ext4: don't verify checksums of dx non-leaf nodes during fallback scan

During a directory entry lookup of a hashed directory, if the
hash-based lookup functions fail and we fall back to a linear scan,
don't try to verify the dirent checksum on the internal nodes of the
hash tree because they don't store a checksum in a hidden dirent like
the leaf nodes do.

Reported-by: George Spelvin <linux@horizon.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/namei.c

@@ -1146,6 +1146,21 @@ static inline int search_dirblock(struct buffer_head *bh,
 	return 0;
 }
 
+static int is_dx_internal_node(struct inode *dir, ext4_lblk_t block,
+			       struct ext4_dir_entry *de)
+{
+	struct super_block *sb = dir->i_sb;
+
+	if (!is_dx(dir))
+		return 0;
+	if (block == 0)
+		return 1;
+	if (de->inode == 0 &&
+	    ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize) ==
+			sb->s_blocksize)
+		return 1;
+	return 0;
+}
 
 /*
  *	ext4_find_entry()
@@ -1246,6 +1261,8 @@ restart:
 			goto next;
 		}
 		if (!buffer_verified(bh) &&
+		    !is_dx_internal_node(dir, block,
+					 (struct ext4_dir_entry *)bh->b_data) &&
 		    !ext4_dirent_csum_verify(dir,
 				(struct ext4_dir_entry *)bh->b_data)) {
 			EXT4_ERROR_INODE(dir, "checksumming directory "