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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 5A94CC2BC61 for ; Tue, 30 Oct 2018 21:42:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 04EC42081B for ; Tue, 30 Oct 2018 21:42:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="XgnxQlPD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 04EC42081B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=joelfernandes.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727762AbeJaGh5 (ORCPT ); Wed, 31 Oct 2018 02:37:57 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:45998 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726287AbeJaGh4 (ORCPT ); Wed, 31 Oct 2018 02:37:56 -0400 Received: by mail-pl1-f193.google.com with SMTP id o19-v6so6183556pll.12 for ; Tue, 30 Oct 2018 14:42:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=8QCqJgAl8VSP/+D43xtXMFyyZG8G6+6kHrj6YGCEpCk=; b=XgnxQlPD2f8Qek79sXGB73Xfa4NzxlSnaepLiclWLwb3CqlyuC17NBzH9tqp8weudx BW4szGyWPtU71JTOy3JPZwci2zAKxZheVzYD2xmaPbyCBaHbAGIcTqckCVu3FkfepKM/ n082dHxnGH/SnK+KgNbIOdKCUJk3EUppztPfw= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=8QCqJgAl8VSP/+D43xtXMFyyZG8G6+6kHrj6YGCEpCk=; b=Zs7bHi9yQBbgJFyPRnZfHiEgUpehUA1qiKVhWtuXTYbK0Oq1vBWJSod2OPSLMf0GSb Tap7QgVJivXhquwB10ulhvF3NVkmThsosf5z5zUROKIMdCM47FalIv/lZrzBj6r+UnQM 1qseeQYJB7OYqRRRWNEn5/4uXpNZtFe5Nz+OlsmVs3ymdSXRuPzYn+Rk9xwOP20iAuR4 KsSyWd7FlLGVQErq9foEgM7fQE2fFLUTI+7BAQj1zW4bPcdslBoaTUX2xmYBw+JGXv1P vbU7B0yV8HMLMI721l/TiJUcX7KAYZNYKHiJEcPKtaVBABekWvRwWwmT2+2a4AHlnaiu wjuA== X-Gm-Message-State: AGRZ1gITG8mLEIgb8VaNqbhe5T7MhvE0IbZQR4+HSjY6R6i83GpyGQPg ryUxDy8TZOvHER7MKjykK1tXVA== X-Google-Smtp-Source: AJdET5fA+ctJuBwPZIErrkAakA+rA5rpjcduM8yHEcnStBRoIDy94qX4NuwzMhl7rQjfIy/YKYUd5g== X-Received: by 2002:a17:902:b784:: with SMTP id e4-v6mr415126pls.45.1540935766477; Tue, 30 Oct 2018 14:42:46 -0700 (PDT) Received: from localhost ([2620:0:1000:1601:3aef:314f:b9ea:889f]) by smtp.gmail.com with ESMTPSA id x189-v6sm20318323pfb.162.2018.10.30.14.42.44 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 30 Oct 2018 14:42:44 -0700 (PDT) Date: Tue, 30 Oct 2018 14:42:43 -0700 From: Joel Fernandes To: Aleksa Sarai Cc: Daniel Colascione , linux-kernel , Tim Murray , Suren Baghdasaryan Subject: Re: [RFC PATCH] Implement /proc/pid/kill Message-ID: <20181030214243.GB32621@google.com> References: <20181029221037.87724-1-dancol@google.com> <20181030050012.u43lcvydy6nom3ul@yavin> <20181030204501.jnbe7dyqui47hd2x@yavin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181030204501.jnbe7dyqui47hd2x@yavin> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 31, 2018 at 07:45:01AM +1100, Aleksa Sarai wrote: [...] > > > (Unfortunately > > > there are lots of things that make it a bit difficult to use /proc/$pid > > > exclusively for introspection of a process -- especially in the context > > > of containers.) > > > > Tons of things already break without a working /proc. What do you have in mind? > > Heh, if only that was the only blocker. :P > > The basic problem is that currently container runtimes either depend on > some non-transient on-disk state (which becomes invalid on machine > reboots or dead processes and so on), or on long-running processes that > keep file descriptors required for administration of a container alive > (think O_PATH to /dev/pts/ptmx to avoid malicious container filesystem > attacks). Usually both. > > What would be really useful would be having some way of "hiding away" a > mount namespace (of the pid1 of the container) that has all of the > information and bind-mounts-to-file-descriptors that are necessary for > administration. If the container's pid1 dies all of the transient state > has disappeared automatically -- because the stashed mount namespace has > died. In addition, if this was done the way I'm thinking with (and this > is the contentious bit) hierarchical mount namespaces you could make it > so that the pid1 could not manipulate its current mount namespace to > confuse the administrative process. You would also then create an > intermediate user namespace to help with several race conditions (that > have caused security bugs like CVE-2016-9962) we've seen when joining > containers. > > Unfortunately this all depends on hierarchical mount namespaces (and > note that this would just be that NS_GET_PARENT gives you the mount > namespace that it was created in -- I'm not suggesting we redesign peers > or anything like that). This makes it basically a non-starter. > > But if, on top of this ground-work, we then referenced containers > entirely via an fd to /proc/$pid then you could also avoid PID reuse > races (as well as being able to find out implicitly whether a container > has died thanks to the error semantics of /proc/$pid). And that's the > way I would suggest doing it (if we had these other things in place). I didn't fully follow exactly what you mean. If you can explain for the layman who doesn't know much experience with containers.. Are you saying that keeping open a /proc/$pid directory handle is not sufficient to prevent PID reuse while the proc entries under /proc/$pid are being looked into? If its not sufficient, then isn't that a bug? If it is sufficient, then can we not just keep the handle open while we do whatever we want under /proc/$pid ? - Joel