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Commit e144ed28 authored by Johan Hovold's avatar Johan Hovold Committed by Greg Kroah-Hartman
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USB: cdc-acm: fix write and resume race 



Fix race between write() and resume() due to improper locking that could
lead to writes being reordered.

Resume must be done atomically and susp_count be protected by the
write_lock in order to prevent racing with write(). This could otherwise
lead to writes being reordered if write() grabs the write_lock after
susp_count is decremented, but before the delayed urb is submitted.

Fixes: 11ea859d ("USB: additional power savings for cdc-acm devices
that support remote wakeup")

Cc: <stable@vger.kernel.org>	# v2.6.27
Signed-off-by: default avatarJohan Hovold <jhovold@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5a345c20

drivers/usb/class/cdc-acm.c

+9 −14
Original line number Diff line number Diff line
@@ -1541,27 +1541,20 @@ static int acm_resume(struct usb_interface *intf) 
	struct acm *acm = usb_get_intfdata(intf);

	struct acm_wb *wb;

	int rv = 0;

	int cnt;



	spin_lock_irq(&acm->read_lock);

	acm->susp_count -= 1;

	cnt = acm->susp_count;

	spin_unlock_irq(&acm->read_lock);

	spin_lock(&acm->write_lock);



	if (cnt)

		return 0;

	if (--acm->susp_count)

		goto out;



	if (test_bit(ASYNCB_INITIALIZED, &acm->port.flags)) {

		rv = usb_submit_urb(acm->ctrlurb, GFP_NOIO);

		rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);



		spin_lock_irq(&acm->write_lock);

		if (acm->delayed_wb) {

			wb = acm->delayed_wb;

			acm->delayed_wb = NULL;

			spin_unlock_irq(&acm->write_lock);

			acm_start_wb(acm, wb);

		} else {

			spin_unlock_irq(&acm->write_lock);

		}



		/*
@@ -1569,12 +1562,14 @@ static int acm_resume(struct usb_interface *intf) 
		 * do the write path at all cost

		 */

		if (rv < 0)

			goto err_out;

			goto out;



		rv = acm_submit_read_urbs(acm, GFP_NOIO);

		rv = acm_submit_read_urbs(acm, GFP_ATOMIC);

	}

out:

	spin_unlock(&acm->write_lock);

	spin_unlock_irq(&acm->read_lock);



err_out:

	return rv;

}