USB: cdc-wdm: fix race between write and disconnect due to flag abuse (1426bd2c) · Commits · 戴 / test

In case of a disconnect an ongoing flush() has to be made fail. Nevertheless we cannot be sure that any pending URB has already finished, so although they will never succeed, they still must not be touched. The clean solution for this is to check for WDM_IN_USE and WDM_DISCONNECTED in flush(). There is no point in ever clearing WDM_IN_USE, as no further writes make sense. The issue is as old as the driver. Fixes: ("USB: CDC WDM driver") Reported-by:

<syzbot+d232cca6ec42c2edb3fc@syzkaller.appspotmail.com> Signed-off-by:

Oliver Neukum <oneukum@suse.com> Cc: stable <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20190827103436.21143-1-oneukum@suse.com Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-wdm.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -587,10 +587,20 @@ static int wdm_flush(struct file *file, fl_owner_t id)
		{
		struct wdm_device *desc = file->private_data;

		wait_event(desc->wait, !test_bit(WDM_IN_USE, &desc->flags));
		wait_event(desc->wait,
		/*
		* needs both flags. We cannot do with one
		* because resetting it would cause a race
		* with write() yet we need to signal
		* a disconnect
		*/
		!test_bit(WDM_IN_USE, &desc->flags) \|\|
		test_bit(WDM_DISCONNECTING, &desc->flags));

		/* cannot dereference desc->intf if WDM_DISCONNECTING */
		if (desc->werr < 0 && !test_bit(WDM_DISCONNECTING, &desc->flags))
		if (test_bit(WDM_DISCONNECTING, &desc->flags))
		return -ENODEV;
		if (desc->werr < 0)
		dev_err(&desc->intf->dev, "Error in flush path: %d\n",
		desc->werr);

		@@ -974,8 +984,6 @@ static void wdm_disconnect(struct usb_interface *intf)
		spin_lock_irqsave(&desc->iuspin, flags);
		set_bit(WDM_DISCONNECTING, &desc->flags);
		set_bit(WDM_READ, &desc->flags);
		/* to terminate pending flushes */
		clear_bit(WDM_IN_USE, &desc->flags);
		spin_unlock_irqrestore(&desc->iuspin, flags);
		wake_up_all(&desc->wait);
		mutex_lock(&desc->rlock);

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