From: René Scharfe <l.s.r@web.de>
Date: Sat, 25 Feb 2017 21:21:45 GMT
Subject: Re: [PATCH 2/2] apply: handle assertion failure gracefully
Message-ID: <a5626d97-e644-65b5-2fd3-41ce870f85a6@web.de>
In-Reply-To: <20170225101307.24067-2-vegard.nossum@oracle.com>

Am 25.02.2017 um 11:13 schrieb Vegard Nossum:
> For the patches in the added testcases, we were crashing with:
>
>     git-apply: apply.c:3665: check_preimage: Assertion `patch->is_new <= 0' failed.
>
> As it turns out, check_preimage() is prepared to handle these conditions,
> so we can remove the assertion.
>
> Found using AFL.
>
> Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
>
> ---
>
> (I'm fully aware of how it looks to just delete an assertion to "fix" a
> bug without any other changes to accomodate the condition that was
> being tested for. I am definitely not an expert on this code, but as far
> as I can tell -- both by reviewing and testing the code -- the function
> really is prepared to handle the case where patch->is_new == 1, as it
> will always hit another error condition if that is true. I've tried to
> add more test cases to show what errors you can expect to see instead of
> the assertion failure when trying to apply these nonsensical patches. If
> you don't want to remove the assertion for whatever reason, please feel
> free to take the testcases and add "# TODO: known breakage" or whatever.)
> ---
>  apply.c                     |  1 -
>  t/t4154-apply-git-header.sh | 36 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/apply.c b/apply.c
> index cbf7cc7f2..9219d2737 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -3652,7 +3652,6 @@ static int check_preimage(struct apply_state *state,
>  	if (!old_name)
>  		return 0;
>
> -	assert(patch->is_new <= 0);

5c47f4c6 (builtin-apply: accept patch to an empty file) added that line. 
  Its intent was to handle diffs that contain an old name even for a 
file that's created.  Citing from its commit message: "When we cannot be 
sure by parsing the patch that it is not a creation patch, we shouldn't 
complain when if there is no such a file."  Why not stop complaining 
also in case we happen to know for sure that it's a creation patch? 
I.e., why not replace the assert() with:

	if (patch->is_new == 1)
		goto is_new;

>  	previous = previous_patch(state, patch, &status);
>
>  	if (status)
> diff --git a/t/t4154-apply-git-header.sh b/t/t4154-apply-git-header.sh
> index d651af4a2..c440c48ad 100755
> --- a/t/t4154-apply-git-header.sh
> +++ b/t/t4154-apply-git-header.sh
> @@ -12,4 +12,40 @@ rename new 0
>  EOF
>  '
>
> +test_expect_success 'apply deleted file mode / new file mode / wrong mode' '
> +	test_must_fail git apply << EOF
> +diff --git a/. b/.
> +deleted file mode
> +new file mode
> +EOF
> +'
> +
> +test_expect_success 'apply deleted file mode / new file mode / wrong type' '
> +	mkdir x &&
> +	chmod 755 x &&
> +	test_must_fail git apply << EOF
> +diff --git a/x b/x
> +deleted file mode 160755
> +new file mode
> +EOF
> +'
> +
> +test_expect_success 'apply deleted file mode / new file mode / already exists' '
> +	touch 1 &&
> +	chmod 644 1 &&
> +	test_must_fail git apply << EOF
> +diff --git a/1 b/1
> +deleted file mode 100644
> +new file mode
> +EOF
> +'
> +
> +test_expect_success 'apply new file mode / copy from / nonexistant file' '
> +	test_must_fail git apply << EOF
> +diff --git a/. b/.
> +new file mode
> +copy from
> +EOF
> +'
> +
>  test_done
>