linux-kernel - Re: [PATCH 0/6] usbip fixes to crashes found by syzbot

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Message-ID: <465479ca-544e-3703-cf4e-30f5be04fa11@i-love.sakura.ne.jp>
Date:   Wed, 17 Mar 2021 15:21:09 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Shuah Khan <skhan@...uxfoundation.org>, shuah@...nel.org
Cc:     valentina.manea.m@...il.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 0/6] usbip fixes to crashes found by syzbot

Shuah, this driver is getting more and more cryptic and buggy.
Please explain the strategy for serialization before you write patches.

> - Fix attach_store() to check usbip_event_happened() before
>   waking up threads.

No, this helps nothing.

> diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
> index c4b4256e5dad3..f0a770adebd97 100644
> --- a/drivers/usb/usbip/vhci_sysfs.c
> +++ b/drivers/usb/usbip/vhci_sysfs.c
> @@ -418,6 +418,15 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
>  	spin_unlock_irqrestore(&vhci->lock, flags);
>  	/* end the lock */
>  
> +	if (usbip_event_happened(&vdev->ud)) {
> +		/*
> +		 * something went wrong - event handler shutting
> +		 * the connection and doing reset - bail out
> +		 */
> +		dev_err(dev, "Event happended - handler is active\n");
> +		return -EAGAIN;
> +	}
> +

detach_store() can queue shutdown event as soon as reaching "/* end the lock */" line
but attach_store() might be preempted immediately after verifying that
usbip_event_happened() was false (i.e. at this location) in order to wait for
shutdown event posted by detach_store() to be processed.

>  	wake_up_process(vdev->ud.tcp_rx);
>  	wake_up_process(vdev->ud.tcp_tx);
>