Re: [PATCH 4.4 58/83] x86/ioapic: Pass the correct data to unmask_ioapic_irq()

[Ben Hutchings]

On Tue, 2017-07-25 at 12:19 -0700, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Seunghun Han <kkamagui@xxxxxxxxx>
> 
> commit e708e35ba6d89ff785b225cd07dcccab04fa954a upstream.
> 
> One of the rarely executed code pathes in check_timer() calls
> unmask_ioapic_irq() passing irq_get_chip_data(0) as argument.
> 
> That's wrong as unmask_ioapic_irq() expects a pointer to the irq data of
> interrupt 0. irq_get_chip_data(0) returns NULL, so the following
> dereference in unmask_ioapic_irq() causes a kernel panic.
> 
> The issue went unnoticed in the first place because irq_get_chip_data()
> returns a void pointer so the compiler cannot do a type check on the
> argument. The code path was added for machines with broken configuration,
> but it seems that those machines are either not running current kernels or
> simply do not longer exist.
>
> Hand in irq_get_irq_data(0) as argument which provides the correct data.
[...]

This just pushes the null dereference down into io_apic_modify_irq().
Maybe unmask_ioapic_irq() shouldn't be used here at all?

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.