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

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	John Garry <john.garry@huawei.com>,
	Jin Yao <yao.jin@linux.intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf parse-events: add defensive null check
Date: Wed, 25 Mar 2020 16:25:39 -0300	[thread overview]
Message-ID: <20200325192539.GH14102@kernel.org> (raw)
In-Reply-To: <20200325164022.41385-1-irogers@google.com>

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@seventh ~]# 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@seventh ~]#

Does this take place only when libfuzzer is being used?

- Arnaldo

> Signed-off-by: Ian Rogers <irogers@google.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