From mboxrd@z Thu Jan 1 00:00:00 1970 From: Flavio Leitner Subject: Re: ICMP redirect issue Date: Wed, 28 Sep 2011 17:19:52 -0300 Message-ID: <20110928171952.0c0d2d05@asterix.rh> References: <20110927162120.30394030@asterix.rh> <20110928.140632.726302773135946390.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: David Miller Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42576 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752221Ab1I1UT4 (ORCPT ); Wed, 28 Sep 2011 16:19:56 -0400 In-Reply-To: <20110928.140632.726302773135946390.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 28 Sep 2011 14:06:32 -0400 (EDT) David Miller wrote: > From: Flavio Leitner > Date: Tue, 27 Sep 2011 16:21:20 -0300 > > > The issue is about the gateway being a LVS, so the servers behind > > use the IP alias address as the default gateway. However, when the > > gateway sends an ICMP redirect, it comes from the primary IP > > address which is ignored on older kernels because of the old_gw > > check: > > > > - if (rth->rt_dst != daddr || > > - rth->rt_src != saddr || > > - rth->dst.error || > > - rth->rt_gateway != old_gw || > > - rth->dst.dev != dev) > > - break; > > > > > > Well, the consequence is that the issue doesn't happen in newer > > kernels because it happily accepts the ICMP redirect. > > > > The admin can still control using shared_media and secure_redirects > > if the host should accept only the ICMP redirects for gateways > > listed in default gateway list or not. > > Unfortunately, shared_media is on by default which means the default > secure_redirects setting of '1' is ignored. > > This means that redirects can be spoofed in the default configuration, > but with the above check they would not be spoofable. I fail to see what that check is preventing because if someone manages to inject a redirect packet into the network, then likely the old_gw can be tweaked to be the network gateway. > I suspect that, because of this, we'll need to add the check back. Or > do something similar. > > We can't "fix" this by turning shared_media off by default because > that changes behavior on input route processing wrt. how we decide > whether to emit a redirect or not. What about something like below? It will change a bit the secure_redirects documentation. shared_media secure_redirect behavior: 0 0 all pass. 0 1 only from gateways and for gateways. 1 0 all pass. 1 1 default, old behavior, only from gateways. If you agree with the approach, I'll run tests here and post the patch with a proper changelog, documentation and signed-off. thanks, fbl diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 075212e..fa00fcd 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1332,6 +1332,9 @@ void ip_rt_redirect(__be32 old_gw, __be32 daddr, __be32 new_gw, goto reject_redirect; } + if (IN_DEV_SEC_REDIRECTS(in_dev) && ip_fib_check_default(old_gw, dev)) + goto reject_redirect; + peer = inet_getpeer_v4(daddr, 1); if (peer) { peer->redirect_learned.a4 = new_gw;