Commit 4c094c33 authored May 03, 2019 by Qu Wenruo Committed by David Sterba Jul 01, 2019

btrfs: tree-checker: Check if the file extent end overflows



Under certain conditions, we could have strange file extent item in log
tree like:

  item 18 key (69599 108 397312) itemoff 15208 itemsize 53
	extent data disk bytenr 0 nr 0
	extent data offset 0 nr 18446744073709547520 ram 18446744073709547520

The num_bytes + ram_bytes overflow 64 bit type.

For num_bytes part, we can detect such overflow along with file offset
(key->offset), as file_offset + num_bytes should never go beyond u64.

For ram_bytes part, it's about the decompressed size of the extent, not
directly related to the size.
In theory it is OK to have a large value, and put extra limitation
on RAM bytes may cause unexpected false alerts.

So in tree-checker, we only check if the file offset and num bytes
overflow.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 2ed95d2d

fs/btrfs/tree-checker.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -132,6 +132,7 @@ static int check_extent_data_item(struct extent_buffer *leaf,
		struct btrfs_file_extent_item *fi;
		u32 sectorsize = fs_info->sectorsize;
		u32 item_size = btrfs_item_size_nr(leaf, slot);
		u64 extent_end;

		if (!IS_ALIGNED(key->offset, sectorsize)) {
		file_extent_err(leaf, slot,
		@@ -207,6 +208,16 @@ static int check_extent_data_item(struct extent_buffer *leaf,
		CHECK_FE_ALIGNED(leaf, slot, fi, num_bytes, sectorsize))
		return -EUCLEAN;

		/* Catch extent end overflow */
		if (check_add_overflow(btrfs_file_extent_num_bytes(leaf, fi),
		key->offset, &extent_end)) {
		file_extent_err(leaf, slot,
		"extent end overflow, have file offset %llu extent num bytes %llu",
		key->offset,
		btrfs_file_extent_num_bytes(leaf, fi));
		return -EUCLEAN;
		}

		/*
		* Check that no two consecutive file extent items, in the same leaf,
		* present ranges that overlap each other.

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