[STABLE][PATCH] IGMP snooping: set mrouters_only flag for IPv6traffic properly

[Fernando Luis Vazquez Cao]

From: Fernando Luis VÃzquez Cao <fernando@xxxxxxxxxxxxx>

commit fc2af6c73fc9449cd5894a36bb76b8f8c0e49fd8 upstream.

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@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxxxxxxxx>
---

diff -urNp linux-2.6.35.13-orig/net/bridge/br_multicast.c linux-2.6.35.13/net/bridge/br_multicast.c
--- linux-2.6.35.13-orig/net/bridge/br_multicast.c	2011-07-28 10:29:17.818721561 +0900
+++ linux-2.6.35.13/net/bridge/br_multicast.c	2011-07-28 10:35:14.959083129 +0900
@@ -1517,7 +1517,7 @@ static int br_multicast_ipv6_rcv(struct
 	case ICMPV6_MGM_REPORT:
 	    {
 		struct mld_msg *mld = (struct mld_msg *)icmp6h;
-		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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