ipv6: probe routes asynchronous in rt6_probe

Routes need to be probed asynchronous otherwise the call stack gets
exhausted when the kernel attemps to deliver another skb inline, like
e.g. xt_TEE does, and we probe at the same time.

We update neigh->updated still at once, otherwise we would send to
many probes.

Cc: Julian Anastasov <[e-mail]>
Signed-off-by: Hannes Frederic Sowa <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv6/route.c

···
 }
 
 #ifdef CONFIG_IPV6_ROUTER_PREF
+struct __rt6_probe_work {
+	struct work_struct work;
+	struct in6_addr target;
+	struct net_device *dev;
+};
+
+static void rt6_probe_deferred(struct work_struct *w)
+{
+	struct in6_addr mcaddr;
+	struct __rt6_probe_work *work =
+		container_of(w, struct __rt6_probe_work, work);
+
+	addrconf_addr_solict_mult(&work->target, &mcaddr);
+	ndisc_send_ns(work->dev, NULL, &work->target, &mcaddr, NULL);
+	dev_put(work->dev);
+	kfree(w);
+}
+
 static void rt6_probe(struct rt6_info *rt)
 {
 	struct neighbour *neigh;
···
 
 	if (!neigh ||
 	    time_after(jiffies, neigh->updated + rt->rt6i_idev->cnf.rtr_probe_interval)) {
-		struct in6_addr mcaddr;
-		struct in6_addr *target;
+		struct __rt6_probe_work *work;
 
-		if (neigh) {
+		work = kmalloc(sizeof(*work), GFP_ATOMIC);
+
+		if (neigh && work)
 			neigh->updated = jiffies;
-			write_unlock(&neigh->lock);
-		}
 
-		target = (struct in6_addr *)&rt->rt6i_gateway;
-		addrconf_addr_solict_mult(target, &mcaddr);
-		ndisc_send_ns(rt->dst.dev, NULL, target, &mcaddr, NULL);
+		if (neigh)
+			write_unlock(&neigh->lock);
+
+		if (work) {
+			INIT_WORK(&work->work, rt6_probe_deferred);
+			work->target = rt->rt6i_gateway;
+			dev_hold(rt->dst.dev);
+			work->dev = rt->dst.dev;
+			schedule_work(&work->work);
+		}
 	} else {
 out:
 		write_unlock(&neigh->lock);