4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Warren <swar...@nvidia.com>

commit daa35bd95634a2a2d72d1049c93576a02711cb1a upstream.

When the gadget serial device has no associated TTY, do not pass any
received data into the TTY layer for processing; simply drop it instead.
This prevents the TTY layer from calling back into the gadget serial
driver, which will then crash in e.g. gs_write_room() due to lack of
gadget serial device to TTY association (i.e. a NULL pointer dereference).

Signed-off-by: Stephen Warren <swar...@nvidia.com>
Signed-off-by: Felipe Balbi <felipe.ba...@linux.intel.com>
Signed-off-by: Krzysztof Kozlowski <k...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/usb/gadget/function/u_serial.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -518,7 +518,7 @@ static void gs_rx_push(unsigned long _po
                }
 
                /* push data to (open) tty */
-               if (req->actual) {
+               if (req->actual && tty) {
                        char            *packet = req->buf;
                        unsigned        size = req->actual;
                        unsigned        n;


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