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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 620BBC3F2C6 for ; Tue, 3 Mar 2020 10:14:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3C41821739 for ; Tue, 3 Mar 2020 10:14:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=szeredi.hu header.i=@szeredi.hu header.b="DGmhYfC5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728390AbgCCKOD (ORCPT ); Tue, 3 Mar 2020 05:14:03 -0500 Received: from mail-io1-f67.google.com ([209.85.166.67]:35481 "EHLO mail-io1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728242AbgCCKOC (ORCPT ); Tue, 3 Mar 2020 05:14:02 -0500 Received: by mail-io1-f67.google.com with SMTP id h8so2970961iob.2 for ; Tue, 03 Mar 2020 02:14:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=szeredi.hu; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=b2RBPOL2BrDy7cKCO1Q5lEU/UoBlA1lcG/mr7sg6aho=; b=DGmhYfC5yifUx3aXvV8ewsx6O+UEOBQA3YCM/g6FC5pPZCL9yDHh0H5nXhEGrlvABM 13rZWLc9/U//n7geEywqlCvA0G/75x1YfkBw95ZRiPc/tSiDPvb39cmStjXS8fjqkOqg EVmoHGDfiX+gCofo6bAPD7JZ3U7pKiqMYrLMU= 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=b2RBPOL2BrDy7cKCO1Q5lEU/UoBlA1lcG/mr7sg6aho=; b=GPTQA7DnFidcHAe4noxJuwFEvsPDq8INJJWFYz7Q9KUU0teJ3vIFWgORw7GJemNVxd f2nUEb0/IjMr+27mFPU2x+xYK8rQPHk+9CzKnJz2ONoJhKAV66VYydnlAWiZS/om8Clp VnztbUbusTyuLc3QcPYl7wO3jLa9lyhsBvOhnO7vusEyCOurH5zqCsAGgWp/nM1Y+KS0 eLUOWI4qE4XN1h5dFSiz/rr1qIKU7yDaSB4hq7WqfEdoqHEoHq1Wilo06zYk7J3kZr4B MeuW1jmFg3dUCwp6Vq5verfLaotJBz7AERQOn32Y5aTQvFEHPyJPH5IVg9vqSywQHRir dEhg== X-Gm-Message-State: ANhLgQ2dYhYKzi6/1HFWAJyfy2H8UAiOiH0xTzJsB3hoPP6HvU7FwEVK IXcfjt/oCJI2dtUR38tHvF6Kf0o+ekouTXoVXamKig== X-Google-Smtp-Source: ADFU+vtYbimVsSQ/gMcWk1r7TNYrGFmLUDHEqAGO+I0gRUGAdGR15kWk81wm/ejVzaxci+dihgL9H4IJMGx7CeV29mo= X-Received: by 2002:a6b:db08:: with SMTP id t8mr3190746ioc.285.1583230441732; Tue, 03 Mar 2020 02:14:01 -0800 (PST) MIME-Version: 1.0 References: <1582644535.3361.8.camel@HansenPartnership.com> <20200228155244.k4h4hz3dqhl7q7ks@wittgenstein> <107666.1582907766@warthog.procyon.org.uk> <0403cda7345e34c800eec8e2870a1917a8c07e5c.camel@themaw.net> <1509948.1583226773@warthog.procyon.org.uk> <20200303100045.zqntjjjv6npvs5zl@wittgenstein> In-Reply-To: <20200303100045.zqntjjjv6npvs5zl@wittgenstein> From: Miklos Szeredi Date: Tue, 3 Mar 2020 11:13:50 +0100 Message-ID: Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17] To: Christian Brauner Cc: David Howells , Ian Kent , James Bottomley , Steven Whitehouse , Miklos Szeredi , viro , Christian Brauner , Jann Horn , "Darrick J. Wong" , Linux API , linux-fsdevel , lkml , Greg Kroah-Hartman Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Mar 3, 2020 at 11:00 AM Christian Brauner wrote: > > On Tue, Mar 03, 2020 at 10:26:21AM +0100, Miklos Szeredi wrote: > > On Tue, Mar 3, 2020 at 10:13 AM David Howells wrote: > > > > > > Miklos Szeredi wrote: > > > > > > > I'm doing a patch. Let's see how it fares in the face of all these > > > > preconceptions. > > > > > > Don't forget the efficiency criterion. One reason for going with fsinfo(2) is > > > that scanning /proc/mounts when there are a lot of mounts in the system is > > > slow (not to mention the global lock that is held during the read). > > > > > > Now, going with sysfs files on top of procfs links might avoid the global > > > lock, and you can avoid rereading the options string if you export a change > > > notification, but you're going to end up injecting a whole lot of pathwalk > > > latency into the system. > > > > Completely irrelevant. Cached lookup is so much optimized, that you > > won't be able to see any of it. > > > > No, I don't think this is going to be a performance issue at all, but > > if anything we could introduce a syscall > > > > ssize_t readfile(int dfd, const char *path, char *buf, size_t > > bufsize, int flags); > > > > that is basically the equivalent of open + read + close, or even a > > vectored variant that reads multiple files. But that's off topic > > again, since I don't think there's going to be any performance issue > > even with plain I/O syscalls. > > > > > > > > On top of that, it isn't going to help with the case that I'm working towards > > > implementing where a container manager can monitor for mounts taking place > > > inside the container and supervise them. What I'm proposing is that during > > > the action phase (eg. FSCONFIG_CMD_CREATE), fsconfig() would hand an fd > > > referring to the context under construction to the manager, which would then > > > be able to call fsinfo() to query it and fsconfig() to adjust it, reject it or > > > permit it. Something like: > > > > > > fd = receive_context_to_supervise(); > > > struct fsinfo_params params = { > > > .flags = FSINFO_FLAGS_QUERY_FSCONTEXT, > > > .request = FSINFO_ATTR_SB_OPTIONS, > > > }; > > > fsinfo(fd, NULL, ¶ms, sizeof(params), buffer, sizeof(buffer)); > > > supervise_parameters(buffer); > > > fsconfig(fd, FSCONFIG_SET_FLAG, "hard", NULL, 0); > > > fsconfig(fd, FSCONFIG_SET_STRING, "vers", "4.2", 0); > > > fsconfig(fd, FSCONFIG_CMD_SUPERVISE_CREATE, NULL, NULL, 0); > > > struct fsinfo_params params = { > > > .flags = FSINFO_FLAGS_QUERY_FSCONTEXT, > > > .request = FSINFO_ATTR_SB_NOTIFICATIONS, > > > }; > > > struct fsinfo_sb_notifications sbnotify; > > > fsinfo(fd, NULL, ¶ms, sizeof(params), &sbnotify, sizeof(sbnotify)); > > > watch_super(fd, "", AT_EMPTY_PATH, watch_fd, 0x03); > > > fsconfig(fd, FSCONFIG_CMD_SUPERVISE_PERMIT, NULL, NULL, 0); > > > close(fd); > > > > > > However, the supervised mount may be happening in a completely different set > > > of namespaces, in which case the supervisor presumably wouldn't be able to see > > > the links in procfs and the relevant portions of sysfs. > > > > It would be a "jump" link to the otherwise invisible directory. > > More magic links to beam you around sounds like a bad idea. We had a > bunch of CVEs around them in containers and they were one of the major > reasons behind us pushing for openat2(). That's why it has a > RESOLVE_NO_MAGICLINKS flag. No, that link wouldn't beam you around at all, it would end up in an internally mounted instance of a mountfs, a safe place where no dangerous CVE's roam. Thanks, Miklos