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    Subject[PATCH 66/76] ACPI: Fix use-after-free in acpi_map_lsapic
    From: Petr Vandrovec <>

    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 <>
    Signed-off-by: Alok N Kataria <>
    Reviewed-by: Toshi Kani <>
    Signed-off-by: Len Brown <>
    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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      Last update: 2012-03-30 14:21    [W:0.022 / U:18.312 seconds]
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