From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751783AbdE3MYx (ORCPT ); Tue, 30 May 2017 08:24:53 -0400 Received: from www.llwyncelyn.cymru ([82.70.14.225]:51716 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751764AbdE3MYt (ORCPT ); Tue, 30 May 2017 08:24:49 -0400 Date: Tue, 30 May 2017 13:24:27 +0100 From: Alan Cox To: Matt Brown Cc: Casey Schaufler , Boris Lukashev , Greg KH , "Serge E. Hallyn" , Kees Cook , kernel-hardening@lists.openwall.com, linux-security-module , linux-kernel Subject: Re: [kernel-hardening] Re: [PATCH v7 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Message-ID: <20170530132427.016053da@alans-desktop> In-Reply-To: References: <20170529213800.29438-1-matt@nmatt.com> <20170529213800.29438-3-matt@nmatt.com> <20170529232640.16211960@alans-desktop> <3738951f-7a4a-b37f-c695-21a2fcd45f76@schaufler-ca.com> <0e078ce7-5b62-f27c-3920-efc2ffdf342b@nmatt.com> Organization: Intel Corporation X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Look there are two problems here 1. TIOCSTI has users 2. You don't actually fix anything The underlying problem is that if you give your tty handle to another process which you don't trust you are screwed. It's fundamental to the design of the Unix tty model and it's made worse in Linux by the fact that we use the tty descriptor to access all sorts of other console state (which makes a ton of sense). Many years ago a few people got this wrong. All those apps got fixes back then. They allocate a tty/pty pair and create a new session over that. The potentially hostile other app only gets to screw itself. If it was only about TIOCSTI then your patch would still not make sense because you could use on of the existing LSMs to actually write yourself some rules about who can and can't use TIOCSTI. For that matter you can even use the seccomp feature today to do this without touching your kernel because the ioctl number is a value so you can just block ioctl with argument 2 of TIOCSTI. So please explain why we need an obscure kernel config option that normal users will not understand which protects against nothing and can be done already ? Alan