pam_xauth
pam_xauth(8) System Administrator's Manual pam_xauth(8)
NAME
pam_xauth - forward xauth keys between users
SYNOPSIS
session optional /lib/security/pam_xauth.so arguments
DESCRIPTION
pam_xauth.so 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 command
to assume another user's priviledges, 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 from an xterm sesssion,
you will be able to run X programs without explicitly dealing with the
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 cook-
ies 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.
ARGUMENTS
debug Turns on debugging messages sent to syslog.
xauthpath=/usr/X11R6/bin/xauth
Specify the path the xauth program (the default is
/usr/X11R6/bin/xauth).
systemuser=number
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=number
Specify a single target UID which is exempt from the systemuser
check.
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 applica-
tion, 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. 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 as the source user to extract the key for $DIS-
PLAY, 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 not to remove the keys when the session is
closed.
SEE ALSO
/usr/share/doc/pam*/html/index.html
FILES
~/.xauth/import ~/.xauth/export
BUGS
Let's hope not, but if you find any, please report them via the "Bug
Track" link at http://bugzilla.redhat.com/bugzilla/
AUTHOR
Nalin Dahyabhai <nalin@redhat.com>, based on original version by
Michael K. Johnson <johnsonm@redhat.com>
Red Hat Linux 2003/7/24 pam_xauth(8)
