Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753912Ab0F1SGK (ORCPT ); Mon, 28 Jun 2010 14:06:10 -0400 Received: from smtp.outflux.net ([198.145.64.163]:53508 "EHLO smtp.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752569Ab0F1SGH (ORCPT ); Mon, 28 Jun 2010 14:06:07 -0400 Date: Mon, 28 Jun 2010 11:04:28 -0700 From: Kees Cook To: Stefani Seibold Cc: KOSAKI Motohiro , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Andrew Morton , Tejun Heo , Veaceslav Falico , Alexander Viro , Oleg Nesterov , Neil Horman , Roland McGrath , Ingo Molnar , Peter Zijlstra , Hidetoshi Seto , Thomas Gleixner , Eric Paris , James Morris , "Andrew G. Morgan" , Dhaval Giani , "Serge E. Hallyn" , Steve Grubb , Christoph Hellwig , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes Message-ID: <20100628180428.GQ4175@outflux.net> References: <20100624190527.GD5917@outflux.net> <20100625082722.8031.A69D9226@jp.fujitsu.com> <1277747318.4840.9.camel@wall-e.seibold.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1277747318.4840.9.camel@wall-e.seibold.net> Organization: Canonical X-HELO: www.outflux.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2437 Lines: 52 On Mon, Jun 28, 2010 at 07:48:38PM +0200, Stefani Seibold wrote: > Am Freitag, den 25.06.2010, 08:56 +0900 schrieb KOSAKI Motohiro: > > > Through get_task_comm() and many direct uses of task->comm in the kernel, > > > it is possible for escape codes and other non-printables to leak into > > > dmesg, syslog, etc. In the worst case, these strings could be used to > > > attack administrators using vulnerable terminal emulators, and at least > > > cause confusion through the injection of \r characters. > > > > > > This patch sanitizes task->comm to only contain printable characters > > > when it is set. Additionally, it redefines get_task_comm so that it is > > > more obvious when misused by callers (presently nothing was incorrectly > > > calling get_task_comm's unsafe use of strncpy). > > > > > > Signed-off-by: Kees Cook > > > > I've reviewed this patch briefly, Here is my personal concern... > > > > On Linux, non-printable leaking is fundamental, only fixing task->comm > > doesn't solve syslog exploit issue. Probably all /proc/kmsg user should > > have escaping non-pritables code. > > > > However, task->comm is one of most easy injection data of kernel, because > > we have prctl(PR_SET_NAME), attacker don't need root privilege. So, > > conservative assumption seems guard from crappy fault. Plus, this patch > > is very small and our small TASK_COMM_LEN lead that we don't need > > big performance concern. > > > > So, I don't find demerit in this proposal. but I'm not security specialist, > > it's only personal thinking. > > > Agree. I think a escaped printk should be a more generic solution. I think sanitizing inputs is more effective than sanitizing outputs. If ->comm is safe internally, then we don't have to filter it going out on printk, audit, /proc output, etc. There is a limited number of places where a process has control over an arbitrary string in kernel structures, so the places where they are set should be fixed instead of fixing every possible usage of it on output. I wouldn't mind sanitizing printk also, but it's tangential to sanitizing task->comm when it is set. -Kees -- Kees Cook Ubuntu Security Team -- 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/