From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752349AbeCEOxK (ORCPT ); Mon, 5 Mar 2018 09:53:10 -0500 Received: from mx2.suse.de ([195.135.220.15]:58030 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751830AbeCEOxI (ORCPT ); Mon, 5 Mar 2018 09:53:08 -0500 Date: Mon, 5 Mar 2018 15:53:06 +0100 From: Petr Mladek To: Andy Shevchenko Cc: "Tobin C . Harding" , linux@rasmusvillemoes.dk, Joe Perches , linux-kernel@vger.kernel.org, Andrew Morton , Michal Hocko Subject: Re: [PATCH] vsprintf: Make "null" pointer dereference more robust Message-ID: <20180305145306.5i643d2oqupc4rba@pathway.suse.cz> References: <20180216210711.79901-1-andriy.shevchenko@linux.intel.com> <20180216210711.79901-8-andriy.shevchenko@linux.intel.com> <20180227155047.o74ohmoyj56up6pa@pathway.suse.cz> <1519752950.10722.231.camel@linux.intel.com> <20180228100437.o4juwxbzomkqjvjx@pathway.suse.cz> <1519814544.10722.266.camel@linux.intel.com> <20180302125118.bjd3tbuu72vgfczo@pathway.suse.cz> <20180302125359.szbin2kznxvoq7sc@pathway.suse.cz> <1520000254.10722.389.camel@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1520000254.10722.389.camel@linux.intel.com> User-Agent: NeoMutt/20170421 (1.8.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 2018-03-02 16:17:34, Andy Shevchenko wrote: > On Fri, 2018-03-02 at 13:53 +0100, Petr Mladek wrote: > > %p has many modifiers where the pointer is dereferenced. An invalid > > pointer might cause kernel to crash silently. > > > > Note that printk() formats the string under logbuf_lock. Any recursive > > printks are redirected to the printk_safe implementation and the > > messages > > are stored into per-CPU buffers. These buffers might be eventually > > flushed > > in printk_safe_flush_on_panic() but it is not guaranteed. > > > > In general, we should do our best to get useful message from printk(). > > All pointers to the first memory page must be invalid. Let's prevent > > the dereference and print "(null)" in this case. This is already done > > in many other situations, including "%s" format handling and many > > page fault handlers. > > > > > With such explanation it makes at least clear for the reader why it's > done. > > Thanks! > > Would you be okay if I take this one as a first in my series and > resubmit the series based on it? Makes sense. Feel free to go on. Best Regards, Petr