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Date: Thu, 17 Dec 2015 23:54:03 +0000
From: Serge Hallyn <>
Cc: John Johansen <>
Subject: Re: Re: CVE Request: Linux kernel: privilege
 escalation in user namespaces

Quoting Jann Horn (
> On Thu, Dec 17, 2015 at 02:39:58PM -0800, John Johansen wrote:
> > I haven't seen CVE request for this one yet so,
> > 
> > Jann Horn reported a privilege escalation in user namespaces to the
> > lkml mailing list
> > 
> >
> > 
> > if a root-owned process wants to enter a user
> > namespace for some reason without knowing who owns it and
> > therefore can't change to the namespace owner's uid and gid
> > before entering, as soon as it has entered the namespace,
> > the namespace owner can attach to it via ptrace and thereby
> > gain access to its uid and gid.
> I'm not sure whether this is CVE-worthy - the user_namespaces
> manpage says "the process has full privileges for operations
> inside the user namespace, but is unprivileged for operations
> outside the namespace". ptrace()ing a process in the
> namespace can reasonably be considered an "operation inside
> the user namespace", and therefore the manpage kinda implies

Except by creating a file in the host namespace, you were, as
root in the container, able to escape your namespace, right?

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