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References: <20220923173142.805896-1-namhyung@kernel.org> <20220923173142.805896-2-namhyung@kernel.org>
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From:   Ian Rogers <irogers@google.com>
Date:   Fri, 23 Sep 2022 16:20:33 -0700
Message-ID: <CAP-5=fUhCL1GFeS-YVYG=cQ-q891BHCkkpcEKbY3+u8ukPZbcg@mail.gmail.com>
Subject: Re: [PATCH 1/4] perf record: Fix a segfault in record__read_lost_samples()
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        linux-perf-users@vger.kernel.org,
        Stephane Eranian <eranian@google.com>
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On Fri, Sep 23, 2022 at 10:32 AM Namhyung Kim <namhyung@kernel.org> wrote:
>
> When it fails to open events record__open() returns without setting the
> session->evlist.  Then it gets a segfault in the function trying to read
> lost sample counts.  You can easily reproduce it as a normal user like:
>
>   $ perf record -p 1 true
>   ...
>   perf: Segmentation fault
>   ...
>
> Skip the function if it has no evlist.  And add more protection for evsels
> which are not properly initialized.
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Acked-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  tools/perf/builtin-record.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 741e763436ca..f4f1619199e5 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1888,6 +1888,10 @@ static void record__read_lost_samples(struct record *rec)
>         struct perf_record_lost_samples *lost;
>         struct evsel *evsel;
>
> +       /* there was an error during record__open */
> +       if (session->evlist == NULL)
> +               return;
> +
>         lost = zalloc(PERF_SAMPLE_MAX_SIZE);
>         if (lost == NULL) {
>                 pr_debug("Memory allocation failed\n");
> @@ -1899,6 +1903,8 @@ static void record__read_lost_samples(struct record *rec)
>         evlist__for_each_entry(session->evlist, evsel) {
>                 struct xyarray *xy = evsel->core.sample_id;
>
> +               if (xy == NULL || evsel->core.fd == NULL)
> +                       continue;
>                 if (xyarray__max_x(evsel->core.fd) != xyarray__max_x(xy) ||
>                     xyarray__max_y(evsel->core.fd) != xyarray__max_y(xy)) {
>                         pr_debug("Unmatched FD vs. sample ID: skip reading LOST count\n");
> --
> 2.37.3.998.g577e59143f-goog
>