Messages in this thread | | | Date | Wed, 18 Nov 2015 11:00:53 +1100 (AEDT) | From | James Morris <> | Subject | Re: [PATCH v3 4/7] fs: Treat foreign mounts as nosuid |
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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>
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