From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org, Taylor Blau <me@ttaylorr.com>
Subject: Re: [PATCH 21/20] t5319: make corrupted large-offset test more robust
Date: Sat, 14 Oct 2023 12:42:01 -0700 [thread overview]
Message-ID: <xmqq4jitt2ie.fsf@gitster.g> (raw)
In-Reply-To: <20231014004348.GA43880@coredump.intra.peff.net> (Jeff King's message of "Fri, 13 Oct 2023 20:43:48 -0400")
Jeff King <peff@peff.net> writes:
> 4b. But sometimes we hit a different error. If another object points
> to X as a delta base, then trying to find the type of that object
> requires walking the delta chain to the base entry (since only the
> base has the concrete type; deltas themselves are either OFS_DELTA
> or REF_DELTA).
>
> Normally this would not require separate offset lookups at all, as
> deltas are usually stored as OFS_DELTA, specifying the relative
> offset to the base. But the corrupt idx created in step 1 is done
> directly with "git pack-objects" and does not pass the
> --delta-base-offset option, meaning we have REF_DELTA entries!
> Those do have to consult an index to find the location of the base
> object, and they use the pack .idx to do this. The same pack .idx
> that we know is corrupted from step 1!
Tricky.
> The set of objects created in the test is deterministic. But the delta
> selection seems not to be (which is not too surprising, as it is
> multi-threaded).
So, the offsets of the objects are also not deterministic?
> I have seen the failure in Windows CI but haven't
> reproduced it locally (not even with --stress). Re-running a failed
> Windows CI job tends to work. But when I download and examine the trash
> directory from a failed run, it shows a different set of deltas than I
> get locally. But the exact source of non-determinism isn't that
> important; our test should be robust against any order.
Yeah, thanks for digging this tricky situation through.
> b. The "objects64" setup could use --delta-base-offset. This would fix
> our problem, but earlier tests have many hard-coded offsets. Using
> OFS_DELTA would change the locations of objects in the pack (this
> might even be OK because I think most of the offsets are within the
> .idx file, but it seems brittle and I'm afraid to touch it).
I am not sure I follow, as it does not sound a solution to anything
if the offsets are not deterministic (and "earlier tests" that have
hard coded offsets are broken no matter what, which is not a problem
this patch introduces). Puzzled, but not curious enough to think
about it further, as you have already rejected this approach ;-)
> d. We could ask directly about object X, rather than enumerating all
> of them. But that requires further hard-coding of the oid (both
> sha1 and sha256) of object X. I'd prefer not to introduce more
> brittleness.
Right.
> e. We can use a --batch-check format that looks at the pack data, but
> doesn't have to chase deltas. The problem in this case is
> %(objecttype), which has to walk to the base. But %(objectsize)
> does not; we can get the value directly from the delta itself.
> Another option would be %(deltabase), where we report the REF_DELTA
> name but don't look at its data.
>
> I've gone with option (e) here. It's kind of subtle, but it's simple and
> has no side effects.
Nice.
> @@ -1129,8 +1129,10 @@ test_expect_success 'reader bounds-checks large offset table' '
> git multi-pack-index --object-dir=../objects64 write &&
> midx=../objects64/pack/multi-pack-index &&
> corrupt_chunk_file $midx LOFF clear &&
> - test_must_fail git cat-file \
> - --batch-check --batch-all-objects 2>err &&
> + # using only %(objectsize) is important here; see the commit
> + # message for more details
> + test_must_fail git cat-file --batch-all-objects \
> + --batch-check="%(objectsize)" 2>err &&
A rather unfriendly message to readers, as it is unclear which
commit you are talking about, and a fun thing is that you cannot
say which one.
Will queue. Thanks.
next prev parent reply other threads:[~2023-10-14 19:42 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-09 20:55 [PATCH 0/20] bounds-checks for chunk-based files Jeff King
2023-10-09 20:58 ` [PATCH 01/20] chunk-format: note that pair_chunk() is unsafe Jeff King
2023-10-10 23:45 ` Taylor Blau
2023-10-11 22:49 ` Jeff King
2023-10-09 20:58 ` [PATCH 02/20] t: add library for munging chunk-format files Jeff King
2023-10-10 23:47 ` Taylor Blau
2023-10-09 20:59 ` [PATCH 03/20] midx: stop ignoring malformed oid fanout chunk Jeff King
2023-10-10 23:50 ` Taylor Blau
2023-10-11 22:52 ` Jeff King
2023-10-09 20:59 ` [PATCH 04/20] commit-graph: check size of " Jeff King
2023-10-11 0:08 ` Taylor Blau
2023-10-11 1:24 ` Taylor Blau
2023-10-11 23:01 ` Jeff King
2023-10-09 21:02 ` [PATCH 05/20] midx: check size of oid lookup chunk Jeff King
2023-10-09 21:04 ` [PATCH 06/20] commit-graph: check consistency of fanout table Jeff King
2023-10-11 14:45 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 07/20] midx: check size of pack names chunk Jeff King
2023-10-11 14:52 ` Taylor Blau
2023-10-11 23:06 ` Jeff King
2023-10-09 21:05 ` [PATCH 08/20] midx: enforce chunk alignment on reading Jeff King
2023-10-11 14:56 ` Taylor Blau
2023-10-11 15:01 ` Taylor Blau
2023-10-11 23:09 ` Jeff King
2023-10-09 21:05 ` [PATCH 09/20] midx: check size of object offset chunk Jeff King
2023-10-11 18:31 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 10/20] midx: bounds-check large " Jeff King
2023-10-11 18:38 ` Taylor Blau
2023-10-11 23:18 ` Jeff King
2023-10-09 21:05 ` [PATCH 11/20] midx: check size of revindex chunk Jeff King
2023-10-11 18:41 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 12/20] commit-graph: check size of commit data chunk Jeff King
2023-10-11 18:46 ` Taylor Blau
2023-10-11 23:22 ` Jeff King
2023-10-09 21:05 ` [PATCH 13/20] commit-graph: detect out-of-bounds extra-edges pointers Jeff King
2023-10-11 19:02 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 14/20] commit-graph: bounds-check base graphs chunk Jeff King
2023-10-11 19:05 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 15/20] commit-graph: check size of generations chunk Jeff King
2023-10-09 21:05 ` [PATCH 16/20] commit-graph: bounds-check generation overflow chunk Jeff King
2023-10-09 21:05 ` [PATCH 17/20] commit-graph: check bounds when accessing BDAT chunk Jeff King
2023-10-11 19:11 ` Taylor Blau
2023-10-11 23:27 ` Jeff King
2023-10-09 21:05 ` [PATCH 18/20] commit-graph: check bounds when accessing BIDX chunk Jeff King
2023-10-11 19:15 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 19/20] commit-graph: detect out-of-order BIDX offsets Jeff King
2023-10-11 19:16 ` Taylor Blau
2023-10-09 21:06 ` [PATCH 20/20] chunk-format: drop pair_chunk_unsafe() Jeff King
2023-10-11 19:19 ` [PATCH 0/20] bounds-checks for chunk-based files Taylor Blau
2023-10-11 23:31 ` Jeff King
2023-10-13 19:25 ` [PATCH 0/8] chunk-format: introduce `pair_chunk_expect()` convenience API Taylor Blau
2023-10-13 19:25 ` [PATCH 1/8] chunk-format: introduce `pair_chunk_expect()` helper Taylor Blau
2023-10-13 19:25 ` [PATCH 2/8] commit-graph: read `OIDF` chunk with `pair_chunk_expect()` Taylor Blau
2023-10-13 19:25 ` [PATCH 3/8] commit-graph: read `CDAT` " Taylor Blau
2023-10-13 19:25 ` [PATCH 4/8] commit-graph: read `GDAT` " Taylor Blau
2023-10-13 19:25 ` [PATCH 5/8] commit-graph: read `BIDX` " Taylor Blau
2023-10-13 19:49 ` Taylor Blau
2023-10-14 16:10 ` Junio C Hamano
2023-10-20 10:31 ` Jeff King
2023-10-13 19:25 ` [PATCH 6/8] midx: read `OIDF` " Taylor Blau
2023-10-13 21:04 ` Junio C Hamano
2023-10-13 19:25 ` [PATCH 7/8] midx: read `OIDL` " Taylor Blau
2023-10-13 19:25 ` [PATCH 8/8] midx: read `OOFF` " Taylor Blau
2023-10-20 10:23 ` [PATCH 0/8] chunk-format: introduce `pair_chunk_expect()` convenience API Jeff King
2023-10-14 0:43 ` [PATCH 21/20] t5319: make corrupted large-offset test more robust Jeff King
2023-10-14 19:42 ` Junio C Hamano [this message]
2023-10-15 3:17 ` Jeff King
2023-10-15 17:04 ` Junio C Hamano
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