[IPV4]: fix IPv4 leave-group group matching

        This patch fixes the multicast group matching for 
IP_DROP_MEMBERSHIP, similar to the IP_ADD_MEMBERSHIP fix in a prior
patch. Groups are identifiedby <group address,interface> and including
the interface address in the match will fail if a leave-group is done
by address when the join was done by index, or if different addresses
on the same interface are used in the join and leave.
Signed-off-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/igmp.c

@@ -1687,24 +1687,25 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)
 {
 	struct inet_sock *inet = inet_sk(sk);
 	struct ip_mc_socklist *iml, **imlp;
+	struct in_device *in_dev;
+	u32 group = imr->imr_multiaddr.s_addr;
+	u32 ifindex;
 
 	rtnl_lock();
+	in_dev = ip_mc_find_dev(imr);
+	if (!in_dev) {
+		rtnl_unlock();
+		return -ENODEV;
+	}
+	ifindex = imr->imr_ifindex;
 	for (imlp = &inet->mc_list; (iml = *imlp) != NULL; imlp = &iml->next) {
-		if (iml->multi.imr_multiaddr.s_addr==imr->imr_multiaddr.s_addr &&
-		    iml->multi.imr_address.s_addr==imr->imr_address.s_addr &&
-		    (!imr->imr_ifindex || iml->multi.imr_ifindex==imr->imr_ifindex)) {
-			struct in_device *in_dev;
-
-			in_dev = inetdev_by_index(iml->multi.imr_ifindex);
-			if (in_dev)
+		if (iml->multi.imr_multiaddr.s_addr == group &&
+		    iml->multi.imr_ifindex == ifindex) {
 			(void) ip_mc_leave_src(sk, iml, in_dev);
 
 			*imlp = iml->next;
 
-			if (in_dev) {
-				ip_mc_dec_group(in_dev, imr->imr_multiaddr.s_addr);
-				in_dev_put(in_dev);
-			}
+			ip_mc_dec_group(in_dev, group);
 			rtnl_unlock();
 			sock_kfree_s(sk, iml, sizeof(*iml));
 			return 0;