linux-kernel - Re: [PATCH 1/1] perf script: Fix allocation of evsel->priv related to per-event dump files

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Date:   Tue, 6 Jun 2023 16:14:51 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] perf script: Fix allocation of evsel->priv related to
 per-event dump files

On Tue, Jun 6, 2023 at 12:15 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> I'm carrying this in my perf-tools-next, please ack :-)
>
> - Arnaldo
>
> ---
>
> When printing output we may want to generate per event files, where the
> --per-event-dump option should be used, creating perf.data.EVENT.dump
> files instead of printing to stdout.
>
> The callback thar processes event thus expects that evsel->priv->fp
> should point to either the per-event FILE descriptor or to stdout.
>
> The a3af66f51bd0bca7 ("perf script: Fix crash because of missing
> evsel->priv") changeset fixed a case where evsel->priv wasn't setup,
> thus set to NULL, causing a segfault when trying to access
> evsel->priv->fp.
>
> But it did it for the non --per-event-dump case by allocating a 'struct
> perf_evsel_script' just to set its ->fp to stdout.
>
> Since evsel->priv is only freed when --per-event-dump is used, we ended
> up with a memory leek, detected using ASAN.

nit: s/leek/leak/

>
> Fix it by using the same method as perf_script__setup_per_event_dump(),
> and reuse that static 'struct perf_evsel_script'.
>
> Also check if evsel_script__new() failed.
>
> Fixes: a3af66f51bd0bca7 ("perf script: Fix crash because of missing evsel->priv")
> Reported-by: Ian Rogers <irogers@...gle.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

Tested on top of my asan work:
Tested-by: Ian Rogers <irogers@...gle.com>

> ---
>  tools/perf/builtin-script.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 70549fc93b125394..b02ad386a55baf07 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -2410,6 +2410,9 @@ static int process_sample_event(struct perf_tool *tool,
>         return ret;
>  }
>
> +// Used when scr->per_event_dump is not set
> +static struct evsel_script es_stdout;
> +
>  static int process_attr(struct perf_tool *tool, union perf_event *event,
>                         struct evlist **pevlist)
>  {
> @@ -2418,7 +2421,6 @@ static int process_attr(struct perf_tool *tool, union perf_event *event,
>         struct evsel *evsel, *pos;
>         u64 sample_type;
>         int err;
> -       static struct evsel_script *es;
>
>         err = perf_event__process_attr(tool, event, pevlist);
>         if (err)
> @@ -2428,14 +2430,13 @@ static int process_attr(struct perf_tool *tool, union perf_event *event,
>         evsel = evlist__last(*pevlist);
>
>         if (!evsel->priv) {
> -               if (scr->per_event_dump) {
> +               if (scr->per_event_dump) {

nit: whitespace issue.

>                         evsel->priv = evsel_script__new(evsel, scr->session->data);
> -               } else {
> -                       es = zalloc(sizeof(*es));
> -                       if (!es)
> +                       if (!evsel->priv)
>                                 return -ENOMEM;
> -                       es->fp = stdout;
> -                       evsel->priv = es;
> +               } else { // Replicate what is done in perf_script__setup_per_event_dump()
> +                       es_stdout.fp = stdout;
> +                       evsel->priv = &es_stdout;
>                 }
>         }
>
> @@ -2741,7 +2742,6 @@ static int perf_script__fopen_per_event_dump(struct perf_script *script)
>  static int perf_script__setup_per_event_dump(struct perf_script *script)
>  {
>         struct evsel *evsel;
> -       static struct evsel_script es_stdout;
>
>         if (script->per_event_dump)
>                 return perf_script__fopen_per_event_dump(script);
> --
> 2.37.1
>