Patch for removing X11 fwding cookies

[Alok Aggarwal]

Currently, openssh-2.9p2 adds cookies to a user's .Xauthority file if X11
forwarding is requested but does not delete them while closing down the
connection. While this may not necessarily be a security vulnerability, but
it's a good idea for the application to cleanup appropriately.

This patch takes care of removing the X forwarding cookies from the user's
.Xauthority file. Please consider integrating this into the OpenSSH code.

Thanks.
-Alok

diff -w -c openssh-2.9p2/session.c modified/session.c
*** 1950,1955 ****
--- 1565,1590 ----
  void
    session_close(Session *s)
      {
      +       char cmd[1024];
      +       FILE *f = NULL;
      +       int xauth_present = s->auth_proto != NULL && s->auth_data != NULL;
      +
      +       memset(cmd, 0, sizeof (cmd));
      +
      +       if (xauth_present && options.xauth_location != NULL) {
      +               debug("Running %.100s remove %.100s",
      +		          options.xauth_location, s->display);
      +               temporarily_use_uid(s->pw->pw_uid);
      +               snprintf(cmd, sizeof (cmd), "%s -q -",
      +		          options.xauth_location);
      +               f = popen(cmd, "w");
      +               if (f) {
      +                       fprintf(f, "remove %s\n", s->display);
      +                       pclose(f);
      +               } else {
      +                       fprintf(stderr, "Could not run %s\n", cmd);
      +               }
      +               restore_uid();
      +       }
	      session_pty_cleanup(s);
	      session_free(s);
	      session_proctitle(s);
***************