Taylor Blau <me@xxxxxxxxxxxx> writes:
> After reading the pseudo-merge extension's metadata table, we allocate
> an array to store information about each pseudo-merge, including its
> byte offset within the .bitmap file itself.
>
> This is done like so:
>
> pseudo_merge_ofs = index_end - 24 -
> (index->pseudo_merges.nr * sizeof(uint64_t));
> for (i = 0; i < index->pseudo_merges.nr; i++) {
> index->pseudo_merges.v[i].at = get_be64(pseudo_merge_ofs);
> pseudo_merge_ofs += sizeof(uint64_t);
> }
>
> But if the pseudo-merge table is corrupt, we'll keep calling get_be64()
> past the end of the pseudo-merge extension, potentially reading off the
> 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).
>
> 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
> below are in bounds.
Can table_size at this point be smaller than 24, which will allow
(table_size - 24) to be a huge number that st_mult() will
comfortably fit?
> Helped-by: Jeff King <peff@xxxxxxxx>
> Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
> ---
> pack-bitmap.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/pack-bitmap.c b/pack-bitmap.c
> index 70230e2647..ad2635c025 100644
> --- a/pack-bitmap.c
> +++ b/pack-bitmap.c
> @@ -238,6 +238,9 @@ 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)
> + return error(_("corrupted bitmap index file, pseudo-merge table too short"));
> +
> CALLOC_ARRAY(index->pseudo_merges.v,
> index->pseudo_merges.nr);
