Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1271751

Re: [PATCH v3 4/7] fs: Treat foreign mounts as nosuid

Show all headers | View raw

On Tue, 17 Nov 2015, Seth Forshee wrote:

> From: Andy Lutomirski <luto@amacapital.net>
> 
> 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 <luto@amacapital.net>
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>


Acked-by: James Morris <james.l.morris@oracle.com>

-- 
James Morris
<jmorris@namei.org>

--
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/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH v3 4/7] fs: Treat foreign mounts as nosuid Seth Forshee <seth.forshee@canonical.com> - 2015-11-17 17:50 +0100
  Re: [PATCH v3 4/7] fs: Treat foreign mounts as nosuid James Morris <jmorris@namei.org> - 2015-11-18 01:10 +0100

csiph-web