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.\" Copyright 2001,2003 Red Hat, Inc.
.\" Written by Nalin Dahyabhai <nalin@redhat.com>, based on the original
.\" version by Michael K. Johnson
.TH pam_xauth 8 2003/7/24 "Red Hat Linux" "System Administrator's Manual"
.SH NAME
pam_xauth \- forward xauth keys between users
.SH SYNOPSIS
.B session optional /lib/security/pam_xauth.so \fIarguments\fP
.SH 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 \fBsu\fP 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 \fBsu\fP 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 \fB~/.xauth/export\fP in the invoking
user's home directory and \fB~/.xauth/import\fP in the target user's home
directory.
If a user has a \fB~/.xauth/import\fP file, the user will only receive cookies
from users listed in the file. If there is no \fB~/.xauth/import\fP file,
the user will accept cookies from any other user.
If a user has a \fB.xauth/export\fP file, the user will only forward cookies
to users listed in the file. If there is no \fB~/.xauth/export\fP file, and
the invoking user is not \fBroot\fP, the user will forward cookies to
any other user. If there is no \fB~/.xauth/export\fP file, and the invoking
user is \fBroot\fP, the user will \fInot\fP forward cookies to other users.
Both the import and export files support wildcards (such as \fI*\fP). Both
the import and export files can be empty, signifying that no users are allowed.
.SH ARGUMENTS
.IP debug
Turns on debugging messages sent to syslog.
.IP xauthpath=\fI/usr/X11R6/bin/xauth\fP
Specify the path the xauth program (the default is /usr/X11R6/bin/xauth).
.IP systemuser=\fInumber\fP
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.
.IP targetuser=\fInumber\fP
Specify a single target UID which is exempt from the systemuser check.
.SH "IMPLEMENTATION DETAILS"
pam_xauth will work \fIonly\fP 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 \fBsu\fP. 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 \fBxauth\fP 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 not to remove the keys when the session
is closed.
.SH "SEE ALSO"
\fI/usr/share/doc/pam*/html/index.html\fP
.SH FILES
\fI~/.xauth/import\fP
\fI~/.xauth/export\fP
.SH BUGS
Let's hope not, but if you find any, please report them via the "Bug Track"
link at http://bugzilla.redhat.com/bugzilla/
.SH AUTHOR
Nalin Dahyabhai <nalin@redhat.com>, based on original version by
Michael K. Johnson <johnsonm@redhat.com>
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