Re: [lxc-devel] Kernel bug? Setuid apps and user namespaces

["Serge E. Hallyn" <serge@hallyn.com>]

(Sorry - the lxc-devel list has moved, so replying to all with the
correct list address;   please reply to this rather than my previous
email)

Quoting Serge Hallyn (serge.hallyn@ubuntu.com):
> Hi Eric,
> 
> (sorry, I don't seem to have the email I actually wanted to reply
> to in my mbox, but it is
> https://lists.linuxcontainers.org/pipermail/lxc-devel/2013-October/005857.html)
> 
> You'd said,
> > Someone needs to read and think through all of the corner cases and see
> > if we can ever have a time when task_dumpable is false but root in the
> > container would not or should not be able to see everything.
> > 
> > In particular I am worried about the case of a setuid app calling setns,
> > and entering a lesser privileged user namespace.  In my foggy mind that
> > might be a security problem.  And there might be other similar crazy
> > cases.
> 
> Can we make use of current->mm->exe_file->f_cred->user_ns?
> 
> So either always use 
> make_kgid(current->mm->exe_file->f_cred->user_ns, 0)
> instead of make_kuid(cred->user_ns, 0), or check that
> (current->mm->exe_file->f_cred->user_ns == cred->user_ns)
> and, if not, assume that the caller has done a setns?
> 
> -serge
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