linux-kernel - Re: [PATCH] perf parse-events: add defensive null check

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Date:   Wed, 25 Mar 2020 16:25:39 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf parse-events: add defensive null check

Em Wed, Mar 25, 2020 at 09:40:22AM -0700, Ian Rogers escreveu:
> Terms may have a null config in which case a strcmp will segv. This can
> be reproduced with:
>   perf stat -e '*/event=?,nr/' sleep 1
> Add a null check to avoid this. This was caught by LLVM's libfuzzer.

Adding the NULL check doesn't hurt, I guess, but I coudln't repro it:

  [root@...enth ~]# perf stat -e '*/event=?,nr/' sleep 1
  WARNING: multiple event parsing errors
  event syntax error: '*/event=?,nr/'
                      \___ 'nr' is not usable in 'perf stat'
  
  Initial error:
  event syntax error: '*/event=?,nr/'
                       \___ Cannot find PMU `*'. Missing kernel support?
  Run 'perf list' for a list of valid events
  
   Usage: perf stat [<options>] [<command>]
  
      -e, --event <event>   event selector. use 'perf list' to list available events
  [root@...enth ~]#

Does this take place only when libfuzzer is being used?

- Arnaldo
 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/pmu.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index 616fbda7c3fc..ef6a63f3d386 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -984,12 +984,11 @@ static int pmu_resolve_param_term(struct parse_events_term *term,
>  	struct parse_events_term *t;
>  
>  	list_for_each_entry(t, head_terms, list) {
> -		if (t->type_val == PARSE_EVENTS__TERM_TYPE_NUM) {
> -			if (!strcmp(t->config, term->config)) {
> -				t->used = true;
> -				*value = t->val.num;
> -				return 0;
> -			}
> +		if (t->type_val == PARSE_EVENTS__TERM_TYPE_NUM &&
> +		    t->config && !strcmp(t->config, term->config)) {
> +			t->used = true;
> +			*value = t->val.num;
> +			return 0;
>  		}
>  	}
>  
> -- 
> 2.25.1.696.g5e7596f4ac-goog
> 

-- 

- Arnaldo