From owner-freebsd-net@freebsd.org Tue Jun 28 17:51:44 2016 Return-Path: Delivered-To: freebsd-net@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A0666B85BC5 for ; Tue, 28 Jun 2016 17:51:44 +0000 (UTC) (envelope-from mmacy@nextbsd.org) Received: from mailman.ysv.freebsd.org (mailman.ysv.freebsd.org [IPv6:2001:1900:2254:206a::50:5]) by mx1.freebsd.org (Postfix) with ESMTP id 8BEAF20CD for ; Tue, 28 Jun 2016 17:51:44 +0000 (UTC) (envelope-from mmacy@nextbsd.org) Received: by mailman.ysv.freebsd.org (Postfix) id 87C56B85BC4; Tue, 28 Jun 2016 17:51:44 +0000 (UTC) Delivered-To: net@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 851BDB85BC3 for ; Tue, 28 Jun 2016 17:51:44 +0000 (UTC) (envelope-from mmacy@nextbsd.org) Received: from sender163-mail.zoho.com (sender163-mail.zoho.com [74.201.84.163]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 72AEA20CA; Tue, 28 Jun 2016 17:51:44 +0000 (UTC) (envelope-from mmacy@nextbsd.org) Received: from mail.zoho.com by mx.zohomail.com with SMTP id 1467136299583362.64681424073865; Tue, 28 Jun 2016 10:51:39 -0700 (PDT) Date: Tue, 28 Jun 2016 10:51:39 -0700 From: Matthew Macy To: "Julien Charbon" Cc: "Randall Stewart" , "" , "" , "" Message-ID: <15598235139.12175f84421756.2471769249719458878@nextbsd.org> In-Reply-To: References: <20160617045319.GE1076@FreeBSD.org> <1f28844b-b4ea-b544-3892-811f2be327b9@freebsd.org> <20160620073917.GI1076@FreeBSD.org> <1d18d0e2-3e42-cb26-928c-2989d0751884@freebsd.org> <20160620095822.GJ1076@FreeBSD.org> <74bb31b7-a9f5-3d0c-eea0-681872e6f09b@freebsd.org> <18D94615-810E-4E79-A889-4B0CC70F9E45@netflix.com> <6E52CA6A-2153-4EF9-A3E1-97CB0D07EB28@freebsd.org> Subject: Re: panic with tcp timers MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Priority: Medium User-Agent: Zoho Mail X-Mailer: Zoho Mail X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Jun 2016 17:51:44 -0000 You guys should really look at Samy Bahra's epoch based reclamation. I solved a similar problem in drm/linuxkpi using it. -M ---- On Tue, 28 Jun 2016 02:58:56 -0700 Julien Charbon wrote ---- > > Hi Randall, > > On 6/25/16 4:41 PM, Randall Stewart via freebsd-net wrote: > > Ok > > > > Lets try this again with my source changed to my @freebsd.net :-) > > > > Now I am also attaching a patch for you Gleb, this will take some poking to > > get in to your NF-head since it incorporates some changes we made earlier. > > > > I think this will fix the problem.. i.e. dealing with two locks in the callout system (which it was > > never meant to have done).. > > > > Note we probably can move the code to use the callout lock init now.. but lets see if this works > > on your setup on c096 and if so we can think about doing that. > > Thanks for proposing a patch. I believe your patch will work with > callout lock init, but not without: You still have a use-after-free > issue on the tcpcb without callout lock init. > > The case being subtle as usual, let me try to describe that could happen: > > With your patch we have: > > void > tcp_timer_keep(void *xtp) > { > struct tcpcb *tp = xtp; > struct tcptemp *t_template; > struct inpcb *inp; > CURVNET_SET(tp->t_vnet); > #ifdef TCPDEBUG > int ostate; > > ostate = tp->t_state; > #endif > inp = tp->t_inpcb; > KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, > tp)); > INP_WLOCK(inp); > if (callout_pending(&tp->t_timers->tt_keep) ### Use after free > of tp here > !callout_active(&tp->t_timers->tt_keep)) { > INP_WUNLOCK(inp); > CURVNET_RESTORE(); > return; > } > ... > > The use-after-free scenario: > > [CPU 1] the callout fires, tcp_timer_keep entered > [CPU 1] blocks on INP_WLOCK(inp); > [CPU 2] schedules tcp_timer_keep with callout_reset() > [CPU 2] tcp_discardcb called > [CPU 2] tcp_timer_keep callout successfully canceled > [CPU 2] tcpcb freed > [CPU 1] unblocks, the tcpcb is used > > Then the tcpcb will used just after being freed... Might also crash or > not depending in the case. > > Extra notes: > > o The invariant I see here is: The "callout successfully canceled" > step should never happen when "the callout is currently being executed". > > o Solutions I see to enforce this invariant: > > - First solution: Use callout lock init with inp lock, your patch > seems to permit that now. > > - Second solution: Change callout_async_drain() behavior: It can > return 0 (fail) when the callout is currently being executed (no matter > what). > > - Third solution: Don't trust callout_async_drain(callout) return > value of 1 (success) if the previous call of callout_reset(callout) > returned 0 (fail). That was the exact purpose of r284261 change, but > this solution is also step backward in modernization of TCP > timers/callout... > > https://svnweb.freebsd.org/base/stable/10/sys/netinet/tcp_timer.c?r1=284261&r2=284260&pathrev=284261 > > Hopefully my description is clear enough... > > -- > Julien > >