linux-kernel - Re: [PATCH 3.3.0-rc3] Fix use-after-free in acpi_map

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Date:	Thu, 08 Mar 2012 15:34:20 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Alok Kataria <akataria@...are.com>
Cc:	Petr Vandrovec <petr@...are.com>,
	the arch/x86 maintainers <x86@...nel.org>, lenb@...nel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	dcovelli@...are.com
Subject: Re: [PATCH 3.3.0-rc3] Fix use-after-free in acpi_map_lsapic

Hi Alok,

On Thu, 2012-03-08 at 13:33 -0800, Alok Kataria wrote:
> Hi Toshi, 
> 

> > 
> > The change looks good. I suggest you also add the following line to
> > prevent such bug in future.
> > 
> >         kfree(buffer.pointer);
> >         buffer.length = ACPI_ALLOCATE_BUFFER;
> >         buffer.pointer = NULL;
> > +       lapic = NULL;
> 
> That's a good suggestion, below is the updated patch. Thanks !!

Looks good. Thanks for the update.
-Toshi


> --
> 
> From: Petr Vandrovec <petr@...are.com>
> 
> When processor is being hot-added to the system, acpi_map_lsapic invokes
> ACPI _MAT method to find APIC ID and flags, verifies that returned structure
> is indeed ACPI's local APIC structure, and that flags contain MADT_ENABLED
> bit.  Then saves APIC ID, frees structure - and accesses structure when
> computing arguments for acpi_register_lapic call.  Which sometime leads
> to acpi_register_lapic call being made with second argument zero, failing
> to bring processor online with error 'Unable to map lapic to logical cpu
> number'.
> 
> As lapic->lapic_flags & ACPI_MADT_ENABLED was already confirmed to be non-zero
> few lines above, we can just pass unconditional ACPI_MADT_ENABLED to the
> acpi_register_lapic.
> 
> Signed-off-by: Petr Vandrovec <petr@...are.com>
> Signed-off-by: Alok N Kataria <akataria@...are.com>
> Cc : Toshi Kani <toshi.kani@...com>
> 
> 
> Index: linux-2.6/arch/x86/kernel/acpi/boot.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/acpi/boot.c	2012-01-24 14:48:56.000000000 -0800
> +++ linux-2.6/arch/x86/kernel/acpi/boot.c	2012-03-08 13:25:39.000000000 -0800
> @@ -642,6 +642,7 @@ static int __cpuinit _acpi_map_lsapic(ac
>  	kfree(buffer.pointer);
>  	buffer.length = ACPI_ALLOCATE_BUFFER;
>  	buffer.pointer = NULL;
> +	lapic = NULL;
>  
>  	if (!alloc_cpumask_var(&tmp_map, GFP_KERNEL))
>  		goto out;
> @@ -650,7 +651,7 @@ static int __cpuinit _acpi_map_lsapic(ac
>  		goto free_tmp_map;
>  
>  	cpumask_copy(tmp_map, cpu_present_mask);
> -	acpi_register_lapic(physid, lapic->lapic_flags & ACPI_MADT_ENABLED);
> +	acpi_register_lapic(physid, ACPI_MADT_ENABLED);
>  
>  	/*
>  	 * If mp_register_lapic successfully generates a new logical cpu
> 
> 
> 
> 


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