Fix CVE-2011-4029: File permission change vulnerability.

Use fchmod() to change permissions of the lock file instead
of chmod(), thus avoid the race that can be exploited to set
a symbolic link to any file or directory in the system.

Signed-off-by: Matthieu Herrb <matthieu.herrb@laas.fr>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>

os/utils.c

@@ -297,7 +297,7 @@ LockServer(void)
     FatalError("Could not create lock file in %s\n", tmp);
   (void) sprintf(pid_str, "%10ld\n", (long)getpid());
   (void) write(lfd, pid_str, 11);
-  (void) chmod(tmp, 0444);
+  (void) fchmod(lfd, 0444);
   (void) close(lfd);
 
   /*