On Tue, Oct 14, 2014 at 04:54:47PM -0700, Andy Lutomirski wrote: > 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 <luto@xxxxxxxxxxxxxx> Now that I'm back from plumbers I've finally had a chance to play around with this and it seems to be working as expected. I'll be considering this patch a prerequisite for the next round of fuse userns patches. Acked-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
