From patchwork Mon Jan 4 18:03:42 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Seth Forshee X-Patchwork-Id: 7950221 Return-Path: X-Original-To: patchwork-selinux@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 41213BEEE5 for ; Mon, 4 Jan 2016 18:40:21 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 6F5CF20306 for ; Mon, 4 Jan 2016 18:40:20 +0000 (UTC) Received: from emvm-gh1-uea08.nsa.gov (emvm-gh1-uea08.nsa.gov [63.239.67.9]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2D39520304 for ; Mon, 4 Jan 2016 18:40:19 +0000 (UTC) X-TM-IMSS-Message-ID: <75d5d5a1001042b3@nsa.gov> Received: from tarius.tycho.ncsc.mil ([144.51.242.1]) by nsa.gov ([10.208.42.193]) with ESMTP (TREND IMSS SMTP Service 7.1) id 75d5d5a1001042b3 ; Mon, 4 Jan 2016 13:38:16 -0500 Received: from prometheus.infosec.tycho.ncsc.mil (prometheus [192.168.25.40]) by tarius.tycho.ncsc.mil (8.14.4/8.14.4) with ESMTP id u04IbK5r016991; Mon, 4 Jan 2016 13:37:24 -0500 Received: from tarius.tycho.ncsc.mil (tarius.infosec.tycho.ncsc.mil [144.51.242.1]) by prometheus.infosec.tycho.ncsc.mil (8.15.2/8.15.2) with ESMTP id u04I4VqH225762 for ; Mon, 4 Jan 2016 13:04:31 -0500 Received: from goalie.tycho.ncsc.mil (goalie [144.51.242.250]) by tarius.tycho.ncsc.mil (8.14.4/8.14.4) with ESMTP id u04I4Bek013312 for ; Mon, 4 Jan 2016 13:04:31 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A1CSAAAys4pWm6vVVdFeGQEBAQEPAQEBAYRJiFm1YQcYhXcCgWgBAQEBAQESAQEBAQEGCwsJIYRjAQEBAxIVGQEBNwEPIDE0AQUBHAYBEiKIDaJOgTE+MYpXhVQBBYweAQEBAQEBAQMCARoGCoQ7ghGMOAxBgTaONYhWlmqFYoxuNYEXgmgNFQeBfFMBhQ8BAQE X-IPAS-Result: A1CSAAAys4pWm6vVVdFeGQEBAQEPAQEBAYRJiFm1YQcYhXcCgWgBAQEBAQESAQEBAQEGCwsJIYRjAQEBAxIVGQEBNwEPIDE0AQUBHAYBEiKIDaJOgTE+MYpXhVQBBYweAQEBAQEBAQMCARoGCoQ7ghGMOAxBgTaONYhWlmqFYoxuNYEXgmgNFQeBfFMBhQ8BAQE X-IronPort-AV: E=Sophos;i="5.20,521,1444708800"; d="scan'208";a="5070746" Received: from emvm-gh1-uea08.nsa.gov ([10.208.42.193]) by goalie.tycho.ncsc.mil with ESMTP; 04 Jan 2016 13:04:16 -0500 X-TM-IMSS-Message-ID: <75b64f900010345c@nsa.gov> Received: from mail-ig0-f171.google.com (mail-ig0-f171.google.com [209.85.213.171]) by nsa.gov ([10.208.42.193]) with ESMTP (TREND IMSS SMTP Service 7.1; TLSv1/SSLv3 AES128-SHA (128/128)) id 75b64f900010345c ; Mon, 4 Jan 2016 13:03:50 -0500 Received: by mail-ig0-f171.google.com with SMTP id mv3so211778igc.0 for ; Mon, 04 Jan 2016 10:04:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=canonical-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=8WNqdXZ0ry06qHl5VOcMJSJORL1RtJ51/Xw8ltpq6gg=; b=D3uzLLG1Be9TQ2k50JdtwP5CujyrAX3h03AK+Vdep4XYeqdvOL6AEj1NTy0xuPy9iN T4f9tvvTan6fHYhjELzGgzDVk9EWvi2TQ731uKe3AEJTMDe6kaLwsZw6tV/1k61LX8wT qo5R5677SBevBYXBEqnWzwYCVX9QZP+eq7mANSC+D0p/z6LZLS64WGlzD1RYhmveMPh5 W9xb0gacb5tTFa2xsQwHnUFryR0qawPgnNRZTR09BazIgRXbtx2oe9ULS7Q5Ku5BVJzg lGFjV1dJETCwZhXakufHZKUNiKCxQZZLmeKFX+99qaYrVpSFxrcd8OCrzT3oCrHslvR3 pJ8w== 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=8WNqdXZ0ry06qHl5VOcMJSJORL1RtJ51/Xw8ltpq6gg=; b=DnrMcArSGr7uQSDm9r4CHRYjnqHkYzrsvSAoVxPApvDjhbYETdeEq5yYWMxqLSpDJs 3EwqTNms4baVSC8BdFog3Q0rW0bipElOWO/mIXZE3GKAyYTGJRLi3nsf9b9pC061+/qB D25+0FHBdbf6xBP1OHO6LRK25xsf9t9cymXbBTYpkBSceU7h53vG4udVILFxfy0tRPvZ 3WAgTs0GtrGAVNMKNSpwaYTJ0TuOHVUr/vhVR5UaUsZnDfDlmuNxTx8g4VOKKRwtQMOC LXV/6I73YzKVbDpQrg7LK0UfPij/VBnhSLcByeKcgkpoNEp4xTpG7w+O5gk+qH9/E8wt Tvtg== X-Gm-Message-State: ALoCoQmDPAtNkn4rVte2V0uUaLwRnzn1sJMroqsb29K2HBtMWzh5e6Odzo7h2HfF4hCB9CsVYp38gttVYT/2MzHqkmEczL4+jQ== X-Received: by 10.50.73.137 with SMTP id l9mr52495487igv.95.1451930654319; Mon, 04 Jan 2016 10:04:14 -0800 (PST) Received: from localhost ([66.64.121.229]) by smtp.gmail.com with ESMTPSA id t69sm21664358ioi.9.2016.01.04.10.04.13 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Mon, 04 Jan 2016 10:04:13 -0800 (PST) From: Seth Forshee To: "Eric W. Biederman" , Alexander Viro , Serge Hallyn , James Morris , "Serge E. Hallyn" , Paul Moore , Stephen Smalley , Eric Paris Subject: [PATCH RESEND v2 03/18] fs: Treat foreign mounts as nosuid Date: Mon, 4 Jan 2016 12:03:42 -0600 Message-Id: <1451930639-94331-4-git-send-email-seth.forshee@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1451930639-94331-1-git-send-email-seth.forshee@canonical.com> References: <1451930639-94331-1-git-send-email-seth.forshee@canonical.com> X-TM-AS-MML: disable X-Mailman-Approved-At: Mon, 04 Jan 2016 13:14:22 -0500 X-BeenThere: selinux@tycho.nsa.gov X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Security-Enhanced Linux \(SELinux\) mailing list" List-Post: List-Help: Cc: linux-security-module@vger.kernel.org, Seth Forshee , dm-devel@redhat.com, Miklos Szeredi , Richard Weinberger , linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, fuse-devel@lists.sourceforge.net, Austin S Hemmelgarn , linux-mtd@lists.infradead.org, selinux@tycho.nsa.gov, linux-fsdevel@vger.kernel.org, Andy Lutomirski MIME-Version: 1.0 Errors-To: selinux-bounces@tycho.nsa.gov Sender: "Selinux" X-Spam-Status: No, score=-6.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,T_DKIM_INVALID,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 Acked-by: James Morris Acked-by: Serge Hallyn --- 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 d0cfaa9f19d0..a5b93df6553f 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)