Re: [PATCH 03/20] midx: stop ignoring malformed oid fanout chunk

> When we load the oid-fanout chunk, our callback checks that its size is
> reasonable and returns an error if not. However, the caller only checks
> our return value against CHUNK_NOT_FOUND, so we end up ignoring the
> error completely! Using a too-small fanout table means we end up
> accessing random memory for the fanout and segfault.
>
> We can fix this by checking for any non-zero return value, rather than
> just CHUNK_NOT_FOUND, and adjusting our error message to cover both
> cases. We could handle each error code individually, but there's not
> much point for such a rare case. The extra message produced in the
> callback makes it clear what is going on.
>
> The same pattern is used in the adjacent code. Those cases are actually
> OK for now because they do not use a custom callback, so the only error
> they can get is CHUNK_NOT_FOUND. But let's convert them, as this is an
> accident waiting to happen (especially as we convert some of them away
> from pair_chunk). The error messages are more verbose, but it should be
> rare for a user to see these anyway.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  midx.c                      | 16 ++++++++--------
>  t/t5319-multi-pack-index.sh | 20 +++++++++++++++++++-
>  2 files changed, 27 insertions(+), 9 deletions(-)
>
> diff --git a/midx.c b/midx.c
> index 3165218ab5..21d7dd15ef 100644
> --- a/midx.c
> +++ b/midx.c
> @@ -143,14 +143,14 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
>  				   MIDX_HEADER_SIZE, m->num_chunks))
>  		goto cleanup_fail;
>
> -	if (pair_chunk_unsafe(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names) == CHUNK_NOT_FOUND)
> -		die(_("multi-pack-index missing required pack-name chunk"));
> -	if (read_chunk(cf, MIDX_CHUNKID_OIDFANOUT, midx_read_oid_fanout, m) == CHUNK_NOT_FOUND)
> -		die(_("multi-pack-index missing required OID fanout chunk"));
> -	if (pair_chunk_unsafe(cf, MIDX_CHUNKID_OIDLOOKUP, &m->chunk_oid_lookup) == CHUNK_NOT_FOUND)
> -		die(_("multi-pack-index missing required OID lookup chunk"));
> -	if (pair_chunk_unsafe(cf, MIDX_CHUNKID_OBJECTOFFSETS, &m->chunk_object_offsets) == CHUNK_NOT_FOUND)
> -		die(_("multi-pack-index missing required object offsets chunk"));
> +	if (pair_chunk_unsafe(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names))
> +		die(_("multi-pack-index required pack-name chunk missing or corrupted"));
> +	if (read_chunk(cf, MIDX_CHUNKID_OIDFANOUT, midx_read_oid_fanout, m))
> +		die(_("multi-pack-index required OID fanout chunk missing or corrupted"));
> +	if (pair_chunk_unsafe(cf, MIDX_CHUNKID_OIDLOOKUP, &m->chunk_oid_lookup))
> +		die(_("multi-pack-index required OID lookup chunk missing or corrupted"));
> +	if (pair_chunk_unsafe(cf, MIDX_CHUNKID_OBJECTOFFSETS, &m->chunk_object_offsets))
> +		die(_("multi-pack-index required object offsets chunk missing or corrupted"));