From: Taylor Blau <me@ttaylorr.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org
Subject: Re: [PATCH 10/20] midx: bounds-check large offset chunk
Date: Wed, 11 Oct 2023 14:38:07 -0400 [thread overview]
Message-ID: <ZSbrj3hmm8H7ce2l@nand.local> (raw)
In-Reply-To: <20231009210530.GJ3282181@coredump.intra.peff.net>
On Mon, Oct 09, 2023 at 05:05:30PM -0400, Jeff King wrote:
> When we see a large offset bit in the regular midx offset table, we
> use the entry as an index into a separate large offset table (just like
> a pack idx does). But we don't bounds-check the access to that large
> offset table (nor even record its size when we parse the chunk!).
>
> The equivalent code for a regular pack idx is in check_pack_index_ptr().
> But things are a bit simpler here because of the chunked format: we can
> just check our array index directly.
>
> As a bonus, we can get rid of the st_mult() here. If our array
> bounds-check is successful, then we know that the result will fit in a
> size_t (and the bounds check uses a division to avoid overflow
> entirely).
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> midx.c | 8 +++++---
> midx.h | 1 +
> t/t5319-multi-pack-index.sh | 20 ++++++++++++++++++++
> 3 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/midx.c b/midx.c
> index 7b1b45f381..3e768d0df0 100644
> --- a/midx.c
> +++ b/midx.c
> @@ -180,7 +180,8 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
> if (read_chunk(cf, MIDX_CHUNKID_OBJECTOFFSETS, midx_read_object_offsets, m))
> die(_("multi-pack-index required object offsets chunk missing or corrupted"));
>
> - pair_chunk_unsafe(cf, MIDX_CHUNKID_LARGEOFFSETS, &m->chunk_large_offsets);
> + pair_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS, &m->chunk_large_offsets,
> + &m->chunk_large_offsets_len);
>
> if (git_env_bool("GIT_TEST_MIDX_READ_RIDX", 1))
> pair_chunk_unsafe(cf, MIDX_CHUNKID_REVINDEX, &m->chunk_revindex);
> @@ -303,8 +304,9 @@ off_t nth_midxed_offset(struct multi_pack_index *m, uint32_t pos)
> die(_("multi-pack-index stores a 64-bit offset, but off_t is too small"));
>
> offset32 ^= MIDX_LARGE_OFFSET_NEEDED;
> - return get_be64(m->chunk_large_offsets +
> - st_mult(sizeof(uint64_t), offset32));
> + if (offset32 >= m->chunk_large_offsets_len / sizeof(uint64_t))
> + die(_("multi-pack-index large offset out of bounds"));
> + return get_be64(m->chunk_large_offsets + sizeof(uint64_t) * offset32);
Makes sense, and this seems very reasonable. I had a couple of thoughts
on this hunk, one nitpick, and one non-nitpick ;-).
The nitpick is the easy one, which is that I typically think of scaling
some index to produce an offset into some chunk, instead of dividing and
going the other way.
So I probably would have written something like:
if (st_mult(offset32, sizeof(uint64_t)) >= m->chunk_large_offsets_len)
die(_("multi-pack-index large offset out of bounds"));
But that is definitely a subjective/minor point, and I would not at all
be sad if you felt differently about it. That said, I do wish for a
little more information in the die() message, perhaps:
if (st_mult(offset32, sizeof(uint64_t)) >= m->chunk_large_offsets_len)
die(_("multi-pack-index large offset for %s out of bounds "
"(%"PRIuMAX" is beyond %"PRIuMAX")"),
(uintmax_t)(offset32 * sizeof(uint64_t)), /* checked earlier */
(uintmax_t)m->chunk_large_offsets_len);
I can imagine that for debugging corrupt MIDXs in the future, having
some extra information like the above would give us a better starting
point than popping into a debugger to get the same information.
Thanks,
Taylor
next prev parent reply other threads:[~2023-10-11 18:38 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 [this message]
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
2023-10-15 3:17 ` Jeff King
2023-10-15 17:04 ` Junio C Hamano
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