From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932080AbeCEPQj (ORCPT ); Mon, 5 Mar 2018 10:16:39 -0500 Received: from mail-io0-f194.google.com ([209.85.223.194]:42060 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbeCEPQi (ORCPT ); Mon, 5 Mar 2018 10:16:38 -0500 X-Google-Smtp-Source: AG47ELvKqiTppalKAYVFtSJEe+CmTRHeppor0vy4U/G2wXudV7vkm3RfYCnvz5YIP1dES1GvKZHhniCrD5At0LjJop8= MIME-Version: 1.0 In-Reply-To: <20180302125359.szbin2kznxvoq7sc@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> From: Rasmus Villemoes Date: Mon, 5 Mar 2018 16:16:37 +0100 Message-ID: Subject: Re: [PATCH] vsprintf: Make "null" pointer dereference more robust To: Petr Mladek Cc: Andy Shevchenko , "Tobin C . Harding" , Joe Perches , linux-kernel@vger.kernel.org, Andrew Morton , Michal Hocko Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2 March 2018 at 13:53, 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. Yeah, it's annoying that we can't reliably WARN for bogus vsprintf() uses. > 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. > > Signed-off-by: Petr Mladek > --- > lib/vsprintf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index d7a708f82559..5c2d1f44218a 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -1849,7 +1849,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, > { > const int default_width = 2 * sizeof(void *); > > - if (!ptr && *fmt != 'K' && *fmt != 'x') { > + if ((unsigned long)ptr < PAGE_SIZE && *fmt != 'K' && *fmt != 'x') { ISTM that accidentally passing an ERR_PTR would be just as likely as passing a NULL pointer (or some small offset from one), so if we do this, shouldn't the test also cover IS_ERR values? Rasmus