sctp: ipv6: avoid touching device refcount

Avoid touching device refcount in sctp/ipv6, thanks to RCU
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/ipv6.c

@@ -837,15 +837,16 @@ static int sctp_inet6_bind_verify(struct sctp_sock *opt, union sctp_addr *addr)
 		if (type & IPV6_ADDR_LINKLOCAL) {
 			if (!addr->v6.sin6_scope_id)
 				return 0;
-			dev = dev_get_by_index(&init_net, addr->v6.sin6_scope_id);
-			if (!dev)
-				return 0;
-			if (!ipv6_chk_addr(&init_net, &addr->v6.sin6_addr,
+			rcu_read_lock();
+			dev = dev_get_by_index_rcu(&init_net,
+						   addr->v6.sin6_scope_id);
+			if (!dev ||
+			    !ipv6_chk_addr(&init_net, &addr->v6.sin6_addr,
 					   dev, 0)) {
-				dev_put(dev);
+				rcu_read_unlock();
 				return 0;
 			}
-			dev_put(dev);
+			rcu_read_unlock();
 		} else if (type == IPV6_ADDR_MAPPED) {
 			if (!opt->v4mapped)
 				return 0;
@@ -873,10 +874,12 @@ static int sctp_inet6_send_verify(struct sctp_sock *opt, union sctp_addr *addr)
 		if (type & IPV6_ADDR_LINKLOCAL) {
 			if (!addr->v6.sin6_scope_id)
 				return 0;
-			dev = dev_get_by_index(&init_net, addr->v6.sin6_scope_id);
+			rcu_read_lock();
+			dev = dev_get_by_index_rcu(&init_net,
+						   addr->v6.sin6_scope_id);
+			rcu_read_unlock();
 			if (!dev)
 				return 0;
-			dev_put(dev);
 		}
 		af = opt->pf->af;
 	}