[PATCH net-next 2/2] ipv6: dont cache cloned routes

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

We can now destroy cloned routes immediately from dst_release() instead
of depending on garbage collection.

Set DST_NOCACHE in rt6_alloc_clone() so that :

1) we avoid calling ip6_ins_rt() on such routes

2) dst_release() can call destroy when refcount becomes 0

This allows machines to resist to DDOS.

Reported-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Tom Herbert <therbert@google.com>
---
 net/ipv6/route.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d4ba3fc..fedbb41 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -840,6 +840,7 @@ static struct rt6_info *rt6_alloc_clone(struct rt6_info *ort,
 	struct rt6_info *rt = ip6_rt_copy(ort, daddr);
 
 	if (rt) {
+		rt->dst.flags |= DST_NOCACHE;
 		rt->rt6i_flags |= RTF_CACHE;
 		rt->n = neigh_clone(ort->n);
 	}
@@ -887,7 +888,7 @@ restart:
 
 	dst_hold(&rt->dst);
 	if (nrt) {
-		err = ip6_ins_rt(nrt);
+		err = (nrt->dst.flags & DST_NOCACHE) ? 0 : ip6_ins_rt(nrt);
 		if (!err)
 			goto out2;
 	}