fs: fix do_last error case when need_reval_dot

When open(2) without O_DIRECTORY opens an existing dir, it should return
EISDIR. In do_last(), the variable 'error' is initialized EISDIR, but it
is changed by d_revalidate() which returns any positive to represent
'the target dir is valid.'

Should we keep and return the initialized 'error' in this case.
Signed-off-by: NNick Piggin <npiggin@kernel.dk>

fs/namei.c

@@ -2122,11 +2122,13 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 		dir = nd->path.dentry;
 	case LAST_DOT:
 		if (need_reval_dot(dir)) {
-			error = d_revalidate(nd->path.dentry, nd);
-			if (!error)
-				error = -ESTALE;
-			if (error < 0)
+			int status = d_revalidate(nd->path.dentry, nd);
+			if (!status)
+				status = -ESTALE;
+			if (status < 0) {
+				error = status;
 				goto exit;
+			}
 		}
 		/* fallthrough */
 	case LAST_ROOT: