Re: [PATCH] mailinfo -b: fix an out of bounds access

[Junio C Hamano <gitster@pobox.com>]

"Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com> writes:

> We have tests that trigger this bug that were added in ae52d57f0b
> (t5100: add some more mailinfo tests, 2017-05-31). The commit message
> mentions that they are marked test_expect_failure as they trigger an
> assertion in strbuf_splice(). While it is reassuring that
> strbuf_splice() detects the problem and dies in retrospect that should
> perhaps have warranted a little more investigation.

Indeed.

> diff --git a/mailinfo.c b/mailinfo.c
> index 9621ba62a39..833d28612f7 100644
> --- a/mailinfo.c
> +++ b/mailinfo.c
> @@ -317,7 +317,7 @@ static void cleanup_subject(struct mailinfo *mi, struct strbuf *subject)
>  			pos = strchr(subject->buf + at, ']');
>  			if (!pos)
>  				break;
> -			remove = pos - subject->buf + at + 1;
> +			remove = pos - (subject->buf + at) + 1;

How embarrassing.  

It really is (&pos[1] - &subject->buf[at]), subtracting from the
address of one past the closing ']' and the address of opening '[',
so the rewrite is correct.

Thanks.

> diff --git a/t/t5100-mailinfo.sh b/t/t5100-mailinfo.sh
> index cebad1048cf..db11cababd3 100755
> --- a/t/t5100-mailinfo.sh
> +++ b/t/t5100-mailinfo.sh
> @@ -201,13 +201,13 @@ test_expect_success 'mailinfo -b double [PATCH]' '
>  	test z"$subj" = z"Subject: message"
>  '
>  
> -test_expect_failure 'mailinfo -b trailing [PATCH]' '
> +test_expect_success 'mailinfo -b trailing [PATCH]' '
>  	subj="$(echo "Subject: [other] [PATCH] message" |
>  		git mailinfo -b /dev/null /dev/null)" &&
>  	test z"$subj" = z"Subject: [other] message"
>  '
>  
> -test_expect_failure 'mailinfo -b separated double [PATCH]' '
> +test_expect_success 'mailinfo -b separated double [PATCH]' '
>  	subj="$(echo "Subject: [PATCH] [other] [PATCH] message" |
>  		git mailinfo -b /dev/null /dev/null)" &&
>  	test z"$subj" = z"Subject: [other] message"
>
> base-commit: dda7228a83e2e9ff584bf6adbf55910565b41e14