Add a MAC check for VOP_LOOKUP() in the Linux getwcd() implementation.

Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories

sys/compat/linux/linux_getcwd.c

@@ -162,6 +162,10 @@ linux_getcwd_scandir(lvpp, uvpp, bpp, bufp, td)
 	 * At this point, lvp is locked and will be unlocked by the lookup.
 	 * On successful return, *uvpp will be locked
 	 */
+#ifdef MAC
+	error = mac_check_vnode_lookup(td->td_ucred, lvp, &cn);
+	if (error == 0)
+#endif
 		error = VOP_LOOKUP(lvp, uvpp, &cn);
 	if (error) {
 		vput(lvp);