From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753588Ab1ABQJa (ORCPT ); Sun, 2 Jan 2011 11:09:30 -0500 Received: from mx1.vsecurity.com ([209.67.252.12]:53008 "EHLO mx1.vsecurity.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751834Ab1ABQJ3 (ORCPT ); Sun, 2 Jan 2011 11:09:29 -0500 Subject: Re: [PATCH v3] Restrict unprivileged access to kernel syslog From: Dan Rosenberg To: Pavel Machek Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, mingo@elte.hu, kees.cook@canonical.com, akpm@linux-foundation.org, security@kernel.org In-Reply-To: <20110102090541.GL32469@atrey.karlin.mff.cuni.cz> References: <1289431735.3847.9.camel@dan> <20110102090541.GL32469@atrey.karlin.mff.cuni.cz> Content-Type: text/plain; charset="UTF-8" Date: Sun, 02 Jan 2011 11:08:55 -0500 Message-ID: <1293984535.9764.65.camel@Dan> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2011-01-02 at 10:05 +0100, Pavel Machek wrote: > Hi! > > > The kernel syslog contains debugging information that is often useful > > during exploitation of other vulnerabilities, such as kernel heap > > addresses. Rather than futilely attempt to sanitize hundreds (or > > thousands) of printk statements and simultaneously cripple useful > > debugging functionality, it is far simpler to create an option that > > prevents unprivileged users from reading the syslog. > > > > This patch, loosely based on grsecurity's GRKERNSEC_DMESG, creates the > > dmesg_restrict sysctl. When set to "0", the default, no restrictions > > are enforced. When set to "1", only users with CAP_SYS_ADMIN can read > > the kernel syslog via dmesg(8) or other mechanisms. > > Ok, this is very very ugly. > > You essentially create a bit to control what other bit does. Clean > solution would be CAP_SYS_DMESG, and make sure that is given to > processes by default... > > ...and that would be actually very good thing -- on cellphones, you > want some users without ability to connect to network, so you could > introduce CAP_NETWORK etc... > > Pavel The CONFIG was added on suggestion that it would make it easier for distributions to enable this behavior by default. The patch was modified to use CAP_SYSLOG, which seems in line with what you want. Thanks, Dan