Subject: Re: [PATCH] rev-parse --parseopt: detect missing opt-spec

From: SZEDER Gábor <[email-masked]>
Date: Fri, 2 Sep 2022 23:00:25 +0200

On Fri, Sep 02, 2022 at 07:59:02PM +0200, Øystein Walle wrote:
> After 2d893dff4c (rev-parse --parseopt: allow [*=?!] in argument hints,
> 2015-07-14)

Oh, no, that's not the first bad commit!  The segfault started
earlier, with commit 9bab5b6061 (rev-parse --parseopt: option argument
name hints, 2014-03-22).

Before that it printed the following for the spec input used in the
new test:

  $ ./git rev-parse --parseopt -- <spec
  set -- --

I'm not sure what the desired behavior should have been back then.

Anyway, since 2d893dff4c the documentation is clear that 'opt-spec'
"May not contain any of the `<flags>` characters", so now erroring out
is the right thing to do.

> updated the parser, a line in parseopts's input can start
> with one of the flag characters and be erroneously parsed as a opt-spec
> where the short name of the option is the flag character itself and the
> long name is after the end of the string. This makes Git want to
> allocate SIZE_MAX bytes of memory at this line:
> 
>     o->long_name = xmemdupz(sb.buf + 2, s - sb.buf - 2);
> 
> Since s and sb.buf are equal the second argument is -2 (except unsigned)
> and xmemdupz allocates len + 1 bytes, ie. -1 meaning SIZE_MAX.
> 
> Avoid this by checking whether a flag character was found in the zeroth
> position.
> 
> Reported-by: Ingy dot Net <[email-masked]>
> Reviewed-by: SZEDER Gábor <[email-masked]>
> Signed-off-by: Øystein Walle <[email-masked]>
> ---
> 
> Hi guys, thanks for the review. I incorporated a reference to the old
> commit into the message (and took the liberty of adding --parseopt to
> the subject like it had). I tried to verify that it was in fact this
> commit, since the code prior to this one had the exact same xmemdupz()
> call. I wasn't able to build that commit,

Yeah, that's why I didn't check it in the morning...

NO_OPENSSL=1 NO_PERL_MAKEMAKER=1 sometimes helps building older
versions on modern setups, and, FWIW, Ubuntu 16.04 can build both
today's Git and v1.6.0 (my goto version when I want to check
historical behavior) even with OPENSSL.

>  builtin/rev-parse.c           | 3 +++
>  t/t1502-rev-parse-parseopt.sh | 7 +++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
> index b259d8990a..85c271acd7 100644
> --- a/builtin/rev-parse.c
> +++ b/builtin/rev-parse.c
> @@ -479,6 +479,9 @@ static int cmd_parseopt(int argc, const char **argv, const char *prefix)
>  		if (!s)
>  			s = help;
>  
> +		if (s == sb.buf)
> +			die(_("missing opt-spec before option flags"));
> +
>  		if (s - sb.buf == 1) /* short option only */
>  			o->short_name = *sb.buf;
>  		else if (sb.buf[1] != ',') /* long option only */
> diff --git a/t/t1502-rev-parse-parseopt.sh b/t/t1502-rev-parse-parseopt.sh
> index 284fe18e72..de1d48f3ba 100755
> --- a/t/t1502-rev-parse-parseopt.sh
> +++ b/t/t1502-rev-parse-parseopt.sh
> @@ -306,6 +306,13 @@ test_expect_success 'test --parseopt help output: "wrapped" options normal "or:"
>  	test_cmp expect actual
>  '
>  
> +test_expect_success 'test --parseopt invalid opt-spec' '
> +	test_write_lines x -- "=, x" >spec &&
> +	echo "fatal: missing opt-spec before option flags" >expect &&
> +	test_must_fail git rev-parse --parseopt -- >out <spec 2>err &&
> +	test_cmp expect err
> +'
> +
>  test_expect_success 'test --parseopt help output: multi-line blurb after empty line' '
>  	sed -e "s/^|//" >spec <<-\EOF &&
>  	|cmd [--some-option]
> -- 
> 2.34.1
>