GFS2: check NULL return value in gfs2_ok_to_move

gfs2_lookupi() can return NULL if the path to the root is broken by
another rename/rmdir. In this case gfs2_ok_to_move() must check for
this NULL pointer and return error.

Resolves: rhbz#1060246
Signed-off-by: NAbhi Das <adas@redhat.com>
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>

fs/gfs2/inode.c

@@ -1299,6 +1299,10 @@ static int gfs2_ok_to_move(struct gfs2_inode *this, struct gfs2_inode *to)
 		}
 
 		tmp = gfs2_lookupi(dir, &gfs2_qdotdot, 1);
+		if (!tmp) {
+			error = -ENOENT;
+			break;
+		}
 		if (IS_ERR(tmp)) {
 			error = PTR_ERR(tmp);
 			break;