net/ipv6: do not copy dst flags on rt init

DST_NOCOUNT in dst_entry::flags tracks whether the entry counts
toward route cache size (net->ipv6.sysctl.ip6_rt_max_size).

If the flag is NOT set, dst_ops::pcpuc_entries counter is incremented
in dist_init() and decremented in dst_destroy().

This flag is tied to allocation/deallocation of dst_entry and
should not be copied from another dst/route. Otherwise it can happen
that dst_ops::pcpuc_entries counter grows until no new routes can
be allocated because the counter reached ip6_rt_max_size due to
DST_NOCOUNT not set and thus no counter decrements on gc-ed routes.

Fixes: 3b6761d1 ("net/ipv6: Move dst flags to booleans in fib entries")
Cc: David Ahern <dsahern@gmail.com>
Acked-by: NWei Wang <weiwan@google.com>
Signed-off-by: NPeter Oskolkov <posk@google.com>
Reviewed-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -946,8 +946,6 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
 
 static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
 {
-	rt->dst.flags |= fib6_info_dst_flags(ort);
-
 	if (ort->fib6_flags & RTF_REJECT) {
 		ip6_rt_init_dst_reject(rt, ort);
 		return;