linux-kernel - Re: [PATCH] perf session: check for null pointer before derefernce

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Message-ID: <7c068167-e8bb-74f3-97d9-dd0c5858ee19@arm.com>
Date:   Mon, 24 Jan 2022 15:30:17 +0000
From:   James Clark <james.clark@....com>
To:     Ameer Hamza <amhamza.mgc@...il.com>,
        German Gomez <german.gomez@....com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        rickyman7@...il.com, alexey.v.bayduraev@...ux.intel.com,
        adrian.hunter@...el.com, leo.yan@...aro.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org
Subject: Re: [PATCH] perf session: check for null pointer before derefernce



On 24/01/2022 15:00, Ameer Hamza wrote:
> Move null pointer check before dereferncing the variable
> 
> Addresses-Coverity: 1497622 ("Derereference before null check")
> 
> Signed-off-by: Ameer Hamza <amhamza.mgc@...il.com>
> ---
>  tools/perf/util/session.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f19348dddd55..e1014ab62c10 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1503,11 +1503,11 @@ static int machines__deliver_event(struct machines *machines,
>  			++evlist->stats.nr_unknown_id;
>  			return 0;
>  		}
> -		dump_sample(evsel, event, sample, perf_env__arch(machine->env));
>  		if (machine == NULL) {
>  			++evlist->stats.nr_unprocessable_samples;
>  			return 0;
>  		}
> +		dump_sample(evsel, event, sample, perf_env__arch(machine->env));
>  		return evlist__deliver_sample(evlist, tool, event, sample, evsel, machine);
>  	case PERF_RECORD_MMAP:
>  		return tool->mmap(tool, event, sample, machine);
> 

Hi Ameer,

This mistake was made recently, but I don't think your change is the desired behavior.

It should be possible to dump stuff if machine is null. null or an empty string
should be passed to dump_sample(). It looks like some of the printfs still attempt to
show something in this case, although I didn't check them all.

James