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

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Date:   Thu, 24 Jun 2021 15:03:50 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     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>,
        "Antonov, Alexander" <alexander.antonov@...ux.intel.com>
Subject: Re: [PATCH] x86: eas should not be NULL when it is referenced


Hi Shengxian,

Thanks for the patch.

On 6/24/2021 3:04 AM, 13145886936@....com wrote:
> From: gushengxian <gushengxian@...ong.com>
> 
> "eas" should not be NULL when it is referenced.
> 

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.

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;
-- 
2.7.4
Thanks,
Kan