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@xxxxxxxx>
---
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);
}
return offset32;
diff --git a/midx.h b/midx.h
index 5b2a7da043..e8e8884d16 100644
--- a/midx.h
+++ b/midx.h
@@ -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;
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 30687d5452..16050f39d9 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -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
--
2.42.0.884.g35e1fe1a6a
