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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Josh Steadmon <steadmon@google.com>
Cc: git@vger.kernel.org, gitster@pobox.com, stolee@gmail.com,
	peff@peff.net, szeder.dev@gmail.com
Subject: Re: [PATCH v6 2/3] commit-graph: fix buffer read-overflow
Date: Wed, 20 Feb 2019 15:55:58 +0100	[thread overview]
Message-ID: <87d0nm5x1d.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <d7b137650f9203148c1fb998a3dd4af7a2105e62.1547590928.git.steadmon@google.com>


On Tue, Jan 15 2019, Josh Steadmon wrote:

> fuzz-commit-graph identified a case where Git will read past the end of
> a buffer containing a commit graph if the graph's header has an
> incorrect chunk count. A simple bounds check in parse_commit_graph()
> prevents this.

This has a 2.21 regression where the test fails on NetBSD:
https://gitlab.com/git-vcs/git-ci/-/jobs/164224275

> Signed-off-by: Josh Steadmon <steadmon@google.com>
> ---
>  commit-graph.c          | 14 ++++++++++++--
>  t/t5318-commit-graph.sh | 16 +++++++++++++---
>  2 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/commit-graph.c b/commit-graph.c
> index 07dd410f3c..836d65a1d3 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -165,10 +165,20 @@ struct commit_graph *parse_commit_graph(void *graph_map, int fd,
>  	last_chunk_offset = 8;
>  	chunk_lookup = data + 8;
>  	for (i = 0; i < graph->num_chunks; i++) {
> -		uint32_t chunk_id = get_be32(chunk_lookup + 0);
> -		uint64_t chunk_offset = get_be64(chunk_lookup + 4);
> +		uint32_t chunk_id;
> +		uint64_t chunk_offset;
>  		int chunk_repeated = 0;
>
> +		if (data + graph_size - chunk_lookup <
> +		    GRAPH_CHUNKLOOKUP_WIDTH) {
> +			error(_("chunk lookup table entry missing; graph file may be incomplete"));
> +			free(graph);
> +			return NULL;
> +		}
> +
> +		chunk_id = get_be32(chunk_lookup + 0);
> +		chunk_offset = get_be64(chunk_lookup + 4);
> +
>  		chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;
>
>  		if (chunk_offset > graph_size - GIT_MAX_RAWSZ) {
> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> index 5fe21db99f..694f26079f 100755
> --- a/t/t5318-commit-graph.sh
> +++ b/t/t5318-commit-graph.sh
> @@ -366,9 +366,10 @@ GRAPH_OCTOPUS_DATA_OFFSET=$(($GRAPH_COMMIT_DATA_OFFSET + \
>  GRAPH_BYTE_OCTOPUS=$(($GRAPH_OCTOPUS_DATA_OFFSET + 4))
>  GRAPH_BYTE_FOOTER=$(($GRAPH_OCTOPUS_DATA_OFFSET + 4 * $NUM_OCTOPUS_EDGES))
>
> -# usage: corrupt_graph_and_verify <position> <data> <string>
> +# usage: corrupt_graph_and_verify <position> <data> <string> [<zero_pos>]
>  # Manipulates the commit-graph file at the position
> -# by inserting the data, then runs 'git commit-graph verify'
> +# by inserting the data, optionally zeroing the file
> +# starting at <zero_pos>, then runs 'git commit-graph verify'
>  # and places the output in the file 'err'. Test 'err' for
>  # the given string.
>  corrupt_graph_and_verify() {
> @@ -376,11 +377,15 @@ corrupt_graph_and_verify() {
>  	data="${2:-\0}"
>  	grepstr=$3
>  	cd "$TRASH_DIRECTORY/full" &&
> +	orig_size=$(wc -c < $objdir/info/commit-graph) &&
> +	zero_pos=${4:-${orig_size}} &&
>  	test_when_finished mv commit-graph-backup $objdir/info/commit-graph &&
>  	cp $objdir/info/commit-graph commit-graph-backup &&
>  	printf "$data" | dd of="$objdir/info/commit-graph" bs=1 seek="$pos" conv=notrunc &&
> +	dd of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=0 &&
> +	dd if=/dev/zero of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=$(($orig_size - $zero_pos)) &&

In the limited time I had to dig it starts failing at test 46, when
count=0 is given. dd on NetBSD exits with 127 when given count=0 it
seems.

>  	test_must_fail git commit-graph verify 2>test_err &&
> -	grep -v "^+" test_err >err
> +	grep -v "^+" test_err >err &&
>  	test_i18ngrep "$grepstr" err
>  }
>
> @@ -484,6 +489,11 @@ test_expect_success 'detect invalid checksum hash' '
>  		"incorrect checksum"
>  '
>
> +test_expect_success 'detect incorrect chunk count' '
> +	corrupt_graph_and_verify $GRAPH_BYTE_CHUNK_COUNT "\377" \
> +		"chunk lookup table entry missing" $GRAPH_CHUNK_LOOKUP_OFFSET
> +'
> +

Hacking around the above (e.g. "dd ... || :") makes all the failing
tests pass except this new one, which I didn't dig into.

  reply	other threads:[~2019-02-20 14:56 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-05 22:32 [PATCH 0/2] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-05 22:32 ` [PATCH 1/2] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-05 22:48   ` Ævar Arnfjörð Bjarmason
2018-12-06  1:00     ` Josh Steadmon
2018-12-06  1:32   ` Junio C Hamano
2018-12-06  1:41     ` Junio C Hamano
2018-12-06  4:47   ` Junio C Hamano
2018-12-05 22:32 ` [PATCH 2/2] commit-graph: fix buffer read-overflow Josh Steadmon
2018-12-06 13:11   ` Derrick Stolee
2018-12-06 20:20 ` [PATCH v2 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-06 20:20   ` [PATCH v2 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-06 20:20   ` [PATCH v2 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2018-12-07  9:07     ` Jeff King
2018-12-07 13:33     ` Derrick Stolee
2018-12-06 20:20   ` [PATCH v2 3/3] Makefile: correct example fuzz build Josh Steadmon
2018-12-07 22:27   ` [PATCH v3 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-07 22:27     ` [PATCH v3 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-07 22:27     ` [PATCH v3 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2018-12-09  4:01       ` Junio C Hamano
2018-12-10  4:28         ` SZEDER Gábor
2018-12-10 21:58           ` Josh Steadmon
2018-12-10 21:56         ` Josh Steadmon
2018-12-11  9:50           ` Jeff King
2018-12-07 22:27     ` [PATCH v3 3/3] Makefile: correct example fuzz build Josh Steadmon
2018-12-13 19:43 ` [PATCH v4 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-13 19:43   ` [PATCH v4 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-13 19:43   ` [PATCH v4 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2019-01-12 10:57     ` SZEDER Gábor
2019-01-15 19:58       ` Josh Steadmon
2018-12-13 19:43   ` [PATCH v4 3/3] Makefile: correct example fuzz build Josh Steadmon
2018-12-18 17:35   ` [PATCH v4 0/3] Add commit-graph fuzzer and fix buffer overflow Jeff King
2018-12-18 21:05     ` Josh Steadmon
2018-12-19 15:51       ` Jeff King
2018-12-20 19:35         ` Johannes Schindelin
2018-12-20 20:11           ` Jeff King
2018-12-26 22:29         ` Junio C Hamano
2019-01-15 19:59 ` [PATCH v5 " Josh Steadmon
2019-01-15 19:59   ` [PATCH v5 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2019-01-15 20:33     ` Junio C Hamano
2019-01-15 19:59   ` [PATCH v5 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2019-01-15 19:59   ` [PATCH v5 3/3] Makefile: correct example fuzz build Josh Steadmon
2019-01-15 20:39     ` Junio C Hamano
2019-01-15 21:59       ` Josh Steadmon
2019-01-15 22:34         ` Junio C Hamano
2019-01-15 22:25 ` [PATCH v6 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2019-01-15 22:25   ` [PATCH v6 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2019-01-15 22:25   ` [PATCH v6 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2019-02-20 14:55     ` Ævar Arnfjörð Bjarmason [this message]
2019-02-20 16:50       ` SZEDER Gábor
2019-01-15 22:25   ` [PATCH v6 3/3] Makefile: correct example fuzz build Josh Steadmon

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