[PATCH] usb: gadget: serial: Fixed KASAN null-ptr-deref in tty_wakeup

[Li Tao]

The port->port.tty maybe reset as NULL, If gs_close() was invoked
unexpectedly during running gserial_connect().

BUG: KASAN: null-ptr-deref in tty_wakeup+0x1c/0x84
Call trace:
[<0000000095c3c837>] dump_backtrace+0x0/0x6d4
[<0000000047726bb8>] show_stack+0x18/0x20
[<00000000bedb4c1e>] --dump_stack+0x20/0x28
[<00000000722f2e2a>] dump_stack+0x84/0xb0
[<00000000325683d4>] kasan_report_error+0x178/0x1e4
[<0000000053079998>] kasan_report_error+0x0/0x1e4
[<00000000b6d33afa>] --asan_load8+0x150/0x15c
[<00000000188745b8>] tty_wakeup+0x1c/0x84
[<0000000064f6dd21>] gs_start_io+0xd0/0x11c
[<0000000063d67b6c>] gserial_connect+0x15c/0x1b0
[<00000000faf7c0f9>] dm_set_alt+0xa8/0x190
[<000000008deb1909>] composite_setup+0xde4/0x1edc
[<00000000792ee16d>] android_setup+0x210/0x294
[<00000000ab32ef30>] dwc3_ep0_delegate_req+0x48/0x68
[<0000000054e26fd2>] dwc3_ep0_interrupt+0xf2c/0x16fc
[<0000000050cb2262>] dwc3_interrupt+0x464/0x1f44
[<00000000fdcaa6e9>] --handle_irq_event_percpu+0x184/0x398
[<000000003b24ff56>] handle_irq_event_percpu+0xa0/0x134
[<00000000aedda5ee>] handle_irq_event+0x60/0xa0
[<000000005f51a570>] handle_fasteoi_irq+0x23c/0x31c
[<000000008db2608d>] generic_handle_irq+0x70/0xa4
[<00000000098683fc>] --handle_domain_irq+0x84/0xe0
[<000000008ed23b46>] gic_handle_irq+0x98/0xb8

Signed-off-by: Li Tao <tao.li@xxxxxxxx>
---
 drivers/usb/gadget/function/u_serial.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 8167d379e115..3c109a8f9ec4 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -565,7 +565,8 @@ static int gs_start_io(struct gs_port *port)
 		gs_start_tx(port);
 		/* Unblock any pending writes into our circular buffer, in case
 		 * we didn't in gs_start_tx() */
-		tty_wakeup(port->port.tty);
+		if (port->port.tty)
+			tty_wakeup(port->port.tty);
 	} else {
 		gs_free_requests(ep, head, &port->read_allocated);
 		gs_free_requests(port->port_usb->in, &port->write_pool,
-- 
2.17.1