linux-kernel - Re: [PATCH 1/1] can: skb: add and set local

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Message-ID: <20220511143620.kphwgp2vhjyoecs5@pengutronix.de>
Date:   Wed, 11 May 2022 16:36:20 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Oliver Hartkopp <socketcan@...tkopp.net>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Devid Antonio Filoni <devid.filoni@...uetechnologies.com>,
        kernel@...gutronix.de, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Jander <david@...tonic.nl>
Subject: Re: [PATCH 1/1] can: skb: add and set local_origin flag

On 11.05.2022 15:24:21, Marc Kleine-Budde wrote:
> On 11.05.2022 14:38:32, Oliver Hartkopp wrote:
> > IMO this patch does not work as intended.
> > 
> > You probably need to revisit every place where can_skb_reserve() is used,
> > e.g. in raw_sendmsg().
> 
> And the loopback for devices that don't support IFF_ECHO:
> 
> | https://elixir.bootlin.com/linux/latest/source/net/can/af_can.c#L257

BTW: There is a bug with interfaces that don't support IFF_ECHO.

Assume an invalid CAN frame is passed to can_send() on an interface that
doesn't support IFF_ECHO. The above mentioned code does happily generate
an echo frame and it's send, even if the driver drops it, due to
can_dropped_invalid_skb(dev, skb).

The echoed back CAN frame is treated in raw_rcv() as if the headroom is valid:

| https://elixir.bootlin.com/linux/v5.17.6/source/net/can/raw.c#L138

But as far as I can see the can_skb_headroom_valid() check never has
been done. What about this patch?

index 1fb49d51b25d..fda4807ad165 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -255,6 +255,9 @@ int can_send(struct sk_buff *skb, int loop)
                 */
 
                if (!(skb->dev->flags & IFF_ECHO)) {
+                       if (can_dropped_invalid_skb(dev, skb))
+                               return -EINVAL;
+
                        /* If the interface is not capable to do loopback
                         * itself, we do it here.
                         */

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
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