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midx: check size of object offset chunk

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The object offset chunk has one fixed-size entry for each object in the
midx. But since we don't check its size, we may access out-of-bounds
memory if we see a corrupt or malicious midx file.

Sine the entries are fixed-size, the total length can be known up-front,
and we can just check it while parsing the chunk (this is similar to
what we do when opening pack idx files, which contain a similar offset
table).

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 17:05:27 -04:00 committed by Junio C Hamano
parent c9b9fefc13
commit 0924869b4e
2 changed files with 24 additions and 1 deletions
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15
midx.c
View File

@ -88,6 +88,19 @@ static int midx_read_oid_lookup(const unsigned char *chunk_start,
return 0;
}
static int midx_read_object_offsets(const unsigned char *chunk_start,
size_t chunk_size, void *data)
{
struct multi_pack_index *m = data;
m->chunk_object_offsets = chunk_start;
if (chunk_size != st_mult(m->num_objects, MIDX_CHUNK_OFFSET_WIDTH)) {
error(_("multi-pack-index object offset chunk is the wrong size"));
return 1;
}
return 0;
}
struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local)
{
struct multi_pack_index *m = NULL;
@ -164,7 +177,7 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
die(_("multi-pack-index required OID fanout chunk missing or corrupted"));
if (read_chunk(cf, MIDX_CHUNKID_OIDLOOKUP, midx_read_oid_lookup, m))
die(_("multi-pack-index required OID lookup chunk missing or corrupted"));
if (pair_chunk_unsafe(cf, MIDX_CHUNKID_OBJECTOFFSETS, &m->chunk_object_offsets))
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);

10
t/t5319-multi-pack-index.sh
View File

@ -1108,4 +1108,14 @@ test_expect_success 'reader handles unaligned chunks' '
test_cmp expect.err err
'
test_expect_success 'reader notices too-small object offset chunk' '
corrupt_chunk OOFF clear 00000000 &&
test_must_fail git log 2>err &&
cat >expect <<-\EOF &&
error: multi-pack-index object offset chunk is the wrong size
fatal: multi-pack-index required object offsets chunk missing or corrupted
EOF
test_cmp expect err
'
test_done