linux-kernel - Re: [PATCH 1/2] perf parse-events: Fix segfault when event parser gets an error

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Message-ID: <CAP-5=fUaDsuYxQRkqWFThX3Su2me-caXxdQqJd0WH-dx-yRaug@mail.gmail.com>
Date:   Mon, 18 Jul 2022 18:10:24 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf parse-events: Fix segfault when event parser
 gets an error

On Tue, Jul 12, 2022 at 4:28 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> parse_events() is often called with parse_events_error set to NULL.
> Make parse_events_error__handle() not segfault in that case.
>
> Fixes: 43eb05d06679 ("perf tests: Support 'Track with sched_switch' test for hybrid")
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/util/parse-events.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 7ed235740431..700c95eafd62 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -2391,9 +2391,12 @@ void parse_events_error__exit(struct parse_events_error *err)
>  void parse_events_error__handle(struct parse_events_error *err, int idx,
>                                 char *str, char *help)
>  {
> -       if (WARN(!str, "WARNING: failed to provide error string\n")) {
> -               free(help);
> -               return;
> +       if (WARN(!str, "WARNING: failed to provide error string\n"))
> +               goto out_free;
> +       if (!err) {
> +               /* Assume caller does not want message printed */
> +               pr_debug("event syntax error: %s\n", str);
> +               goto out_free;


It feels like a simpler invariant (as done elsewhere) to have the
caller always pass err and then in the caller to call
parse_events_error__exit. Any reason for behavior change?

Thanks,
Ian

>         }
>         switch (err->num_errors) {
>         case 0:
> @@ -2419,6 +2422,11 @@ void parse_events_error__handle(struct parse_events_error *err, int idx,
>                 break;
>         }
>         err->num_errors++;
> +       return;
> +
> +out_free:
> +       free(str);
> +       free(help);
>  }
>
>  #define MAX_WIDTH 1000
> --
> 2.25.1
>