From: Dave Chinner dchinner@redhat.com
commit d8f4c2d0398fa1d92cacf854daf80d21a46bfefc upstream.
From the department of "WTAF? How did we miss that!?"...
When we are recovering a buffer, the first thing we do is check the buffer magic number and extract the LSN from the buffer. If the LSN is older than the current LSN, we replay the modification to it. If the metadata on disk is newer than the transaction in the log, we skip it. This is a fundamental v5 filesystem metadata recovery behaviour.
generic/482 failed with an attribute writeback failure during log recovery. The write verifier caught the corruption before it got written to disk, and the attr buffer dump looked like:
XFS (dm-3): Metadata corruption detected at xfs_attr3_leaf_verify+0x275/0x2e0, xfs_attr3_leaf block 0x19be8 XFS (dm-3): Unmount and run xfs_repair XFS (dm-3): First 128 bytes of corrupted metadata buffer: 00000000: 00 00 00 00 00 00 00 00 3b ee 00 00 4d 2a 01 e1 ........;...M*.. 00000010: 00 00 00 00 00 01 9b e8 00 00 00 01 00 00 05 38 ...............8 ^^^^^^^^^^^^^^^^^^^^^^^ 00000020: df 39 5e 51 58 ac 44 b6 8d c5 e7 10 44 09 bc 17 .9^QX.D.....D... 00000030: 00 00 00 00 00 02 00 83 00 03 00 cc 0f 24 01 00 .............$.. 00000040: 00 68 0e bc 0f c8 00 10 00 00 00 00 00 00 00 00 .h.............. 00000050: 00 00 3c 31 0f 24 01 00 00 00 3c 32 0f 88 01 00 ..<1.$....<2.... 00000060: 00 00 3c 33 0f d8 01 00 00 00 00 00 00 00 00 00 ..<3............ 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ .....
The highlighted bytes are the LSN that was replayed into the buffer: 0x100000538. This is cycle 1, block 0x538. Prior to replay, that block on disk looks like this:
$ sudo xfs_db -c "fsb 0x417d" -c "type attr3" -c p /dev/mapper/thin-vol hdr.info.hdr.forw = 0 hdr.info.hdr.back = 0 hdr.info.hdr.magic = 0x3bee hdr.info.crc = 0xb5af0bc6 (correct) hdr.info.bno = 105448 hdr.info.lsn = 0x100000900 ^^^^^^^^^^^ hdr.info.uuid = df395e51-58ac-44b6-8dc5-e7104409bc17 hdr.info.owner = 131203 hdr.count = 2 hdr.usedbytes = 120 hdr.firstused = 3796 hdr.holes = 1 hdr.freemap[0-2] = [base,size]
Note the LSN stamped into the buffer on disk: 1/0x900. The version on disk is much newer than the log transaction that was being replayed. That's a bug, and should -never- happen.
So I immediately went to look at xlog_recover_get_buf_lsn() to check that we handled the LSN correctly. I was wondering if there was a similar "two commits with the same start LSN skips the second replay" problem with buffers. I didn't get that far, because I found a much more basic, rudimentary bug: xlog_recover_get_buf_lsn() doesn't recognise buffers with XFS_ATTR3_LEAF_MAGIC set in them!!!
IOWs, attr3 leaf buffers fall through the magic number checks unrecognised, so trigger the "recover immediately" behaviour instead of undergoing an LSN check. IOWs, we incorrectly replay ATTR3 leaf buffers and that causes silent on disk corruption of inode attribute forks and potentially other things....
Git history shows this is *another* zero day bug, this time introduced in commit 50d5c8d8e938 ("xfs: check LSN ordering for v5 superblocks during recovery") which failed to handle the attr3 leaf buffers in recovery. And we've failed to handle them ever since...
Signed-off-by: Dave Chinner dchinner@redhat.com Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Amir Goldstein amir73il@gmail.com Acked-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/xfs/xfs_buf_item_recover.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/xfs/xfs_buf_item_recover.c +++ b/fs/xfs/xfs_buf_item_recover.c @@ -796,6 +796,7 @@ xlog_recover_get_buf_lsn( switch (magicda) { case XFS_DIR3_LEAF1_MAGIC: case XFS_DIR3_LEAFN_MAGIC: + case XFS_ATTR3_LEAF_MAGIC: case XFS_DA3_NODE_MAGIC: lsn = be64_to_cpu(((struct xfs_da3_blkinfo *)blk)->lsn); uuid = &((struct xfs_da3_blkinfo *)blk)->uuid;