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

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Message-ID: <8983b963-2139-ecb3-3a31-b5e225db389c@arm.com>
Date:   Tue, 25 Jan 2022 09:35:49 +0000
From:   James Clark <james.clark@....com>
To:     Ameer Hamza <amhamza.mgc@...il.com>
Cc:     German Gomez <german.gomez@....com>, 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 20:29, Ameer Hamza wrote:
> On Mon, Jan 24, 2022 at 03:30:17PM +0000, James Clark wrote:
>>
>>
>> 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.
> 
> Hi James,
> 
> Thank you for your response. I understand your point.
> 
> Do you think following changes would be ok?

Yep looks good. With that change:

Reviewed-by: James Clark <james.clark@....com>

> 
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f19348dddd55..210eeee3dd70 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1503,11 +1503,12 @@ 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;
> +                       dump_sample(evsel, event, sample, perf_env__arch(NULL));
>                         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);
> 
> Thanks,
> Hamza
>