Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756765AbbGQGqU (ORCPT ); Fri, 17 Jul 2015 02:46:20 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:38833 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752674AbbGQGqS (ORCPT ); Fri, 17 Jul 2015 02:46:18 -0400 Message-ID: <55A8A4B4.3050202@siteground.com> Date: Fri, 17 Jul 2015 09:46:12 +0300 From: Nikolay Borisov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Seth Forshee , "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 Subject: Re: [PATCH 4/7] fs: Treat foreign mounts as nosuid References: <1436989569-69582-1-git-send-email-seth.forshee@canonical.com> <1436989569-69582-5-git-send-email-seth.forshee@canonical.com> In-Reply-To: <1436989569-69582-5-git-send-email-seth.forshee@canonical.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5224 Lines: 133 On 07/15/2015 10:46 PM, Seth Forshee wrote: > From: Andy Lutomirski > > If a process gets access to a mount from a different namespace user > namespace, that process should not be able to take advantage of > setuid files or selinux entrypoints from that filesystem. > Technically, trusting mounts created by the same or ancestor user > namespaces ought to be safe, but it's simpler to distrust all > foreign mounts. > > 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 > [ saf: Forward ported to 4.2 ] > 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 423001de32a2..2bfd7ca92247 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -3252,6 +3252,19 @@ 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 real_mount(mnt)->mnt_ns == current->nsproxy->mnt_ns && > + !(mnt->mnt_flags & MNT_NOSUID); Maybe check_mnt() from fs/namespace.c can be exported and used here, instead of open coding it. > +} > + > 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) > -- 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/