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

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Message-ID: <20220511145437.oezwkcprqiv5lfda@pengutronix.de>
Date:   Wed, 11 May 2022 16:54:37 +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 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

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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