From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Ricardo Leitner Subject: Re: [PATCH net-next 1/5] sctp: add the rhashtable apis for sctp global transport hashtable Date: Mon, 11 Jan 2016 16:19:57 -0200 Message-ID: <20160111181957.GD6074@mrl.redhat.com> References: <20151230.125046.310343849422003518.davem@davemloft.net> <20160111093210.GA23557@gondor.apana.org.au> <20160111163337.GC6074@mrl.redhat.com> <5693EFB8.4090604@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Herbert Xu , David Miller , eric.dumazet@gmail.com, lucien.xin@gmail.com, netdev@vger.kernel.org, linux-sctp@vger.kernel.org, mleitner@redhat.com, vyasevic@redhat.com, daniel@iogearbox.net To: Vlad Yasevich Return-path: Received: from mx1.redhat.com ([209.132.183.28]:35203 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932541AbcAKSUC (ORCPT ); Mon, 11 Jan 2016 13:20:02 -0500 Content-Disposition: inline In-Reply-To: <5693EFB8.4090604@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Jan 11, 2016 at 01:08:56PM -0500, Vlad Yasevich wrote: > On 01/11/2016 11:33 AM, Marcelo Ricardo Leitner wrote: > > On Mon, Jan 11, 2016 at 05:32:10PM +0800, Herbert Xu wrote: > >> David Miller wrote: > >>> From: Eric Dumazet > >>> Date: Wed, 30 Dec 2015 11:57:31 -0500 > >>> > >>>> I am against using rhashtable in SCTP (or TCP) at this stage, given the > >>>> number of bugs we have with it. > >>> > >>> Come on Eric, we've largely dealt with all of these problems. I haven't > >>> seen a serious report in a while. > >> > >> Well there is still the outstanding issue with softirq insertion > >> potentially failing with ENOMEM if we fail to expand the hash > >> table using just kmalloc. > >> > >> So if the target user does softirq insertions, I would wait until > >> the fix for that is ready. > > > > It does some, yes. If listening socket is not backlogged, there will be > > N inserts at each new association, where N is the number of IP addresses > > that the client is advertising. > > > > This is done on the second stage of the SCTP handshake. Not easily > > DoS-able as it requires receiving a packet from server and replying > > based on it, plus N is limited by MTU. > > How is N limited by MTU? INIT and COOKIE chunks are allowed to exceed > mtu and will be IP fragmented. So it seems that N is limited by 65535-overhead, > where overhead is all the headers plus the sctp cookie info. That can > be quite a lot of addresses. Oups, you're right. One then can trigger quite some inserts with a single new assoc attempt, yes. Marcelo