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Date: Thu, 20 Nov 2014 08:49:23 +0000
From: Vitor Ventura <>
Subject: Re: Re: Linux user namespaces can bypass group-based restrictions

I was wondering if this might pose a problem to android's application file
sandboxing. If an application can run a native lib that could exploits this
it might have access to other aplication files.

A 0h24 qui, 20 de Nov de 2014, Andy Lutomirski <>

> On 11/17/2014 10:43 AM, Andy Lutomirski wrote:
> > This is a heads-up, as there is no fix right now.
> >
> > On Linux, if you can unshare your user namespace (which is the case on
> > many distributions), then you can map your fsuid and fsgid into the
> > new namespace and, inside that namespace, drop all of your other
> > groups.
> >
> > This may allow you to access files protected by POSIX ACLs as "other",
> > even if the ACL should have prohibited it based on one of your
> > supplementary group IDs.
> >
> > This does not appear to allow you to violate negative sudoers
> > group entries and the like, since sudo(8) would be confined to the
> > user namespace as well and will therefore not gain privilege.
> >
> > To those who care about credit: this was discovered by some
> > combination of me, Theodore Ts'o, Eric Biederman, Alan Cox, and Casey
> > Schaufler.
> >
> > See here for some more discussion:
> >
> >
> > Disabling CONFIG_USER_NS works around this issue.
> Does this need a CVE?  Fedora and Ubuntu are likely to be affected in
> their default configurations.  I don't know about the other distributions.
> --Andy
> >
> > --Andy
> >

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