Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755619Ab0LHAin (ORCPT ); Tue, 7 Dec 2010 19:38:43 -0500 Received: from kroah.org ([198.145.64.141]:54820 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755369Ab0LHAej (ORCPT ); Tue, 7 Dec 2010 19:34:39 -0500 X-Mailbox-Line: From gregkh@clark.site Tue Dec 7 16:06:42 2010 Message-Id: <20101208000642.151033921@clark.site> User-Agent: quilt/0.48-11.2 Date: Tue, 07 Dec 2010 16:04:25 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Nelson Elhage , KOSAKI Motohiro Subject: [26/44] do_exit(): make sure that we run with get_fs() == USER_DS In-Reply-To: <20101208003205.GA4286@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2222 Lines: 61 2.6.27-stable review patch. If anyone has any objections, please let us know. ------------------ From: Nelson Elhage commit 33dd94ae1ccbfb7bf0fb6c692bc3d1c4269e6177 upstream. If a user manages to trigger an oops with fs set to KERNEL_DS, fs is not otherwise reset before do_exit(). do_exit may later (via mm_release in fork.c) do a put_user to a user-controlled address, potentially allowing a user to leverage an oops into a controlled write into kernel memory. This is only triggerable in the presence of another bug, but this potentially turns a lot of DoS bugs into privilege escalations, so it's worth fixing. I have proof-of-concept code which uses this bug along with CVE-2010-3849 to write a zero to an arbitrary kernel address, so I've tested that this is not theoretical. A more logical place to put this fix might be when we know an oops has occurred, before we call do_exit(), but that would involve changing every architecture, in multiple places. Let's just stick it in do_exit instead. [akpm@linux-foundation.org: update code comment] Signed-off-by: Nelson Elhage Cc: KOSAKI Motohiro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/exit.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1004,6 +1004,15 @@ NORET_TYPE void do_exit(long code) if (unlikely(!tsk->pid)) panic("Attempted to kill the idle task!"); + /* + * If do_exit is called because this processes oopsed, it's possible + * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before + * continuing. Amongst other possible reasons, this is to prevent + * mm_release()->clear_child_tid() from writing to a user-controlled + * kernel address. + */ + set_fs(USER_DS); + tracehook_report_exit(&code); /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/