From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [PATCH net v2 1/9] bridge: Fix the way to find old local fdb entries in br_fdb_changeaddr Date: Tue, 07 Jan 2014 12:45:53 -0500 Message-ID: <52CC3D51.6090903@redhat.com> References: <1387281821-21342-1-git-send-email-makita.toshiaki@lab.ntt.co.jp> <1387281821-21342-2-git-send-email-makita.toshiaki@lab.ntt.co.jp> <52C70F63.4020604@redhat.com> <52C7218C.2000205@redhat.com> <1388935578.1906.26.camel@localhost.localdomain> <52CA9398.3090603@redhat.com> <1389098578.3768.12.camel@ubuntu-vm-makita> <52CC12CA.7030001@redhat.com> <1389112385.1751.17.camel@localhost.localdomain> Reply-To: vyasevic@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Toshiaki Makita , "David S . Miller" , Stephen Hemminger , netdev@vger.kernel.org To: Toshiaki Makita Return-path: Received: from mx1.redhat.com ([209.132.183.28]:23241 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751963AbaAGRqC (ORCPT ); Tue, 7 Jan 2014 12:46:02 -0500 In-Reply-To: <1389112385.1751.17.camel@localhost.localdomain> Sender: netdev-owner@vger.kernel.org List-ID: On 01/07/2014 11:33 AM, Toshiaki Makita wrote: > On Tue, 2014-01-07 at 09:44 -0500, Vlad Yasevich wrote: >> On 01/07/2014 07:42 AM, Toshiaki Makita wrote: >>> On Mon, 2014-01-06 at 06:29 -0500, Vlad Yasevich wrote: >>>> On 01/05/2014 10:26 AM, Toshiaki Makita wrote: >>>>> On Fri, 2014-01-03 at 15:46 -0500, Vlad Yasevich wrote: >>>>>> On 01/03/2014 02:28 PM, Vlad Yasevich wrote: >>>>>>> On 12/17/2013 07:03 AM, Toshiaki Makita wrote: >>>>>>>> br_fdb_changeaddr() assumes that there is at most one local entry per port >>>>>>>> per vlan. It used to be true, but since commit 36fd2b63e3b4 ("bridge: allow >>>>>>>> creating/deleting fdb entries via netlink"), it has not been so. >>>>>>>> Therefore, the function might fail to search a correct previous address >>>>>>>> to be deleted and delete an arbitrary local entry if user has added local >>>>>>>> entries manually. >>>>>>>> >>>>>>>> Example of problematic case: >>>>>>>> ip link set eth0 address ee:ff:12:34:56:78 >>>>>>>> brctl addif br0 eth0 >>>>>>>> bridge fdb add 12:34:56:78:90:ab dev eth0 master >>>>>>>> ip link set eth0 address aa:bb:cc:dd:ee:ff >>>>>>>> Then, the address 12:34:56:78:90:ab might be deleted instead of >>>>>>>> ee:ff:12:34:56:78, the original mac address of eth0. >>>>>>>> >>>>>>>> Address this issue by introducing a new flag, added_by_user, to struct >>>>>>>> net_bridge_fdb_entry. >>>>>>>> >>>>>>>> Note that br_fdb_delete_by_port() has to set added_by_user to 0 in case >>>>>>>> like: >>>>>>>> ip link set eth0 address 12:34:56:78:90:ab >>>>>>>> ip link set eth1 address aa:bb:cc:dd:ee:ff >>>>>>>> brctl addif br0 eth0 >>>>>>>> bridge fdb add aa:bb:cc:dd:ee:ff dev eth0 master >>>>>>>> brctl addif br0 eth1 >>>>>>>> brctl delif br0 eth0 >>>>>>>> In this case, kernel should delete the user-added entry aa:bb:cc:dd:ee:ff, >>>>>>>> but it also should have been added by "brctl addif br0 eth1" originally, >>>>>>>> so we don't delete it and treat it a new kernel-created entry. >>>>>>>> >>>>>>> >>>>>>> I was looking over my patch series that adds something similar to this >>>>>>> and noticed that you are not handing the NTF_USE case. That case was >>>>>>> always troublesome for me as it allows for 2 different way to create >>>>>>> the same FDB: one through br_fdb_update() and one through fdb_add_entry(). >>>>>>> >>>>>>> It is possible, though I haven't found any users yet, that NTF_USE >>>>>>> may be used and in that case, bridge will create a dynamic fdb and >>>>>>> disregard all NUD flags. In case case, add_by_user will not be set >>>>>>> either. >>>>>>> >>>>>>> I think that the above is broken and plan to submit a fix shortly. >>>>>> >>>>>> Just looked again at my NTF_USE patch and while it seems ok, the whole >>>>>> NTF_USE usage is racy to begin with and I am really starting to question >>>>>> it's validity. >>>>>> >>>>>> Presently, br_fdb_update() will not update local fdb entries. Instead >>>>>> it will log a misleading warning... It will only let you update >>>>>> non-local entries. This is fine for user-created entries, but any >>>>>> operation on dynamically created entries will only persist until >>>>>> the next packet. It also races against the packet, so there is >>>>>> absolutely no guarantee that the values of fdb->dst and fdb->updated >>>>>> will be consistent.. >>>>>> >>>>>> It seems to me that the update capability of NTF_USE would actually be >>>>>> of more value on local or user-created fdb entries. >>>>>> >>>>>> The fdb creation capability of NTF_USE should be disabled. >>>>>> >>>>>> Thoughts? >>>>> >>>>> I ignored NTF_USE in this patch because I regard it as emulating kernel >>>>> creating entries after investigating git log. >>>>> >>>>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=0c5c2d3089068d4aa378f7a40d2b5ad9d4f52ce8 >>>>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=292d1398983f3514a0eab13b7606df7f4730b498 >>>>> >>>>> So I think NTF_USE shouldn't set added_by_user. >>>>> And to emulate kernel creating entries, simply calling br_fdb_update() >>>>> is the right way, isn't it? >>>> >>>> You can create dynamic entries (emulating the kernel) without NTF_USE. >>>> Just set the NUD_REACHABLE. Notice that arp cache only uses NTF_USE >>>> to trigger and arp notification. The creation is still triggered via >>>> other netlink flags. >>>> >>>> The more I look at this the more I think NTF_USE should not create >>>> an entry all by itself. >>> >>> I haven't fully understood you yet. >>> Currently NTF_USE behaves as if the port receives a frame and it seems >>> to work, though the ability to create entries is different from neigh >>> subsystem. >>> Why do you want to change the behavior? >>> Are you worried about inconsistency of NLM-flags/NUD-state with NTF_USE >>> between neigh and bridge? >> >> No, it is inconsistent with other NLM/NUD-state within bridge. As >> an fdb creation flag NTF_USE is confusing. It will create an entry >> without NLM_F_CREATE being set. It will ignore NLM_F_EXCL flag as >> well. It will additionally ignore any NUD-state flags that may be set >> in the netlink message. So it may not be doing what the user wishes. > > I don't know which of NTF-flags and NLM-flags/NUD-state should be given > high priority on setting. For now, in bridge, NTF_USE masks any other > flags. If this is not proper way for netlink/neighbour, I will agree > with you. If not sure, I have no motivation to change existing behavior > that might be expected by some users. > >> >> It also provides duplicate functionality. The same results are achieved >> by setting NLM_F_CREATE flag and NUD_REACHABLE state in the message. > > br_fdb_update() never updates fdb->used, which is visible by user, > unlike fdb_add_entry(). Thanks for pointing this out. It looks like there are some inconsistencies in the fdb->used markings as well. > > If it is duplicate functionality, isn't NTF_USE itself no use? > What can be achieved by changing capability of creation and update of > local entries? Update of local entries gives you port redirection, but doing it under rcu. Not sure if it really makes much sense though... NTF_USE makes since for neighbor cache as it triggers an ARP and a refresh of the entry. Suppose, NTF_USE on the fdb entry should trigger a refresh as well, but causing a create has to be explicit. I think I'll just send my patch and we can continue this discussion there. -vlad > > Thanks, > Toshiaki Makita >