Re: [PATCH 3/3] spi: spi-axi: take extra controller reference before deregistration

[Lars-Peter Clausen]

On 10/29/2017 12:56 PM, Johan Hovold wrote:
> Take an extra reference to the controller to avoid use-after-free in
> free_irq() which is called only after the controller has been
> deregistered and freed.
> 
> Note that this is not an issue for this particular driver which does not
> use shared interrupts, but free_irq() could otherwise end up accessing
> the freed controller when CONFIG_DEBUG_SHIRQ is set.

Strictly speaking there is no guarantee that the IRQ handler does not run
until free_irq() has been called. And since the SPI master is referenced in
the IRQ handler there could be an use-after-free condition. So there is kind
of a real issue here as well. But it should be really really hard to trigger
it unless the hardware misbehaves.

> 
> Defer controller release until free_irq() returns to prevent this
> from ever becoming an issue should this code be replicated in other
> drivers.
> 
> Cc: Lars-Peter Clausen <lars@xxxxxxxxxx>
> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>

Acked-by: Lars-Peter Clausen <lars@xxxxxxxxxx>

Thanks.