linux-kernel - Re: [PATCH] x86: eas should not be NULL when it is referenced

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Date:   Fri, 25 Jun 2021 16:33:31 +0300
From:   Alexander Antonov <alexander.antonov@...ux.intel.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>, 13145886936@....com,
        tglx@...utronix.de, bp@...en8.de, x86@...nel.org
Cc:     linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        gushengxian <gushengxian@...ong.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86: eas should not be NULL when it is referenced

Hello Kan,
> On 6/24/2021 3:03 PM, Liang, Kan wrote:
>> I think the NULL pointer dereference of eas should not happen, 
>> because die is -1 if eas is NULL. But the whole error handling path 
>> looks fragile.
>>
>> We already fixed one issue caused by it in commit ID f797f05d917f 
>> ("perf/x86/intel/uncore: Fix for iio mapping on Skylake Server")
>> https://lore.kernel.org/lkml/160149233331.7002.10919231011379055356.tip-bot2@tip-bot2/ 
>>
>>
>> Maybe something as below?
>>
>>  From 3de81ba3b04262ef3346297d82f6c4ffb4af7029 Mon Sep 17 00:00:00 2001
>> From: Kan Liang <kan.liang@...ux.intel.com>
>> Date: Thu, 24 Jun 2021 11:17:57 -0700
>> Subject: [PATCH] perf/x86/intel/uncore: Clean up error handling path 
>> of iio mapping
>>
>> The error handling path of iio mapping looks fragile. We already fixed
>> one issue caused by it, commit ID f797f05d917f ("perf/x86/intel/uncore:
>> Fix for iio mapping on Skylake Server"). Clean up the error handling
>> path and make the code robust.
I didn't catch why does the current error handling path look fragile?
Are there cases when it works incorrect?

Thanks,
Alexander
>>
>> Reported-by: gushengxian <gushengxian@...ong.com>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>>   arch/x86/events/intel/uncore_snbep.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/events/intel/uncore_snbep.c 
>> b/arch/x86/events/intel/uncore_snbep.c
>> index 7622762..6d4a5a9 100644
>> --- a/arch/x86/events/intel/uncore_snbep.c
>> +++ b/arch/x86/events/intel/uncore_snbep.c
>> @@ -3802,11 +3802,11 @@ pmu_iio_set_mapping(struct intel_uncore_type 
>> *type, struct attribute_group *ag)
>>       /* One more for NULL. */
>>       attrs = kcalloc((uncore_max_dies() + 1), sizeof(*attrs), 
>> GFP_KERNEL);
>>       if (!attrs)
>> -        goto err;
>> +        goto clear_topology;
>>
>>       eas = kcalloc(uncore_max_dies(), sizeof(*eas), GFP_KERNEL);
>>       if (!eas)
>> -        goto err;
>> +        goto clear_attrs;
>>
>>       for (die = 0; die < uncore_max_dies(); die++) {
>>           sprintf(buf, "die%ld", die);
>> @@ -3827,7 +3827,9 @@ pmu_iio_set_mapping(struct intel_uncore_type 
>> *type, struct attribute_group *ag)
>>       for (; die >= 0; die--)
>>           kfree(eas[die].attr.attr.name);
>>       kfree(eas);
>> +clear_attrs:
>>       kfree(attrs);
>> +clear_topology:
>>       kfree(type->topology);
>>   clear_attr_update:
>>       type->attr_update = NULL;