Subject: [PATCH v2 0/2] pseudo-merge: various small fixes

From: Taylor Blau <[email-masked]>
Date: Fri, 14 Jun 2024 15:23:52 -0400

Here is a small reroll of a couple of patches I wrote to fix various
small issues with the tb/pseudo-merge-reachability-bitmaps topic.

The only change since last time is replacing:

    if (st_mult(index->pseudo_merges.nr, sizeof(uint64_t)) > table_size - 24)

with:

    if (st_add(st_mult(index->pseudo_merges.nr, sizeof(uint64_t)), 24) > table_size)

based on helpful review from Junio. For convenience, a range-diff is
below. Thanks in advance for any final review on this topic :-).

Taylor Blau (2):
  Documentation/technical/bitmap-format.txt: add missing position table
  pack-bitmap.c: ensure pseudo-merge offset reads are bounded

 Documentation/technical/bitmap-format.txt | 9 +++++++++
 pack-bitmap.c                             | 5 +++++
 2 files changed, 14 insertions(+)

Range-diff against v1:
-:  ---------- > 1:  a71ec05e5d Documentation/technical/bitmap-format.txt: add missing position table
1:  0a16399d14 ! 2:  8abd564e7c pack-bitmap.c: ensure pseudo-merge offset reads are bounded
    @@ Commit message
         end of the mmap'd region.

         Prevent this by ensuring that we have at least `table_size - 24` many
    -    bytes available to read (subtracting 24 as the length of the metadata
    -    component).
    +    bytes available to read (adding 24 to the left-hand side of our
    +    inequality to account for the length of the metadata component).

         This is sufficient to prevent us from reading off the end of the
         pseudo-merge extension, and ensures that all of the get_be64() calls
    @@ pack-bitmap.c: static int load_bitmap_header(struct bitmap_index *index)
      				index->pseudo_merges.commits_nr = get_be32(index_end - 20);
      				index->pseudo_merges.nr = get_be32(index_end - 24);

    -+				if (st_mult(index->pseudo_merges.nr, sizeof(uint64_t)) > table_size - 24)
    ++				if (st_add(st_mult(index->pseudo_merges.nr,
    ++						   sizeof(uint64_t)),
    ++					   24) > table_size)
     +					return error(_("corrupted bitmap index file, pseudo-merge table too short"));
     +
      				CALLOC_ARRAY(index->pseudo_merges.v,

base-commit: 0b7500dc66ffcb6b1ccc3332715936a59c6b5ce4
--
2.45.0.33.g0a16399d14.dirty