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

From: Alexander Antonov
Date: Fri Jun 25 2021 - 10:26:28 EST



On 6/25/2021 5:11 PM, Liang, Kan wrote:


On 6/25/2021 9:33 AM, Alexander Antonov wrote:
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@xxxxxxxxxxxxxxx>
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?



I don't think it causes any severe problem for now, e.g., crash, because current code checks die before the dereference.
But I think it violates the Linux kernel coding style (one err bug) and may bring potential issues.

https://www.kernel.org/doc/html/v4.10/process/coding-style.html

Thanks,
Kan

OK,
Thank you for the explanation.

- Alexander

Thanks,
Alexander

Reported-by: gushengxian <gushengxian@xxxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
  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;