Re: [PATCH 04/12] builtin/for-each-repo: remove unnecessary argv copy to plug leak

>
> From: Andrzej Hunt <ajrhunt@google.com>
>
> cmd_for_each_repo() copies argv into args (a strvec), which is later
> passed into run_command_on_repo(), which in turn copies that strvec onto
> the end of child.args. The initial copy is unnecessary (we never modify
> args). We therefore choose to just pass argv directly into
> run_command_on_repo(), which lets us avoid the copy and fixes the leak.
>
> LSAN output from t0068:
>
> Direct leak of 192 byte(s) in 1 object(s) allocated from:
>     #0 0x7f63bd4ab8b0 in realloc (/usr/lib64/libasan.so.4+0xdc8b0)
>     #1 0x98d7e6 in xrealloc wrapper.c:126
>     #2 0x916914 in strvec_push_nodup strvec.c:19
>     #3 0x916a6e in strvec_push strvec.c:26
>     #4 0x4be4eb in cmd_for_each_repo builtin/for-each-repo.c:49
>     #5 0x410dcd in run_builtin git.c:475
>     #6 0x410dcd in handle_builtin git.c:729
>     #7 0x414087 in run_argv git.c:818
>     #8 0x414087 in cmd_main git.c:949
>     #9 0x40e9ec in main common-main.c:52
>     #10 0x7f63bc9fa349 in __libc_start_main (/lib64/libc.so.6+0x24349)
>
> Indirect leak of 22 byte(s) in 2 object(s) allocated from:
>     #0 0x7f63bd445e30 in __interceptor_strdup (/usr/lib64/libasan.so.4+0x76e30)
>     #1 0x98d698 in xstrdup wrapper.c:29
>     #2 0x916a63 in strvec_push strvec.c:26
>     #3 0x4be4eb in cmd_for_each_repo builtin/for-each-repo.c:49
>     #4 0x410dcd in run_builtin git.c:475
>     #5 0x410dcd in handle_builtin git.c:729
>     #6 0x414087 in run_argv git.c:818
>     #7 0x414087 in cmd_main git.c:949
>     #8 0x40e9ec in main common-main.c:52
>     #9 0x7f63bc9fa349 in __libc_start_main (/lib64/libc.so.6+0x24349)
>
> See also discussion about the original implementation below - this code
> appears to have evolved from a callback explaining the double-strvec-copy
> pattern, but there's no strong reason to keep that now:
>   https://lore.kernel.org/git/68bbeca5-314b-08ee-ef36-040e3f3814e9@gmail.com/

> Signed-off-by: Andrzej Hunt <andrzej@ahunt.org>
> ---
>  builtin/for-each-repo.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/builtin/for-each-repo.c b/builtin/for-each-repo.c
> index 52be64a437..fd86e5a861 100644
> --- a/builtin/for-each-repo.c
> +++ b/builtin/for-each-repo.c
> @@ -10,18 +10,16 @@ static const char * const for_each_repo_usage[] = {
>         NULL
>  };
>
> -static int run_command_on_repo(const char *path,
> -                              void *cbdata)
> +static int run_command_on_repo(const char *path, int argc, const char ** argv)
>  {
>         int i;
>         struct child_process child = CHILD_PROCESS_INIT;
> -       struct strvec *args = (struct strvec *)cbdata;
>
>         child.git_cmd = 1;
>         strvec_pushl(&child.args, "-C", path, NULL);
>
> -       for (i = 0; i < args->nr; i++)
> -               strvec_push(&child.args, args->v[i]);
> +       for (i = 0; i < argc; i++)
> +               strvec_push(&child.args, argv[i]);
>
>         return run_command(&child);
>  }
> @@ -29,37 +27,33 @@ static int run_command_on_repo(const char *path,
>  int cmd_for_each_repo(int argc, const char **argv, const char *prefix)
>  {
>         static const char *config_key = NULL;
>         int i, result = 0;
>         const struct string_list *values;
> -       struct strvec args = STRVEC_INIT;
>
>         const struct option options[] = {
>                 OPT_STRING(0, "config", &config_key, N_("config"),
>                            N_("config key storing a list of repository paths")),
>                 OPT_END()
>         };
>
>         argc = parse_options(argc, argv, prefix, options, for_each_repo_usage,
>                              PARSE_OPT_STOP_AT_NON_OPTION);
>
>         if (!config_key)
>                 die(_("missing --config=<config>"));
>
> -       for (i = 0; i < argc; i++)
> -               strvec_push(&args, argv[i]);
> -
>         values = repo_config_get_value_multi(the_repository,
>                                              config_key);
>
>         /*
>          * Do nothing on an empty list, which is equivalent to the case
>          * where the config variable does not exist at all.
>          */
>         if (!values)
>                 return 0;
>
>         for (i = 0; !result && i < values->nr; i++)
> -               result = run_command_on_repo(values->items[i].string, &args);
> +               result = run_command_on_repo(values->items[i].string, argc, argv);
>
>         return result;
>  }
> --
> 2.26.2