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=-10.3 required=3.0 tests=BAYES_00,DATE_IN_PAST_12_24, DKIMWL_WL_MED,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no 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 6BEBBC4363A for ; Thu, 29 Oct 2020 00:05:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1294E207DE for ; Thu, 29 Oct 2020 00:05:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="HFAjXWqA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725951AbgJ2AEM (ORCPT ); Wed, 28 Oct 2020 20:04:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390741AbgJ2ADY (ORCPT ); Wed, 28 Oct 2020 20:03:24 -0400 Received: from mail-wr1-x431.google.com (mail-wr1-x431.google.com [IPv6:2a00:1450:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6483FC0613CF for ; Wed, 28 Oct 2020 17:03:23 -0700 (PDT) Received: by mail-wr1-x431.google.com with SMTP id s9so879536wro.8 for ; Wed, 28 Oct 2020 17:03:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AFQ11nKNwZI/oGFeZxcljdz8x6kEb8+uWHBsNPCDUO0=; b=HFAjXWqAbYshDr2yDxrNzRjLAazYy3NYleGOwhPwLv1pzOgTqSzUGl4QAew8/0Ue0Z UoM2bHGRSrCMkFFIE/eRm1e9A6GSJQQnBj0G0icXRTO3f42Z/TOgD2ZwXEDyH4EQzhtk ywG5wEF7+x5kI5uzusYn+VP7eFH2BvWpSYX2QaSH7NVhnOuxIXe879Y+CazILhKsmJD6 IL/m69v/0hvM8YmGddWOL1C5qP87stMvRtBRmf4MLpcBB3WPUywYeyXiWwll/+B6xjhd 0IHI4V6rTlKalnDT1Hs7tkfxy9/KFXAims9NH7Xvmh8xuaLNrqF4bCuC4UhMykb0uAU1 +C5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AFQ11nKNwZI/oGFeZxcljdz8x6kEb8+uWHBsNPCDUO0=; b=tBqZ3fNWTCSedwPoaQdcQZuanFnN9KAEUhctM/eXTEqigGdn3hbikLCiPeG2t3Wn1z a+RRco7edwCE02RjYGsZJ388NU4E9+Mk2oEqE8gFvUpPHJ1zAH2kHr8eBM40+6qx6/Q/ CmWKfWITzOHpxH3U8Pzd9zjDMleocRCBkEO0R9enGPBad9kk7/PfxU4oAG/ViEzW5Hvr PQA37Whf8Ow+f4HNMUwuRMLQqxamsegQMggiF4TlWAvhcAKqKEMJQQpTodfMIkyt4gGX BEmO/e5exiONoff5YK0A2pF6je8KNXQAQACZoiMLxD0cI+b6kT/IBzdShf98wI73tJ8s mLPg== X-Gm-Message-State: AOAM531FmGCIX26NjsnDAJ6tfIsf5ll0oi6FHqyZZgAzEoH2Q6N5IeT9 vv0epvqgwasRkOle4RwIbvAP3o+o5FLLcRaUaudqONpT6x8= X-Google-Smtp-Source: ABdhPJwVRGG3pvmn4VHogbgp0mRkC+3Vo3abv5ijmC6QlpCo8lhtrVsa4JWD3BkVHYUkQR8qg4e+R3v66NEu2I+If+A= X-Received: by 2002:a05:6512:1054:: with SMTP id c20mr2561887lfb.576.1603878221599; Wed, 28 Oct 2020 02:43:41 -0700 (PDT) MIME-Version: 1.0 References: <45f07f17-18b6-d187-0914-6f341fe90857@gmail.com> <20200930150330.GC284424@cisco> <8bcd956f-58d2-d2f0-ca7c-0a30f3fcd5b8@gmail.com> <20200930230327.GA1260245@cisco> <20200930232456.GB1260245@cisco> <656a37b5-75e3-0ded-6ba8-3bb57b537b24@gmail.com> In-Reply-To: From: Jann Horn Date: Wed, 28 Oct 2020 10:43:14 +0100 Message-ID: Subject: Re: For review: seccomp_user_notif(2) manual page To: Sargun Dhillon Cc: "Michael Kerrisk (man-pages)" , Tycho Andersen , Kees Cook , Christian Brauner , linux-man , lkml , Aleksa Sarai , Alexei Starovoitov , Will Drewry , bpf , Song Liu , Daniel Borkmann , Andy Lutomirski , Linux Containers , Giuseppe Scrivano , Robert Sesek Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org On Wed, Oct 28, 2020 at 7:32 AM Sargun Dhillon wrote: > On Tue, Oct 27, 2020 at 3:28 AM Jann Horn wrote: > > On Tue, Oct 27, 2020 at 7:14 AM Michael Kerrisk (man-pages) > > wrote: > > > On 10/26/20 4:54 PM, Jann Horn wrote: > > > > I'm a bit on the fence now on whether non-blocking mode should use > > > > ENOTCONN or not... I guess if we returned ENOENT even when there are > > > > no more listeners, you'd have to disambiguate through the poll() > > > > revents, which would be kinda ugly? > > > > > > I must confess, I'm not quite clear on which two cases you > > > are trying to distinguish. Can you elaborate? > > > > Let's say someone writes a program whose responsibilities are just to > > handle seccomp events and to listen on some other fd for commands. And > > this is implemented with an event loop. Then once all the target > > processes are gone (including zombie reaping), we'll start getting > > EPOLLERR. > > > > If NOTIF_RECV starts returning -ENOTCONN at this point, the event loop > > can just call into the seccomp logic without any arguments; it can > > just call NOTIF_RECV one more time, see the -ENOTCONN, and terminate. > > The downside is that there's one more error code userspace has to > > special-case. > > This would be more consistent with what we'd be doing in the blocking case. > > > > If NOTIF_RECV keeps returning -ENOENT, the event loop has to also tell > > the seccomp logic what the revents are. > > > > I guess it probably doesn't really matter much. > > So, in practice, if you're emulating a blocking syscall (such as open, > perf_event_open, or any of a number of other syscalls), you probably > have to do it on a separate thread in the supervisor because you want > to continue to be able to receive new notifications if any other process > generates a seccomp notification event that you need to handle. > > In addition to that, some of these syscalls are preemptible, so you need > to poll SECCOMP_IOCTL_NOTIF_ID_VALID to make sure that the program > under supervision hasn't left the syscall. > > If we're to implement a mechanism that makes the seccomp ioctl receive > non-blocking, it would be valuable to address this problem as well (getting > a notification when the supervisor is processing a syscall and needs to > preempt it). In the best case, this can be a minor inconvenience, and > in the worst case this can result in weird errors where you're keeping > resources open that the container expects to be closed. Does "a notification" mean signals? Or would you want to have a second thread in userspace that poll()s for cancellation events on the seccomp fd and then somehow takes care of interrupting the first thread, or something like that? Either way, I think your proposal goes beyond the scope of patching the existing weirdness, and should be a separate patch.