From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933168Ab2JKAiE (ORCPT ); Wed, 10 Oct 2012 20:38:04 -0400 Received: from smtp.outflux.net ([198.145.64.163]:36495 "EHLO smtp.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932921Ab2JKAiB (ORCPT ); Wed, 10 Oct 2012 20:38:01 -0400 Date: Wed, 10 Oct 2012 17:37:52 -0700 From: Kees Cook To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Andi Kleen , PaX Team , Brad Spengler Subject: [PATCH v3] fix stack memory content leak via UNAME26 Message-ID: <20121011003752.GA21731@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-HELO: www.outflux.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Calling uname() with the UNAME26 personality set allows a leak of kernel stack contents. This fixes it by defensively calculating the length of copy_to_user() call, making the len argument unsigned, and initializing the stack buffer to zero (now technically unneeded, but hey, overkill). CVE-2012-0957 Reported-by: PaX Team Cc: Andrew Morton Cc: Andi Kleen Cc: PaX Team Cc: Brad Spengler Cc: stable@vger.kernel.org Signed-off-by: Kees Cook --- v3: - use scnprintf, suggested by Andrew Morton. - proactively handle impossible len == 0 case. v2: - corrected credit to PaX Team. - moved stack clearing into if case to avoid penalty to common case. --- kernel/sys.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/sys.c b/kernel/sys.c index c5cb5b9..01865c6 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1265,15 +1265,16 @@ DECLARE_RWSEM(uts_sem); * Work around broken programs that cannot handle "Linux 3.0". * Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40 */ -static int override_release(char __user *release, int len) +static int override_release(char __user *release, size_t len) { int ret = 0; - char buf[65]; if (current->personality & UNAME26) { - char *rest = UTS_RELEASE; + const char *rest = UTS_RELEASE; + char buf[65] = { 0 }; int ndots = 0; unsigned v; + size_t copy; while (*rest) { if (*rest == '.' && ++ndots >= 3) @@ -1283,8 +1284,9 @@ static int override_release(char __user *release, int len) rest++; } v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40; - snprintf(buf, len, "2.6.%u%s", v, rest); - ret = copy_to_user(release, buf, len); + copy = min(sizeof(buf), max_t(size_t, 1, len)); + copy = scnprintf(buf, copy, "2.6.%u%s", v, rest); + ret = copy_to_user(release, buf, copy + 1); } return ret; } -- 1.7.9.5 -- Kees Cook Chrome OS Security