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

[Greg Kroah-Hartman]

On Sun, Jan 12, 2025 at 09:55:58AM +0000, Qasim Ijaz 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@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Closes: https://syzkaller.appspot.com/bug?extid=506479ebf12fe435d01a

Oh wow, syzbot is now starting to fuzz random USB devices?  And this is
the only thing it found for this device?  That's not all that bad, I
expected much worse.


> Signed-off-by: Qasim Ijaz <qasdev00@xxxxxxxxx>
> ---
>  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);

Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>