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

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Message-ID: <002d234f-a7d6-7b1a-72f4-157d7a283446@hartkopp.net>
Date:   Wed, 11 May 2022 16:50:06 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
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 5/11/22 16:36, Marc Kleine-Budde 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;
> +

Good point!

But please check the rest of the code.
You need 'goto inval_skb;' instead of the return ;-)

Best,
Oliver

>                          /* If the interface is not capable to do loopback
>                           * itself, we do it here.
>                           */
> 
> Marc
>