From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: Re: [PATCH 1/3 v4] ipv6: do not disable temp_address when reaching max_address Date: Thu, 15 Aug 2013 03:24:57 +0200 Message-ID: <20130815012457.GD13066@order.stressinduktion.org> References: <520B48AE.8050103@huawei.com> <20130814101511.GC16264@order.stressinduktion.org> <520C241A.2030708@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , Jon Maloy , Eric Dumazet , Netdev , kargig@void.gr, ppandit@redhat.com To: Ding Tianhong Return-path: Received: from order.stressinduktion.org ([87.106.68.36]:52619 "EHLO order.stressinduktion.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758345Ab3HOBY6 (ORCPT ); Wed, 14 Aug 2013 21:24:58 -0400 Content-Disposition: inline In-Reply-To: <520C241A.2030708@huawei.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Aug 15, 2013 at 08:43:06AM +0800, Ding Tianhong wrote: > On 2013/8/14 18:15, Hannes Frederic Sowa wrote: > > On Wed, Aug 14, 2013 at 05:06:54PM +0800, Ding Tianhong wrote: > >> A LAN user can remotely disable temporary address which may lead > >> to privacy violatins and information disclosure. > >> > >> The reason is that the linux kernel uses the 'ipv6.max_addresses' > >> option to specify how many ipv6 addresses and interface may have. > >> The 'ipv6.regen_max_retry' (default value 3) option specifies > >> how many times the kernel will try to create a new address. > >> > >> But the kernel is not distinguish between the event of reaching > >> max_addresses for an interface and failing to generate a new address. > >> the kernel disable the temporary address after regenerate a new > >> address 'regen_max_retry' times. > >> > >> According RFC4941 3.3.7: > >> > >> --------------------------------------- > >> > >> If DAD indicates the address is already in use, > >> the node must generate a new randomized interface > >> identifier as described in section 3.2 above, and > >> repeat the previous steps as appropriate up to > >> TEMP_IDGEN_RETRIES times. > >> > >> If after TEMP_IDGEN_RETRIES consecutive attempts no > >> non-unique address was generated, the node must log > >> a system error and must not attempt to generate > >> temporary address for that interface. > >> > >> ------------------------------------------ > >> > >> RFC4941 3.3.7 specifies that disabling the temp_address must happen > >> upon the address is already in use, not reach the max_address, > >> So we have to check the return err and distinguish the correct retry path. > >> > >> This fixes CVE-2013-0343 > > > > I don't think this patch fixes CVE-2013-0343. > > > >> > >> Signed-off-by: Ding Tianhong > >> Tested-by: Wang Weidong > >> Cc: David S. Miller > >> Cc: Sergei Shtylyov > >> Cc: Eric Dumazet > >> --- > >> net/ipv6/addrconf.c | 26 ++++++++++++++++++++++---- > >> 1 file changed, 22 insertions(+), 4 deletions(-) > >> > >> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c > >> index da4241c..7b55464 100644 > >> --- a/net/ipv6/addrconf.c > >> +++ b/net/ipv6/addrconf.c > >> @@ -1134,10 +1134,28 @@ retry: > >> if (IS_ERR_OR_NULL(ift)) { > >> in6_ifa_put(ifp); > >> in6_dev_put(idev); > >> - pr_info("%s: retry temporary address regeneration\n", __func__); > >> - tmpaddr = &addr; > >> - write_lock(&idev->lock); > >> - goto retry; > >> + > >> + /* According RFC4941 3.3.7: > >> + * If DAD indicates the address is already in use, > >> + * the node must generate a new randomized interface > >> + * identifier as described in section 3.2 above, and > >> + * repeat the previous steps as appropriate up to > >> + * TEMP_IDGEN_RETRIES times. > >> + * If after TEMP_IDGEN_RETRIES consecutive attempts no > >> + * non-unique address was generated, the node must log > >> + * a system error and must not attempt to generate > >> + * temporary address for that interface. > >> + * So we have to check the return err and distinguish > >> + * the correct retry path. > >> + */ > >> + if (PTR_ERR(ift) == -EEXIST) { > > > > -EEXIST is not the same as "ipv6 address is is already used on the > > subnet". I really don't see the point here. IMHO this breaks the intended > > regeneration logic. > > > > I fear a fix of CVE-2013-0343 will be a bit more complicated. ;) I give it a > > thought. > > > > Greetings, > > > > Hannes > > > > > ok, thanks for your feedback, I'll waiting you for more information to fix the problem.:) [added George Kargiotakis and P J P to Cc and full quote] I wonder if the easiest solution would be to just drop the max_addresses limit from ipv6_create_tempaddr. max_addresses protects the kernel from installing an unlimited amount of addresses on an interface which gets flooded by RAs. Because we have a direct relation between interface address to temp address, I don't see that we would create the possiblity of DoS. Sure, an audit and testing is needed. Greetings, Hannes