Re: [PATCH 1/3] t/t5318: introduce failing 'git commit-graph write' tests

> When invoking 'git commit-graph' in a corrupt repository, one can cause
> a segfault when ancestral commits are corrupt in one way or another.
> This is due to two function calls in the 'commit-graph.c' code that may
> return NULL, but are not checked for NULL-ness before dereferencing.
> 
> Before fixing the bug, introduce two failing tests that demonstrate the
> problem. The first test corrupts an ancestral commit's parent to point
> to a non-existent object. The second test instead corrupts an ancestral
> tree by removing the 'tree' information entirely from the commit. Both
> of these cases cause segfaults, each at different lines.

> 
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
>  t/t5318-commit-graph.sh | 43 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> index ab3eccf0fa..c855f81930 100755
> --- a/t/t5318-commit-graph.sh
> +++ b/t/t5318-commit-graph.sh
> @@ -585,4 +585,47 @@ test_expect_success 'get_commit_tree_in_graph works for non-the_repository' '
>  	test_cmp expect actual
>  '
>  
> +test_expect_failure 'corrupt commit-graph write (broken parent)' '
> +	rm -rf repo &&
> +	git init repo &&
> +	(
> +		cd repo &&
> +		empty="$(git mktree </dev/null)" &&
> +		cat >broken <<-EOF &&
> +		tree $empty
> +		parent 0000000000000000000000000000000000000000
> +		author whatever <whatever@example.com> 1234 -0000
> +		committer whatever <whatever@example.com> 1234 -0000
> +
> +		broken commit
> +		EOF
> +		broken="$(git hash-object -w -t commit --literally broken)" &&
> +		git commit-tree -p "$broken" -m "good commit" "$empty" >good &&
> +		test_must_fail git commit-graph write --stdin-commits \
> +			<good 2>test_err &&
> +		test_i18ngrep "unable to parse commit" test_err
> +	)
> +'
> +
> +test_expect_failure 'corrupt commit-graph write (missing tree)' '
> +	rm -rf repo &&
> +	git init repo &&
> +	(
> +		cd repo &&
> +		tree="$(git mktree </dev/null)" &&
> +		cat >broken <<-EOF &&
> +		parent 0000000000000000000000000000000000000000
> +		author whatever <whatever@example.com> 1234 -0000
> +		committer whatever <whatever@example.com> 1234 -0000
> +
> +		broken commit
> +		EOF
> +		broken="$(git hash-object -w -t commit --literally broken)" &&
> +		git commit-tree -p "$broken" -m "good" "$tree" >good &&
> +		test_must_fail git commit-graph write --stdin-commits \
> +			<good 2>test_err &&
> +		test_i18ngrep "unable to get tree for" test_err
> +	)
> +'
> +
>  test_done
>