Re: [PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

On Tue, Aug 25, 2026 at 11:45:45PM +0000, Jameson Thies wrote:
> The UCSI displayport driver indexes the connector's port altmode array
> with the GET_CURRENT_CAM response after checking it is not 0xff. The
> port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
> returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
> not equal to 0xff, the kernel may crash with an array index OOB error.
> 
> Update the UCSI displayport driver to verify the current cam is less
> than UCSI_MAX_ALTMODES before accessing the port altmode array.
> 
> Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jameson Thies <jthies@google.com>
> ---
>  drivers/usb/typec/ucsi/displayport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> index 7067f2561b84..8d2032d0762c 100644
> --- a/drivers/usb/typec/ucsi/displayport.c
> +++ b/drivers/usb/typec/ucsi/displayport.c
> @@ -74,7 +74,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
>  		cur = 0xff;

Can you remove the above line while at it?

>  	}
>  
> -	if (cur != 0xff) {
> +	if (cur < UCSI_MAX_ALTMODES) {

Shouldn't that be the other way around?

>  		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
>  		goto err_unlock;
>  	}

Thanks,

-- 
heikki