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>

net/unix/af_unix.c

@@ -839,7 +839,7 @@ static int unix_mknod(const char *sun_path, umode_t mode, struct path *res)
 	 */
 	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);