[3.16.y-ckt stable] Patch "ipv4: igmp: Allow removing groups from a removed interface" has been added to staging queue

[Luis Henriques]

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

    ipv4: igmp: Allow removing groups from a removed interface

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-ckt22.

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 fd4a0bf3faabfb18d326930d9724592c7e3db691 Mon Sep 17 00:00:00 2001
From: Andrew Lunn <andrew at lunn.ch>
Date: Tue, 1 Dec 2015 16:31:08 +0100
Subject: ipv4: igmp: Allow removing groups from a removed interface

commit 4eba7bb1d72d9bde67d810d09bf62dc207b63c5c upstream.

When a multicast group is joined on a socket, a struct ip_mc_socklist
is appended to the sockets mc_list containing information about the
joined group.

If the interface is hot unplugged, this entry becomes stale. Prior to
commit 52ad353a5344f ("igmp: fix the problem when mc leave group") it
was possible to remove the stale entry by performing a
IP_DROP_MEMBERSHIP, passing either the old ifindex or ip address on
the interface. However, this fix enforces that the interface must
still exist. Thus with time, the number of stale entries grows, until
sysctl_igmp_max_memberships is reached and then it is not possible to
join and more groups.

The previous patch fixes an issue where a IP_DROP_MEMBERSHIP is
performed without specifying the interface, either by ifindex or ip
address. However here we do supply one of these. So loosen the
restriction on device existence to only apply when the interface has
not been specified. This then restores the ability to clean up the
stale entries.

Signed-off-by: Andrew Lunn <andrew at lunn.ch>
Fixes: 52ad353a5344f "(igmp: fix the problem when mc leave group")
Signed-off-by: David S. Miller <davem at davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ipv4/igmp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index fbb230ea039a..719c3d707327 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1943,7 +1943,7 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)

 	rtnl_lock();
 	in_dev = ip_mc_find_dev(net, imr);
-	if (!in_dev) {
+	if (!imr->imr_ifindex && !imr->imr_address.s_addr && !in_dev) {
 		ret = -ENODEV;
 		goto out;
 	}
@@ -1964,7 +1964,8 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)

 		*imlp = iml->next_rcu;

-		ip_mc_dec_group(in_dev, group);
+		if (in_dev)
+			ip_mc_dec_group(in_dev, group);
 		rtnl_unlock();
 		/* decrease mem now to avoid the memleak warning */
 		atomic_sub(sizeof(*iml), &sk->sk_omem_alloc);