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

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Date:   Sat, 14 May 2022 12:43:48 +0900
From:   Vincent Mailhol <vincent.mailhol@...il.com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     Oliver Hartkopp <socketcan@...tkopp.net>,
        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 Sat. 14 May 2022 at 12:29, Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> 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;
> +

This means that can_dropped_invalid_skb() would be called twice: one
time in can_send() and one time in the driver's xmit() function,
right?
It would be nice to find a trick to detect whether the skb was
injected through the packet socket or not in order not to execute
can_dropped_invalid_skb() twice. I guess the information of the
provenance of the skb is available somewhere, just not sure where (not
familiar with the packet socket).


Yours sincerely,
Vincent Mailhol