[PATCH v2] usb: Fix null-ptr-deref in qt2_process_read_urb()

[Qasim Ijaz <qasdev00@gmail.com>]

This patch addresses a null-ptr-deref in qt2_process_read_urb() due to
an incorrect bounds check in the following:

""
       if (newport > serial->num_ports) {
               dev_err(&port->dev,
                       "%s - port change to invalid port: %i\n",
                       __func__, newport);
               break;
       }
""

The condition doesn't account for the valid range of the serial->port
buffer, which is from 0 to serial->num_ports - 1. When newport is equal
to serial->num_ports, the assignment of "port" in the
following code is out-of-bounds and NULL:

""
       serial_priv->current_port = newport;
       port = serial->port[serial_priv->current_port];

""

The fix checks if newport is greater than or equal to serial->num_ports
indicating it is out-of-bounds.

Reported-by: syzbot <syzbot+506479ebf12fe435d01a@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=506479ebf12fe435d01a
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
 drivers/usb/serial/quatech2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/serial/quatech2.c b/drivers/usb/serial/quatech2.c
index a317bdbd00ad..72fe83a6c978 100644
--- a/drivers/usb/serial/quatech2.c
+++ b/drivers/usb/serial/quatech2.c
@@ -503,7 +503,7 @@ static void qt2_process_read_urb(struct urb *urb)

                                newport = *(ch + 3);

-                               if (newport > serial->num_ports) {
+                               if (newport >= serial->num_ports) {
                                        dev_err(&port->dev,
                                                "%s - port change to invalid port: %i\n",
                                                __func__, newport);
-- 
2.39.5