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
Tested-by: syzbot <syzbot+506479ebf12fe435d01a@syzkaller.appspotmail.com>
Tested-by: Qasim Ijaz <qasdev00@gmail.com>
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

On Sat, Jan 11, 2025 at 08:08:49PM +0000, qasdev wrote:
> 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
> Tested-by: syzbot <syzbot+506479ebf12fe435d01a@syzkaller.appspotmail.com>
> Tested-by: Qasim Ijaz <qasdev00@gmail.com>
> Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>

Your signed-off-by does not match your "From:" line :(

Also, no need to add a tested-by when you sign off on your own patch,
that is usually implied.

thanks,

greg k-h

On Sun, Jan 12, 2025 at 09:42:45AM +0100, Greg Kroah-Hartman wrote:
> On Sat, Jan 11, 2025 at 08:08:49PM +0000, qasdev wrote:
> > 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
> > Tested-by: syzbot <syzbot+506479ebf12fe435d01a@syzkaller.appspotmail.com>
> > Tested-by: Qasim Ijaz <qasdev00@gmail.com>
> > Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
> 
> Your signed-off-by does not match your "From:" line :(
> 
> Also, no need to add a tested-by when you sign off on your own patch,
> that is usually implied.
> 
> thanks,
> 
> greg k-h

Hi Greg,

Thank you for your feedback on my patch. I’ve sent a v2 patch in a new thread, addressing the issues with the From: line and removing the redundant Tested-by tag.

Best regards,
Qasim