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SubjectRe: [PATCH 3.3.0-rc3] Fix use-after-free in acpi_map_lsapic
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Hi Toshi, 

On Thu, 2012-03-08 at 14:01 -0700, Toshi Kani wrote:
> On Wed, 2012-03-07 at 11:48 -0800, Alok Kataria wrote:
> > Len, anyone else,
> >
> > Any comments on this one ? This fixes a important bug during cpu hotadd
> > where the kernel fails to recognize all the newly added cpus.
> >
> > Thanks,
> > Alok
> >
> >
> > On Wed, 2012-02-15 at 16:06 -0800, Petr Vandrovec wrote:
> > > From: Petr Vandrovec <petr@vmware.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.
> > >
> > > Thanks, Petr
> > >
> > > Signed-off-by: Petr Vandrovec <petr@vmware.com>
> > > Signed-off-by: Alok Kataria <akataria@vmware.com>
> > >
> > >
> > > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> > > index ce664f3..a4a0901 100644
> > > --- a/arch/x86/kernel/acpi/boot.c
> > > +++ b/arch/x86/kernel/acpi/boot.c
> > > @@ -650,7 +650,7 @@ static int __cpuinit _acpi_map_lsapic(acpi_handle handle, int *pcpu)
> > > 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);
>
> 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 !!
--

From: Petr Vandrovec <petr@vmware.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@vmware.com>
Signed-off-by: Alok N Kataria <akataria@vmware.com>
Cc : Toshi Kani <toshi.kani@hp.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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