From patchwork Wed Jul 22 20:25:22 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stephen Smalley X-Patchwork-Id: 6846521 Return-Path: X-Original-To: patchwork-linux-fsdevel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 31DB79F1D4 for ; Wed, 22 Jul 2015 20:27:04 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 4414620663 for ; Wed, 22 Jul 2015 20:27:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F0B5205E7 for ; Wed, 22 Jul 2015 20:27:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752194AbbGVU0q (ORCPT ); Wed, 22 Jul 2015 16:26:46 -0400 Received: from emvm-gh1-uea08.nsa.gov ([63.239.67.9]:64670 "EHLO emvm-gh1-uea08.nsa.gov" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbbGVU0o (ORCPT ); Wed, 22 Jul 2015 16:26:44 -0400 X-TM-IMSS-Message-ID: <386af3e700075995@nsa.gov> Received: from tarius.tycho.ncsc.mil ([144.51.242.1]) by nsa.gov ([63.239.67.9]) with ESMTP (TREND IMSS SMTP Service 7.1) id 386af3e700075995 ; Wed, 22 Jul 2015 16:26:34 -0400 Received: from moss-pluto.infosec.tycho.ncsc.mil (moss-pluto [192.168.25.131]) by tarius.tycho.ncsc.mil (8.14.4/8.14.4) with ESMTP id t6MKPuTR020133; Wed, 22 Jul 2015 16:26:06 -0400 Message-ID: <55AFFC32.6070701@tycho.nsa.gov> Date: Wed, 22 Jul 2015 16:25:22 -0400 From: Stephen Smalley Organization: National Security Agency User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Seth Forshee CC: Serge Hallyn , linux-kernel@vger.kernel.org, Andy Lutomirski , linux-security-module@vger.kernel.org, James Morris , linux-fsdevel@vger.kernel.org, selinux@tycho.nsa.gov, Alexander Viro Subject: Re: [PATCH 6/7] selinux: Ignore security labels on user namespace mounts References: <1436989569-69582-1-git-send-email-seth.forshee@canonical.com> <1436989569-69582-7-git-send-email-seth.forshee@canonical.com> <55A7B055.4050809@tycho.nsa.gov> <55AFBE85.6010809@tycho.nsa.gov> <20150722161422.GC124342@ubuntu-hedt> In-Reply-To: <20150722161422.GC124342@ubuntu-hedt> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Spam-Status: No, score=-8.1 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 07/22/2015 12:14 PM, Seth Forshee wrote: > On Wed, Jul 22, 2015 at 12:02:13PM -0400, Stephen Smalley wrote: >> On 07/16/2015 09:23 AM, Stephen Smalley wrote: >>> On 07/15/2015 03:46 PM, Seth Forshee wrote: >>>> Unprivileged users should not be able to supply security labels >>>> in filesystems, nor should they be able to supply security >>>> contexts in unprivileged mounts. For any mount where s_user_ns is >>>> not init_user_ns, force the use of SECURITY_FS_USE_NONE behavior >>>> and return EPERM if any contexts are supplied in the mount >>>> options. >>>> >>>> Signed-off-by: Seth Forshee >>> >>> I think this is obsoleted by the subsequent discussion, but just for the >>> record: this patch would cause the files in the userns mount to be left >>> with the "unlabeled" label, and therefore under typical policies, >>> completely inaccessible to any process in a confined domain. >> >> The right way to handle this for SELinux would be to automatically use >> mountpoint labeling (SECURITY_FS_USE_MNTPOINT, normally set by >> specifying a context= mount option), with the sbsec->mntpoint_sid set >> from some related object (e.g. the block device file context, as in your >> patches for Smack). That will cause SELinux to use that value instead >> of any xattr value from the filesystem and will cause attempts by >> userspace to set the security.selinux xattr to fail on that filesystem. >> That is how SELinux normally deals with untrusted filesystems, except >> that it is normally specified as a mount option by a trusted mounting >> process, whereas in your case you need to automatically set it. > > Excellent, thank you for the advice. I'll start on this when I've > finished with Smack. Not tested, but something like this should work. Note that it should come after the call to security_fs_use() so we know whether SELinux would even try to use xattrs supplied by the filesystem in the first place. rc = may_context_mount_sb_relabel(fscontext_sid, sbsec, cred); @@ -813,6 +837,7 @@ static int selinux_set_mnt_opts(struct super_block *sb, sbsec->def_sid = defcontext_sid; } +out_set_opts: rc = sb_finish_set_opts(sb); out: mutex_unlock(&sbsec->lock); --- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 564079c..84da3a2 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -745,6 +745,30 @@ static int selinux_set_mnt_opts(struct super_block *sb, goto out; } } + + /* + * If this is a user namespace mount, no contexts are allowed + * on the command line and security labels must be ignored. + */ + if (sb->s_user_ns != &init_user_ns) { + if (context_sid || fscontext_sid || rootcontext_sid || + defcontext_sid) { + rc = -EACCES; + goto out; + } + if (sbsec->behavior == SECURITY_FS_USE_XATTR) { + struct block_device *bdev = sb->s_bdev; + sbsec->behavior = SECURITY_FS_USE_MNTPOINT; + if (bdev) { + struct inode_security_struct *isec = bdev->bd_inode; + sbsec->mntpoint_sid = isec->sid; + } else { + sbsec->mntpoint_sid = current_sid(); + } + } + goto out_set_opts; + } + /* sets the context of the superblock for the fs being mounted. */ if (fscontext_sid) {