Re: [PATCH v2] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Benson Leung]

On Fri, Sep 04, 2026 at 11:44:01PM +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@xxxxxxxxxxxxxxx
> Signed-off-by: Jameson Thies <jthies@xxxxxxxxxx>

Reviewed-by: Benson Leung <bleung@xxxxxxxxxxxx>


> ---
> Changes in v2:
>  - removed 0xff alt mode assignement when GET_CURRENT_CAM returns an error.
>  - return -EINVAL when alt mode index above UCSI_MAX_ALTMODES is returned.
> 
>  drivers/usb/typec/ucsi/displayport.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> index 7067f2561b84..572da7bbd29c 100644
> --- a/drivers/usb/typec/ucsi/displayport.c
> +++ b/drivers/usb/typec/ucsi/displayport.c
> @@ -71,11 +71,14 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
>  	if (ret < 0) {
>  		if (ucsi->version > 0x0100)
>  			goto err_unlock;
> -		cur = 0xff;
>  	}
>  
>  	if (cur != 0xff) {
> -		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
> +		if (cur < UCSI_MAX_ALTMODES)
> +			ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
> +		else
> +			ret = -EINVAL;
> +
>  		goto err_unlock;
>  	}
>  
> 
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> -- 
> 2.55.0.979.g7e5102b832-goog
>

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