From patchwork Wed Sep 23 20:16:05 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Seth Forshee X-Patchwork-Id: 7252271 Return-Path: X-Original-To: patchwork-linux-fsdevel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id F0C84BEEC1 for ; Wed, 23 Sep 2015 20:17:14 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id ED7D520A29 for ; Wed, 23 Sep 2015 20:17:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCEAC20A1C for ; Wed, 23 Sep 2015 20:17:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755083AbbIWUQi (ORCPT ); Wed, 23 Sep 2015 16:16:38 -0400 Received: from mail-io0-f174.google.com ([209.85.223.174]:36326 "EHLO mail-io0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755042AbbIWUQf (ORCPT ); Wed, 23 Sep 2015 16:16:35 -0400 Received: by ioii196 with SMTP id i196so55324349ioi.3 for ; Wed, 23 Sep 2015 13:16:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=2J5/qzveZZ4iSRdgZfp6/6fQf8H3EU+TcJw7M4NG4+c=; b=lmIzynXabBOOFhSmpYpIJkADORlC7DcnCy6Kj/55CQeqaxgrVJjUovMqzdNWEoI8NV rekYMbKkGBJMuVmddQIMG08cq0tU+cJF7M3asRl0YdVDPHVAK4BUS2lORC7u1ZMzWS9N SHDaj+aLgyGpQCe0scNmoO5REtZx4KF8ZopaLjfFgl/rC1I83Cau41uaOKhNETwkZ3Qy mSS4uSpgy8ZkkqcNYMxGs5hWEzaMCCaeNYwgDlFbqQlOMGWaZBAwByeuKrncpeZcH9HY tOmq15OSKviEK0IrpFoIwRKhtSMFdO5rUnTkgEVSN/okA6dxrRzhy5vpboci9GshgJ09 JD4Q== X-Gm-Message-State: ALoCoQkpmgIKmM602g8xmfdF5tMcrxh8ceLivzeSSfzqCKC8Fm/eAUt86tDIIiLQJzg+UqW+5R9L X-Received: by 10.107.168.228 with SMTP id e97mr45493927ioj.7.1443039394618; Wed, 23 Sep 2015 13:16:34 -0700 (PDT) Received: from localhost (199-87-125-144.dyn.kc.surewest.net. [199.87.125.144]) by smtp.gmail.com with ESMTPSA id a193sm4189777ioe.37.2015.09.23.13.16.33 (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Wed, 23 Sep 2015 13:16:33 -0700 (PDT) From: Seth Forshee To: "Eric W. Biederman" , Alexander Viro , Serge Hallyn , James Morris , "Serge E. Hallyn" , Paul Moore , Stephen Smalley , Eric Paris Cc: Andy Lutomirski , linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, Seth Forshee Subject: [PATCH v4 5/7] fs: Treat foreign mounts as nosuid Date: Wed, 23 Sep 2015 15:16:05 -0500 Message-Id: <1443039368-55445-6-git-send-email-seth.forshee@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1443039368-55445-1-git-send-email-seth.forshee@canonical.com> References: <1443039368-55445-1-git-send-email-seth.forshee@canonical.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Spam-Status: No, score=-6.9 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 From: Andy Lutomirski If a process gets access to a mount from a different user namespace, that process should not be able to take advantage of setuid files or selinux entrypoints from that filesystem. Prevent this by treating mounts from other mount namespaces and those not owned by current_user_ns() or an ancestor as nosuid. This will make it safer to allow more complex filesystems to be mounted in non-root user namespaces. This does not remove the need for MNT_LOCK_NOSUID. The setuid, setgid, and file capability bits can no longer be abused if code in a user namespace were to clear nosuid on an untrusted filesystem, but this patch, by itself, is insufficient to protect the system from abuse of files that, when execed, would increase MAC privilege. As a more concrete explanation, any task that can manipulate a vfsmount associated with a given user namespace already has capabilities in that namespace and all of its descendents. If they can cause a malicious setuid, setgid, or file-caps executable to appear in that mount, then that executable will only allow them to elevate privileges in exactly the set of namespaces in which they are already privileges. On the other hand, if they can cause a malicious executable to appear with a dangerous MAC label, running it could change the caller's security context in a way that should not have been possible, even inside the namespace in which the task is confined. As a hardening measure, this would have made CVE-2014-5207 much more difficult to exploit. Signed-off-by: Andy Lutomirski Signed-off-by: Seth Forshee --- fs/exec.c | 2 +- fs/namespace.c | 13 +++++++++++++ include/linux/mount.h | 1 + security/commoncap.c | 2 +- security/selinux/hooks.c | 2 +- 5 files changed, 17 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index b06623a9347f..ea7311d72cc3 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1295,7 +1295,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm) bprm->cred->euid = current_euid(); bprm->cred->egid = current_egid(); - if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + if (!mnt_may_suid(bprm->file->f_path.mnt)) return; if (task_no_new_privs(current)) diff --git a/fs/namespace.c b/fs/namespace.c index da70f7c4ece1..2101ce7b96ab 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3276,6 +3276,19 @@ found: return visible; } +bool mnt_may_suid(struct vfsmount *mnt) +{ + /* + * Foreign mounts (accessed via fchdir or through /proc + * symlinks) are always treated as if they are nosuid. This + * prevents namespaces from trusting potentially unsafe + * suid/sgid bits, file caps, or security labels that originate + * in other namespaces. + */ + return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) && + in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns); +} + static struct ns_common *mntns_get(struct task_struct *task) { struct ns_common *ns = NULL; diff --git a/include/linux/mount.h b/include/linux/mount.h index f822c3c11377..54a594d49733 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -81,6 +81,7 @@ extern void mntput(struct vfsmount *mnt); extern struct vfsmount *mntget(struct vfsmount *mnt); extern struct vfsmount *mnt_clone_internal(struct path *path); extern int __mnt_is_readonly(struct vfsmount *mnt); +extern bool mnt_may_suid(struct vfsmount *mnt); struct path; extern struct vfsmount *clone_private_mount(struct path *path); diff --git a/security/commoncap.c b/security/commoncap.c index 400aa224b491..6243aef5860e 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -448,7 +448,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c if (!file_caps_enabled) return 0; - if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + if (!mnt_may_suid(bprm->file->f_path.mnt)) return 0; if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns)) return 0; diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index e4369d86e588..de05207eb665 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2171,7 +2171,7 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm, const struct task_security_struct *new_tsec) { int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS); - int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID); + int nosuid = !mnt_may_suid(bprm->file->f_path.mnt); int rc; if (!nnp && !nosuid)