From: Taylor Blau <me@ttaylorr.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org
Subject: Re: [PATCH 12/20] commit-graph: check size of commit data chunk
Date: Wed, 11 Oct 2023 14:46:28 -0400 [thread overview]
Message-ID: <ZSbthK5919QdrEPx@nand.local> (raw)
In-Reply-To: <20231009210536.GL3282181@coredump.intra.peff.net>
On Mon, Oct 09, 2023 at 05:05:36PM -0400, Jeff King wrote:
> We expect a commit-graph file to have a fixed-size data record for each
> commit in the file (and we know the number of commits to expct from the
> size of the lookup table). If we encounter a file where this is too
> small, we'll look past the end of the chunk (and possibly even off the
> mapped memory).
>
> We can fix this by checking the size up front when we record the
> pointer.
>
> The included test doesn't segfault, since it ends up reading bytes
> from another chunk. But it produces nonsense results, since the values
> it reads are garbage. Our test notices this by comparing the output to a
> non-corrupted run of the same command (and of course we also check that
> the expected error is printed to stderr).
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> commit-graph.c | 12 +++++++++++-
> t/t5318-commit-graph.sh | 9 +++++++++
> 2 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/commit-graph.c b/commit-graph.c
> index 472332f603..9b80bbd75b 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -340,6 +340,16 @@ static int graph_read_oid_lookup(const unsigned char *chunk_start,
> return 0;
> }
>
> +static int graph_read_commit_data(const unsigned char *chunk_start,
> + size_t chunk_size, void *data)
> +{
> + struct commit_graph *g = data;
> + if (chunk_size != g->num_commits * GRAPH_DATA_WIDTH)
Should this be guarded with an st_mult? I think that GRAPH_DATA_WIDTH is
defined as (the_hash_algo->rawsz + 16), so I *think* that the expression
in the parenthesis would get done as a size_t, and then g->num_commits
would be widened to a size_t for the purposes of evaluating this
expression.
So I think that this is all OK in the sense that we'd never underflow
the 64-bit space, and having more than 2^64-1/36 (some eighteen
quintillion) commits is... unlikely ;-).
But it may be worth wrapping this computation in an st_mult() anyway to
avoid future readers having to think about this.
> + return error("commit-graph commit data chunk is wrong size");
> + g->chunk_commit_data = chunk_start;
> + return 0;
> +}
> +
> static int graph_read_bloom_data(const unsigned char *chunk_start,
> size_t chunk_size, void *data)
> {
> @@ -422,7 +432,7 @@ struct commit_graph *parse_commit_graph(struct repo_settings *s,
>
> read_chunk(cf, GRAPH_CHUNKID_OIDFANOUT, graph_read_oid_fanout, graph);
> read_chunk(cf, GRAPH_CHUNKID_OIDLOOKUP, graph_read_oid_lookup, graph);
> - pair_chunk_unsafe(cf, GRAPH_CHUNKID_DATA, &graph->chunk_commit_data);
> + read_chunk(cf, GRAPH_CHUNKID_DATA, graph_read_commit_data, graph);
Here again would be a good use-case for a `pair_chunk_expect()`
function, but I don't want to beat a dead horse ;-).
Thanks,
Taylor
next prev parent reply other threads:[~2023-10-11 18:47 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-09 20:55 [PATCH 0/20] bounds-checks for chunk-based files Jeff King
2023-10-09 20:58 ` [PATCH 01/20] chunk-format: note that pair_chunk() is unsafe Jeff King
2023-10-10 23:45 ` Taylor Blau
2023-10-11 22:49 ` Jeff King
2023-10-09 20:58 ` [PATCH 02/20] t: add library for munging chunk-format files Jeff King
2023-10-10 23:47 ` Taylor Blau
2023-10-09 20:59 ` [PATCH 03/20] midx: stop ignoring malformed oid fanout chunk Jeff King
2023-10-10 23:50 ` Taylor Blau
2023-10-11 22:52 ` Jeff King
2023-10-09 20:59 ` [PATCH 04/20] commit-graph: check size of " Jeff King
2023-10-11 0:08 ` Taylor Blau
2023-10-11 1:24 ` Taylor Blau
2023-10-11 23:01 ` Jeff King
2023-10-09 21:02 ` [PATCH 05/20] midx: check size of oid lookup chunk Jeff King
2023-10-09 21:04 ` [PATCH 06/20] commit-graph: check consistency of fanout table Jeff King
2023-10-11 14:45 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 07/20] midx: check size of pack names chunk Jeff King
2023-10-11 14:52 ` Taylor Blau
2023-10-11 23:06 ` Jeff King
2023-10-09 21:05 ` [PATCH 08/20] midx: enforce chunk alignment on reading Jeff King
2023-10-11 14:56 ` Taylor Blau
2023-10-11 15:01 ` Taylor Blau
2023-10-11 23:09 ` Jeff King
2023-10-09 21:05 ` [PATCH 09/20] midx: check size of object offset chunk Jeff King
2023-10-11 18:31 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 10/20] midx: bounds-check large " Jeff King
2023-10-11 18:38 ` Taylor Blau
2023-10-11 23:18 ` Jeff King
2023-10-09 21:05 ` [PATCH 11/20] midx: check size of revindex chunk Jeff King
2023-10-11 18:41 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 12/20] commit-graph: check size of commit data chunk Jeff King
2023-10-11 18:46 ` Taylor Blau [this message]
2023-10-11 23:22 ` Jeff King
2023-10-09 21:05 ` [PATCH 13/20] commit-graph: detect out-of-bounds extra-edges pointers Jeff King
2023-10-11 19:02 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 14/20] commit-graph: bounds-check base graphs chunk Jeff King
2023-10-11 19:05 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 15/20] commit-graph: check size of generations chunk Jeff King
2023-10-09 21:05 ` [PATCH 16/20] commit-graph: bounds-check generation overflow chunk Jeff King
2023-10-09 21:05 ` [PATCH 17/20] commit-graph: check bounds when accessing BDAT chunk Jeff King
2023-10-11 19:11 ` Taylor Blau
2023-10-11 23:27 ` Jeff King
2023-10-09 21:05 ` [PATCH 18/20] commit-graph: check bounds when accessing BIDX chunk Jeff King
2023-10-11 19:15 ` Taylor Blau
2023-10-09 21:05 ` [PATCH 19/20] commit-graph: detect out-of-order BIDX offsets Jeff King
2023-10-11 19:16 ` Taylor Blau
2023-10-09 21:06 ` [PATCH 20/20] chunk-format: drop pair_chunk_unsafe() Jeff King
2023-10-11 19:19 ` [PATCH 0/20] bounds-checks for chunk-based files Taylor Blau
2023-10-11 23:31 ` Jeff King
2023-10-13 19:25 ` [PATCH 0/8] chunk-format: introduce `pair_chunk_expect()` convenience API Taylor Blau
2023-10-13 19:25 ` [PATCH 1/8] chunk-format: introduce `pair_chunk_expect()` helper Taylor Blau
2023-10-13 19:25 ` [PATCH 2/8] commit-graph: read `OIDF` chunk with `pair_chunk_expect()` Taylor Blau
2023-10-13 19:25 ` [PATCH 3/8] commit-graph: read `CDAT` " Taylor Blau
2023-10-13 19:25 ` [PATCH 4/8] commit-graph: read `GDAT` " Taylor Blau
2023-10-13 19:25 ` [PATCH 5/8] commit-graph: read `BIDX` " Taylor Blau
2023-10-13 19:49 ` Taylor Blau
2023-10-14 16:10 ` Junio C Hamano
2023-10-20 10:31 ` Jeff King
2023-10-13 19:25 ` [PATCH 6/8] midx: read `OIDF` " Taylor Blau
2023-10-13 21:04 ` Junio C Hamano
2023-10-13 19:25 ` [PATCH 7/8] midx: read `OIDL` " Taylor Blau
2023-10-13 19:25 ` [PATCH 8/8] midx: read `OOFF` " Taylor Blau
2023-10-20 10:23 ` [PATCH 0/8] chunk-format: introduce `pair_chunk_expect()` convenience API Jeff King
2023-10-14 0:43 ` [PATCH 21/20] t5319: make corrupted large-offset test more robust Jeff King
2023-10-14 19:42 ` Junio C Hamano
2023-10-15 3:17 ` Jeff King
2023-10-15 17:04 ` Junio C Hamano
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