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=-0.8 required=3.0 tests=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 8FFB1C3F2D7 for ; Tue, 3 Mar 2020 10:25:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69CAE214D8 for ; Tue, 3 Mar 2020 10:25:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728613AbgCCKZw (ORCPT ); Tue, 3 Mar 2020 05:25:52 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:37483 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728473AbgCCKZw (ORCPT ); Tue, 3 Mar 2020 05:25:52 -0500 Received: from ip5f5bf7ec.dynamic.kabel-deutschland.de ([95.91.247.236] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1j94k9-00048f-UU; Tue, 03 Mar 2020 10:25:42 +0000 Date: Tue, 3 Mar 2020 11:25:41 +0100 From: Christian Brauner To: Miklos Szeredi 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 Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17] Message-ID: <20200303102541.diud7za3vvjvqco4@wittgenstein> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Mar 03, 2020 at 11:13:50AM +0100, Miklos Szeredi wrote: > 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 Even if it is a magic link to a safe place it's a magic link. They aren't a great solution to this problem. fsinfo() is cleaner and simpler as it creates a context for a supervised mount which gives the a managing application fine-grained control and makes it easily extendable. Also, we're apparently at the point where it seems were suggesting another (pseudo)filesystem to get information about filesystems. Christian