[PATCH 2/2] USB(u_serial.c): it has a NULL point

[hui yang]

From: YangHui <yanghui.def@xxxxxxxxx>

Unable to handle kernel NULL pointer dereference at virtual address 000002a0
Kernel BUG at tty_wakeup+0x18/0x8c
[<0000000095135e9d>] tty_wakeup+0x18/0x8c
[<00000000c35f19e4>] gs_start_io+0xc8/0x158
[<00000000b11b184e>] gserial_connect+0xd0/0x174
[<00000000642201de>] acm_set_alt+0x70/0x180
[<00000000a9d38e8b>] composite_setup+0x1848/0x1a7c
[<0000000072c88781>] android_setup+0x1ec/0x1f4
[<000000004c0127a5>] msm_udc_irq+0x8d0/0xc0c
[<00000000f8bb9acf>] __handle_irq_event_percpu+0x74/0x294
[<00000000afd57256>] handle_irq_event+0x60/0xc8
[<0000000076719b24>] handle_fasteoi_irq+0xc8/0x1c4
[<00000000421f3d87>] generic_handle_irq+0x34/0x4c
[<00000000b2f2d343>] __handle_domain_irq+0x6c/0xbc
[<00000000c74325e8>] gic_handle_irq+0x6c/0xe0
yes,we can see the port->port.tty==NULL, so system crashed

Signed-off-by: YangHui <yanghui.def@xxxxxxxxx>
---
 drivers/usb/gadget/function/u_serial.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 65f634e..a1c2ac2 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -562,6 +562,8 @@ static int gs_start_io(struct gs_port *port)
 
 	/* unblock any pending writes into our circular buffer */
 	if (started) {
+		if (port->port.tty == NULL)
+			return -EIO;
 		tty_wakeup(port->port.tty);
 	} else {
 		gs_free_requests(ep, head, &port->read_allocated);
-- 
2.7.4