bionic (8) pam_xauth.8.gz

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>.