linux-kernel - Re: [RFC PATCH 12/13] can: slcan: extend the protocol with error info

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Date:   Tue, 7 Jun 2022 12:56:37 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 12/13] can: slcan: extend the protocol with error info

On 07.06.2022 11:47:51, Dario Binacchi wrote:
> It extends the protocol to receive the adapter CAN communication errors
> and forward them to the netdev upper levels.
> 
> Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> ---
> 
>  drivers/net/can/slcan/slcan-core.c | 104 ++++++++++++++++++++++++++++-
>  1 file changed, 103 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
> index b813a59534a3..02e7c14de45c 100644
> --- a/drivers/net/can/slcan/slcan-core.c
> +++ b/drivers/net/can/slcan/slcan-core.c
> @@ -182,8 +182,92 @@ int slcan_enable_err_rst_on_open(struct net_device *ndev, bool on)
>    *			STANDARD SLCAN DECAPSULATION			 *
>    ************************************************************************/
>  
> +static void slc_bump_err(struct slcan *sl)
> +{
> +	struct net_device *dev = sl->dev;
> +	struct sk_buff *skb;
> +	struct can_frame *cf;
> +	char *cmd = sl->rbuff;
> +	bool rx_errors = false, tx_errors = false;
> +	int i, len;
> +
> +	if (*cmd != 'e')
> +		return;
> +
> +	cmd += SLC_CMD_LEN;
> +	/* get len from sanitized ASCII value */

What happens is a malicious device sends a wrong len value, that's
longer than the RX'ed data?

> +	len = *cmd++;
> +	if (len >= '0' && len < '9')
> +		len -= '0';
> +	else
> +		return;
> +
> +	skb = alloc_can_err_skb(dev, &cf);

Please continue error handling, even if no skb can be allocated.

> +	if (unlikely(!skb))
> +		return;
> +
> +	cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
> +	for (i = 0; i < len; i++, cmd++) {
> +		switch (*cmd) {
> +		case 'a':
> +			netdev_dbg(dev, "ACK error\n");
> +			cf->can_id |= CAN_ERR_ACK;
> +			cf->data[3] = CAN_ERR_PROT_LOC_ACK;
> +			tx_errors = true;
> +			break;
> +		case 'b':
> +			netdev_dbg(dev, "Bit0 error\n");
> +			cf->data[2] |= CAN_ERR_PROT_BIT0;
> +			tx_errors = true;
> +			break;
> +		case 'B':
> +			netdev_dbg(dev, "Bit1 error\n");
> +			cf->data[2] |= CAN_ERR_PROT_BIT1;
> +			tx_errors = true;
> +			break;
> +		case 'c':
> +			netdev_dbg(dev, "CRC error\n");
> +			cf->data[2] |= CAN_ERR_PROT_BIT;
> +			cf->data[3] = CAN_ERR_PROT_LOC_CRC_SEQ;
> +			rx_errors = true;
> +			break;
> +		case 'f':
> +			netdev_dbg(dev, "Form Error\n");
> +			cf->data[2] |= CAN_ERR_PROT_FORM;
> +			rx_errors = true;
> +			break;
> +		case 'o':
> +			netdev_dbg(dev, "Rx overrun error\n");
> +			cf->can_id |= CAN_ERR_CRTL;
> +			cf->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
> +			dev->stats.rx_over_errors++;
> +			dev->stats.rx_errors++;
> +			break;
> +		case 'O':
> +			netdev_dbg(dev, "Tx overrun error\n");
> +			cf->can_id |= CAN_ERR_CRTL;
> +			cf->data[1] = CAN_ERR_CRTL_TX_OVERFLOW;
> +			dev->stats.tx_errors++;
> +			break;
> +		case 's':
> +			netdev_dbg(dev, "Stuff error\n");
> +			cf->data[2] |= CAN_ERR_PROT_STUFF;
> +			rx_errors = true;
> +			break;
> +		}
> +	}
> +
> +	if (rx_errors)
> +		dev->stats.rx_errors++;
> +
> +	if (tx_errors)
> +		dev->stats.tx_errors++;
> +
> +	netif_rx(skb);
> +}
> +

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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