netdev - [PATCH 2/2] IGMP snooping: set mrouters_only flag for IPv6 traffic properly

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Date:	Tue, 14 Jun 2011 10:06:58 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Stephen Hemminger <shemminger@...tta.com>, netdev@...r.kernel.org,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 2/2] IGMP snooping: set mrouters_only flag for IPv6 traffic
 properly

Upon reception of a MGM report packet the kernel sets the mrouters_only flag
in a skb that is a clone of the original skb, which means that the bridge
loses track of MGM packets (cb buffers are tied to a specific skb and not
shared) and it ends up forwading join requests to the bridge interface.

This can cause unexpected membership timeouts and intermitent/permanent loss
of connectivity as described in RFC 4541 [2.1.1. IGMP Forwarding Rules]:

    A snooping switch should forward IGMP Membership Reports only to
    those ports where multicast routers are attached.
    [...]
    Sending membership reports to other hosts can result, for IGMPv1
    and IGMPv2, in unintentionally preventing a host from joining a
    specific multicast group.


Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
---

diff -urNp linux-3.0-rc2-orig/net/bridge/br_multicast.c linux-3.0-rc2/net/bridge/br_multicast.c
--- linux-3.0-rc2-orig/net/bridge/br_multicast.c	2011-06-13 12:10:27.805554187 +0900
+++ linux-3.0-rc2/net/bridge/br_multicast.c	2011-06-13 12:12:27.591626915 +0900
@@ -1543,7 +1543,7 @@ static int br_multicast_ipv6_rcv(struct
 			goto out;
 		}
 		mld = (struct mld_msg *)skb_transport_header(skb2);
-		BR_INPUT_SKB_CB(skb2)->mrouters_only = 1;
+		BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
 		err = br_ip6_multicast_add_group(br, port, &mld->mld_mca);
 		break;
 	    }


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