inet: add a redirect generation id in inetpeer

Now inetpeer is the place where we cache redirect information for ipv4
destinations, we must be able to invalidate informations when a route is
added/removed on host.

As inetpeer is not yet namespace aware, this patch adds a shared
redirect_genid, and a per inetpeer redirect_genid. This might be changed
later if inetpeer becomes ns aware.

Cache information for one inerpeer is valid as long as its
redirect_genid has the same value than global redirect_genid.
Reported-by: Arkadiusz Miśkiewicz <a.miskiewicz@gmail.com>
Tested-by: Arkadiusz Miśkiewicz <a.miskiewicz@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inetpeer.h

@@ -35,6 +35,7 @@ struct inet_peer {
 
 	u32			metrics[RTAX_MAX];
 	u32			rate_tokens;	/* rate limiting for ICMP */
+	int			redirect_genid;
 	unsigned long		rate_last;
 	unsigned long		pmtu_expires;
 	u32			pmtu_orig;

net/ipv4/route.c

@@ -131,6 +131,7 @@ static int ip_rt_mtu_expires __read_mostly	= 10 * 60 * HZ;
 static int ip_rt_min_pmtu __read_mostly		= 512 + 20 + 20;
 static int ip_rt_min_advmss __read_mostly	= 256;
 static int rt_chain_length_max __read_mostly	= 20;
+static int redirect_genid;
 
 /*
  *	Interface to generic destination cache.
@@ -837,6 +838,7 @@ static void rt_cache_invalidate(struct net *net)
 
 	get_random_bytes(&shuffle, sizeof(shuffle));
 	atomic_add(shuffle + 1U, &net->ipv4.rt_genid);
+	redirect_genid++;
 }
 
 /*
@@ -1391,8 +1393,10 @@ void ip_rt_redirect(__be32 old_gw, __be32 daddr, __be32 new_gw,
 
 				peer = rt->peer;
 				if (peer) {
-					if (peer->redirect_learned.a4 != new_gw) {
+					if (peer->redirect_learned.a4 != new_gw ||
+					    peer->redirect_genid != redirect_genid) {
 						peer->redirect_learned.a4 = new_gw;
+						peer->redirect_genid = redirect_genid;
 						atomic_inc(&__rt_peer_genid);
 					}
 					check_peer_redir(&rt->dst, peer);
@@ -1701,6 +1705,8 @@ static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie)
 		if (peer) {
 			check_peer_pmtu(dst, peer);
 
+			if (peer->redirect_genid != redirect_genid)
+				peer->redirect_learned.a4 = 0;
 			if (peer->redirect_learned.a4 &&
 			    peer->redirect_learned.a4 != rt->rt_gateway) {
 				if (check_peer_redir(dst, peer))
@@ -1857,6 +1863,8 @@ static void rt_init_metrics(struct rtable *rt, const struct flowi4 *fl4,
 		dst_init_metrics(&rt->dst, peer->metrics, false);
 
 		check_peer_pmtu(&rt->dst, peer);
+		if (peer->redirect_genid != redirect_genid)
+			peer->redirect_learned.a4 = 0;
 		if (peer->redirect_learned.a4 &&
 		    peer->redirect_learned.a4 != rt->rt_gateway) {
 			rt->rt_gateway = peer->redirect_learned.a4;