linux-kernel - Re: [PATCH 1/1] perf probe: Use zfree() to avoid possibly accessing dangling pointers

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Date: Wed, 8 May 2024 23:43:15 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>, Jiri Olsa <jolsa@...nel.org>, 
	Kan Liang <kan.liang@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/1] perf probe: Use zfree() to avoid possibly accessing
 dangling pointers

On Tue, May 7, 2024 at 7:58 AM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>
> When freeing a->b it is good practice to set a->b to NULL using
> zfree(&a->b) so that when we have a bug where a reference to a freed 'a'
> pointer is kept somewhere, we can more quickly cause a segfault if some
> code tries to use a->b.
>
> Convert one such case in the 'perf probe' codebase.
>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/builtin-probe.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index 019fef8da6a8e60f..003a3bcebfdfc2d1 100644
> --- a/tools/perf/builtin-probe.c
> +++ b/tools/perf/builtin-probe.c
> @@ -325,7 +325,7 @@ static void cleanup_params(void)
>         for (i = 0; i < params->nevents; i++)
>                 clear_perf_probe_event(params->events + i);
>         line_range__clear(&params->line_range);
> -       free(params->target);
> +       zfree(&params->target);
>         strfilter__delete(params->filter);
>         nsinfo__put(params->nsi);
>         zfree(&params);

The change is fine but params is freed here, so the potential to read
"->target" is small.

Reviewed-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> --
> 2.44.0
>