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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 0B415C43460 for ; Tue, 4 May 2021 15:31:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA58F6101C for ; Tue, 4 May 2021 15:31:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231147AbhEDPcj (ORCPT ); Tue, 4 May 2021 11:32:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:59894 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230193AbhEDPci (ORCPT ); Tue, 4 May 2021 11:32:38 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3D39B610FA; Tue, 4 May 2021 15:31:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1620142303; bh=oKmsd9bot90Pfy//TFn+A9MEIZp+so+1aFWQQcmfOsA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mf49REO47RdZ+qg74EScE2J991TdYrQklg/imZPFsn2659v6c/dV6/U0arj29aAKJ eyjX72WkpfY5w3HeCesfmfRSVWmai+oyI+XpvLeD6nxy6dLORctu8R0zexxiuiJM6M hl2byM0dl5WMqBG06W3q0CR7ZzapjySmvV+vNKjA= Date: Tue, 4 May 2021 17:31:40 +0200 From: Greg Kroah-Hartman To: "Rafael J. Wysocki" Cc: Kees Cook , Wenwen Wang , "Rafael J. Wysocki" , Len Brown , Linux Kernel Mailing List , ACPI Devel Maling List , Mark Langsdorf Subject: Re: [PATCH] Revert "ACPI: custom_method: fix memory leaks" Message-ID: References: <20210502172326.2060025-1-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 04, 2021 at 04:59:40PM +0200, Rafael J. Wysocki wrote: > On Mon, May 3, 2021 at 6:55 AM Greg Kroah-Hartman > wrote: > > > > On Sun, May 02, 2021 at 10:23:26AM -0700, Kees Cook wrote: > > > This reverts commit 03d1571d9513369c17e6848476763ebbd10ec2cb. > > > > > > While /sys/kernel/debug/acpi/custom_method is already a privileged-only > > > API providing proxied arbitrary write access to kernel memory[1][2], > > > with existing race conditions[3] in buffer allocation and use that could > > > lead to memory leaks and use-after-free conditions, the above commit > > > appears to accidentally make the use-after-free conditions even easier > > > to accomplish. ("buf" is a global variable and prior kfree()s would set > > > buf back to NULL.) > > > > > > This entire interface needs to be reworked (if not entirely removed). > > > > > > [1] https://lore.kernel.org/lkml/20110222193250.GA23913@outflux.net/ > > > [2] https://lore.kernel.org/lkml/201906221659.B618D83@keescook/ > > > [3] https://lore.kernel.org/lkml/20170109231323.GA89642@beast/ > > > > > > Cc: Wenwen Wang > > > Signed-off-by: Kees Cook > > > --- > > > drivers/acpi/custom_method.c | 5 +---- > > > 1 file changed, 1 insertion(+), 4 deletions(-) > > > > > > diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c > > > index 7b54dc95d36b..36d95a02cd30 100644 > > > --- a/drivers/acpi/custom_method.c > > > +++ b/drivers/acpi/custom_method.c > > > @@ -53,10 +53,8 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf, > > > if ((*ppos > max_size) || > > > (*ppos + count > max_size) || > > > (*ppos + count < count) || > > > - (count > uncopied_bytes)) { > > > - kfree(buf); > > > + (count > uncopied_bytes)) > > > return -EINVAL; > > > - } > > > > > > if (copy_from_user(buf + (*ppos), user_buf, count)) { > > > kfree(buf); > > > @@ -76,7 +74,6 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf, > > > add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE); > > > } > > > > > > - kfree(buf); > > > return count; > > > } > > > > > > -- > > > > Thanks for the revert, I'll queue it up on my larger "umn.edu reverts" > > branch that I'll be sending out for review in a day or so. > > This will conflict with the material that I'm going to push on > Thursday that includes the two commits mentioned by Mark elsewhere in > this thread. I'll drop this from my patch series now that you all have this covered. thanks! greg k-h