From: Josef Bacik josef@toxicpanda.com

commit 1119a72e223f3073a604f8fccb3a470ccd8a4416 upstream.

The tree checker checks the extent ref hash at read and write time to make sure we do not corrupt the file system. Generally extent references go inline, but if we have enough of them we need to make an item, which looks like

key.objectid = <bytenr> key.type = <BTRFS_EXTENT_DATA_REF_KEY|BTRFS_TREE_BLOCK_REF_KEY> key.offset = hash(tree, owner, offset)

However if key.offset collide with an unrelated extent reference we'll simply key.offset++ until we get something that doesn't collide. Obviously this doesn't match at tree checker time, and thus we error while writing out the transaction. This is relatively easy to reproduce, simply do something like the following

xfs_io -f -c "pwrite 0 1M" file offset=2

for i in {0..10000} do xfs_io -c "reflink file 0 ${offset}M 1M" file offset=$(( offset + 2 )) done

xfs_io -c "reflink file 0 17999258914816 1M" file xfs_io -c "reflink file 0 35998517829632 1M" file xfs_io -c "reflink file 0 53752752058368 1M" file

btrfs filesystem sync

And the sync will error out because we'll abort the transaction. The magic values above are used because they generate hash collisions with the first file in the main subvol.

The fix for this is to remove the hash value check from tree checker, as we have no idea which offset ours should belong to.

Reported-by: Tuomas Lähdekorpi tuomas.lahdekorpi@gmail.com Fixes: 0785a9aacf9d ("btrfs: tree-checker: Add EXTENT_DATA_REF check") CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: David Sterba dsterba@suse.com [ add comment] Signed-off-by: David Sterba dsterba@suse.com ---

Generated on 5.4 where it applies cleanly and on 5.10 with line offset but otherwise clean.

fs/btrfs/tree-checker.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c index 7d06842a3d74..368c43c6cbd0 100644 --- a/fs/btrfs/tree-checker.c +++ b/fs/btrfs/tree-checker.c @@ -1285,22 +1285,14 @@ static int check_extent_data_ref(struct extent_buffer *leaf, return -EUCLEAN; } for (; ptr < end; ptr += sizeof(*dref)) { - u64 root_objectid; - u64 owner; u64 offset; - u64 hash;

+ /* + * We cannot check the extent_data_ref hash due to possible + * overflow from the leaf due to hash collisions. + */ dref = (struct btrfs_extent_data_ref *)ptr; - root_objectid = btrfs_extent_data_ref_root(leaf, dref); - owner = btrfs_extent_data_ref_objectid(leaf, dref); offset = btrfs_extent_data_ref_offset(leaf, dref); - hash = hash_extent_data_ref(root_objectid, owner, offset); - if (hash != key->offset) { - extent_err(leaf, slot, - "invalid extent data ref hash, item has 0x%016llx key has 0x%016llx", - hash, key->offset); - return -EUCLEAN; - } if (!IS_ALIGNED(offset, leaf->fs_info->sectorsize)) { extent_err(leaf, slot, "invalid extent data backref offset, have %llu expect aligned to %u",