[PATCH 66/76] ACPI: Fix use-after-free in acpi_map_lsapic

From: Len Brown
Date: Fri Mar 30 2012 - 08:18:46 EST

From: Petr Vandrovec <petr@xxxxxxxxxx>

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

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

Signed-off-by: Petr Vandrovec <petr@xxxxxxxxxx>
Signed-off-by: Alok N Kataria <akataria@xxxxxxxxxx>
Reviewed-by: Toshi Kani <toshi.kani@xxxxxx>
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
arch/x86/kernel/acpi/boot.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index ce664f3..bbcc2c3 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -642,6 +642,7 @@ static int __cpuinit _acpi_map_lsapic(acpi_handle handle, int *pcpu)
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(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);

* If mp_register_lapic successfully generates a new logical cpu

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