Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755059AbbLDQzL (ORCPT ); Fri, 4 Dec 2015 11:55:11 -0500 Received: from h2.hallyn.com ([78.46.35.8]:41683 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753763AbbLDQzI (ORCPT ); Fri, 4 Dec 2015 11:55:08 -0500 Date: Fri, 4 Dec 2015 10:55:05 -0600 From: "Serge E. Hallyn" To: Seth Forshee Cc: "Eric W. Biederman" , Alexander Viro , Serge Hallyn , James Morris , "Serge E. Hallyn" , Paul Moore , Stephen Smalley , Eric Paris , Richard Weinberger , Austin S Hemmelgarn , Miklos Szeredi , linux-bcache@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-kernel@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, Andy Lutomirski Subject: Re: [PATCH 03/19] fs: Treat foreign mounts as nosuid Message-ID: <20151204165505.GE1722@mail.hallyn.com> References: <1449070821-73820-1-git-send-email-seth.forshee@canonical.com> <1449070821-73820-4-git-send-email-seth.forshee@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1449070821-73820-4-git-send-email-seth.forshee@canonical.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5236 Lines: 130 On Wed, Dec 02, 2015 at 09:40:03AM -0600, Seth Forshee wrote: > 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) > -- > 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/