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

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Date:   Wed, 11 May 2022 16:57:50 +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 16:54, Marc Kleine-Budde wrote:
> On 11.05.2022 16:50:06, Oliver Hartkopp wrote:
>>
>>
>> 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 ;-)
> 
> Why? To free the skb? That's what can_dropped_invalid_skb() does, too:
> 
> | https://elixir.bootlin.com/linux/v5.17.6/source/include/linux/can/skb.h#L130
> 

My bad!

Pointing you not reading the code ... should better have looked myself :-D