linux-kernel - Re: [PATCH] perf/x86/uncore: avoid null-ptr-deref on error in pmu_alloc

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Date: Mon, 5 Feb 2024 10:08:27 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Fedor Pchelkin <pchelkin@...ras.ru>, Peter Zijlstra
 <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, x86@...nel.org,
 Alexander Antonov <alexander.antonov@...ux.intel.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 lvc-project@...uxtesting.org
Subject: Re: [PATCH] perf/x86/uncore: avoid null-ptr-deref on error in
 pmu_alloc_topology



On 2024-02-04 8:48 a.m., Fedor Pchelkin wrote:
> If topology[die] array allocation fails then topology[die][idx] elements
> can't be accessed on error path.
> 
> Checking this on the error path probably looks more readable than
> decrementing the counter in the allocation loop.
> 
> Found by Linux Verification Center (linuxtesting.org).
> 
> Fixes: 4d13be8ab5d4 ("perf/x86/intel/uncore: Generalize IIO topology support")
> Signed-off-by: Fedor Pchelkin <pchelkin@...ras.ru>
> ---

It seems the code just jumps to the wrong kfree on the error path.
Does the below patch work?

diff --git a/arch/x86/events/intel/uncore_snbep.c
b/arch/x86/events/intel/uncore_snbep.c
index 8250f0f59c2b..5481fd00d861 100644
--- a/arch/x86/events/intel/uncore_snbep.c
+++ b/arch/x86/events/intel/uncore_snbep.c
@@ -3808,7 +3808,7 @@ static int pmu_alloc_topology(struct
intel_uncore_type *type, int topology_type)
 	for (die = 0; die < uncore_max_dies(); die++) {
 		topology[die] = kcalloc(type->num_boxes, sizeof(**topology), GFP_KERNEL);
 		if (!topology[die])
-			goto clear;
+			goto free_topology;
 		for (idx = 0; idx < type->num_boxes; idx++) {
 			topology[die][idx].untyped = kcalloc(type->num_boxes,
 							     topology_size[topology_type],
@@ -3827,6 +3827,7 @@ static int pmu_alloc_topology(struct
intel_uncore_type *type, int topology_type)
 			kfree(topology[die][idx].untyped);
 		kfree(topology[die]);
 	}
+free_topology:
 	kfree(topology);
 err:
 	return -ENOMEM;

Thanks,
Kan

>  arch/x86/events/intel/uncore_snbep.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
> index a96496bef678..7d4deb9126be 100644
> --- a/arch/x86/events/intel/uncore_snbep.c
> +++ b/arch/x86/events/intel/uncore_snbep.c
> @@ -3831,9 +3831,11 @@ static int pmu_alloc_topology(struct intel_uncore_type *type, int topology_type)
>  	return 0;
>  clear:
>  	for (; die >= 0; die--) {
> -		for (idx = 0; idx < type->num_boxes; idx++)
> -			kfree(topology[die][idx].untyped);
> -		kfree(topology[die]);
> +		if (topology[die]) {
> +			for (idx = 0; idx < type->num_boxes; idx++)
> +				kfree(topology[die][idx].untyped);
> +			kfree(topology[die]);
> +		}
>  	}
>  	kfree(topology);
>  err: