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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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




[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux