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[23.128.96.18]) by mx.google.com with ESMTP id qp3si338744ejb.382.2020.11.09.03.50.58; Mon, 09 Nov 2020 03:51:21 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=canonical.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729697AbgKILsj (ORCPT + 99 others); Mon, 9 Nov 2020 06:48:39 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:49915 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726410AbgKILsj (ORCPT ); Mon, 9 Nov 2020 06:48:39 -0500 Received: from 1.general.cascardo.us.vpn ([10.172.70.58] helo=mussarela) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1kc5f1-0007u3-1s; Mon, 09 Nov 2020 11:48:35 +0000 Date: Mon, 9 Nov 2020 08:48:28 -0300 From: Thadeu Lima de Souza Cascardo To: Jakub Kicinski Cc: Kleber Sacilotto de Souza , Eric Dumazet , netdev@vger.kernel.org, Gerrit Renker , "David S. Miller" , "Gustavo A. R. Silva" , "Alexander A. Klimov" , Kees Cook , Alexey Kodanev , dccp@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] dccp: ccid: move timers to struct dccp_sock Message-ID: <20201109114828.GP595944@mussarela> References: <20201013171849.236025-1-kleber.souza@canonical.com> <20201013171849.236025-2-kleber.souza@canonical.com> <20201016153016.04bffc1e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201016153016.04bffc1e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 16, 2020 at 03:30:16PM -0700, Jakub Kicinski wrote: > On Tue, 13 Oct 2020 19:18:48 +0200 Kleber Sacilotto de Souza wrote: > > From: Thadeu Lima de Souza Cascardo > > > > When dccps_hc_tx_ccid is freed, ccid timers may still trigger. The reason > > del_timer_sync can't be used is because this relies on keeping a reference > > to struct sock. But as we keep a pointer to dccps_hc_tx_ccid and free that > > during disconnect, the timer should really belong to struct dccp_sock. > > > > This addresses CVE-2020-16119. > > > > Fixes: 839a6094140a (net: dccp: Convert timers to use timer_setup()) > > Signed-off-by: Thadeu Lima de Souza Cascardo > > Signed-off-by: Kleber Sacilotto de Souza > > I've been mulling over this fix. > > The layering violation really doesn't sit well. > > We're reusing the timer object. What if we are really unlucky, the > fires and gets blocked by a cosmic ray just as it's about to try to > lock the socket, then user manages to reconnect, and timer starts > again. Potentially with a different CCID algo altogether? > > Is disconnect ever called under the BH lock? Maybe plumb a bool > argument through to ccid*_hc_tx_exit() and do a sk_stop_timer_sync() > when called from disconnect()? > > Or do refcounting on ccid_priv so that the timer holds both the socket > and the priv? Sorry about too late a response. I was on vacation, then came back and spent a couple of days testing this further, and had to switch to other tasks. So, while testing this, I had to resort to tricks like having a very small expire and enqueuing on a different CPU. Then, after some minutes, I hit a UAF. That's with or without the first of the second patch. I also tried to refcount ccid instead of the socket, keeping the timer on the ccid, but that still hit the UAF, and that's when I had to switch tasks. Oh, and in the meantime, I found one or two other fixes that we should apply, will send them shortly. But I would argue that we should apply the revert as it addresses the CVE, without really regressing the other UAF, as I argued. Does that make sense? Thank you. Cascardo.