ACPI: Fix use-after-free in acpi_map_lsapic

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>
Reviewed-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index ce664f33ea8e..bbcc2c389ade 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)
         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(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