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

[Jeff King <peff@peff.net>]

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

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.

-Peff