Re: IPv6 multicast snooping behaviour on 2.6.39-rc2 and later

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 24 août 2011 à 15:04 +0800, Yan, Zheng a écrit :
> On Wed, Aug 24, 2011 at 1:24 AM, Ang Way Chuang <wcang@sfc.wide.ad.jp> wrote:
> > This is what I found so far from debugging.
> >
> > The packet is not forwarded due to the failed checksum at
> > br_multicast.c:1533
> >
> >        case CHECKSUM_NONE:
> >                skb2->csum = 0;
> >                if (skb_checksum_complete(skb2))
> >                        goto out;
> >        }
> >
> > Contrary to description of commit ff9a57a6, when the patch of commit
> > ff9a57a6 is applied,
> > pskb_trim_rcsum is never called at all on my testbed. When commit ff9a57a6
> > is reverted,
> > pskb_trim_rcsum will be called. The difference is:
> >
> > with commit ff9a57a6,
> >   pskb_trim_rcsum is never called, br_multicast_ipv6_rcv returns -EINVAL
> > which causes
> >   br_handle_frame_finish to drop the packet
> >
> > without commit ff9a57a6,
> >   pskb_trim_rcsum is called overwriting err with 0. br_multicast_ipv6_rcv
> > still fails on the
> >   same line (skb_checksum_complete). But the difference is err is set to 0
> > this time. Thereby,
> >   allowing the packet to be forwarded.
> >
> > Anyway, I don't think the behaviour is correct with or without commit
> > ff9a57a6
> >
> >
> 
> Looks like a checksum calculation bug. Please try below patch, Thanks.
> 
> ---
> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> index 2d85ca7..22d2d1a 100644
> --- a/net/bridge/br_multicast.c
> +++ b/net/bridge/br_multicast.c
> @@ -1520,16 +1520,23 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
>  		err = pskb_trim_rcsum(skb2, len);
>  		if (err)
>  			goto out;
> +		err = -EINVAL;
>  	}
> 
> +	ip6h = ipv6_hdr(skb2);
> +
>  	switch (skb2->ip_summed) {
>  	case CHECKSUM_COMPLETE:
> -		if (!csum_fold(skb2->csum))
> +		if (!csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr, skb2->len,
> +					IPPROTO_ICMPV6, skb2->csum))
>  			break;
>  		/*FALLTHROUGH*/
>  	case CHECKSUM_NONE:
> -		skb2->csum = 0;
> -		if (skb_checksum_complete(skb2))
> +		skb2->csum = ~csum_unfold(csum_ipv6_magic(&ip6h->saddr,
> +							&ip6h->daddr,
> +							skb2->len,
> +							IPPROTO_ICMPV6, 0));
> +		if (__skb_checksum_complete(skb2))
>  			goto out;
>  	}
> 
> ---


We also could reuse/factorize code, say the one from icmpv6_rcv()