Subject: Re: [PATCH v4 2/3] commit-graph: fix buffer read-overflow

From: SZEDER Gábor <[email-masked]>
Date: Sat, 12 Jan 2019 11:57:57 +0100

On Thu, Dec 13, 2018 at 11:43:57AM -0800, Josh Steadmon wrote:
> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> index 5fe21db99f..a1b5a75882 100755
> --- a/t/t5318-commit-graph.sh
> +++ b/t/t5318-commit-graph.sh
> @@ -366,21 +366,26 @@ 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() {
>  	pos=$1
>  	data="${2:-\0}"
>  	grepstr=$3
> +	orig_size=$(wc -c < $objdir/info/commit-graph) &&

A minor nit: this test script is unusually prudent about which
directory/repository each test is executed in, as the first thing each
test does is to 'cd' into the right directory.  (I think this is a
Good Thing, and other test scripts should follow suit if they use a
repo other than $TRASH_DIRECTORY.)  Though it doesn't cause any
immediate issues (the previous test happens to use the same
repository), the above line violates this, as it accesses the
'.git/.../commit-graph' file ...

> +	zero_pos=${4:-${orig_size}} &&
>  	cd "$TRASH_DIRECTORY/full" &&

... before this line could ensure that it's in the right repository.

>  	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 - $zero_pos)) &&
>  	test_must_fail git commit-graph verify 2>test_err &&
> -	grep -v "^+" test_err >err
> +	grep -v "^+" test_err >err &&
>  	test_i18ngrep "$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" $GRAPH_CHUNK_LOOKUP_OFFSET
> +'
> +
>  test_expect_success 'git fsck (checks commit-graph)' '
>  	cd "$TRASH_DIRECTORY/full" &&
>  	git fsck &&
> -- 
> 2.20.0.rc2.10.g21101b961a
>