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Date: Mon, 5 Feb 2024 18:18:56 +0300
From: Fedor Pchelkin <pchelkin@ispras.ru>
To: "Liang, Kan" <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Arnaldo Carvalho de Melo <acme@kernel.org>, x86@kernel.org, 
	Alexander Antonov <alexander.antonov@linux.intel.com>, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
	lvc-project@linuxtesting.org
Subject: Re: Re: [PATCH] perf/x86/uncore: avoid null-ptr-deref on error in
 pmu_alloc_topology
Message-ID: <2b5c4fbc-67c8-42f6-84a0-2adb4fbb0a2a-pchelkin@ispras.ru>
References: <20240204134841.80003-1-pchelkin@ispras.ru>
 <a5e8e3fe-a8c2-45e7-9139-84967cba06eb@linux.intel.com>
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In-Reply-To: <a5e8e3fe-a8c2-45e7-9139-84967cba06eb@linux.intel.com>

Hello,

On 24/02/05 10:08AM, Liang, Kan wrote:
> 
> 
> 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@ispras.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
> 

In this way the already allocated topology[die] elements won't be freed.

--
Fedor