Re: [PATCH] x86: check for valid irq_cfg pointer in smp_irq_move_cleanup_interrupt

[Dimitri Sivanich <sivanich@sgi.com>]

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.