linux-kernel - Re: [PATCH v3 3/3] uio: fix crash after the device is unregistered

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Date:   Fri, 6 Jul 2018 13:23:44 -0500
From:   Mike Christie <mchristi@...hat.com>
To:     xiubli@...hat.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org
Cc:     hamish.martin@...iedtelesis.co.nz, jannh@...gle.com,
        pkalever@...hat.com, pkarampu@...hat.com, atumball@...hat.com,
        sabose@...hat.com
Subject: Re: [PATCH v3 3/3] uio: fix crash after the device is unregistered

On 07/05/2018 09:57 PM, xiubli@...hat.com wrote:
>  static irqreturn_t uio_interrupt(int irq, void *dev_id)
>  {
>  	struct uio_device *idev = (struct uio_device *)dev_id;
> -	irqreturn_t ret = idev->info->handler(irq, idev->info);
> +	irqreturn_t ret;
> +
> +	mutex_lock(&idev->info_lock);
> +	if (!idev->info) {
> +		ret = IRQ_NONE;
> +		goto out;
> +	}
>  
> +	ret = idev->info->handler(irq, idev->info);
>  	if (ret == IRQ_HANDLED)
>  		uio_event_notify(idev->info);
>  
> +out:
> +	mutex_unlock(&idev->info_lock);
>  	return ret;
>  }


Do you need the interrupt related changes in this patch and the first
one? When we do uio_unregister_device -> free_irq does free_irq return
when there are no longer running interrupt handlers that we requested?

If that is not the case then I think we can hit a similar bug. We do:

__uio_register_device -> device_register -> device's refcount goes to
zero so we do -> uio_device_release -> kfree(idev)

and if it is possible the interrupt handler could still run after
free_irq then we would end up doing:

uio_interrupt -> mutex_lock(&idev->info_lock) -> idev access freed memory.