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=-2.3 required=3.0 tests=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 1E790C4321E for ; Mon, 10 Sep 2018 12:29:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D77D12087E for ; Mon, 10 Sep 2018 12:29:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D77D12087E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728646AbeIJRXC (ORCPT ); Mon, 10 Sep 2018 13:23:02 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35372 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728226AbeIJRXC (ORCPT ); Mon, 10 Sep 2018 13:23:02 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ED64640216E7; Mon, 10 Sep 2018 12:29:10 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 3289963F32; Mon, 10 Sep 2018 12:29:08 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 10 Sep 2018 14:29:10 +0200 (CEST) Date: Mon, 10 Sep 2018 14:29:07 +0200 From: Oleg Nesterov To: Kees Cook Cc: Rik van Riel , Michal Hocko , Stanislav Kozina , linux-kernel@vger.kernel.org Subject: get_arg_page() && ptr_size accounting Message-ID: <20180910122907.GA23963@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Mon, 10 Sep 2018 12:29:10 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Mon, 10 Sep 2018 12:29:10 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Kees, I was thinking about backporting the commit 98da7d08850fb8bde ("fs/exec.c: account for argv/envp pointers"), but I am not sure I understand it... So get_arg_page() does /* * Since the stack will hold pointers to the strings, we * must account for them as well. * * The size calculation is the entire vma while each arg page is * built, so each time we get here it's calculating how far it * is currently (rather than each call being just the newly * added size from the arg page). As a result, we need to * always add the entire size of the pointers, so that on the * last call to get_arg_page() we'll actually have the entire * correct size. */ ptr_size = (bprm->argc + bprm->envc) * sizeof(void *); if (ptr_size > ULONG_MAX - size) goto fail; size += ptr_size; OK, but acct_arg_size(bprm, size / PAGE_SIZE); after that doesn't look exactly right. This additional space will be used later when the process already uses bprm->mm, right? so it shouldn't be accounted by acct_arg_size(). Not to mention that ptr_size/PAGE_SIZE doesn't look right in any case... In short. Am I totally confused or the patch below makes sense? This way we do not need the fat comment. Oleg. --- x/fs/exec.c +++ x/fs/exec.c @@ -222,25 +222,17 @@ static struct page *get_arg_page(struct unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; unsigned long ptr_size, limit; + acct_arg_size(bprm, size / PAGE_SIZE); + /* * Since the stack will hold pointers to the strings, we * must account for them as well. - * - * The size calculation is the entire vma while each arg page is - * built, so each time we get here it's calculating how far it - * is currently (rather than each call being just the newly - * added size from the arg page). As a result, we need to - * always add the entire size of the pointers, so that on the - * last call to get_arg_page() we'll actually have the entire - * correct size. */ ptr_size = (bprm->argc + bprm->envc) * sizeof(void *); if (ptr_size > ULONG_MAX - size) goto fail; size += ptr_size; - acct_arg_size(bprm, size / PAGE_SIZE); - /* * We've historically supported up to 32 pages (ARG_MAX) * of argument strings even with small stacks