net: Handle null dst in rtnl_put_cacheinfo

Need to keep expires time for IPv6 routes in a dump of FIB entries.
Update rtnl_put_cacheinfo to allow dst to be NULL in which case
rta_cacheinfo will only contain non-dst data.
Signed-off-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -785,13 +785,15 @@ int rtnl_put_cacheinfo(struct sk_buff *skb, struct dst_entry *dst, u32 id,
 		       long expires, u32 error)
 {
 	struct rta_cacheinfo ci = {
-		.rta_lastuse = jiffies_delta_to_clock_t(jiffies - dst->lastuse),
-		.rta_used = dst->__use,
-		.rta_clntref = atomic_read(&(dst->__refcnt)),
 		.rta_error = error,
 		.rta_id =  id,
 	};
 
+	if (dst) {
+		ci.rta_lastuse = jiffies_delta_to_clock_t(jiffies - dst->lastuse);
+		ci.rta_used = dst->__use;
+		ci.rta_clntref = atomic_read(&dst->__refcnt);
+	}
 	if (expires) {
 		unsigned long clock;