Re: [PATCH] can: dev: drop CAN XL skbs when CAN XL mode is disabled

[Oliver Hartkopp <socketcan@hartkopp.net>]

Thanks for your patch.

Please take a look at the latest activities on the Linux-CAN ML.

There's already a patch available I would prefer to solve the issue:

https://lore.kernel.org/linux-can/20260731-drop_canxl_frames-v1-1-7387b70353b3@kernel.org/

Many thanks,
Oliver

On 01.08.26 11:29, Cunhao Lu wrote:
> Valid CAN XL skbs can be injected through AF_PACKET. Although
> can_dropped_invalid_skb() verifies the CAN XL frame layout, it does not
> check whether CAN XL is enabled on the target device.
> 
> can_dev_dropped_skb() already rejects CAN FD skbs when CAN FD is
> disabled, but lacks the equivalent CAN XL check. Consequently, drivers
> without CAN XL support may interpret a CAN XL skb as struct canfd_frame
> or struct can_frame.
> 
> For example, rockchip_canfd interprets the mandatory CANXL_XLF flag at
> offset 4 as struct canfd_frame.len. The resulting value is at least 128,
> so the driver reads beyond the skb frame data and writes beyond the
> controller TX data register window.
> 
> Reject CAN XL skbs in the common transmit validation helper unless
> CAN_CTRLMODE_XL is enabled.
> 
> Fixes: fb08cba12b52 ("can: canxl: update CAN infrastructure for CAN XL frames")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://lore.kernel.org/linux-can/20260731105402.B7A451F000E9@smtp.kernel.org/
> Cc: stable@vger.kernel.org
> Signed-off-by: Cunhao Lu <1579567540@qq.com>
> ---
>   include/linux/can/dev.h | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
> index 6d0710d6f571..13fa607474b7 100644
> --- a/include/linux/can/dev.h
> +++ b/include/linux/can/dev.h
> @@ -167,6 +167,11 @@ static inline bool can_dev_dropped_skb(struct net_device *dev, struct sk_buff *s
>   		goto invalid_skb;
>   	}
>   
> +	if (!(priv->ctrlmode & CAN_CTRLMODE_XL) && can_is_canxl_skb(skb)) {
> +		netdev_info_once(dev, "CAN XL is disabled, dropping skb\n");
> +		goto invalid_skb;
> +	}
> +
>   	if (can_dev_in_xl_only_mode(priv) && !can_is_canxl_skb(skb)) {
>   		netdev_info_once(dev,
>   				 "Error signaling is disabled, dropping skb\n");
> 
> ---
> base-commit: 02dc699f83d04069fdabc996fc22d47cda47a4a9
> change-id: 20260801-master-bc2e15d668f5
> 
> Best regards,
> --
> Cunhao Lu <1579567540@qq.com>
>