"Darrick J. Wong" <djwong@xxxxxxxxxx> writes:
> On Wed, Apr 30, 2025 at 11:23:57AM +0200, Carlos Maiolino wrote:
>> On Sat, Apr 12, 2025 at 08:03:57PM +0000, Charalampos Mitrodimas wrote:
>> > The xfs_da3_node_verify() function checks the integrity of directory
>> > and attribute B-tree node blocks. However, it was missing a check to
>> > ensure that the hash values of the btree entries within the node are
>> > strictly increasing, as required by the B-tree structure.
>> >
>> > Add a loop to iterate through the btree entries and verify that each
>> > entry's hash value is greater than the previous one. If an
>> > out-of-order hash value is detected, return failure to indicate
>> > corruption.
>> >
>> > This addresses the "XXX: hash order check?" comment and improves
>> > corruption detection for DA node blocks.
>> >
>> > Signed-off-by: Charalampos Mitrodimas <charmitro@xxxxxxxxxx>
>> > ---
>> > fs/xfs/libxfs/xfs_da_btree.c | 11 ++++++++++-
>> > 1 file changed, 10 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
>> > index 17d9e6154f1978ce5a5cb82176eea4d6b9cd768d..6c748911e54619c3ceae9b81f55cf61da6735f01 100644
>> > --- a/fs/xfs/libxfs/xfs_da_btree.c
>> > +++ b/fs/xfs/libxfs/xfs_da_btree.c
>> > @@ -247,7 +247,16 @@ xfs_da3_node_verify(
>> > ichdr.count > mp->m_attr_geo->node_ents)
>> > return __this_address;
>> >
>> > - /* XXX: hash order check? */
>> > + /* Check hash order */
>> > + uint32_t prev_hash = be32_to_cpu(ichdr.btree[0].hashval);
>> > +
>> > + for (int i = 1; i < ichdr.count; i++) {
>> > + uint32_t curr_hash = be32_to_cpu(ichdr.btree[i].hashval);
>> > +
>> > + if (curr_hash <= prev_hash)
>> > + return __this_address;
>> > + prev_hash = curr_hash;
>> > + }
>>
>> Hmmm. Do you have any numbers related to the performance impact of this patch?
>>
>> IIRC for very populated directories we can end up having many entries here. It's
>> not uncommon to have filesystems with millions of entries in a single directory.
>> Now we'll be looping over all those entries here during verification, which could
>> scale to many interactions on this loop.
>> I'm not sure if I'm right here, but this seems to add a big performance penalty
>> for directory writes, so I'm curious about the performance implications of this
>> patch.
>
> It's only a single dabtree block, which will likely be warm in cache
> due to the crc32c validation.
Regardless, what is a good method of measuring the penalty, if any?
>
> But if memory serves, one can create a large enough dir (or xattr)
> structure such that a dabtree node gets written out with a bunch of
> entries with the same hashval. That was the subject of the correction
> made in commit b7b81f336ac02f ("xfs_repair: fix incorrect dabtree
> hashval comparison") so I've been wondering if this passes the xfs/599
> test? Or am I just being dumb?
I'll rebase (in case) give it a try over the next weekend and reach
back. AFAIR all tests where okay, but might gives us a hint if it is
failing now.
Thanks for the review Darrick and Carlos.
C. Mitrodimas
>
> --D
>
>> >
>> > return NULL;
>> > }
>> >
>> > ---
>> > base-commit: ecd5d67ad602c2c12e8709762717112ef0958767
>> > change-id: 20250412-xfs-hash-check-be7397881a2c
>> >
>> > Best regards,
>> > --
>> > Charalampos Mitrodimas <charmitro@xxxxxxxxxx>
>> >
>>
