From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752023AbcGYFUn (ORCPT ); Mon, 25 Jul 2016 01:20:43 -0400 Received: from mail-pa0-f49.google.com ([209.85.220.49]:34016 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbcGYFUf (ORCPT ); Mon, 25 Jul 2016 01:20:35 -0400 Subject: Re: [PATCH] net: neigh: disallow state transition DELAY->STALE in neigh_update() To: Chunhui He , ja@ssi.bg References: <1469123890-2715-1-git-send-email-hchunhui@mail.ustc.edu.cn> <20160722.124757.283248020246505940.hchunhui@mail.ustc.edu.cn> Cc: hideaki.yoshifuji@miraclelinux.com, davem@davemloft.net, dsa@cumulusnetworks.com, nicolas.dichtel@6wind.com, roopa@cumulusnetworks.com, rshearma@brocade.com, dbarroso@fastly.com, martinbj2008@gmail.com, rick.jones2@hp.com, koct9i@gmail.com, edumazet@google.com, tgraf@suug.ch, ebiederm@xmission.com, yoshfuji@linux-ipv6.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org From: =?UTF-8?B?WU9TSElGVUpJIEhpZGVha2kv5ZCJ6Jek6Iux5piO?= Organization: MIRACLE LINUX CORPORATION Message-ID: Date: Mon, 25 Jul 2016 14:20:29 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160722.124757.283248020246505940.hchunhui@mail.ustc.edu.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Chunhui He wrote: > Hi, > > On Fri, 22 Jul 2016 10:20:01 +0300 (EEST), Julian Anastasov wrote: >> >> Hello, >> >> On Thu, 21 Jul 2016, Chunhui He wrote: >> >>> If neigh entry was CONNECTED and address is not changed, and if new state is >>> STALE, entry state will not change. Because DELAY is not in CONNECTED, it's >>> possible to change state from DELAY to STALE. >>> >>> That is bad. Consider a host in IPv4 nerwork, a neigh entry in STALE state >>> is referenced to send packets, so goes to DELAY state. If the entry is not >>> confirmed by upper layer, it goes to PROBE state, and sends ARP request. >>> The neigh host sends ARP reply, then the entry goes to REACHABLE state. >>> But the entry state may be reseted to STALE by broadcast ARP packets, before >>> the entry goes to PROBE state. So it's possible that the entry will never go >>> to REACHABLE state, without external confirmation. >>> >>> In my case, the gateway refuses to send unicast packets to me, before it sees >>> my ARP request. So it's critical to enter REACHABLE state by sending ARP >>> request, but not by external confirmation. >>> >>> This fixes neigh_update() not to change to STALE if old state is CONNECTED or >>> DELAY. >>> >>> Signed-off-by: Chunhui He >>> --- >>> net/core/neighbour.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c >>> index 510cd62..29429eb 100644 >>> --- a/net/core/neighbour.c >>> +++ b/net/core/neighbour.c >>> @@ -1152,7 +1152,7 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new, >>> } else { >>> if (lladdr == neigh->ha && new == NUD_STALE && >>> ((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) || >>> - (old & NUD_CONNECTED)) >>> + (old & (NUD_CONNECTED | NUD_DELAY))) >>> ) >>> new = old; >>> } >> >> You change looks correct to me. But this place >> has more problems. There is no good reason to set NUD_STALE >> for any state that is NUD_VALID if address is not changed. >> This matches perfectly the comment above this code: >> NUD_STALE should change a NUD_VALID state only when >> address changes. It also means that IPv6 does not need >> to provide NEIGH_UPDATE_F_WEAK_OVERRIDE anymore when >> NEIGH_UPDATE_F_OVERRIDE is also present. >> > > The NEIGH_UPDATE_F_WEAK_OVERRIDE is confusing to me, so I choose not to deal > with the flag. IPv6 depends on WEAK_OVERRIDE. Please do not change. > >> By this way the state machine can continue with >> the resolving: NUD_STALE -> NUD_DELAY (traffic) -> >> NUD_PROBE (retries) -> NUD_REACHABLE (unicast reply) >> while the address is not changed. Your change covers only >> NUD_DELAY, not NUD_PROBE, so it is better to allow more >> retries to send. We should not give up until success (NUD_REACHABLE). >> > > I have thought about this. > The origin code allows NUD_DELAY -> NUD_STALE and NUD_PROBE -> NUD_STALE. > This part was imported to kernel since v2.1.79, I don't know clearly why it > allows that. > > My analysis: > (1) As shown in my previous mail, NUD_DELAY -> NUD_STALE may cause "dead loop", > so it should be fixed. > > (2) But NUD_PROBE -> NUD_STALE is acceptable, because in NUD_PROBE, ARP request > has been sent, it is sufficient to break the "dead loop". > More attempts are accomplished by the following sequence: > NUD_STALE --> NUD_DELAY -(sent req)-> NUD_PROBE -(reset by neigh_update())-> > NUD_STALE --> NUD_DELAY -(send req again)-> ... --> > NUD_REACHABLE > > > But I also agree your change. > >> Second problem: NEIGH_UPDATE_F_WEAK_OVERRIDE has no >> priority over NEIGH_UPDATE_F_ADMIN. For example, now I can not >> change from NUD_PERMANENT to NUD_STALE: >> >> # ip neigh add 192.168.168.111 lladdr 00:11:22:33:44:55 nud perm dev wlan0 >> # ip neigh show to 192.168.168.111 >> 192.168.168.111 dev wlan0 lladdr 00:11:22:33:44:55 PERMANENT >> # ip neigh change 192.168.168.111 lladdr 00:11:22:33:44:55 nud stale dev wlan0 >> # ip neigh show to 192.168.168.111 >> 192.168.168.111 dev wlan0 lladdr 00:11:22:33:44:55 PERMANENT >> >> IMHO, here is how this place should look: >> >> diff --git a/net/core/neighbour.c b/net/core/neighbour.c >> index 5cdc62a..2b1cb91 100644 >> --- a/net/core/neighbour.c >> +++ b/net/core/neighbour.c >> @@ -1151,10 +1151,8 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new, >> goto out; >> } else { >> if (lladdr == neigh->ha && new == NUD_STALE && >> - ((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) || >> - (old & NUD_CONNECTED)) >> - ) >> - new = old; >> + !(flags & NEIGH_UPDATE_F_ADMIN)) >> + goto out; >> } >> } >> >> Any thoughts? >> >> Regards >> >> -- >> Julian Anastasov > > Regards, > Chunhui He > -- 吉藤英明 ミラクル・リナックス株式会社 技術本部 サポート部