PAM_XAUTH(8)              (06/08/2020)               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

     Page 1                  Linux-PAM Manual        (printed 5/25/22)

     PAM_XAUTH(8)              (06/08/2020)               PAM_XAUTH(8)

          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

     Page 2                  Linux-PAM Manual        (printed 5/25/22)

     PAM_XAUTH(8)              (06/08/2020)               PAM_XAUTH(8)

          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>.

     Page 3                  Linux-PAM Manual        (printed 5/25/22)