linux-kernel - Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty

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Date:   Tue, 25 Apr 2017 15:55:21 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Matt Brown <matt@...tt.com>
Cc:     serge@...lyn.com, jmorris@...ei.org, gregkh@...uxfoundation.org,
        jslaby@...e.com, corbet@....net, keescook@...omium.org,
        akpm@...ux-foundation.org, jannh@...gle.com,
        kernel-hardening@...ts.openwall.com,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to
 tty_struct

On Mon, 24 Apr 2017 01:15:11 -0400
Matt Brown <matt@...tt.com> wrote:

> This patch adds struct user_namespace *owner_user_ns to the tty_struct.
> Then it is set to current_user_ns() in the alloc_tty_struct function.
> 
> This is done to facilitate capability checks against the original user
> namespace that allocated the tty.
> 
> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)
> 
> This combined with the use of user namespace's will allow hardening
> protections to be built to mitigate container escapes that utilize TTY
> ioctls such as TIOCSTI.

Regardles of the TIOCSTI usefulness this makes complete sense.

Alan