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Commit f563926f authored by Bjørn Mork's avatar Bjørn Mork Committed by Greg Kroah-Hartman
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usb: cdc-wdm: resp_count can be 0 even if WDM_READ is set 



Do not decrement resp_count if it's already 0.

We set resp_count to 0 when the device is closed.  The next open and
read will try to clear the WDM_READ flag if there was leftover data
in the read buffer. This fix is necessary to prevent resubmitting
the read URB in a tight loop because resp_count becomes negative.

The bug can easily be triggered from userspace by not reading all
data in the read buffer, and then closing and reopening the chardev.

Fixes: 8dd5cd53 ("usb: cdc-wdm: avoid hanging on zero length reads")
Cc: <stable@vger.kernel.org> # 3.13
Signed-off-by: default avatarBjørn Mork <bjorn@mork.no>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 52a6966c

drivers/usb/class/cdc-wdm.c

+1 −1
Original line number Diff line number Diff line
@@ -445,7 +445,7 @@ static int clear_wdm_read_flag(struct wdm_device *desc) 
	clear_bit(WDM_READ, &desc->flags);



	/* submit read urb only if the device is waiting for it */

	if (!--desc->resp_count)

	if (!desc->resp_count || !--desc->resp_count)

		goto out;



	set_bit(WDM_RESPONDING, &desc->flags);