment=bool
                       Set to true if the user specified the --EE flag,
                       indicating that the user wishes to preserve the
                       environment.

                 preserve_groups=bool
                       Set to true if the user specified the --PP flag,
                       indicating that the user wishes to preserve the group
                       vector instead of setting it based on the runas user.

                 progname=string
                       The command name that sudo was run as, typically
                       ``sudo'' or ``sudoedit''.

                 prompt=string
                       The prompt to use when requesting a password, if
                       specified via the --pp flag.

                 remote_host=string
                       The name of the remote host to run the command on, if
                       specified via the --hh 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 ssuuddoo 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 --ss flag,
                       indicating that the user wishes to run a shell.

                 runas_group=string
                       The group name or gid to run the command as, if
                       specified via the --gg flag.

                 runas_user=string
                       The user name or uid to run the command as, if
                       specified via the --uu flag.

                 selinux_role=string
                       SELinux role to use when executing the command, if
                       specified by the --rr flag.

                 selinux_type=string
                       SELinux type to use when executing the command, if
                       specified by the --tt flag.

                 set_home=bool
                       Set to true if the user specified the --HH flag.  If
                       true, set the HOME environment variable to the target
                       user's home directory.

                 sudoedit=bool
                       Set to true when the --ee flag is is specified or if
                       invoked as ssuuddooeeddiitt.  The plugin shall substitute an
                       editor into _a_r_g_v in the cchheecckk__ppoolliiccyy() function or
                       return -2 with a usage error if the plugin does not
                       support _s_u_d_o_e_d_i_t.  For more information, see the
                       _c_h_e_c_k___p_o_l_i_c_y section.

                 Additional settings may be added in the future so the plugin
                 should silently ignore settings that it does not recognize.

           user_info
                 A vector of information about the user running the command in
                 the form of ``name=value'' strings.  The vector is terminated
                 by a NULL pointer.

                 When parsing _u_s_e_r___i_n_f_o, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e might.

                 cols=int
                       The number of columns the user's terminal supports.  If
                       there is no terminal device available, a default value
                       of 80 is used.

                 cwd=string
                       The user's current working directory.

                 egid=gid_t
                       The effective group ID of the user invoking ssuuddoo.

                 euid=uid_t
                       The effective user ID of the user invoking ssuuddoo.

                 gid=gid_t
                       The real group ID of the user invoking ssuuddoo.

                 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 ssuuddoo
                       process is a member of.  Only available starting with
                       API version 1.2.

                 pid=int
                       The process ID of the running ssuuddoo process.  Only
                       available starting with API version 1.2.

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

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

                 ppid=int
                       The parent process ID of the running ssuuddoo process.
                       Only available starting with API version 1.2.

                 sid=int
                       The session ID of the running ssuuddoo process or 0 if ssuuddoo
                       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 ssuuddoo process or
                       -1 if there is no terminal present.  Only available
                       starting with API version 1.2.

                 tty=string
                       The path to the user's terminal device.  If the user
                       has no terminal device associated with the session, the
                       value will be empty, as in ``tty=''.

                 uid=uid_t
                       The real user ID of the user invoking ssuuddoo.

                 user=string
                       The name of the user invoking ssuuddoo.

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

                 When parsing _u_s_e_r___e_n_v, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e might.

     close
           void (*close)(int exit_status, int error);

           The cclloossee() function is called when the command being run by ssuuddoo
           finishes.

           The function arguments are as follows:

           exit_status
                 The command's exit status, as returned by the wait(2) system
                 call.  The value of exit_status is undefined if error is non-
                 zero.

           error
                 If the command could not be executed, this is set to the
                 value of errno set by the execve(2) system call.  The plugin
                 is responsible for displaying error information via the
                 ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff() function.  If the command
                 was successfully executed, the value of error is 0.

           If no cclloossee() function is defined, no I/O logging plugins are
           loaded, and neither the _t_i_m_e_o_u_t not _u_s_e___p_t_y options are set in the
           command_info list, the ssuuddoo front end may execute the command
           directly instead of running it as a child process.

     show_version
           int (*show_version)(int verbose);

           The sshhooww__vveerrssiioonn() function is called by ssuuddoo when the user
           specifies the --VV option.  The plugin may display its version
           information to the user via the ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff()
           function using SUDO_CONV_INFO_MSG.  If the user requests detailed
           version information, the verbose flag will be set.

     check_policy
           int (*check_policy)(int argc, char * const argv[]
                               char *env_add[], char **command_info[],
                               char **argv_out[], char **user_env_out[]);

           The cchheecckk__ppoolliiccyy() function is called by ssuuddoo to determine whether
           the user is allowed to run the specified commands.

           If the _s_u_d_o_e_d_i_t option was enabled in the _s_e_t_t_i_n_g_s array passed to
           the ooppeenn() function, the user has requested _s_u_d_o_e_d_i_t mode.
           _s_u_d_o_e_d_i_t is a mechanism for editing one or more files where an
           editor is run with the user's credentials instead of with elevated
           privileges.  ssuuddoo 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 _s_u_d_o_e_d_i_t, it should choose the editor to be used,
           potentially from a variable in the user's environment, such as
           EDITOR, and include it in _a_r_g_v___o_u_t (note that environment variables
           may include command line flags).  The files to be edited should be
           copied from _a_r_g_v into _a_r_g_v___o_u_t, separated from the editor and its
           arguments by a ``--'' element.  The ``--'' will be removed by ssuuddoo
           before the editor is executed.  The plugin should also set
           _s_u_d_o_e_d_i_t_=_t_r_u_e in the _c_o_m_m_a_n_d___i_n_f_o list.

           The cchheecckk__ppoolliiccyy() 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 _s_u_d_o_e_d_i_t was specified but is unsupported by the plugin.  In the
           latter case, ssuuddoo will print a usage message before it exits.  If
           an error occurs, the plugin may optionally call the ccoonnvveerrssaattiioonn()
           or pplluuggiinn__pprriinnttff() 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 _a_r_g_v, 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 _e_n_v___a_d_d, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e might.

           command_info
                 Information about the command being run in the form of
                 ``name=value'' strings.  These values are used by ssuuddoo 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 ssuuddoo:

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

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

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

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

                 exec_background=bool
                       By default, ssuuddoo runs a command as the foreground
                       process as long as ssuuddoo itself is running in the
                       foreground.  When _e_x_e_c___b_a_c_k_g_r_o_u_n_d is enabled and the
                       command is being run in a pty (due to I/O logging or
                       the _u_s_e___p_t_y 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 ssuuddoo 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 ssuuddoo 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 _s_u_d_o behavior
                       or when the command is not being run in a pty.

                       For this to work seamlessly, the operating system must
                       support the automatic restarting of system calls.
                       Unfortunately, not all operating systems do this by
                       default, and even those that do may have bugs.  For
                       example, Mac OS X fails to restart the ttccggeettaattttrr() and
                       ttccsseettaattttrr() system calls (this is a bug in Mac OS X).
                       Furthermore, because this behavior depends on the
                       command stopping with the SIGTTIN or SIGTTOU signals,
                       programs that catch these signals and suspend
                       themselves with a different signal (usually SIGTOP)
                       will not be automatically foregrounded.  Some versions
                       of the linux su(1) command behave this way.  Because of
                       this, a plugin should not set _e_x_e_c___b_a_c_k_g_r_o_u_n_d 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 _u_s_e___p_t_y is enabled.

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

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

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

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

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

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

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

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

                 nice=int
                       Nice value (priority) to use when executing the
                       command.  The nice value, if specified, overrides the
                       priority associated with the _l_o_g_i_n___c_l_a_s_s 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 _c_l_o_s_e_f_r_o_m
                       setting.  Only available starting with API version 1.5.

                 preserve_groups=bool
                       If set, ssuuddoo 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 _r_u_n_a_s___g_i_d is used.

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

                 runas_gid=gid
                       Group ID to run the command as.

                 runas_groups=list
                       The supplementary group vector to use for the command
                       in the form of a comma-separated list of group IDs.  If
                       _p_r_e_s_e_r_v_e___g_r_o_u_p_s is set, this option is ignored.

                 runas_uid=uid
                       User ID to run the command as.

                 selinux_role=string
                       SELinux role to use when executing the command.

                 selinux_type=string
                       SELinux type to use when executing the command.

                 set_utmp=bool
                       Create a utmp (or utmpx) entry when a pseudo-tty is
                       allocated.  By default, the new entry will be a copy of
                       the user's existing utmp entry (if any), with the tty,
                       time, type and pid fields updated.

                 sudoedit=bool
                       Set to true when in _s_u_d_o_e_d_i_t mode.  The plugin may
                       enable _s_u_d_o_e_d_i_t mode even if ssuuddoo was not invoked as
                       ssuuddooeeddiitt.  This allows the plugin to perform command
                       substitution and transparently enable _s_u_d_o_e_d_i_t when the
                       user attempts to run an editor.

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

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

                 use_pty=bool
                       Allocate a pseudo-tty to run the command in, regardless
                       of whether or not I/O logging is in use.  By default,
                       ssuuddoo will only run the command in a pty when an I/O log
                       plugin is loaded.

                 utmp_user=string
                       User name to use when constructing a new utmp (or
                       utmpx) entry when _s_e_t___u_t_m_p 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, ssuuddoo will base the new entry on the
                       invoking user's existing entry.

                 Unsupported values will be ignored.

           argv_out
                 The NULL-terminated argument vector to pass to the execve(2)
                 system call when executing the command.  The plugin is
                 responsible for allocating and populating the vector.

           user_env_out
                 The NULL-terminated environment vector to use when executing
                 the command.  The plugin is responsible for allocating and
                 populating the vector.

     list
           int (*list)(int verbose, const char *list_user,
                       int argc, char * const argv[]);

           List available privileges for the invoking user.  Returns 1 on
           success, 0 on failure and -1 on error.  On error, the plugin may
           optionally call the ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff() function with
           SUDO_CONF_ERROR_MSG to present additional error information to the
           user.

           Privileges should be output via the ccoonnvveerrssaattiioonn() or
           pplluuggiinn__pprriinnttff() function using SUDO_CONV_INFO_MSG,

           verbose
                 Flag indicating whether to list in verbose mode or not.

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

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

           argv  If non-NULL, an argument vector describing a command the user
                 wishes to check against the policy in the same form as what
                 would be passed to the execve(2) system call.  If the command
                 is permitted by the policy, the fully-qualified path to the
                 command should be displayed along with any command line
                 arguments.

     validate
           int (*validate)(void);

           The vvaalliiddaattee() function is called when ssuuddoo is run with the --vv
           flag.  For policy plugins such as ssuuddooeerrss that cache authentication
           credentials, this function will validate and cache the credentials.

           The vvaalliiddaattee() 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 ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff()
           function with SUDO_CONF_ERROR_MSG to present additional error
           information to the user.

     invalidate
           void (*invalidate)(int remove);

           The iinnvvaalliiddaattee() function is called when ssuuddoo is called with the --kk
           or --KK flag.  For policy plugins such as ssuuddooeerrss that cache
           authentication credentials, this function will invalidate the
           credentials.  If the _r_e_m_o_v_e flag is set, the plugin may remove the
           credentials instead of simply invalidating them.

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

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

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

           The _p_w_d 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 _u_s_e_r___e_n_v 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 _u_s_e_r___e_n_v___o_u_t parameter.  If the iinniitt__sseessssiioonn()
           function needs to modify the user environment, it should update the
           pointer stored in _u_s_e_r___e_n_v.  The expected use case is to merge the
           contents of the PAM environment (if any) with the contents of
           _u_s_e_r___e_n_v.  NOTE: the _u_s_e_r___e_n_v parameter is only available starting
           with API version 1.2.  A plugin mmuusstt check the API version
           specified by the ssuuddoo front end before using _u_s_e_r___e_n_v.  Failure to
           do so may result in a crash.

           Returns 1 on success, 0 on failure and -1 on error.  On error, the
           plugin may optionally call the ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff()
           function with SUDO_CONF_ERROR_MSG to present additional error
           information to the user.

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

           The rreeggiisstteerr__hhooookkss() 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 _v_e_r_s_i_o_n argument describes the version of the hooks API
           supported by the ssuuddoo front end.

           The rreeggiisstteerr__hhooookk() 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 _H_o_o_k _f_u_n_c_t_i_o_n _A_P_I section below for more information about
           hooks.

           NOTE: the rreeggiisstteerr__hhooookkss() function is only available starting with
           API version 1.2.  If the ssuuddoo 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 ddeerreeggiisstteerr__hhooookkss() 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 _v_e_r_s_i_o_n argument describes the version of the hooks API
           supported by the ssuuddoo front end.

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

           See the _H_o_o_k _f_u_n_c_t_i_o_n _A_P_I section below for more information about
           hooks.

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

     _P_o_l_i_c_y _P_l_u_g_i_n _V_e_r_s_i_o_n _M_a_c_r_o_s

     /* Plugin API version major/minor. */
     #define SUDO_API_VERSION_MAJOR 1
     #define SUDO_API_VERSION_MINOR 2
     #define SUDO_API_MKVERSION(x, y) ((x << 16) | y)
     #define SUDO_API_VERSION SUDO_API_MKVERSION(SUDO_API_VERSION_MAJOR,\
                                                 SUDO_API_VERSION_MINOR)

     /* Getters and setters for API version */
     #define SUDO_API_VERSION_GET_MAJOR(v) ((v) >> 16)
     #define SUDO_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
     #define SUDO_API_VERSION_SET_MAJOR(vp, n) do { \
         *(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
     } while(0)
     #define SUDO_VERSION_SET_MINOR(vp, n) do { \
         *(vp) = (*(vp) & 0xffff0000) | (n); \
     } while(0)

   II//OO pplluuggiinn AAPPII
     struct io_plugin {
     #define SUDO_IO_PLUGIN 2
         unsigned int type; /* always SUDO_IO_PLUGIN */
         unsigned int version; /* always SUDO_API_VERSION */
         int (*open)(unsigned int version, sudo_conv_t conversation,
                     sudo_printf_t plugin_printf, char * const settings[],
                     char * const user_info[], char * const command_info[],
                     int argc, char * const argv[], char * const user_env[],
                     char * const plugin_options[]);
         void (*close)(int exit_status, int error); /* wait status or error */
         int (*show_version)(int verbose);
         int (*log_ttyin)(const char *buf, unsigned int len);
         int (*log_ttyout)(const char *buf, unsigned int len);
         int (*log_stdin)(const char *buf, unsigned int len);
         int (*log_stdout)(const char *buf, unsigned int len);
         int (*log_stderr)(const char *buf, unsigned int len);
         void (*register_hooks)(int version,
            int (*register_hook)(struct sudo_hook *hook));
         void (*deregister_hooks)(int version,
            int (*deregister_hook)(struct sudo_hook *hook));
     };

     When an I/O plugin is loaded, ssuuddoo runs the command in a pseudo-tty.
     This makes it possible to log the input and output from the user's
     session.  If any of the standard input, standard output or standard error
     do not correspond to a tty, ssuuddoo will open a pipe to capture the I/O for
     logging before passing it on.

     The log_ttyin function receives the raw user input from the terminal
     device (note that this will include input even when echo is disabled,
     such as when a password is read).  The log_ttyout function receives
     output from the pseudo-tty that is suitable for replaying the user's
     session at a later time.  The lloogg__ssttddiinn(), lloogg__ssttddoouutt() and lloogg__ssttddeerrrr()
     functions are only called if the standard input, standard output or
     standard error respectively correspond to something other than a tty.

     Any of the logging functions may be set to the NULL pointer if no logging
     is to be performed.  If the open function returns 0, no I/O will be sent
     to the plugin.

     The io_plugin struct has the following fields:

     type  The type field should always be set to SUDO_IO_PLUGIN.

     version
           The version field should be set to SUDO_API_VERSION.

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

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

           The ooppeenn() function is run before the lloogg__iinnppuutt(), lloogg__oouuttppuutt() or
           sshhooww__vveerrssiioonn() functions are called.  It is only called if the
           version is being requested or the cchheecckk__ppoolliiccyy() 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, ssuuddoo will print a usage message before it exits.
           If an error occurs, the plugin may optionally call the
           ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff() 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 ssuuddoo allows the plugin to determine
                 the major and minor version number of the plugin API
                 supported by ssuuddoo.

           conversation
                 A pointer to the ccoonnvveerrssaattiioonn() function that may be used by
                 the sshhooww__vveerrssiioonn() function to display version information
                 (see sshhooww__vveerrssiioonn() below).  The ccoonnvveerrssaattiioonn() function may
                 also be used to display additional error message to the user.
                 The ccoonnvveerrssaattiioonn() function returns 0 on success and -1 on
                 failure.

           plugin_printf
                 A pointer to a pprriinnttff()-style function that may be used by
                 the sshhooww__vveerrssiioonn() function to display version information
                 (see show_version below).  The pplluuggiinn__pprriinnttff() function may
                 also be used to display additional error message to the user.
                 The pplluuggiinn__pprriinnttff() function returns number of characters
                 printed on success and -1 on failure.

           settings
                 A vector of user-supplied ssuuddoo settings in the form of
                 ``name=value'' strings.  The vector is terminated by a NULL
                 pointer.  These settings correspond to flags the user
                 specified when running ssuuddoo.  As such, they will only be
                 present when the corresponding flag has been specified on the
                 command line.

                 When parsing _s_e_t_t_i_n_g_s, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e might.

                 See the _P_o_l_i_c_y _p_l_u_g_i_n _A_P_I 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 _u_s_e_r___i_n_f_o, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e might.

                 See the _P_o_l_i_c_y _p_l_u_g_i_n _A_P_I section for a list of all possible
                 strings.

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

           argv  If non-NULL, an argument vector describing a command the user
                 wishes to run in the same form as what would be passed to the
                 execve(2) system call.

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

                 When parsing _u_s_e_r___e_n_v, the plugin should split on the ffiirrsstt
                 equal sign (`=') since the _n_a_m_e field will never include one
                 itself but the _v_a_l_u_e 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, _p_l_u_g_i_n___o_p_t_i_o_n_s will be the NULL
                 pointer.

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

     close
           void (*close)(int exit_status, int error);

           The cclloossee() function is called when the command being run by ssuuddoo
           finishes.

           The function arguments are as follows:

           exit_status
                 The command's exit status, as returned by the wait(2) system
                 call.  The value of exit_status is undefined if error is non-
                 zero.

           error
                 If the command could not be executed, this is set to the
                 value of errno set by the execve(2) system call.  If the
                 command was successfully executed, the value of error is 0.

     show_version
           int (*show_version)(int verbose);

           The sshhooww__vveerrssiioonn() function is called by ssuuddoo when the user
           specifies the --VV option.  The plugin may display its version
           information to the user via the ccoonnvveerrssaattiioonn() or pplluuggiinn__pprriinnttff()
           function using SUDO_CONV_INFO_MSG.  If the user requests detailed
           version information, the verbose flag will be set.

     log_ttyin
           int (*log_ttyin)(const char *buf, unsigned int len);

           The lloogg__ttttyyiinn() function is called whenever data can be read from
           the user but before it is passed to the running command.  This
           allows the plugin to reject data if it chooses to (for instance if
           the input contains banned content).  Returns 1 if the data should
           be passed to the command, 0 if the data is rejected (which will
           terminate the command) or -1 if an error occurred.

           The function arguments are as follows:

           buf   The buffer containing user input.

           len   The length of _b_u_f in bytes.

     log_ttyout
           int (*log_ttyout)(const char *buf, unsigned int len);

           The lloogg__ttttyyoouutt() function is called whenever data can be read from
           the command but before it is written to the user's terminal.  This
           allows the plugin to reject data if it chooses to (for instance if
           the output contains banned content).  Returns 1 if the data should
           be passed to the user, 0 if the data is rejected (which will
           terminate the command) or -1 if an error occurred.

           The function arguments are as follows:

           buf   The buffer containing command output.

           len   The length of _b_u_f in bytes.

     log_stdin
           int (*log_stdin)(const char *buf, unsigned int len);

           The lloogg__ssttddiinn() function is only used if the standard input does
           not correspond to a tty device.  It is called whenever data can be
           read from the standard input but before it is passed to the running
           command.  This allows the plugin to reject data if it chooses to
           (for instance if the input contains banned content).  Returns 1 if
           the data should be passed to the command, 0 if the data is rejected
           (which will terminate the command) or -1 if an error occurred.

           The function arguments are as follows:

           buf   The buffer containing user input.

           len   The length of _b_u_f in bytes.

     log_stdout
           int (*log_stdout)(const char *buf, unsigned int len);

           The lloogg__ssttddoouutt() function is only used if the standard output does
           not correspond to a tty device.  It is called whenever data can be
           read from the command but before it is written to the standard
           output.  This allows the plugin to reject data if it chooses to
           (for instance if the output contains banned content).  Returns 1 if
           the data should be passed to the user, 0 if the data is rejected
           (which will terminate the command) or -1 if an error occurred.

           The function arguments are as follows:

           buf   The buffer containing command output.

           len   The length of _b_u_f in bytes.

     log_stderr
           int (*log_stderr)(const char *buf, unsigned int len);

           The lloogg__ssttddeerrrr() function is only used if the standard error does
           not correspond to a tty device.  It is called whenever data can be
           read from the command but before it is written to the standard
           error.  This allows the plugin to reject data if it chooses to (for
           instance if the output contains banned content).  Returns 1 if the
           data should be passed to the user, 0 if the data is rejected (which
           will terminate the command) or -1 if an error occurred.

           The function arguments are as follows:

           buf   The buffer containing command output.

           len   The length of _b_u_f in bytes.

     register_hooks
           See the _P_o_l_i_c_y _p_l_u_g_i_n _A_P_I section for a description of
           register_hooks.

     deregister_hooks
           See the _P_o_l_i_c_y _p_l_u_g_i_n _A_P_I section for a description of
           deregister_hooks.

     _I_/_O _P_l_u_g_i_n _V_e_r_s_i_o_n _M_a_c_r_o_s

     Same as for the _P_o_l_i_c_y _p_l_u_g_i_n _A_P_I.

   SSiiggnnaall hhaannddlleerrss
     The ssuuddoo 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:

     oo   SIGALRM
     oo   SIGHUP
     oo   SIGINT
     oo   SIGQUIT
     oo   SIGTERM
     oo   SIGTSTP
     oo   SIGUSR1
     oo   SIGUSR2

     If a fatal signal is received before the command is executed, ssuuddoo will
     call the plugin's cclloossee() 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 cclloossee() function.

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

   HHooookk ffuunnccttiioonn AAPPII
     Beginning with plugin API version 1.2, it is possible to install hooks
     for certain functions called by the ssuuddoo 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 ssuuddoo front end
     functions as well.

     _H_o_o_k _s_t_r_u_c_t_u_r_e

     Hooks in ssuuddoo are described by the following structure:

     typedef int (*sudo_hook_fn_t)();

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

     The sudo_hook structure has the following fields:

     hook_version
           The hook_version field should be set to SUDO_HOOK_VERSION.

     hook_type
           The hook_type field may be one of the following supported hook
           types:

           SUDO_HOOK_SETENV
                 The C library setenv(3) function.  Any registered hooks will
                 run before the C library implementation.  The hook_fn field
                 should be a function that matches the following typedef:

                 typedef int (*sudo_hook_fn_setenv_t)(const char *name,
                    const char *value, int overwrite, void *closure);

                 If the registered hook does not match the typedef the results
                 are unspecified.

           SUDO_HOOK_UNSETENV
                 The C library unsetenv(3) function.  Any registered hooks
                 will run before the C library implementation.  The hook_fn
                 field should be a function that matches the following
                 typedef:

                 typedef int (*sudo_hook_fn_unsetenv_t)(const char *name,
                    void *closure);

           SUDO_HOOK_GETENV
                 The C library getenv(3) function.  Any registered hooks will
                 run before the C library implementation.  The hook_fn field
                 should be a function that matches the following typedef:

                 typedef int (*sudo_hook_fn_getenv_t)(const char *name,
                    char **value, void *closure);

                 If the registered hook does not match the typedef the results
                 are unspecified.

           SUDO_HOOK_PUTENV
                 The C library putenv(3) function.  Any registered hooks will
                 run before the C library implementation.  The hook_fn field
                 should be a function that matches the following typedef:

                 typedef int (*sudo_hook_fn_putenv_t)(char *string,
                    void *closure);

                 If the registered hook does not match the typedef the results
                 are unspecified.

     hook_fn
           sudo_hook_fn_t hook_fn;

           The hook_fn field should be set to the plugin's hook
           implementation.  The actual function arguments will vary depending
           on the hook_type (see hook_type above).  In all cases, the closure
           field of struct sudo_hook is passed as the last function parameter.
           This can be used to pass arbitrary data to the plugin's hook
           implementation.

           The function return value may be one of the following:

           SUDO_HOOK_RET_ERROR
                 The hook function encountered an error.

           SUDO_HOOK_RET_NEXT
                 The hook completed without error, go on to the next hook
                 (including the native implementation if applicable).  For
                 example, a getenv(3) hook might return SUDO_HOOK_RET_NEXT if
                 the specified variable was not found in the private copy of
                 the environment.

           SUDO_HOOK_RET_STOP
                 The hook completed without error, stop processing hooks for
                 this invocation.  This can be used to replace the native
                 implementation.  For example, a setenv hook that operates on
                 a private copy of the environment but leaves environ
                 unchanged.

     Note that it is very easy to create an infinite loop when hooking C
     library functions.  For example, a getenv(3) hook that calls the
     snprintf(3) function may create a loop if the snprintf(3) implementation
     calls getenv(3) to check the locale.  To prevent this, you may wish to
     use a static variable in the hook function to guard against nested calls.
     For example:

     static int in_progress = 0; /* avoid recursion */
     if (in_progress)
         return SUDO_HOOK_RET_NEXT;
     in_progress = 1;
     ...
     in_progress = 0;
     return SUDO_HOOK_RET_STOP;

     _H_o_o_k _A_P_I _V_e_r_s_i_o_n _M_a_c_r_o_s

     /* Hook API version major/minor */
     #define SUDO_HOOK_VERSION_MAJOR 1
     #define SUDO_HOOK_VERSION_MINOR 0
     #define SUDO_HOOK_MKVERSION(x, y) ((x << 16) | y)
     #define SUDO_HOOK_VERSION SUDO_HOOK_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\
                                                   SUDO_HOOK_VERSION_MINOR)

     /* Getters and setters for hook API version */
     #define SUDO_HOOK_VERSION_GET_MAJOR(v) ((v) >> 16)
     #define SUDO_HOOK_VERSION_GET_MINOR(v) ((v) & 0xffff)
     #define SUDO_HOOK_VERSION_SET_MAJOR(vp, n) do { \
         *(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
     } while(0)
     #define SUDO_HOOK_VERSION_SET_MINOR(vp, n) do { \
         *(vp) = (*(vp) & 0xffff0000) | (n); \
     } while(0)

   RReemmoottee ccoommmmaanndd eexxeeccuuttiioonn
     The ssuuddoo front end does not have native support for running remote
     commands.  However, starting with ssuuddoo 1.8.8, the --hh option may be used
     to specify a remote host that is passed to the policy plugin.  A plugin
     may also accept a _r_u_n_a_s___u_s_e_r in the form of ``user@hostname'' which will
     work with older versions of ssuuddoo.  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 ssuuddoo 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 sssshh to perform remote
     command execution.  The helper program would be responsible for running
     sssshh with the proper options to use a private key or certificate that the
     remote host will accept and run a program on the remote host that would
     setup the execution environment accordingly.

     Note that remote ssuuddooeeddiitt functionality must be handled by the policy
     plugin, not ssuuddoo 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.

   CCoonnvveerrssaattiioonn AAPPII
     If the plugin needs to interact with the user, it may do so via the
     ccoonnvveerrssaattiioonn() function.  A plugin should not attempt to read directly
     from the standard input or the user's tty (neither of which are
     guaranteed to exist).  The caller must include a trailing newline in msg
     if one is to be printed.

     A pprriinnttff()-style function is also available that can be used to display
     informational or error messages to the user, which is usually more
     convenient for simple messages where no use input is required.

     struct sudo_conv_message {
     #define SUDO_CONV_PROMPT_ECHO_OFF  0x0001 /* do not echo user input */
     #define SUDO_CONV_PROMPT_ECHO_ON   0x0002 /* echo user input */
     #define SUDO_CONV_ERROR_MSG        0x0003 /* error message */
     #define SUDO_CONV_INFO_MSG         0x0004 /* informational message */
     #define SUDO_CONV_PROMPT_MASK      0x0005 /* mask user input */
     #define SUDO_CONV_DEBUG_MSG        0x0006 /* debugging message */
     #define SUDO_CONV_PROMPT_ECHO_OK   0x1000 /* flag: allow echo if no tty */
         int msg_type;
         int timeout;
         const char *msg;
     };

     #define SUDO_CONV_REPL_MAX      255

     struct sudo_conv_reply {
         char *reply;
     };

     typedef int (*sudo_conv_t)(int num_msgs,
                  const struct sudo_conv_message msgs[],
                  struct sudo_conv_reply replies[]);

     typedef int (*sudo_printf_t)(int msg_type, const char *fmt, ...);

     Pointers to the ccoonnvveerrssaattiioonn() and pprriinnttff()-style functions are passed in
     to the plugin's ooppeenn() function when the plugin is initialized.

     To use the ccoonnvveerrssaattiioonn() function, the plugin must pass an array of
     sudo_conv_message and sudo_conv_reply structures.  There must be a struct
     sudo_conv_message and struct sudo_conv_reply for each message in the
     conversation.  The plugin is responsible for freeing the reply buffer
     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 ssuuddoo will support.  It is also useful as a maximum value
     for the mmeemmsseett__ss() function when clearing passwords filled in by the
     conversation function.

     The pprriinnttff()-style function uses the same underlying mechanism as the
     ccoonnvveerrssaattiioonn() function but only supports SUDO_CONV_INFO_MSG,
     SUDO_CONV_ERROR_MSG and SUDO_CONV_DEBUG_MSG for the _m_s_g___t_y_p_e parameter.
     It can be more convenient than using the ccoonnvveerrssaattiioonn() function if no
     user reply is needed and supports standard pprriinnttff() escape sequences.

     Unlike, SUDO_CONV_INFO_MSG and Dv SUDO_CONV_ERROR_MSG , messages sent
     with the SUDO_CONV_DEBUG_MSG _m_s_g___t_y_p_e are not directly user-visible.
     Instead, they are logged to the file specified in the Debug statement (if
     any) in the sudo.conf(4).  file.  This allows a plugin to log debugging
     information and is intended to be used in conjunction with the
     _d_e_b_u_g___f_l_a_g_s setting.

     See the sample plugin for an example of the ccoonnvveerrssaattiioonn() function
     usage.

   SSuuddooeerrss ggrroouupp pplluuggiinn AAPPII
     The ssuuddooeerrss 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
     ssuuddoo, _g_r_o_u_p___f_i_l_e and _s_y_s_t_e_m___g_r_o_u_p, are detailed in sudoers(4).  Third
     party group plugins include a QAS AD plugin available from Quest
     Software.

     A group plugin must declare and populate a sudoers_group_plugin struct in
     the global scope.  This structure contains pointers to the functions that
     implement plugin initialization, cleanup and group lookup.

     struct sudoers_group_plugin {
        unsigned int version;
        int (*init)(int version, sudo_printf_t sudo_printf,
                    char *const argv[]);
        void (*cleanup)(void);
        int (*query)(const char *user, const char *group,
                     const struct passwd *pwd);
     };

     The sudoers_group_plugin struct has the following fields:

     version
           The version field should be set to GROUP_API_VERSION.

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

     init
           int (*init)(int version, sudo_printf_t plugin_printf,
                       char *const argv[]);

           The iinniitt() function is called after _s_u_d_o_e_r_s 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 pplluuggiinn__pprriinnttff()
           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 ssuuddooeerrss allows the plugin to
                 determine the major and minor version number of the group
                 plugin API supported by ssuuddooeerrss.

           plugin_printf
                 A pointer to a pprriinnttff()-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
                 _g_r_o_u_p___p_l_u_g_i_n option in _s_u_d_o_e_r_s.  If no arguments were given,
                 _a_r_g_v will be NULL.

     cleanup
           void (*cleanup)();

           The cclleeaannuupp() function is called when ssuuddooeerrss 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 qquueerryy() function is used to ask the group plugin whether _u_s_e_r
           is a member of _g_r_o_u_p.

           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 _u_s_e_r, if any.  If _u_s_e_r is not
                 present in the password database, _p_w_d will be NULL.

     _G_r_o_u_p _A_P_I _V_e_r_s_i_o_n _M_a_c_r_o_s

     /* Sudoers group plugin version major/minor */
     #define GROUP_API_VERSION_MAJOR 1
     #define GROUP_API_VERSION_MINOR 0
     #define GROUP_API_VERSION ((GROUP_API_VERSION_MAJOR << 16) | \
                                GROUP_API_VERSION_MINOR)

     /* Getters and setters for group version */
     #define GROUP_API_VERSION_GET_MAJOR(v) ((v) >> 16)
     #define GROUP_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
     #define GROUP_API_VERSION_SET_MAJOR(vp, n) do { \
         *(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \
     } while(0)
     #define GROUP_API_VERSION_SET_MINOR(vp, n) do { \
         *(vp) = (*(vp) & 0xffff0000) | (n); \
     } while(0)

PPLLUUGGIINN AAPPII CCHHAANNGGEELLOOGG
     The following revisions have been made to the Sudo Plugin API.

     Version 1.0
           Initial API version.

     Version 1.1 (sudo 1.8.0)
           The I/O logging plugin's ooppeenn() function was modified to take the
           command_info list as an argument.

     Version 1.2 (sudo 1.8.5)
           The Policy and I/O logging plugins' ooppeenn() functions are now passed
           a list of plugin parameters if any are specified in sudo.conf(4).

           A simple hooks API has been introduced to allow plugins to hook in
           to the system's environment handling functions.

           The init_session Policy plugin function is now passed a pointer to
           the user environment which can be updated as needed.  This can be
           used to merge in environment variables stored in the PAM handle
           before a command is run.

     Version 1.3 (sudo 1.8.7)
           Support for the _e_x_e_c___b_a_c_k_g_r_o_u_n_d entry has been added to the
           command_info list.

           The _m_a_x___g_r_o_u_p_s and _p_l_u_g_i_n___d_i_r entries were added to the settings
           list.

           The vveerrssiioonn() and cclloossee() functions are now optional.  Previously,
           a missing vveerrssiioonn() or cclloossee() function would result in a crash.
           If no policy plugin cclloossee() function is defined, a default cclloossee()
           function will be provided by the ssuuddoo front end that displays a
           warning if the command could not be executed.

           The ssuuddoo front end now installs default signal handlers to trap
           common signals while the plugin functions are run.

     Version 1.4 (sudo 1.8.8)
           The _r_e_m_o_t_e___h_o_s_t entry was added to the settings list.

     Version 1.5 (sudo 1.8.9)
           The entry was added to the command_info list.

SSEEEE AALLSSOO
     sudo.conf(4), sudoers(4), sudo(1m)

BBUUGGSS
     If you feel you have found a bug in ssuuddoo, please submit a bug report at
     http://www.sudo.ws/sudo/bugs/

SSUUPPPPOORRTT
     Limited free support is available via the sudo-users mailing list, see
     http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the
     archives.

DDIISSCCLLAAIIMMEERR
     ssuuddoo is provided ``AS IS'' and any express or implied warranties,
     including, but not limited to, the implied warranties of merchantability
     and fitness for a particular purpose are disclaimed.  See the LICENSE
     file distributed with ssuuddoo or http://www.sudo.ws/sudo/license.html for
     complete details.

Sudo 1.8.10                    December 20, 2013                   Sudo 1.8.10