Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1163915AbdDXBJw (ORCPT ); Sun, 23 Apr 2017 21:09:52 -0400 Received: from h2.hallyn.com ([78.46.35.8]:54624 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1163841AbdDXBJn (ORCPT ); Sun, 23 Apr 2017 21:09:43 -0400 Date: Sun, 23 Apr 2017 20:09:41 -0500 From: "Serge E. Hallyn" To: Matt Brown Cc: serge@hallyn.com, jmorris@namei.org, gregkh@linuxfoundation.org, jslaby@suse.com, corbet@lwn.net, keescook@chromium.org, akpm@linux-foundation.org, jannh@google.com, kernel-hardening@lists.openwall.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct Message-ID: <20170424010941.GA32715@mail.hallyn.com> References: <20170423235417.12809-1-matt@nmatt.com> <20170423235417.12809-2-matt@nmatt.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170423235417.12809-2-matt@nmatt.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2468 Lines: 79 Quoting Matt Brown (matt@nmatt.com): > 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. > > See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > > Signed-off-by: Matt Brown > --- > drivers/tty/tty_io.c | 4 ++++ > include/linux/tty.h | 2 ++ > 2 files changed, 6 insertions(+) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index e6d1a65..03d5ea2 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -161,6 +161,7 @@ static void release_tty(struct tty_struct *tty, int idx); > * @tty: tty struct to free > * > * Free the write buffers, tty queue and tty memory itself. > + * Decrement the owner_user_ns count. > * > * Locking: none. Must be called after tty is definitely unused > */ > @@ -171,6 +172,7 @@ static void free_tty_struct(struct tty_struct *tty) > put_device(tty->dev); > kfree(tty->write_buf); > tty->magic = 0xDEADDEAD; > + atomic_dec(&tty->owner_user_ns->count); > kfree(tty); > } > > @@ -3191,6 +3193,8 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) > tty->index = idx; > tty_line_name(driver, idx, tty->name); > tty->dev = tty_get_device(tty); > + tty->owner_user_ns = current_user_ns(); > + atomic_inc(&tty->owner_user_ns->count); Hi, CONFIG_USER_NS is an option, so unfortunately you need to do tty->owner_user_ns = get_user_ns(current_user_ns()); > > return tty; > } > diff --git a/include/linux/tty.h b/include/linux/tty.h > index 1017e904..d902d42 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -12,6 +12,7 @@ > #include > #include > #include > +#include > > > /* > @@ -333,6 +334,7 @@ struct tty_struct { > /* If the tty has a pending do_SAK, queue it here - akpm */ > struct work_struct SAK_work; > struct tty_port *port; > + struct user_namespace *owner_user_ns; > }; > > /* Each of a tty's open files has private_data pointing to tty_file_private */ > -- > 2.10.2