ipv6: fix incorrect route 'expires' value passed to userspace

When userspace use RTM_GETROUTE to dump route table, with an already
expired route entry, we always got an 'expires' value(2147157)
calculated base on INT_MAX.

The reason of this problem is in the following satement:
	rt->dst.expires - jiffies < INT_MAX
gcc promoted the type of both sides of '<' to unsigned long, thus
a small negative value would be considered greater than INT_MAX.

With the help of Eric Dumazet, do the out of bound checks in
rtnl_put_cacheinfo(), _after_ conversion to clock_t.
Signed-off-by: Li Wei <lw@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -625,9 +625,13 @@ int rtnl_put_cacheinfo(struct sk_buff *skb, struct dst_entry *dst, u32 id,
 		.rta_id =  id,
 	};
 
-	if (expires)
-		ci.rta_expires = jiffies_to_clock_t(expires);
+	if (expires) {
+		unsigned long clock;
 
+		clock = jiffies_to_clock_t(abs(expires));
+		clock = min_t(unsigned long, clock, INT_MAX);
+		ci.rta_expires = (expires > 0) ? clock : -clock;
+	}
 	return nla_put(skb, RTA_CACHEINFO, sizeof(ci), &ci);
 }
 EXPORT_SYMBOL_GPL(rtnl_put_cacheinfo);

net/ipv6/route.c

@@ -2480,12 +2480,8 @@ static int rt6_fill_node(struct net *net,
 		goto nla_put_failure;
 	if (nla_put_u32(skb, RTA_PRIORITY, rt->rt6i_metric))
 		goto nla_put_failure;
-	if (!(rt->rt6i_flags & RTF_EXPIRES))
-		expires = 0;
-	else if (rt->dst.expires - jiffies < INT_MAX)
-		expires = rt->dst.expires - jiffies;
-	else
-		expires = INT_MAX;
+
+	expires = (rt->rt6i_flags & RTF_EXPIRES) ? rt->dst.expires - jiffies : 0;
 
 	if (rtnl_put_cacheinfo(skb, &rt->dst, 0, expires, rt->dst.error) < 0)
 		goto nla_put_failure;