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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 309B8C2BBCA for ; Wed, 16 Dec 2020 16:40:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 058C5233EB for ; Wed, 16 Dec 2020 16:40:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726745AbgLPQjr (ORCPT ); Wed, 16 Dec 2020 11:39:47 -0500 Received: from mx2.suse.de ([195.135.220.15]:47338 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726725AbgLPQjr (ORCPT ); Wed, 16 Dec 2020 11:39:47 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 6A76CAC7F; Wed, 16 Dec 2020 16:39:05 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 8FA5FDA6E1; Wed, 16 Dec 2020 17:37:25 +0100 (CET) Date: Wed, 16 Dec 2020 17:37:25 +0100 From: David Sterba To: Ondrej Mosnacek Cc: linux-fsdevel@vger.kernel.org, David Howells , Al Viro , linux-btrfs@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, Paul Moore , Stephen Smalley , Richard Haines Subject: Re: [PATCH] vfs: fix fsconfig(2) LSM mount option handling for btrfs Message-ID: <20201216163725.GG6430@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Ondrej Mosnacek , linux-fsdevel@vger.kernel.org, David Howells , Al Viro , linux-btrfs@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, Paul Moore , Stephen Smalley , Richard Haines References: <20201118102342.154277-1-omosnace@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201118102342.154277-1-omosnace@redhat.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Wed, Nov 18, 2020 at 11:23:42AM +0100, Ondrej Mosnacek wrote: > When SELinux security options are passed to btrfs via fsconfig(2) rather > than via mount(2), the operation aborts with an error. What happens is > roughly this sequence: > > 1. vfs_parse_fs_param() eats away the LSM options and parses them into > fc->security. > 2. legacy_get_tree() finds nothing in ctx->legacy_data, passes this > nothing to btrfs. > [here btrfs calls another layer of vfs_kern_mount(), but let's ignore > that for simplicity] > 3. btrfs calls security_sb_set_mnt_opts() with empty options. > 4. vfs_get_tree() then calls its own security_sb_set_mnt_opts() with the > options stashed in fc->security. > 5. SELinux doesn't like that different options were used for the same > superblock and returns -EINVAL. > > In the case of mount(2), the options are parsed by > legacy_parse_monolithic(), which skips the eating away of security > opts because of the FS_BINARY_MOUNTDATA flag, so they are passed to the > FS via ctx->legacy_data. The second call to security_sb_set_mnt_opts() > (from vfs_get_tree()) now passes empty opts, but the non-empty -> empty > sequence is allowed by SELinux for the FS_BINARY_MOUNTDATA case. > > It is a total mess, but the only sane fix for now seems to be to skip > processing the security opts in vfs_parse_fs_param() if the fc has > legacy opts set AND the fs specfies the FS_BINARY_MOUNTDATA flag. This > combination currently matches only btrfs and coda. For btrfs this fixes > the fsconfig(2) behavior, and for coda it makes setting security opts > via fsconfig(2) fail the same way as it would with mount(2) (because > FS_BINARY_MOUNTDATA filesystems are expected to call the mount opts LSM > hooks themselves, but coda never cared enough to do that). I believe > that is an acceptable state until both filesystems (or at least btrfs) > are converted to the new mount API (at which point btrfs won't need to > pretend it takes binary mount data any more and also won't need to call > the LSM hooks itself, assuming it will pass the fc->security information > properly). > > Note that we can't skip LSM opts handling in vfs_parse_fs_param() solely > based on FS_BINARY_MOUNTDATA because that would break NFS. > > See here for the original report and reproducer: > https://lore.kernel.org/selinux/c02674c970fa292610402aa866c4068772d9ad4e.camel@btinternet.com/ > > Reported-by: Richard Haines > Fixes: 3e1aeb00e6d1 ("vfs: Implement a filesystem superblock creation/configuration context") > Signed-off-by: Ondrej Mosnacek Can we get this merged via the vfs tree, please? Possibly with CC: stable@vger.kernel.org # 5.4+ > + /* > + * In the legacy+binary mode, skip the security_fs_context_parse_param() > + * call and let the legacy handler process also the security options. > + * It will format them into the monolithic string, where the FS can > + * process them (with FS_BINARY_MOUNTDATA it is expected to do it). > + * > + * Currently, this matches only btrfs and coda. Coda is broken with > + * fsconfig(2) anyway, because it does actually take binary data. Btrfs > + * only *pretends* to take binary data to work around the SELinux's > + * no-remount-with-different-options check, so this allows it to work > + * with fsconfig(2) properly. > + * > + * Once btrfs is ported to the new mount API, this hack can be reverted. > + */ > + if (fc->ops != &legacy_fs_context_ops || !(fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)) { Line is way over 80, it could be split like if (fc->ops != &legacy_fs_context_ops || !(fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)) { > + ret = security_fs_context_parse_param(fc, param); > + if (ret != -ENOPARAM) > + /* Param belongs to the LSM or is disallowed by the LSM; > + * so don't pass to the FS. > + */ The multi line comment should have the /* on a separate line (yes it's in the original code too but such things could be fixed when the code is moved). > + return ret; > + } > > if (fc->ops->parse_param) { > ret = fc->ops->parse_param(fc, param);