Hi all, Last week I found some time to spend auditing the effectiveness of the online repair prototype code, and discovered a serious bug in the rmap code. Each btree type provides four comparison predicates: one for comparing a key against the current record; one for comparing two arbitrary record keys, and one each for checking if a btree block's records or keys are in the correct order. Unfortunately, I encoded a major thinko into those last three functions. The XFS_RMAP_OFF macro masks off the three namespace bits before we perform a comparison, which means that key comparisons do not notice differences between the unwritten, bmbt, or attr fork status. On a consistent filesystem this is not an issue because there can only ever be overlapping rmap records for written inode data fork extents, which is why we've not yet seen any problems in the field. Fortunately, the last two functions are used by debugging asserts and online scrub to check the contents of a btree block, so the severity of the flaw there is not high. Unfortunately, the flaw in _diff_two_keys is more severe, because it is used for query_range requests. Ranged queries are used by the regular rmap handling code when reflink is enabled; and it is used in the rmap btree validation routines of both xfs_scrub and xfs_repair. As I mentioned above, the flaw should not manifest on a *consistent* filesystem, but for fuzzed (or corrupt) filesystems, this seriously impacts our ability to detect problems. The first two patches in this series fix two places where we pass the wrong flags arguments to the rmap query functions (which didn't previously cause lookup failures due to the broken code) and the third patch fixes the comparison functions. If you're going to start using this mess, you probably ought to just pull from my git trees, which are linked below. This is an extraordinary way to destroy everything. Enjoy! Comments and questions are, as always, welcome. --D kernel git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=rmap-fixes-5.10 --- fs/xfs/libxfs/xfs_rmap.c | 2 +- fs/xfs/libxfs/xfs_rmap_btree.c | 16 ++++++++-------- fs/xfs/scrub/bmap.c | 2 ++ 3 files changed, 11 insertions(+), 9 deletions(-)
