Patch "net: Allow IP_MULTICAST_IF to set index to L3 slave" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

net: Allow IP_MULTICAST_IF to set index to L3 slave

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-allow-ip_multicast_if-to-set-index-to-l3-slave.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Ahern <[email protected]>
Date: Thu, 29 Dec 2016 15:39:37 -0800
Subject: net: Allow IP_MULTICAST_IF to set index to L3 slave

From: David Ahern <[email protected]>

[ Upstream commit 7bb387c5ab12aeac3d5eea28686489ff46b53ca9 ]

IP_MULTICAST_IF fails if sk_bound_dev_if is already set and the new index does not match it. e.g.,

    ntpd[15381]: setsockopt IP_MULTICAST_IF 192.168.1.23 fails: Invalid argument

Relax the check in setsockopt to allow setting mc_index to an L3 slave if sk_bound_dev_if points to an L3 master.

Make a similar change for IPv6. In this case change the device lookup to take the rcu_read_lock avoiding a refcnt. The rcu lock is also needed for the lookup of a potential L3 master device.

This really only silences a setsockopt failure since uses of mc_index are secondary to sk_bound_dev_if if it is set. In both cases, if either index is an L3 slave or master, lookups are directed to the same FIB table so relaxing the check at setsockopt time causes no harm.

Patch is based on a suggested change by Darwin for a problem noted in their code base.

---
 net/ipv4/ip_sockglue.c   |    7 ++++++-
 net/ipv6/ipv6_sockglue.c |   16 ++++++++++++----
 2 files changed, 18 insertions(+), 5 deletions(-)

@@ -808,6 +808,7 @@ static int do_ip_setsockopt(struct sock
 	{
 		struct ip_mreqn mreq;
 		struct net_device *dev = NULL;
+		int midx;
 
 		if (sk->sk_type == SOCK_STREAM)
 			goto e_inval;

@@ -852,11 +853,15 @@ static int do_ip_setsockopt(struct sock
 		err = -EADDRNOTAVAIL;
 		if (!dev)
 			break;
+
+		midx = l3mdev_master_ifindex(dev);
+
 		dev_put(dev);
 
 		err = -EINVAL;
 		if (sk->sk_bound_dev_if &&
-		    mreq.imr_ifindex != sk->sk_bound_dev_if)
+		    mreq.imr_ifindex != sk->sk_bound_dev_if &&
+		    (!midx || midx != sk->sk_bound_dev_if))
 			break;
 
 		inet->mc_index = mreq.imr_ifindex;

@@ -583,16 +583,24 @@ done:
 
 		if (val) {
 			struct net_device *dev;
+			int midx;
 
-			if (sk->sk_bound_dev_if && sk->sk_bound_dev_if != val)
-				goto e_inval;
+			rcu_read_lock();
 
-			dev = dev_get_by_index(net, val);
+			dev = dev_get_by_index_rcu(net, val);
 			if (!dev) {
+				rcu_read_unlock();
 				retv = -ENODEV;
 				break;
 			}
-			dev_put(dev);
+			midx = l3mdev_master_ifindex_rcu(dev);
+
+			rcu_read_unlock();
+
+			if (sk->sk_bound_dev_if &&
+			    sk->sk_bound_dev_if != val &&
+			    (!midx || midx != sk->sk_bound_dev_if))
+				goto e_inval;
 		}
 		np->mcast_oif = val;
 		retv = 0;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/net-allow-ip_multicast_if-to-set-index-to-l3-slave.patch