Merge: CVE-2025-21689: USB: serial: quatech2: fix null-ptr-deref in qt2_process_read_urb()

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6369

JIRA: https://issues.redhat.com/browse/RHEL-78682
CVE: CVE-2025-21689

```
commit 575a5ad
Author: Qasim Ijaz <qasdev00@gmail.com>
Date:   Mon Jan 13 18:00:34 2025 +0000

    USB: serial: quatech2: fix null-ptr-deref in qt2_process_read_urb()

    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
    Fixes: f7a33e6 ("USB: serial: add quatech2 usb to serial driver")
    Cc: <stable@vger.kernel.org>      # 3.5
    Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
    Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Johan Hovold <johan@kernel.org>```

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

<small>Created 2025-02-10 19:12 UTC by backporter - [KWF FAQ](https://red.ht/kernel_workflow_doc) - [Slack #team-kernel-workflow](https://redhat-internal.slack.com/archives/C04LRUPMJQ5) - [Source](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/webhook/utils/backporter.py) - [Documentation](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/docs/README.backporter.md) - [Report an issue](https://gitlab.com/cki-project/kernel-workflow/-/issues/new?issue%5Btitle%5D=backporter%20webhook%20issue)</small>

Approved-by: Desnes Nunes <desnesn@redhat.com>
Approved-by: Daniel Horak <dhorak@redhat.com>
Approved-by: John W. Linville <linville@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Patrick Talbert <ptalbert@redhat.com>

Author: ptalbert

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);