btrfs: tree-checker: Check item size before reading file extent type

In check_extent_data_item(), we read file extent type without verifying
if the item size is valid.

Add such check to ensure the file extent type we read is correct.

The check is not as accurate as we need to cover both inline and regular
extents, so it only checks if the item size is larger or equal to inline
header.
So the existing size checks on inline/regular extents are still needed.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-checker.c

@@ -221,6 +221,17 @@ static int check_extent_data_item(struct extent_buffer *leaf,
 
 	fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
 
+	/*
+	 * Make sure the item contains at least inline header, so the file
+	 * extent type is not some garbage.
+	 */
+	if (item_size < BTRFS_FILE_EXTENT_INLINE_DATA_START) {
+		file_extent_err(leaf, slot,
+				"invalid item size, have %u expect [%lu, %u)",
+				item_size, BTRFS_FILE_EXTENT_INLINE_DATA_START,
+				SZ_4K);
+		return -EUCLEAN;
+	}
 	if (btrfs_file_extent_type(leaf, fi) >= BTRFS_NR_FILE_EXTENT_TYPES) {
 		file_extent_err(leaf, slot,
 		"invalid type for file extent, have %u expect range [0, %u]",