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midx: bounds-check large offset chunk

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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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2023-10-09 17:05:30 -04:00 committed by Junio C Hamano
parent 0924869b4e
commit 2abd56e9b2
3 changed files with 26 additions and 3 deletions
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8
midx.c
View File

@ -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);
}
return offset32;

1
midx.h
View File

@ -37,6 +37,7 @@ struct multi_pack_index {
const unsigned char *chunk_oid_lookup;
const unsigned char *chunk_object_offsets;
const unsigned char *chunk_large_offsets;
size_t chunk_large_offsets_len;
const unsigned char *chunk_revindex;
const char **pack_names;

20
t/t5319-multi-pack-index.sh
View File

@ -1118,4 +1118,24 @@ test_expect_success 'reader notices too-small object offset chunk' '
test_cmp expect err
'
test_expect_success 'reader bounds-checks large offset table' '
# re-use the objects64 dir here to cheaply get access to a midx
# with large offsets.
git init repo &&
test_when_finished "rm -rf repo" &&
(
cd repo &&
(cd ../objects64 && pwd) >.git/objects/info/alternates &&
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 &&
cat >expect <<-\EOF &&
fatal: multi-pack-index large offset out of bounds
EOF
test_cmp expect err
)
'
test_done