linux-kernel - Re: [PATCH v2] lib subcmd: Avoid segv/use-after-free when commands aren't excluded

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Date:   Tue, 11 Jul 2023 10:36:59 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Chenyuan Mi <cymi20@...an.edu.cn>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] lib subcmd: Avoid segv/use-after-free when commands
 aren't excluded

On Fri, Jul 7, 2023 at 4:09 PM Ian Rogers <irogers@...gle.com> wrote:
>
> The array shortening may perform unnecessary array copies. Before
> commit 657a3efee43a ("lib subcmd: Avoid memory leak in exclude_cmds")
> this was benign, but afterwards this could lead to a segv.
>
> Fixes: 657a3efee43a ("lib subcmd: Avoid memory leak in exclude_cmds")
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
>  tools/lib/subcmd/help.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c
> index 67a8d6b740ea..adfbae27dc36 100644
> --- a/tools/lib/subcmd/help.c
> +++ b/tools/lib/subcmd/help.c
> @@ -68,8 +68,13 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
>         while (ci < cmds->cnt && ei < excludes->cnt) {
>                 cmp = strcmp(cmds->names[ci]->name, excludes->names[ei]->name);
>                 if (cmp < 0) {
> -                       zfree(&cmds->names[cj]);
> -                       cmds->names[cj++] = cmds->names[ci++];
> +                       if (ci == cj) {
> +                               ci++;
> +                               cj++;
> +                       } else {
> +                               zfree(&cmds->names[cj]);
> +                               cmds->names[cj++] = cmds->names[ci++];
> +                       }
>                 } else if (cmp == 0) {
>                         ci++;
>                         ei++;
> @@ -77,10 +82,11 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
>                         ei++;
>                 }
>         }
> -
> -       while (ci < cmds->cnt) {
> -               zfree(&cmds->names[cj]);
> -               cmds->names[cj++] = cmds->names[ci++];
> +       if (ci != cj) {
> +               while (ci < cmds->cnt) {
> +                       zfree(&cmds->names[cj]);
> +                       cmds->names[cj++] = cmds->names[ci++];
> +               }
>         }
>         for (ci = cj; ci < cmds->cnt; ci++)
>                 zfree(&cmds->names[ci]);
> --
> 2.41.0.390.g38632f3daf-goog
>