ipv4: check rt_genid in dst_check

commit d11a4dc1
Author: Timo Teräs <timo.teras@iki.fi>
Date:   Thu Mar 18 23:20:20 2010 +0000

    ipv4: check rt_genid in dst_check

    Xfrm_dst keeps a reference to ipv4 rtable entries on each
    cached bundle. The only way to renew xfrm_dst when the underlying
    route has changed, is to implement dst_check for this. This is
    what ipv6 side does too.

    The problems started after 87c1e12b
    ("ipsec: Fix bogus bundle flowi") which fixed a bug causing xfrm_dst
    to not get reused, until that all lookups always generated new
    xfrm_dst with new route reference and path mtu worked. But after the
    fix, the old routes started to get reused even after they were expired
    causing pmtu to break (well it would occationally work if the rtable
    gc had run recently and marked the route obsolete causing dst_check to
    get called).
Signed-off-by: Timo Teras <timo.teras@iki.fi>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

This commit is based on the above, with the addition of verifying blackhole
routes in the same manner.

Fixing the issue with blackhole routes as it was accomplished in mainline
would require pulling in a lot more code, and people were not interested
in pulling in all of the dependencies given the much higher risk of trying
to select the right subset of changes to include.  The addition of the
single line of "dst->obsolete = -1;" in ipv4_dst_blackhole() was much
easier to verify, and is in the spirit of the patch in question.
This is the minimal set of changes to fix the bug in question.

A test case is available here :
  http://marc.info/?l=linux-netdev&m=135015076708950&w=2Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

net/ipv4/route.c

@@ -1412,7 +1412,7 @@ void ip_rt_redirect(__be32 old_gw, __be32 daddr, __be32 new_gw,
 					dev_hold(rt->u.dst.dev);
 				if (rt->idev)
 					in_dev_hold(rt->idev);
-				rt->u.dst.obsolete	= 0;
+				rt->u.dst.obsolete	= -1;
 				rt->u.dst.lastuse	= jiffies;
 				rt->u.dst.path		= &rt->u.dst;
 				rt->u.dst.neighbour	= NULL;
@@ -1477,7 +1477,7 @@ static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
 	struct dst_entry *ret = dst;
 
 	if (rt) {
-		if (dst->obsolete) {
+		if (dst->obsolete > 0) {
 			ip_rt_put(rt);
 			ret = NULL;
 		} else if ((rt->rt_flags & RTCF_REDIRECTED) ||
@@ -1700,7 +1700,9 @@ static void ip_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
 
 static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie)
 {
-	return NULL;
+	if (rt_is_expired((struct rtable *)dst))
+		return NULL;
+	return dst;
 }
 
 static void ipv4_dst_destroy(struct dst_entry *dst)
@@ -1862,7 +1864,8 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 	if (!rth)
 		goto e_nobufs;
 
-	rth->u.dst.output= ip_rt_bug;
+	rth->u.dst.output = ip_rt_bug;
+	rth->u.dst.obsolete = -1;
 
 	atomic_set(&rth->u.dst.__refcnt, 1);
 	rth->u.dst.flags= DST_HOST;
@@ -2023,6 +2026,7 @@ static int __mkroute_input(struct sk_buff *skb,
 	rth->fl.oif 	= 0;
 	rth->rt_spec_dst= spec_dst;
 
+	rth->u.dst.obsolete = -1;
 	rth->u.dst.input = ip_forward;
 	rth->u.dst.output = ip_output;
 	rth->rt_genid = rt_genid(dev_net(rth->u.dst.dev));
@@ -2187,6 +2191,7 @@ out:	return err;
 		goto e_nobufs;
 
 	rth->u.dst.output= ip_rt_bug;
+	rth->u.dst.obsolete = -1;
 	rth->rt_genid = rt_genid(net);
 
 	atomic_set(&rth->u.dst.__refcnt, 1);
@@ -2411,7 +2416,8 @@ static int __mkroute_output(struct rtable **result,
 	rth->rt_gateway = fl->fl4_dst;
 	rth->rt_spec_dst= fl->fl4_src;
 
-	rth->u.dst.output=ip_output;
+	rth->u.dst.output = ip_output;
+	rth->u.dst.obsolete = -1;
 	rth->rt_genid = rt_genid(dev_net(dev_out));
 
 	RT_CACHE_STAT_INC(out_slow_tot);
@@ -2741,6 +2747,7 @@ static int ipv4_dst_blackhole(struct net *net, struct rtable **rp, struct flowi
 	if (rt) {
 		struct dst_entry *new = &rt->u.dst;
 
+		new->obsolete = -1;
 		atomic_set(&new->__refcnt, 1);
 		new->__use = 1;
 		new->input = dst_discard;