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midx: check size of oid lookup chunk

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When reading an on-disk multi-pack-index, we take the number of objects
in the midx from the final value of the fanout table. But we just
blindly assume that the chunk containing the actual oid entries is the
correct size. This can lead to us reading out-of-bounds memory if the
lookup chunk is too small (or if the fanout is corrupted; when they
don't agree we cannot tell which one is wrong).

Note that we bump the assignment of m->num_objects into the fanout
parser callback, so that it's set when we parse the lookup table
(otherwise we'd have to manually record the lookup table size and check
it later).

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 17:02:03 -04:00
committed by Junio C Hamano
parent 52e2e8d43d
commit fc926567ed
2 changed files with 25 additions and 3 deletions
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18
midx.c
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@ -71,6 +71,20 @@ static int midx_read_oid_fanout(const unsigned char *chunk_start,
error(_("multi-pack-index OID fanout is of the wrong size"));
return 1;
}
m->num_objects = ntohl(m->chunk_oid_fanout[255]);
return 0;
}
static int midx_read_oid_lookup(const unsigned char *chunk_start,
size_t chunk_size, void *data)
{
struct multi_pack_index *m = data;
m->chunk_oid_lookup = chunk_start;
if (chunk_size != st_mult(m->hash_len, m->num_objects)) {
error(_("multi-pack-index OID lookup chunk is the wrong size"));
return 1;
}
return 0;
}
@ -147,7 +161,7 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
die(_("multi-pack-index required pack-name chunk missing or corrupted"));
if (read_chunk(cf, MIDX_CHUNKID_OIDFANOUT, midx_read_oid_fanout, m))
die(_("multi-pack-index required OID fanout chunk missing or corrupted"));
if (pair_chunk_unsafe(cf, MIDX_CHUNKID_OIDLOOKUP, &m->chunk_oid_lookup))
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))
die(_("multi-pack-index required object offsets chunk missing or corrupted"));
@ -157,8 +171,6 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
if (git_env_bool("GIT_TEST_MIDX_READ_RIDX", 1))
pair_chunk_unsafe(cf, MIDX_CHUNKID_REVINDEX, &m->chunk_revindex);
m->num_objects = ntohl(m->chunk_oid_fanout[255]);
CALLOC_ARRAY(m->pack_names, m->num_packs);
CALLOC_ARRAY(m->packs, m->num_packs);