ipv6: rate-limit probes for neighbourless routes

When commit 270972554c91 ("[IPV6]: ROUTE: Add Router Reachability
Probing (RFC4191).") introduced router probing, the rt6_probe() function
required that a neighbour entry existed. This neighbour entry is used to
record the timestamp of the last probe via the ->updated field.

Later, commit 2152caea7196 ("ipv6: Do not depend on rt->n in rt6_probe().")
removed the requirement for a neighbour entry. Neighbourless routes skip
the interval check and are not rate-limited.

This patch adds rate-limiting for neighbourless routes, by recording the
timestamp of the last probe in the fib6_info itself.

Fixes: 2152caea7196 ("ipv6: Do not depend on rt->n in rt6_probe().")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -159,6 +159,10 @@ struct fib6_info {
 	struct rt6_info * __percpu	*rt6i_pcpu;
 	struct rt6_exception_bucket __rcu *rt6i_exception_bucket;
 
+#ifdef CONFIG_IPV6_ROUTER_PREF
+	unsigned long			last_probe;
+#endif
+
 	u32				fib6_metric;
 	u8				fib6_protocol;
 	u8				fib6_type;

net/ipv6/route.c

@@ -520,10 +520,11 @@ static void rt6_probe_deferred(struct work_struct *w)
 
 static void rt6_probe(struct fib6_info *rt)
 {
-	struct __rt6_probe_work *work;
+	struct __rt6_probe_work *work = NULL;
 	const struct in6_addr *nh_gw;
 	struct neighbour *neigh;
 	struct net_device *dev;
+	struct inet6_dev *idev;
 
 	/*
 	 * Okay, this does not seem to be appropriate
@@ -539,15 +540,12 @@ static void rt6_probe(struct fib6_info *rt)
 	nh_gw = &rt->fib6_nh.nh_gw;
 	dev = rt->fib6_nh.nh_dev;
 	rcu_read_lock_bh();
+	idev = __in6_dev_get(dev);
 	neigh = __ipv6_neigh_lookup_noref(dev, nh_gw);
 	if (neigh) {
-		struct inet6_dev *idev;
-
 		if (neigh->nud_state & NUD_VALID)
 			goto out;
 
-		idev = __in6_dev_get(dev);
-		work = NULL;
 		write_lock(&neigh->lock);
 		if (!(neigh->nud_state & NUD_VALID) &&
 		    time_after(jiffies,
@@ -557,11 +555,13 @@ static void rt6_probe(struct fib6_info *rt)
 				__neigh_set_probe_once(neigh);
 		}
 		write_unlock(&neigh->lock);
-	} else {
+	} else if (time_after(jiffies, rt->last_probe +
+				       idev->cnf.rtr_probe_interval)) {
 		work = kmalloc(sizeof(*work), GFP_ATOMIC);
 	}
 
 	if (work) {
+		rt->last_probe = jiffies;
 		INIT_WORK(&work->work, rt6_probe_deferred);
 		work->target = *nh_gw;
 		dev_hold(dev);