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    SubjectRe: [PATCH] x86: check for valid irq_cfg pointer in smp_irq_move_cleanup_interrupt
    On Wed, May 23, 2012 at 12:24:46PM -0700, Suresh Siddha wrote:
    > On Wed, 2012-05-23 at 14:04 -0500, Dimitri Sivanich wrote:
    > > On Wed, May 23, 2012 at 01:16:36PM -0500, Dimitri Sivanich wrote:
    > > > In create_irq_nr() there is a window where we have set vector_irq in
    > > > __assign_irq_vector(), but not yet called irq_set_chip_data() to set the
    > > > irq_cfg pointer.
    >
    > Ha. Now I understand how it can happen during boot/module load time.
    > Thanks.
    >
    > > BTW - is there a reason why we're calling irq_set_chip_data() in create_irq_nr()
    > > rather than in __assign_irq_vector() for the case where irq_cfg is NULL?
    >
    > assign_irq_vector() is also for setting up vectors during irq migration.
    > So may be we could have done the irq_set_chip_data() in create_irq_nr()
    > itself before calling assign_irq_vector(). Anyways, this change can't
    > help in case of destroy irq path which can also lead to the same issue
    > of de-referencing null pointer.
    >
    > Also, it will be nice if you can refer to this destroy irq path in your
    > changelog.
    >
    > Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>

    OK. Hopefully this covers it.



    A NULL pointer dereference can occur in smp_irq_move_cleanup_interrupt() if
    we haven't yet setup the irq_cfg pointer in the irq_desc.irq_data.chip_data.

    In create_irq_nr() there is a window where we have set vector_irq in
    __assign_irq_vector(), but not yet called irq_set_chip_data() to set the
    irq_cfg pointer.

    Should an IRQ_MOVE_CLEANUP_VECTOR hit the cpu in question during this time,
    smp_irq_move_cleanup_interrupt() will attempt to process the aforementioned
    irq, but panic when accessing irq_cfg.

    There is also a window in destroy_irq() where we've cleared the irq_cfg
    pointer in free_irq_cfg(), but have not yet called irq_free_desc(). Note
    that we have cleared vector_irq in __clear_irq_vector() prior to free_irq_cfg(),
    but smp_irq_move_cleanup_interrupt() might've already referenced the irq_desc.

    Only continue processing the irq if irq_cfg is non-NULL.

    Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
    ---
    arch/x86/kernel/apic/io_apic.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    Index: linux/arch/x86/kernel/apic/io_apic.c
    ===================================================================
    --- linux.orig/arch/x86/kernel/apic/io_apic.c
    +++ linux/arch/x86/kernel/apic/io_apic.c
    @@ -2478,9 +2478,12 @@ asmlinkage void smp_irq_move_cleanup_int
    if (!desc)
    continue;

    - cfg = irq_cfg(irq);
    raw_spin_lock(&desc->lock);

    + cfg = irq_cfg(irq);
    + if (!cfg)
    + goto unlock;
    +
    /*
    * Check if the irq migration is in progress. If so, we
    * haven't received the cleanup request yet for this irq.

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      Last update: 2012-05-23 22:42    [W:0.030 / U:91.124 seconds]
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