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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: 8dd5cd5395 ("usb: cdc-wdm: avoid hanging on zero length reads")
Cc: <stable@vger.kernel.org> # 3.13
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Bjørn Mork 2014-01-12 21:48:53 +01:00 committed by Greg Kroah-Hartman
parent 52a6966c35
commit f563926fed
1 changed files with 1 additions and 1 deletions
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2
drivers/usb/class/cdc-wdm.c
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@ -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);