From patchwork Tue Apr 26 19:36:19 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Seth Forshee X-Patchwork-Id: 8943961 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 57EB9BF440 for ; Tue, 26 Apr 2016 19:46:48 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 5483F200FE for ; Tue, 26 Apr 2016 19:46:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E41420125 for ; Tue, 26 Apr 2016 19:46:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752865AbcDZTqj (ORCPT ); Tue, 26 Apr 2016 15:46:39 -0400 Received: from mail-ig0-f169.google.com ([209.85.213.169]:38090 "EHLO mail-ig0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752504AbcDZTg4 (ORCPT ); Tue, 26 Apr 2016 15:36:56 -0400 Received: by mail-ig0-f169.google.com with SMTP id m9so22479981ige.1 for ; Tue, 26 Apr 2016 12:36:55 -0700 (PDT) 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=MPLhsonP/9xhn9KHapaFYigvUMsYtA5c20UuB7nSdQ0=; b=kqFS97zlO25mB+SBjzy0lMKcbFA4TX5zrkQH/fDHBSqJajLX9z/fOEkmHSTlzOWajq PwrySybLsfoBEtr1Do4Rh+wm5/wTfiGBKdzIidMei6E7+O6yGrPH9lXNhlNMO6J5MLrb SF5K0L1aZEIsbXbPAe9wpMkd8CHiLLLSIJR7AIviC823WUkCyL91mbd7i1EKdNFMz4Hr 9b4LwroJQEOOiijFnQroINJVk981F2hMYCLZdLj1U6GuwC13kqSmx0X9ujOkXFL9P4rX Uh7+C+NjLXhjiDFBFI3HF85nIVsVfVyE3LBjmCd6vnL7aT7SS8OW+Ylf7alck9blUKP/ h6FQ== 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=MPLhsonP/9xhn9KHapaFYigvUMsYtA5c20UuB7nSdQ0=; b=EWofgInnDpNfk1oIQSkdiFJLSeWBw2fVSUPjHHenaqlrI3BXnDGMq0W5vS2sFhe9OF M5oOgjI4Yg7LVmjHaZu5hVqeSs6hIbfoqSf2a/yHtOgymbBvwAe1mM8XmOqvNNDsilgb smm1stOtxzQWumOoixy8bNhiQtU/JqKSQKJpjj7GUunLwG6RVY1s4CLOTnAKt5L+MClr SiVm9Kgc8pOi7iLjX+EBeK1O1chtauMLmfWupJ29aEye4ghEruR4NvXvq0M0ANBgk6N2 JQpeUe1IIRkcC+1cM/l2zjVnqv/W3biaJaB9aY9NrP3GzUrIeOmiXNnzexwZW/X6vp2M Mk4g== X-Gm-Message-State: AOPr4FWsXEnbeO9kfRjwOv5NqslJJ0FXv/YIvcd2/xSUjwZJZgEiEmb2+Z3eCfHHkPfCWMfL X-Received: by 10.50.160.41 with SMTP id xh9mr5560244igb.64.1461699415231; Tue, 26 Apr 2016 12:36:55 -0700 (PDT) Received: from localhost ([2605:a601:aab:f920:39a1:5bcf:aa:5b00]) by smtp.gmail.com with ESMTPSA id m143sm2345985ioe.43.2016.04.26.12.36.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Apr 2016 12:36:54 -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: Richard Weinberger , Austin S Hemmelgarn , Miklos Szeredi , Pavel Tikhomirov , linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.sourceforge.net, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, cgroups@vger.kernel.org, Seth Forshee , Andy Lutomirski Subject: [PATCH v4 06/21] fs: Treat foreign mounts as nosuid Date: Tue, 26 Apr 2016 14:36:19 -0500 Message-Id: <1461699396-33000-7-git-send-email-seth.forshee@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1461699396-33000-1-git-send-email-seth.forshee@canonical.com> References: <1461699396-33000-1-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=-7.8 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 | 8 +++++++- security/selinux/hooks.c | 2 +- 5 files changed, 23 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index c4010b8207a1..706088dd0cb1 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1391,7 +1391,7 @@ 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 c133318bec35..6e9db4c166b4 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3284,6 +3284,19 @@ 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 8912ef117faa..a306c5d90709 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -453,8 +453,14 @@ 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; + + /* + * This check is redundant with mnt_may_suid() but is kept to make + * explicit that capability bits are limited to s_user_ns and its + * descendants. + */ 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 912deee3f01e..1350167635cb 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2234,7 +2234,7 @@ 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)