VFS: AF_UNIX sockets should call mknod on the top layer only

AF_UNIX sockets should call mknod on the top layer only and should not attempt
to modify the lower layer in a layered filesystem such as overlayfs.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 433f287..8b8f5e6d 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -839,7 +839,7 @@
 	 */
 	err = security_path_mknod(&path, dentry, mode, 0);
 	if (!err) {
-		err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
+		err = vfs_mknod(d_inode(path.dentry), dentry, mode, 0);
 		if (!err) {
 			res->mnt = mntget(path.mnt);
 			res->dentry = dget(dentry);