From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A75CC10F11 for ; Wed, 10 Apr 2019 09:45:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1637320830 for ; Wed, 10 Apr 2019 09:45:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730048AbfDJJpL (ORCPT ); Wed, 10 Apr 2019 05:45:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41688 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730039AbfDJJpL (ORCPT ); Wed, 10 Apr 2019 05:45:11 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 09EAF8124D; Wed, 10 Apr 2019 09:45:11 +0000 (UTC) Received: from bistromath.localdomain (unknown [10.40.205.249]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ACF5E608EB; Wed, 10 Apr 2019 09:45:09 +0000 (UTC) Date: Wed, 10 Apr 2019 11:45:07 +0200 From: Sabrina Dubroca To: Eric Dumazet Cc: netdev@vger.kernel.org, Jianlin Shi , Stefano Brivio Subject: Re: [PATCH net] net: enforce xmit_recursion for devices with a queue Message-ID: <20190410094507.GA16112@bistromath.localdomain> References: <6d9ed6c448a5c855e05abf19c205f33a66b6ff40.1552557395.git.sd@queasysnail.net> <20190314141505.GA1953@bistromath.localdomain> <20190314174038.GA18679@bistromath.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Wed, 10 Apr 2019 09:45:11 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi Eric, 2019-03-14, 10:51:49 -0700, Eric Dumazet wrote: > On 03/14/2019 10:40 AM, Sabrina Dubroca wrote: > > 2019-03-14, 07:56:10 -0700, Eric Dumazet wrote: > >> On 03/14/2019 07:15 AM, Sabrina Dubroca wrote: > >>> 2019-03-14, 05:58:03 -0700, Eric Dumazet wrote: > >>>> On 03/14/2019 03:15 AM, Sabrina Dubroca wrote: > >>>>> Commit 745e20f1b626 ("net: add a recursion limit in xmit path") > >>>>> introduced a recursion limit, but it only applies to devices without a > >>>>> queue. Virtual devices with a queue (either because they don't have > >>>>> the IFF_NO_QUEUE flag, or because the administrator added one) can > >>>>> still cause an unbounded recursion, via __dev_queue_xmit -> > >>>>> __dev_xmit_skb -> qdisc_run -> __qdisc_run -> qdisc_restart -> > >>>>> sch_direct_xmit -> dev_hard_start_xmit . Jianlin reported this in a > >>>>> setup with 16 gretap devices stacked on top of one another. > >>>>> > >>>>> This patch prevents the stack overflow by incrementing xmit_recursion in > >>>>> code paths that can call dev_hard_start_xmit() (like commit 745e20f1b626 > >>>>> did). If the recursion limit is exceeded, the packet is enqueued and the > >>>>> qdisc is scheduled. > >>>>> > >>>>> Reported-by: Jianlin Shi > >>>>> Signed-off-by: Sabrina Dubroca > >>>>> Reviewed-by: Stefano Brivio > >>>> > >>>> Hi Sabrina, thanks for the patch. > >>>> > >>>> Can't we detect this in the control path instead ? > >>> > >>> I don't see how. You could have a perfectly reasonable set of gretap > >>> devices that trigger this situation from simply reshuffling the IP > >>> addresses: > >>> > >>> gretap$x remote 1.1.$((x-1)).{1,2} > >>> (all those addresses set on a single veth device) > >>> > >>> Then you move those addresses to the corresponding device > >>> (1.1.${x}.{1,2} on gretap$x), and your machine crashes. > >>> > >> > >> If this only can be done with gretap, why gretap cant implement the protection, > >> outside of the fast path ? > > > > It's not just gretap. VXLAN will do the same as long as you add a > > qdisc. I expect other types of tunnels to behave like that. > > > > It might make sense to add a helper using dev_queue_xmit() > for tunnel users. > > Then remove the xmit recursion stuff out of the dev_queue_xmit() > > Lets make the fast path fast again. I've been looking into this. Ignoring devices that link themselves to their upper/lower (which would be easy to handle at setup time), we're left with IP/UDP tunnels (also easy to handle, they all xmit via a few output functions), and then a couple of weird cases: - vti/xfrmi call dst_output - ppp can end up calling ip_local_out, ip_queue_xmit, or ip6_xmit - some devices call dev_queue_xmit. we'd need a recursion-limited wrapper for those, without putting the penalty for users that respect the rules (core, linked devices). I don't see a way to enforce that (ipv6 needs dev_queue_xmit to be EXPORT'ed), and human review is not perfect, so some devices could slip in using the wrong dev_queue_xmit. I'm not convinced this change is worth the risk. -- Sabrina