ipv6: Check expire on DST_NOCACHE route

Since the expires of the DST_NOCACHE rt can be set during
the ip6_rt_update_pmtu(), we also need to consider the expires
value when doing ip6_dst_check().

This patches creates __rt6_check_expired() to only
check the expire value (if one exists) of the current rt.

In rt6_dst_from_check(), it adds __rt6_check_expired() as
one of the condition check.
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -404,6 +404,14 @@ static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 	}
 }
 
+static bool __rt6_check_expired(const struct rt6_info *rt)
+{
+	if (rt->rt6i_flags & RTF_EXPIRES)
+		return time_after(jiffies, rt->dst.expires);
+	else
+		return false;
+}
+
 static bool rt6_check_expired(const struct rt6_info *rt)
 {
 	if (rt->rt6i_flags & RTF_EXPIRES) {
@@ -1252,7 +1260,8 @@ static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie)
 
 static struct dst_entry *rt6_dst_from_check(struct rt6_info *rt, u32 cookie)
 {
-	if (rt->dst.obsolete == DST_OBSOLETE_FORCE_CHK &&
+	if (!__rt6_check_expired(rt) &&
+	    rt->dst.obsolete == DST_OBSOLETE_FORCE_CHK &&
 	    rt6_check((struct rt6_info *)(rt->dst.from), cookie))
 		return &rt->dst;
 	else