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

On Wed, Aug 24, 2011 at 1:24 AM, Ang Way Chuang [off-list ref] wrote:

quoted

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;
 	}

---
--

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