neighbour: fix data-races around n->output

n->output field can be read locklessly, while a writer
might change the pointer concurrently.

Add missing annotations to prevent load-store tearing.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/neighbour.h

@@ -539,7 +539,7 @@ static inline int neigh_output(struct neighbour *n, struct sk_buff *skb,
 	    READ_ONCE(hh->hh_len))
 		return neigh_hh_output(hh, skb);
 
-	return n->output(n, skb);
+	return READ_ONCE(n->output)(n, skb);
 }
 
 static inline struct neighbour *

net/bridge/br_netfilter_hooks.c

@@ -294,7 +294,7 @@ int br_nf_pre_routing_finish_bridge(struct net *net, struct sock *sk, struct sk_
 			/* tell br_dev_xmit to continue with forwarding */
 			nf_bridge->bridged_dnat = 1;
 			/* FIXME Need to refragment */
-			ret = neigh->output(neigh, skb);
+			ret = READ_ONCE(neigh->output)(neigh, skb);
 		}
 		neigh_release(neigh);
 		return ret;

net/core/neighbour.c

@@ -410,7 +410,7 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 				 */
 				__skb_queue_purge(&n->arp_queue);
 				n->arp_queue_len_bytes = 0;
-				n->output = neigh_blackhole;
+				WRITE_ONCE(n->output, neigh_blackhole);
 				if (n->nud_state & NUD_VALID)
 					n->nud_state = NUD_NOARP;
 				else
@@ -920,7 +920,7 @@ static void neigh_suspect(struct neighbour *neigh)
 {
 	neigh_dbg(2, "neigh %p is suspected\n", neigh);
 
-	neigh->output = neigh->ops->output;
+	WRITE_ONCE(neigh->output, neigh->ops->output);
 }
 
 /* Neighbour state is OK;
@@ -932,7 +932,7 @@ static void neigh_connect(struct neighbour *neigh)
 {
 	neigh_dbg(2, "neigh %p is connected\n", neigh);
 
-	neigh->output = neigh->ops->connected_output;
+	WRITE_ONCE(neigh->output, neigh->ops->connected_output);
 }
 
 static void neigh_periodic_work(struct work_struct *work)
@@ -1449,7 +1449,7 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
 				if (n2)
 					n1 = n2;
 			}
-			n1->output(n1, skb);
+			READ_ONCE(n1->output)(n1, skb);
 			if (n2)
 				neigh_release(n2);
 			rcu_read_unlock();
@@ -3155,7 +3155,7 @@ int neigh_xmit(int index, struct net_device *dev,
 			rcu_read_unlock();
 			goto out_kfree_skb;
 		}
-		err = neigh->output(neigh, skb);
+		err = READ_ONCE(neigh->output)(neigh, skb);
 		rcu_read_unlock();
 	}
 	else if (index == NEIGH_LINK_TABLE) {