midx: check size of object offset chunk

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>

diff --git a/midx.c b/midx.c
index 98f84fbe61539dbe4cbb05e3b3731967d8abcf88..7b1b45f381c88cbf9ec0411250145f7bf49837eb 100644 (file)
--- a/midx.c
+++ b/midx.c
@@ -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);

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 34f594414243d9d07d2531a7d6a6ea3eafa7cf71..30687d5452f25e74890cd9f6bfdb4c5bf1362417 100755 (executable)
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -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