Subject: Re: Crash when using git blame on untracked file

From: Junio C Hamano <[email-masked]>
Date: Mon, 29 Aug 2016 11:27:13 -0700

Thomas Gummerer <[email-masked]> writes:

> Subject: [PATCH] blame: fix segfault on untracked files
>
> Since 3b75ee9 ("blame: allow to blame paths freshly added to the index",
> 2016-07-16) git blame also looks at the index to determine if there is a
> file that was freshly added to the index.
>
> cache_name_pos returns -pos - 1 in case there is no match is found, or
> if the name matches, but the entry has a stage other than 0.  As git
> blame should work for unmerged files, it uses strcmp to determine
> whether the name of the returned position matches, in which case the
> file exists, but is merely unmerged, or if the file actually doesn't
> exist in the index.
>
> If the repository is empty, or if the file would lexicographically be
> sorted as the last file in the repository, -cache_name_pos - 1 is
> outside of the length of the active_cache array, causing git blame to
> segfault.  Guard against that, and die() normally to restore the old
> behaviour.
>
> Reported-by: Simon Ruderich <[email-masked]>
> Signed-off-by: Thomas Gummerer <[email-masked]>
> ---

This is a recent regression and unfortunately is also in 2.9.3; the
patch looks obviously correct.

>  builtin/blame.c  | 3 ++-
>  t/t8002-blame.sh | 7 +++++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/builtin/blame.c b/builtin/blame.c
> index 7ec7823..a5bbf91 100644
> --- a/builtin/blame.c
> +++ b/builtin/blame.c
> @@ -2244,7 +2244,8 @@ static void verify_working_tree_path(struct commit *work_tree, const char *path)
>  	pos = cache_name_pos(path, strlen(path));
>  	if (pos >= 0)
>  		; /* path is in the index */
> -	else if (!strcmp(active_cache[-1 - pos]->name, path))
> +	else if (-1 - pos < active_nr &&
> +		 !strcmp(active_cache[-1 - pos]->name, path))
>  		; /* path is in the index, unmerged */
>  	else
>  		die("no such path '%s' in HEAD", path);
> diff --git a/t/t8002-blame.sh b/t/t8002-blame.sh
> index ff09ace..7983bb7 100755
> --- a/t/t8002-blame.sh
> +++ b/t/t8002-blame.sh
> @@ -6,6 +6,13 @@ test_description='git blame'
>  PROG='git blame -c'
>  . "$TEST_DIRECTORY"/annotate-tests.sh
>  
> +test_expect_success 'blame untracked file in empty repo' '
> +	touch untracked &&
> +	test_must_fail git blame untracked 2>actual.err &&
> +	echo "fatal: no such path '\''untracked'\'' in HEAD" >expected.err &&
> +	test_cmp expected.err actual.err
> +'

The point of this fix is not that we show the exact error message,
but we fail in a controlled manner.  I think

        test_expect_success 'blame untracked file in empty repo' '
                >untracked &&
                test_must_fail git blame untracked
        '

is sufficient.

Thanks.

>  PROG='git blame -c -e'
>  test_expect_success 'blame --show-email' '
>  	check_count \