Re: [PATCH 1/2] perf intel-pt: Fix segfault in intel_pt_print_info() with uClibc

[Namhyung Kim]

Hi Adrian,

On Wed, Oct 12, 2022 at 1:23 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> uClibc segfaulted because NULL was passed as the format to fprintf().

Sounds like glibc has a NULL check in fprintf().

>
> That happened because one of the format strings was missing and
> intel_pt_print_info() didn't check that before calling fprintf().
>
> Add the missing format string, and check format is not NULL before calling
> fprintf().
>
> Fixes: 11fa7cb86b56 ("perf tools: Pass Intel PT information for decoding MTC and CYC")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> ---
>  tools/perf/util/intel-pt.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
> index b34cb3dec1aa..e3548ddef254 100644
> --- a/tools/perf/util/intel-pt.c
> +++ b/tools/perf/util/intel-pt.c
> @@ -4046,6 +4046,7 @@ static const char * const intel_pt_info_fmts[] = {
>         [INTEL_PT_SNAPSHOT_MODE]        = "  Snapshot mode       %"PRId64"\n",
>         [INTEL_PT_PER_CPU_MMAPS]        = "  Per-cpu maps        %"PRId64"\n",
>         [INTEL_PT_MTC_BIT]              = "  MTC bit             %#"PRIx64"\n",
> +       [INTEL_PT_MTC_FREQ_BITS]        = "  MTC freq bits       %#"PRIx64"\n",
>         [INTEL_PT_TSC_CTC_N]            = "  TSC:CTC numerator   %"PRIu64"\n",
>         [INTEL_PT_TSC_CTC_D]            = "  TSC:CTC denominator %"PRIu64"\n",
>         [INTEL_PT_CYC_BIT]              = "  CYC bit             %#"PRIx64"\n",
> @@ -4060,8 +4061,12 @@ static void intel_pt_print_info(__u64 *arr, int start, int finish)
>         if (!dump_trace)
>                 return;
>
> -       for (i = start; i <= finish; i++)
> -               fprintf(stdout, intel_pt_info_fmts[i], arr[i]);
> +       for (i = start; i <= finish; i++) {
> +               const char *fmt = intel_pt_info_fmts[i];
> +
> +               if (fmt)
> +                       fprintf(stdout, fmt, arr[i]);
> +       }
>  }
>
>  static void intel_pt_print_info_str(const char *name, const char *str)
> --
> 2.25.1
>