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midx: check size of pack names chunk 

We parse the pack-name chunk as a series of NUL-terminated strings. But
since we don't look at the chunk size, there's nothing to guarantee that
we don't parse off the end of the chunk (or even off the end of the
mapped file).

We can record the length, and then as we parse make sure that we never
walk past it.

The new test exercises the case, though note that it does not actually
segfault before this patch. It hits a NUL byte somewhere in one of the
other chunks, and comes up with a garbage pack name. You could construct
one that reads out-of-bounds (e.g., a PNAM chunk at the end of file),
but this case is simple and sufficient to check that we detect the
problem.

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 17:05:14 -04:00 committed by Junio C Hamano
parent 4169d89645
commit 72a9a08283
3 changed files with 21 additions and 2 deletions
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11
midx.c
View File

@ -157,7 +157,7 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
MIDX_HEADER_SIZE, m->num_chunks))
goto cleanup_fail;
if (pair_chunk_unsafe(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names))
if (pair_chunk(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names, &m->chunk_pack_names_len))
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"));
@ -176,9 +176,16 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
cur_pack_name = (const char *)m->chunk_pack_names;
for (i = 0; i < m->num_packs; i++) {
const char *end;
size_t avail = m->chunk_pack_names_len -
(cur_pack_name - (const char *)m->chunk_pack_names);
m->pack_names[i] = cur_pack_name;
cur_pack_name += strlen(cur_pack_name) + 1;
end = memchr(cur_pack_name, '\0', avail);
if (!end)
die(_("multi-pack-index pack-name chunk is too short"));
cur_pack_name = end + 1;
if (i && strcmp(m->pack_names[i], m->pack_names[i - 1]) <= 0)
die(_("multi-pack-index pack names out of order: '%s' before '%s'"),

1
midx.h
View File

@ -32,6 +32,7 @@ struct multi_pack_index {
int local;
const unsigned char *chunk_pack_names;
size_t chunk_pack_names_len;
const uint32_t *chunk_oid_fanout;
const unsigned char *chunk_oid_lookup;
const unsigned char *chunk_object_offsets;

11
t/t5319-multi-pack-index.sh
View File

@ -1083,4 +1083,15 @@ test_expect_success 'reader notices too-small oid lookup chunk' '
test_cmp expect err
'
test_expect_success 'reader notices too-small pack names chunk' '
# There is no NUL to terminate the name here, so the
# chunk is too short.
corrupt_chunk PNAM clear 70656666 &&
test_must_fail git log 2>err &&
cat >expect <<-\EOF &&
fatal: multi-pack-index pack-name chunk is too short
EOF
test_cmp expect err
'
test_done