From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E3D2C43381 for ; Tue, 19 Feb 2019 03:30:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 599C221773 for ; Tue, 19 Feb 2019 03:30:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="sSID8mpY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726142AbfBSDaJ (ORCPT ); Mon, 18 Feb 2019 22:30:09 -0500 Received: from mail-pf1-f194.google.com ([209.85.210.194]:40398 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725536AbfBSDaJ (ORCPT ); Mon, 18 Feb 2019 22:30:09 -0500 Received: by mail-pf1-f194.google.com with SMTP id h1so9519240pfo.7 for ; Mon, 18 Feb 2019 19:30:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=OXK6fp4pusxSkcr3snEhbgyXQ6Ejx4HHzW7W0he3jqs=; b=sSID8mpYPyllKQFqI5RB+8DiBfRjGWRdLPeKmWzVibbPRi6Hd8t1nigc/G2WkOBoYM MvbnYgfXpSRUDFxPhyr2a4mKsCBP9gusjFqqGW9fIU+KrEm/KOYhRta5kuoySp+UnW60 GggK4YD+p7w7MOeNF7Wffu9O2oUiHlnArKQswgHqUSyouDxbtpaGAMb1e27mHgZl6LoI NBk3cTJjk5gwOw/c8Yxhcl80yJD9IvAySa3qcC7DvZ3AguVnZppQJJR1u4MhCR1duPdA uo16zr8PkF+RC4HAVXZLkGKYzPHU1v69/dAi/NE15r+XT6MAgfJSDiZ+TNunbJ8nVz2n CHJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=OXK6fp4pusxSkcr3snEhbgyXQ6Ejx4HHzW7W0he3jqs=; b=DCHa1WgRkUCS9DdfznpqOYeCenMU1HaVxKLFrEPksD2+YGKwWxZSFzurXVrgHoiA4E CSdgZnp4AILF+Uj60l2JUgPJIqFVbq9Mt6uHW7VDD89SCe1GAR0Tj8mtMiqEdvzoqxIL NXBitFzomMJ2GpWH7pehMYwEyFofsYUsHgeOY0FDb3vwt2KTgGmjuTb8AgolWQZytWSC doId/BYM4OMV6+jrLywj9qoXU4wZhb6O+P67oOZxLmj4ROTjy2s3mdEEzyTDTFRIC/Rc ax3YbPeIm/0VokJkhec9M5eA3ErZR/URk2v3whmOIl2FN3n84bPG9ZFH0A53Qj1MI1S8 SyFw== X-Gm-Message-State: AHQUAubgViER/Mawljqi7Zw2g5hME/uyYjsa63l8rCDkvdH2MG5soZ3u iY2M73tzy0qH9a0MhrIr1T4= X-Google-Smtp-Source: AHgI3IYOz8O60tSlTTwfjTYKwYxUPnB9Io+WeiEidlWccmrDELoxDCsp2HcMipfryi5nTLIR9Wq4WA== X-Received: by 2002:a62:6282:: with SMTP id w124mr27545777pfb.168.1550547008379; Mon, 18 Feb 2019 19:30:08 -0800 (PST) Received: from localhost ([175.223.35.193]) by smtp.gmail.com with ESMTPSA id v22sm11713490pfa.49.2019.02.18.19.30.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 18 Feb 2019 19:30:07 -0800 (PST) Date: Tue, 19 Feb 2019 12:30:03 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: Andy Shevchenko , Rasmus Villemoes , Linus Torvalds , "Tobin C . Harding" , Joe Perches , Andrew Morton , Michal Hocko , Sergey Senozhatsky , Steven Rostedt , Sergey Senozhatsky , linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 8/9] vsprintf: Prevent crash when dereferencing invalid pointers Message-ID: <20190219033003.GA2284@jagdpanzerIV> References: <20190208152310.29531-1-pmladek@suse.com> <20190208152310.29531-9-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190208152310.29531-9-pmladek@suse.com> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (02/08/19 16:23), Petr Mladek wrote: [..] > + /* > + * This is not a fool-proof test. 99% of the time that this will fault is > + * due to a bad pointer, not one that crosses into bad memory. Just test > + * the address to make sure it doesn't fault due to a poorly added printk > + * during debugging. > + */ > +static const char *check_pointer_msg(const void *ptr) > +{ > + char byte; > + > + if (!ptr) > + return "(null)"; > + > + if (probe_kernel_address(ptr, byte)) > + return "(efault)"; > + > + return NULL; > +} Hmm... So the assumption here is that the target buffer always has at least strlen("(efault)") bytes and, thus, we always can write the error message to it. > +static int check_pointer(char **buf, char *end, const void *ptr, > + struct printf_spec spec) > +{ > + const char *err_msg; > + > + err_msg = check_pointer_msg(ptr); > + if (err_msg) { > + *buf = string_nocheck(*buf, end, err_msg, spec); > + return -EFAULT; > + } > + > + return 0; > +} Suppose in my driver I sprintf() pointers to 4-bytes strings and, thus, have only 5 spare bytes in target buffer. But one of the pointers is faulty and now sprintf() writes "(efault)" to target buffer which can hold only 5 bytes. -ss