netdev - [PATCH 1/2] IGMP snooping: set mrouters_only flag for IPv4 traffic properly

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Date:	Tue, 14 Jun 2011 10:04:43 +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,
	Hayato Kakuta <kakuta.hayato@....ntt.co.jp>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 1/2] IGMP snooping: set mrouters_only flag for IPv4 traffic
 properly

Upon reception of a IGMP/IGMPv2 membership report the kernel sets the
mrouters_only flag in a skb that may be a clone of the original skb, which
means that sometimes the bridge loses track of membership report 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>
Tested-by: Hayato Kakuta <kakuta.hayato@....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	2011-06-09 13:34:04.164261031 +0900
+++ linux-3.0-rc2/net/bridge/br_multicast.c	2011-06-09 20:04:23.473930447 +0900
@@ -1424,7 +1424,7 @@ static int br_multicast_ipv4_rcv(struct
 	switch (ih->type) {
 	case IGMP_HOST_MEMBERSHIP_REPORT:
 	case IGMPV2_HOST_MEMBERSHIP_REPORT:
-		BR_INPUT_SKB_CB(skb2)->mrouters_only = 1;
+		BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
 		err = br_ip4_multicast_add_group(br, port, ih->group);
 		break;
 	case IGMPV3_HOST_MEMBERSHIP_REPORT:


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