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

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Message-ID: <2a83c1f1-9203-eb97-5595-7a8da7261128@metafoo.de>
Date:   Mon, 30 Oct 2017 10:48:23 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Johan Hovold <johan@...nel.org>, Mark Brown <broonie@...nel.org>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] spi: spi-axi: take extra controller reference before
 deregistration

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@...afoo.de>
> Signed-off-by: Johan Hovold <johan@...nel.org>

Acked-by: Lars-Peter Clausen <lars@...afoo.de>

Thanks.