pam_xauth

PAM_XAUTH(8)                   Linux-PAM Manual                   PAM_XAUTH(8)

NAME
       pam_xauth - PAM module to forward xauth keys between users

SYNOPSIS
       pam_xauth.so [debug] [xauthpath=/path/to/xauth] [systemuser=UID]
                    [targetuser=UID]

DESCRIPTION
       The pam_xauth PAM module is designed to forward xauth keys (sometimes
       referred to as "cookies") between users.

       Without pam_xauth, when xauth is enabled and a user uses the su(1)
       command to assume another user's privileges, that user is no longer
       able to access the original user's X display because the new user does
       not have the key needed to access the display. pam_xauth solves the
       problem by forwarding the key from the user running su (the source
       user) to the user whose identity the source user is assuming (the
       target user) when the session is created, and destroying the key when
       the session is torn down.

       This means, for example, that when you run su(1) from an xterm session,
       you will be able to run X programs without explicitly dealing with the
       xauth(1) xauth command or ~/.Xauthority files.

       pam_xauth will only forward keys if xauth can list a key connected to
       the $DISPLAY environment variable.

       Primitive access control is provided by ~/.xauth/export in the invoking
       user's home directory and ~/.xauth/import in the target user's home
       directory.

       If a user has a ~/.xauth/import file, the user will only receive
       cookies from users listed in the file. If there is no ~/.xauth/import
       file, the user will accept cookies from any other user.

       If a user has a .xauth/export file, the user will only forward cookies
       to users listed in the file. If there is no ~/.xauth/export file, and
       the invoking user is not root, the user will forward cookies to any
       other user. If there is no ~/.xauth/export file, and the invoking user
       is root, the user will not forward cookies to other users.

       Both the import and export files support wildcards (such as *). Both
       the import and export files can be empty, signifying that no users are
       allowed.

OPTIONS
       debug
           Print debug information.

       xauthpath=/path/to/xauth
           Specify the path the xauth program (it is expected in
           /usr/X11R6/bin/xauth, /usr/bin/xauth, or /usr/bin/X11/xauth by
           default).

       systemuser=UID
           Specify the highest UID which will be assumed to belong to a
           "system" user. pam_xauth will refuse to forward credentials to
           users with UID less than or equal to this number, except for root
           and the "targetuser", if specified.

       targetuser=UID
           Specify a single target UID which is exempt from the systemuser
           check.

MODULE TYPES PROVIDED
       Only the session type is provided.

RETURN VALUES
       PAM_BUF_ERR
           Memory buffer error.

       PAM_PERM_DENIED
           Permission denied by import/export file.

       PAM_SESSION_ERR
           Cannot determine user name, UID or access users home directory.

       PAM_SUCCESS
           Success.

       PAM_USER_UNKNOWN
           User not known.

EXAMPLES
       Add the following line to /etc/pam.d/su to forward xauth keys between
       users when calling su:

           session  optional  pam_xauth.so

IMPLEMENTATION DETAILS
       pam_xauth will work only if it is used from a setuid application in
       which the getuid() call returns the id of the user running the
       application, and for which PAM can supply the name of the account that
       the user is attempting to assume. The typical application of this type
       is su(1). The application must call both pam_open_session() and
       pam_close_session() with the ruid set to the uid of the calling user
       and the euid set to root, and must have provided as the PAM_USER item
       the name of the target user.

       pam_xauth calls xauth(1) as the source user to extract the key for
       $DISPLAY, then calls xauth as the target user to merge the key into the
       a temporary database and later remove the database.

       pam_xauth cannot be told to not remove the keys when the session is
       closed.

FILES
       ~/.xauth/import
           XXX

       ~/.xauth/export
           XXX

SEE ALSO
       pam.conf(5), pam.d(5), pam(7)

AUTHOR
       pam_xauth was written by Nalin Dahyabhai <nalin@redhat.com>, based on
       original version by Michael K. Johnson <johnsonm@redhat.com>.

Linux-PAM Manual                  05/18/2017                      PAM_XAUTH(8)