[3.16.y-ckt stable] Patch "bridge: fix multicast router rlist endless loop" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    bridge: fix multicast router rlist endless loop

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt15.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 54bf9f92d3df33c3ea758499915cef4d9e5fda57 Mon Sep 17 00:00:00 2001
From: Nikolay Aleksandrov <razor at blackwall.org>
Date: Tue, 9 Jun 2015 10:23:57 -0700
Subject: bridge: fix multicast router rlist endless loop

commit 1a040eaca1a22f8da8285ceda6b5e4a2cb704867 upstream.

Since the addition of sysfs multicast router support if one set
multicast_router to "2" more than once, then the port would be added to
the hlist every time and could end up linking to itself and thus causing an
endless loop for rlist walkers.
So to reproduce just do:
echo 2 > multicast_router; echo 2 > multicast_router;
in a bridge port and let some igmp traffic flow, for me it hangs up
in br_multicast_flood().
Fix this by adding a check in br_multicast_add_router() if the port is
already linked.
The reason this didn't happen before the addition of multicast_router
sysfs entries is because there's a !hlist_unhashed check that prevents
it.

Signed-off-by: Nikolay Aleksandrov <razor at blackwall.org>
Fixes: 0909e11758bd ("bridge: Add multicast_router sysfs entries")
Acked-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/bridge/br_multicast.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 799379e81264..32de99bf6e42 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1166,6 +1166,9 @@ static void br_multicast_add_router(struct net_bridge *br,
 	struct net_bridge_port *p;
 	struct hlist_node *slot = NULL;

+	if (!hlist_unhashed(&port->rlist))
+		return;
+
 	hlist_for_each_entry(p, &br->router_list, rlist) {
 		if ((unsigned long) port >= (unsigned long) p)
 			break;
@@ -1193,12 +1196,8 @@ static void br_multicast_mark_router(struct net_bridge *br,
 	if (port->multicast_router != 1)
 		return;

-	if (!hlist_unhashed(&port->rlist))
-		goto timer;
-
 	br_multicast_add_router(br, port);

-timer:
 	mod_timer(&port->multicast_router_timer,
 		  now + br->multicast_querier_interval);
 }