Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1164517AbdDXDcm (ORCPT ); Sun, 23 Apr 2017 23:32:42 -0400 Received: from relay7-d.mail.gandi.net ([217.70.183.200]:37961 "EHLO relay7-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1164490AbdDXDce (ORCPT ); Sun, 23 Apr 2017 23:32:34 -0400 X-Originating-IP: 72.66.113.207 Subject: Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct To: "Serge E. Hallyn" References: <20170423235417.12809-1-matt@nmatt.com> <20170423235417.12809-2-matt@nmatt.com> <20170424010941.GA32715@mail.hallyn.com> Cc: 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 From: Matt Brown Message-ID: <7c4370cd-65ce-bc73-b93a-6825b7508f06@nmatt.com> Date: Sun, 23 Apr 2017 23:31:57 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170424010941.GA32715@mail.hallyn.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2720 Lines: 84 On 04/23/2017 09:09 PM, Serge E. Hallyn wrote: > 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()); > Does this mean I need to also use put_user_ns(tty->owner_user_ns) in free_tty_struct instead of atomic_dec(&tty->owner_user_ns->count) ? >> >> 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