From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752564AbeBDUdy (ORCPT ); Sun, 4 Feb 2018 15:33:54 -0500 Received: from mail.kernel.org ([198.145.29.99]:55332 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751797AbeBDUdq (ORCPT ); Sun, 4 Feb 2018 15:33:46 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 33813217B4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org X-Google-Smtp-Source: AH8x224stQo7p+C+wx3/xW/i1VcRFIIrBhpqAgFE1d5n7s9UpTld2WXsM8Gnc/EfXcY1VGZ/31MwYYB/mkmFNec2Lcs= MIME-Version: 1.0 In-Reply-To: <20180204200129.2bgq5yfaimg6xdg5@cisco> References: <20180204104946.25559-1-tycho@tycho.ws> <20180204104946.25559-2-tycho@tycho.ws> <20180204200129.2bgq5yfaimg6xdg5@cisco> From: Andy Lutomirski Date: Sun, 4 Feb 2018 20:33:25 +0000 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC 1/3] seccomp: add a return code to trap to userspace To: Tycho Andersen Cc: LKML , Linux Containers , Kees Cook , Oleg Nesterov , "Eric W . Biederman" , "Serge E . Hallyn" , Christian Brauner , Tyler Hicks , Akihiro Suda Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Feb 4, 2018 at 8:01 PM, Tycho Andersen wrote: > Hi Andy, > > On Sun, Feb 04, 2018 at 05:36:33PM +0000, Andy Lutomirski wrote: >> > The actual implementation of this is fairly small, although getting the >> > synchronization right was/is slightly complex. Also worth noting that there >> > is one race still present: >> > >> > 1. a task does a SECCOMP_RET_USER_NOTIF >> > 2. the userspace handler reads this notification >> > 3. the task dies >> > 4. a new task with the same pid starts >> > 5. this new task does a SECCOMP_RET_USER_NOTIF, gets the same cookie id >> > that the previous one did >> > 6. the userspace handler writes a response >> >> I'm slightly confused. I thought the id was never reused for a given >> struct seccomp_filter. (Also, shouldn't the id be u64, not u32?) > > Well, what happens when u32/64 overflows? Eventually it will wrap. I think we can safely assume that u64 won't overflow. Even if we processed one user return notification on a given seccomp_filter every nanosecond (which would be insanely fast), that's 584 years. > >> On very quick reading, I have a question. What happens if a process >> has two seccomp_filters attached, one of them returns >> SECCOMP_RET_USER_NOTIF, and the *other* one has a listener? > > Good question, in seccomp_run_filters(), the first (lowest, last > applied) filter who returns SECCOMP_RET_USER_NOTIF is the one that > gets the notification and the other receives nothing. > > I don't really have any reason to prefer this behavior, it's just what > happened without much thought. Hmm. This won't nest right. Maybe we should just disallow a user-notification-using filter from being applied if there is already one in the stack. Then, if anyone cares about making these things nest right, they can fix it.