ovl: set lower layer st_dev only if setting lower st_ino

For broken hardlinks, we do not return lower st_ino, so we should
also not return lower pseudo st_dev.

Fixes: a0c5ad307ac0 ("ovl: relax same fs constraint for constant st_ino")
Cc: <stable@vger.kernel.org> #v4.15
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/inode.c

@@ -118,13 +118,10 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 			 */
 			if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
 			    (!ovl_verify_lower(dentry->d_sb) &&
-			     (is_dir || lowerstat.nlink == 1)))
+			     (is_dir || lowerstat.nlink == 1))) {
 				stat->ino = lowerstat.ino;
-
-			if (samefs)
-				WARN_ON_ONCE(stat->dev != lowerstat.dev);
-			else
 				stat->dev = ovl_get_pseudo_dev(dentry);
+			}
 		}
 		if (samefs) {
 			/*