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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 9A1EAC10F11 for ; Wed, 24 Apr 2019 12:24:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7187021773 for ; Wed, 24 Apr 2019 12:24:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729806AbfDXMY4 (ORCPT ); Wed, 24 Apr 2019 08:24:56 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:42568 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727270AbfDXMYz (ORCPT ); Wed, 24 Apr 2019 08:24:55 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7FCD7A78; Wed, 24 Apr 2019 05:24:55 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 659603F238; Wed, 24 Apr 2019 05:24:54 -0700 (PDT) Date: Wed, 24 Apr 2019 13:24:51 +0100 From: Mark Rutland To: Weikang shi Cc: keescook@chromium.org, arnd@arndb.de, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] lkdtm: fix potential use after free Message-ID: <20190424122451.GC24502@lakrids.cambridge.arm.com> References: <20190424102103.11816-1-swkhack@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190424102103.11816-1-swkhack@gmail.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 24, 2019 at 06:21:03PM +0800, Weikang shi wrote: > From: swkhack > > The function lkdtm_WRITE_AFTER_FREE calls kfree(base) to free the memory > of base. However, following kfree(base), > it write the memory which base point to via base[offset] = 0x0abcdef0. This may result in a > use-after-free bug. This patch moves kfree(base) after the write. As with lkdtm_READ_AFTER_FREE, this is deliberate, and we should not make this change. Thanks, Mark. > > Signed-off-by: swkhack > --- > drivers/misc/lkdtm/heap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c > index 65026d7de..0b9141525 100644 > --- a/drivers/misc/lkdtm/heap.c > +++ b/drivers/misc/lkdtm/heap.c > @@ -40,8 +40,8 @@ void lkdtm_WRITE_AFTER_FREE(void) > pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]); > pr_info("Attempting bad write to freed memory at %p\n", > &base[offset]); > - kfree(base); > base[offset] = 0x0abcdef0; > + kfree(base); > /* Attempt to notice the overwrite. */ > again = kmalloc(len, GFP_KERNEL); > kfree(again); > -- > 2.17.1 >