linux-kernel - Re: [PATCH] perf jevents: Fix segfault in perf_pmu__find_events

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Date:   Mon, 18 Sep 2023 16:55:08 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf jevents: Fix segfault in perf_pmu__find_events_table

Hello,

On Sun, Sep 17, 2023 at 8:05 PM Yang Jihong <yangjihong1@...wei.com> wrote:
>
> Before caching the JSON events table, perf_pmu__find_events_table() need
> to check whether table is empty.
>
> For example, AuthenticAMD-15-6B-1 is used. The matching events table cannot
> be found. As a result, a null pointer is accessed when caching JSON events
> table, causing segfault.
>
> Before:
>   # perf record -vv true
>   DEBUGINFOD_URLS=
>   Using CPUID AuthenticAMD-15-6B-1
>   Segmentation fault (core dumped)
>
> After:
>   # perf record -vv true
>   DEBUGINFOD_URLS=
>   Using CPUID AuthenticAMD-15-6B-1
>   <SNIP>
>   [ perf record: Woken up 1 times to write data ]
>   [ perf record: Captured and wrote 0.005 MB perf.data ]
>
> Fixes: 7c52f10c0d4d ("perf pmu: Cache JSON events table")
> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>

Thanks for the fix but please see

https://lore.kernel.org/all/20230913125157.2790375-1-tmricht@linux.ibm.com/

Thanks,
Namhyung


> ---
>  tools/perf/pmu-events/jevents.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
> index a7e88332276d..72ba4a9239c6 100755
> --- a/tools/perf/pmu-events/jevents.py
> +++ b/tools/perf/pmu-events/jevents.py
> @@ -991,7 +991,7 @@ const struct pmu_events_table *perf_pmu__find_events_table(struct perf_pmu *pmu)
>                  }
>          }
>          free(cpuid);
> -        if (!pmu)
> +        if (!pmu || !table)
>                  return table;
>
>          for (i = 0; i < table->num_pmus; i++) {
> --
> 2.34.1
>