Re: [PATCH 0/3] fix parse-opt string_list leaks

[Duy Nguyen <pclouds@gmail.com>]

On Mon, Jun 13, 2016 at 12:32 PM, Jeff King <peff@peff.net> wrote:
> On Mon, Jun 13, 2016 at 07:08:55AM +0700, Duy Nguyen wrote:
>
>> > So if we are doing the conservative thing, then I think the resulting
>> > code should either look like:
>> >
>> >   if (!v->strdup_strings)
>> >         die("BUG: OPT_STRING_LIST should always use strdup_strings");
>> >   string_list_append(v, arg);
>>
>> I agree with the analysis. But this die() would hit all callers
>> (except interpret-trailers) because they all initialize with _NODUP
>> and setting strdup_strings may require auditing all access to the
>> string list in question, e.g. to change string_list_append(v,
>> xstrdup(xxx)) to string_list_append(xxx). it may cause side effects if
>> we are not careful.
>
> Yep. It is not really fixing anything, so much as alerting us to broken
> callers. We'd still have to fix the callers. :)
>
>> So far all callers are in builtin/, I think it will not take much time
>> to verify that they all call parse_options() with global argv, then we
>> can just lose extra xstrdup() and stick to string_list_append().
>> OPTION_STRING already assumes that argument strings are stable because
>> they are passed back as-is. Can we go with an easier route, adding a
>> comment on top of parse_options() stating that argv[] pointers may be
>> passed back as-is and it's up to the caller to xstrdup() appropriately
>> before argv[] memory is freed?
>
> Yeah, the two options I laid out were the "conservative" side, where we
> didn't make any assumptions about what is in passed into parse_options.
> But I agree in practice that it's not likely to be a problem to just
> point to the existing strings, and the fact that OPTION_STRING does so
> already makes me even more confident.
>
> So I'd suggest these patches:
>
>   [1/3]: parse_opt_string_list: stop allocating new strings
>   [2/3]: interpret-trailers: don't duplicate option strings
>   [3/3]: blame,shortlog: don't make local option variables static

As usual, it's hard to find things to complain in your patches.

> The first one is what we've been discussing, and the others are just
> follow-on cleanups.  I stopped short of a fourth patch to convert more
> cases of:
>
>   static struct string_list foo;
>
> to:
>
>   static struct string_list foo = STRING_LIST_INIT_NODUP;
>
> The two are equivalent (mostly due to historical reasons). I tend to
> think explicit is better than implicit for something like this (not
> because BSS auto-initialization isn't OK, but because there is an
> explicit choice of dup/nodup that the writer made, and it is good to
> communicate that). But maybe people don't want the extra noise.

I'm on the explicit side. Unless you work a lot with string lists, I
don't think you can remember whether "all zero" initialization is dup
or no dup.
-- 
Duy