[PATCH] usb: gadget: u_serial: Add null pointer check in gserial_suspend

[Prashanth K <quic_prashk@quicinc.com>]

Consider a case where gserial_disconnect has already cleared
gser->ioport. And if gserial_suspend gets called afterwards,
it will lead to accessing of gser->ioport and thus causing
null pointer dereference.

Avoid this by adding a null pointer check. Added a static
spinlock to prevent gser->ioport from becoming null after
the newly added null pointer check.

Fixes: aba3a8d01d62 ("usb: gadget: u_serial: add suspend resume callbacks")
Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
---
 drivers/usb/gadget/function/u_serial.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index a0ca47f..e5d522d 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -1420,10 +1420,19 @@ EXPORT_SYMBOL_GPL(gserial_disconnect);
 
 void gserial_suspend(struct gserial *gser)
 {
-	struct gs_port	*port = gser->ioport;
+	struct gs_port	*port;
 	unsigned long	flags;
 
-	spin_lock_irqsave(&port->port_lock, flags);
+	spin_lock_irqsave(&serial_port_lock, flags);
+	port = gser->ioport;
+
+	if (!port) {
+		spin_unlock_irqrestore(&serial_port_lock, flags);
+		return;
+	}
+
+	spin_lock(&port->port_lock);
+	spin_unlock(&serial_port_lock);
 	port->suspended = true;
 	spin_unlock_irqrestore(&port->port_lock, flags);
 }
-- 
2.7.4