Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935247AbcKNRRi (ORCPT ); Mon, 14 Nov 2016 12:17:38 -0500 Received: from mail-pg0-f49.google.com ([74.125.83.49]:36637 "EHLO mail-pg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933841AbcKNRRf (ORCPT ); Mon, 14 Nov 2016 12:17:35 -0500 Subject: Re: [PATCH v3] ip6_output: ensure flow saddr actually belongs to device To: Hannes Frederic Sowa , "Jason A. Donenfeld" , Netdev , WireGuard mailing list , LKML , YOSHIFUJI Hideaki References: <27cccef1-06d9-74b3-5b8a-912850119a76@cumulusnetworks.com> <20161113232813.28926-1-Jason@zx2c4.com> <1479141867.3723362.787321689.4A3DCFD6@webmail.messagingengine.com> <7d8c0210-9132-c755-9053-6ec19409e343@stressinduktion.org> From: David Ahern Message-ID: Date: Mon, 14 Nov 2016 10:17:32 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <7d8c0210-9132-c755-9053-6ec19409e343@stressinduktion.org> 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 Content-Length: 2893 Lines: 65 On 11/14/16 10:04 AM, Hannes Frederic Sowa wrote: > On 14.11.2016 17:55, David Ahern wrote: >> On 11/14/16 9:44 AM, Hannes Frederic Sowa wrote: >>> On Mon, Nov 14, 2016, at 00:28, Jason A. Donenfeld wrote: >>>> This puts the IPv6 routing functions in parity with the IPv4 routing >>>> functions. Namely, we now check in v6 that if a flowi6 requests an >>>> saddr, the returned dst actually corresponds to a net device that has >>>> that saddr. This mirrors the v4 logic with __ip_dev_find in >>>> __ip_route_output_key_hash. In the event that the returned dst is not >>>> for a dst with a dev that has the saddr, we return -EINVAL, just like >>>> v4; this makes it easy to use the same error handlers for both cases. >>>> >>>> Signed-off-by: Jason A. Donenfeld >>>> Cc: David Ahern >>>> --- >>>> Changes from v2: >>>> It turns out ipv6_chk_addr already has the device enumeration >>>> logic that we need by simply passing NULL. >>>> >>>> net/ipv6/ip6_output.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c >>>> index 6001e78..b3b5cb6 100644 >>>> --- a/net/ipv6/ip6_output.c >>>> +++ b/net/ipv6/ip6_output.c >>>> @@ -926,6 +926,10 @@ static int ip6_dst_lookup_tail(struct net *net, >>>> const struct sock *sk, >>>> int err; >>>> int flags = 0; >>>> >>>> + if (!ipv6_addr_any(&fl6->saddr) && >>>> + !ipv6_chk_addr(net, &fl6->saddr, NULL, 1)) >>>> + return -EINVAL; >>> >>> Hmm, this check is too permissive, no? >>> >>> E.g. what happens if you move a link local address from one interface to >>> another? In this case this code would still allow the saddr to be used. >> >> This check -- like the ipv4 variant -- only verifies the saddr is locally assigned. If the address moves interfaces it should be fine. > > But in this case we should actually bail out, no? > > Let's say, user assumes we are on ifindex eth0 with LL address from > eth0. Suddenly the LL address from eth0 is moved to eth1, we can't > accept this source address anymore and need to return -EINVAL, too. so you mean if rt6_need_strict(&fl6->saddr) then the dev needs to be considered. > >>> I just also quickly read up on the history (sorry was travelling last >>> week) and wonder if you ever saw a user space facing bug or if this is >>> basically some difference you saw while writing out of tree code? >> >> I checked the userspace API this morning. bind and cmsg for example check that the address is valid with calls to ipv6_chk_addr. > > Hmm, so it fixes no real bug. > > Because of translations of flowi6_oif we actually can't do a correct > check of source address for cases like the one I outlined above? Hmm, > maybe we should simply depend on user space checks. I believe Jason's case is forwarding path and the ipv6_stub->ipv6_dst_lookup API.