From patchwork Mon Aug 10 21:05:16 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Seth Forshee X-Patchwork-Id: 6986151 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 939FD9F344 for ; Mon, 10 Aug 2015 21:05:58 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 8E57A2078D for ; Mon, 10 Aug 2015 21:05:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B9F92078F for ; Mon, 10 Aug 2015 21:05:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933325AbbHJVFx (ORCPT ); Mon, 10 Aug 2015 17:05:53 -0400 Received: from mail-ig0-f179.google.com ([209.85.213.179]:33366 "EHLO mail-ig0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933249AbbHJVFo (ORCPT ); Mon, 10 Aug 2015 17:05:44 -0400 Received: by igbpg9 with SMTP id pg9so78175964igb.0 for ; Mon, 10 Aug 2015 14:05:43 -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=IE8t7UYgz5GY0ej3/p7aJy4C8e1qWPBRIMwpQ8gq1BU=; b=nK+0ei5lKdIw8vSdmXGhqG6p9kNymKAWOlEE2u2PiObRAFW184WIkRxuWR9YWFjoZN RVGMy9tsLnliSH9BEns7VJROEGhrU0Doig446oujwfRq90JffJKudua+/5NGe3z1p0E4 fKzqWHekT6ajzeMyEe7szOW56u0g3E+ewFNMdqxo4afqywQwHBdynIpR93EmywK27M+4 rGUn6/Q0S6k0VvUANrJiGkSBDMQUzAMj1TuaZFtoAIUYnaERSqas1RDk0vZC9ITyyCYm UqH6vI6TbxSn+8DlYUlLOX950TulrV15UWntKMnsEfI7QU5hz/aLU8mVJhZipGw8jfxA JggQ== X-Gm-Message-State: ALoCoQksOngsoFlcMm1a51CAW9AJYYRBscN8cvbNMBhNhhepJWCCPvi2gFva8ybtqux31OhhftJY X-Received: by 10.50.36.1 with SMTP id m1mr3329167igj.4.1439240743687; Mon, 10 Aug 2015 14:05:43 -0700 (PDT) Received: from localhost (199-87-125-144.dyn.kc.surewest.net. [199.87.125.144]) by smtp.gmail.com with ESMTPSA id c91sm15947ioj.43.2015.08.10.14.05.43 (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Mon, 10 Aug 2015 14:05:43 -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 v2 5/7] fs: Treat foreign mounts as nosuid Date: Mon, 10 Aug 2015 16:05:16 -0500 Message-Id: <1439240719-46850-6-git-send-email-seth.forshee@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1439240719-46850-1-git-send-email-seth.forshee@canonical.com> References: <1439240719-46850-1-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=ham 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 e48fa1c23378..710aaa05cdaa 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 175ab497e810..858d86a1b73c 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -437,7 +437,7 @@ 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 564079c5c49d..459e71ddbc9d 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2137,7 +2137,7 @@ 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)