fsck: check rev-index position values

When checking a rev-index file, it may be helpful to identify exactly
which positions are incorrect. Compare the rev-index to a
freshly-computed in-memory rev-index and report the comparison failures.

This additional check (on top of the checksum validation) can help find
files that were corrupt by a single bit flip on-disk or perhaps were
written incorrectly due to a bug in Git.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/pack-revindex.c b/pack-revindex.c
index 007a806994fd606984f9b28c51a61eee16bc9140..62a9846470c792aa6bdbfcbfd0d3beefa1e7d40b 100644 (file)
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -310,16 +310,33 @@ int load_pack_revindex(struct repository *r, struct packed_git *p)
  */
 int verify_pack_revindex(struct packed_git *p)
 {
+       int res = 0;
+
        /* Do not bother checking if not initialized. */
-       if (!p->revindex_map)
-               return 0;
+       if (!p->revindex_map || !p->revindex_data)
+               return res;
 
        if (!hashfile_checksum_valid((const unsigned char *)p->revindex_map, p->revindex_size)) {
                error(_("invalid checksum"));
-               return -1;
+               res = -1;
        }
 
-       return 0;
+       /* This may fail due to a broken .idx. */
+       if (create_pack_revindex_in_memory(p))
+               return res;
+
+       for (size_t i = 0; i < p->num_objects; i++) {
+               uint32_t nr = p->revindex[i].nr;
+               uint32_t rev_val = get_be32(p->revindex_data + i);
+
+               if (nr != rev_val) {
+                       error(_("invalid rev-index position at %"PRIu64": %"PRIu32" != %"PRIu32""),
+                             (uint64_t)i, nr, rev_val);
+                       res = -1;
+               }
+       }
+
+       return res;
 }
 
 int load_midx_revindex(struct multi_pack_index *m)

diff --git a/t/t5325-reverse-index.sh b/t/t5325-reverse-index.sh
index 6b7c709a1f6706e80f4835389785a1a7911b5ae7..5c3c80f88f07d979750fac69f51ae4fe83180560 100755 (executable)
--- a/t/t5325-reverse-index.sh
+++ b/t/t5325-reverse-index.sh
@@ -185,4 +185,9 @@ test_expect_success 'fsck catches invalid checksum' '
                "invalid checksum"
 '
 
+test_expect_success 'fsck catches invalid row position' '
+       corrupt_rev_and_verify 14 "\07" \
+               "invalid rev-index position"
+'
+
 test_done