netdev - Re: [GIT PULL] Namespace file descriptors for 2.6.40

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Message-ID: <20110525213806.GA4590@mail.hallyn.com>
Date:	Wed, 25 May 2011 16:38:06 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	C Anthony Risinger <anthony@...x.me>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.osdl.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] Namespace file descriptors for 2.6.40

Quoting C Anthony Risinger (anthony@...x.me):
> On Mon, May 23, 2011 at 4:05 PM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
> >
> > This tree adds the files /proc/<pid>/ns/net, /proc/<pid>/ns/ipc,
> > /proc/<pid>/ns/uts that can be opened to refer to the namespaces of a
> > process at the time those files are opened, and can be bind mounted to
> > keep the specified namespace alive without a process.
> >
> > This tree adds the setns system call that can be used to change the
> > specified namespace of a process to the namespace specified by a system
> > call.
> 
> i just have a quick question regarding these, apologies if wrong place
> to respond -- i trimmed to lists only.
> 
> if i understand correctly, mount namespaces (for example), allow one
> to build such constructs as "private /tmp" and similar that even
> `root` cannot access ... and there are many reasons `root` does not
> deserve to completely know/interact with user processes (FUSE makes a
> good example ... just because i [user] have SSH access to a machine,
> why should `root`?)
> 
> would these /proc additions break such guarantees?  IOW, would it now
> become possible for `root` to inject stuff into my private namespaces,
> and/or has these guarantees never existed and i am mistaken?  is there
> any kind of ACL mechanism that endows the origin process (or similar)
> with the ability to dictate who can hold and/or interact with these
> references?

If for instance you have a file open in your private /tmp, then root
in another mounts ns can open the file through /proc/$$/fd/N anyway.
If it's a directory, he can now traverse the whole fs.

-serge
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