From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753641AbcGVJmE (ORCPT ); Fri, 22 Jul 2016 05:42:04 -0400 Received: from out5-smtp.messagingengine.com ([66.111.4.29]:59708 "EHLO out5-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752059AbcGVJmB (ORCPT ); Fri, 22 Jul 2016 05:42:01 -0400 X-Sasl-enc: hNDrqVDOTJNSaRGoT+tVI/Hr8+HiKWm4j5oAts34Uvt6 1469180519 Subject: Re: [PATCH] net: neigh: disallow state transition DELAY->STALE in neigh_update() To: Julian Anastasov , Chunhui He References: <1469123890-2715-1-git-send-email-hchunhui@mail.ustc.edu.cn> Cc: "David S. Miller" , David Ahern , Nicolas Dichtel , Roopa Prabhu , Robert Shearman , David Barroso , Martin Zhang , Rick Jones , Konstantin Khlebnikov , Eric Dumazet , Thomas Graf , "Eric W. Biederman" , YOSHIFUJI Hideaki , netdev@vger.kernel.org, linux-kernel@vger.kernel.org From: Hannes Frederic Sowa Message-ID: Date: Fri, 22 Jul 2016 11:41:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22.07.2016 09:20, 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. > > 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). > > 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? This change makes perfectly sense to me. Reviewed-by: Hannes Frederic Sowa Thanks, Hannes