Re: [PATCH usb-next v1] USB: serial: keyspan: Fixing use-after-free in usa49_glocont_callback()

[Johan Hovold]

On Thu, Aug 20, 2026 at 12:06:21AM -0700, Rafael Alejandro Diaz Cruz wrote:
> usa49_glocont_callback() obtains the private data from all
> ports of a serial device using usb_get_serial_port_data().
> This can happen during keyspan_port_remove() which frees
> the private data which can cause UAF.
> 
> Fix this by calling usb_set_serial_port_data(port, NULL)
> inside keyspan_port_remove() right before kfree() of
> private data. This in turn allows "if (!p_priv) continue;"
> condition within usa49_glocont_callback() to execute
> properly.
> 
> Reported-by: syzbot+e5e28c3e953b2eebb16e@xxxxxxxxxxxxxxxxxxxxxxxxx

Please include a Link to the report as well (and a Fixes tag).

> Signed-off-by: Rafael Alejandro Diaz Cruz <rafad900@xxxxxxxxx>
> ---
>  drivers/usb/serial/keyspan.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/serial/keyspan.c b/drivers/usb/serial/keyspan.c
> index 4d3746c7a94e..0e08acb99970 100644
> --- a/drivers/usb/serial/keyspan.c
> +++ b/drivers/usb/serial/keyspan.c
> @@ -2997,6 +2997,8 @@ static void keyspan_port_remove(struct usb_serial_port *port)
>  	for (i = 0; i < ARRAY_SIZE(p_priv->in_buffer); ++i)
>  		kfree(p_priv->in_buffer[i]);
>  
> +	usb_set_serial_port_data(port, NULL);
> +

This doesn't work as nothing prevents the completion handler from
loading the pointer just before you set it to NULL here.

>  	kfree(p_priv);
>  }

The UAF syzbot reported is a symptom of a general problem with the
disconnect handling. I've just sent a fix to address this here:

	https://lore.kernel.org/all/20260820145402.434447-2-johan@xxxxxxxxxx/

Johan