ipv6: make mc_forwarding atomic

This fixes minor data-races in ip6_mc_input() and
batadv_mcast_mla_rtr_flags_softif_get_ipv6()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: edumazet

include/linux/ipv6.h

@@ -51,7 +51,7 @@ struct ipv6_devconf {
 	__s32		use_optimistic;
 #endif
 #ifdef CONFIG_IPV6_MROUTE
-	__s32		mc_forwarding;
+	atomic_t	mc_forwarding;
 #endif
 	__s32		disable_ipv6;
 	__s32		drop_unicast_in_l2_multicast;

net/batman-adv/multicast.c

@@ -134,7 +134,7 @@ static u8 batadv_mcast_mla_rtr_flags_softif_get_ipv6(struct net_device *dev)
 {
 	struct inet6_dev *in6_dev = __in6_dev_get(dev);
 
-	if (in6_dev && in6_dev->cnf.mc_forwarding)
+	if (in6_dev && atomic_read(&in6_dev->cnf.mc_forwarding))
 		return BATADV_NO_FLAGS;
 	else
 		return BATADV_MCAST_WANT_NO_RTR6;

net/ipv6/addrconf.c

@@ -554,7 +554,7 @@ static int inet6_netconf_fill_devconf(struct sk_buff *skb, int ifindex,
 #ifdef CONFIG_IPV6_MROUTE
 	if ((all || type == NETCONFA_MC_FORWARDING) &&
 	    nla_put_s32(skb, NETCONFA_MC_FORWARDING,
-			devconf->mc_forwarding) < 0)
+			atomic_read(&devconf->mc_forwarding)) < 0)
 		goto nla_put_failure;
 #endif
 	if ((all || type == NETCONFA_PROXY_NEIGH) &&
@@ -5533,7 +5533,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	array[DEVCONF_USE_OPTIMISTIC] = cnf->use_optimistic;
 #endif
 #ifdef CONFIG_IPV6_MROUTE
-	array[DEVCONF_MC_FORWARDING] = cnf->mc_forwarding;
+	array[DEVCONF_MC_FORWARDING] = atomic_read(&cnf->mc_forwarding);
 #endif
 	array[DEVCONF_DISABLE_IPV6] = cnf->disable_ipv6;
 	array[DEVCONF_ACCEPT_DAD] = cnf->accept_dad;

net/ipv6/ip6_input.c

@@ -508,7 +508,7 @@ int ip6_mc_input(struct sk_buff *skb)
 	/*
 	 *      IPv6 multicast router mode is now supported ;)
 	 */
-	if (dev_net(skb->dev)->ipv6.devconf_all->mc_forwarding &&
+	if (atomic_read(&dev_net(skb->dev)->ipv6.devconf_all->mc_forwarding) &&
 	    !(ipv6_addr_type(&hdr->daddr) &
 	      (IPV6_ADDR_LOOPBACK|IPV6_ADDR_LINKLOCAL)) &&
 	    likely(!(IP6CB(skb)->flags & IP6SKB_FORWARDED))) {

net/ipv6/ip6mr.c

@@ -732,7 +732,7 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
 
 	in6_dev = __in6_dev_get(dev);
 	if (in6_dev) {
-		in6_dev->cnf.mc_forwarding--;
+		atomic_dec(&in6_dev->cnf.mc_forwarding);
 		inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF,
 					     NETCONFA_MC_FORWARDING,
 					     dev->ifindex, &in6_dev->cnf);
@@ -900,7 +900,7 @@ static int mif6_add(struct net *net, struct mr_table *mrt,
 
 	in6_dev = __in6_dev_get(dev);
 	if (in6_dev) {
-		in6_dev->cnf.mc_forwarding++;
+		atomic_inc(&in6_dev->cnf.mc_forwarding);
 		inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF,
 					     NETCONFA_MC_FORWARDING,
 					     dev->ifindex, &in6_dev->cnf);
@@ -1551,7 +1551,7 @@ static int ip6mr_sk_init(struct mr_table *mrt, struct sock *sk)
 	} else {
 		rcu_assign_pointer(mrt->mroute_sk, sk);
 		sock_set_flag(sk, SOCK_RCU_FREE);
-		net->ipv6.devconf_all->mc_forwarding++;
+		atomic_inc(&net->ipv6.devconf_all->mc_forwarding);
 	}
 	write_unlock_bh(&mrt_lock);
 
@@ -1584,7 +1584,7 @@ int ip6mr_sk_done(struct sock *sk)
 			 * so the RCU grace period before sk freeing
 			 * is guaranteed by sk_destruct()
 			 */
-			net->ipv6.devconf_all->mc_forwarding--;
+			atomic_dec(&net->ipv6.devconf_all->mc_forwarding);
 			write_unlock_bh(&mrt_lock);
 			inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
 						     NETCONFA_MC_FORWARDING,