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 34B1CC433F5 for ; Mon, 10 Sep 2018 17:18:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E5C2720880 for ; Mon, 10 Sep 2018 17:18:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5C2720880 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 S1729038AbeIJWNb (ORCPT ); Mon, 10 Sep 2018 18:13:31 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:47798 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727701AbeIJWNb (ORCPT ); Mon, 10 Sep 2018 18:13:31 -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 B65FB4B75B; Mon, 10 Sep 2018 17:18:25 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id F231742238; Mon, 10 Sep 2018 17:18:22 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 10 Sep 2018 19:18:25 +0200 (CEST) Date: Mon, 10 Sep 2018 19:18:22 +0200 From: Oleg Nesterov To: Kees Cook Cc: Rik van Riel , Michal Hocko , Stanislav Kozina , LKML Subject: Re: get_arg_page() && ptr_size accounting Message-ID: <20180910171822.GA27005@redhat.com> References: <20180910122907.GA23963@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 [10.11.55.1]); Mon, 10 Sep 2018 17:18:25 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Mon, 10 Sep 2018 17:18:25 +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 On 09/10, Kees Cook wrote: > > > 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(). > > My understanding (based on the comment about acct_arg_size()) is that > before exec_mmap() happens, the memory used to build the new arguments > copy memory area gets accounted to the MM_ANONPAGES resource limit of > the execing process. Yes, because otherwise oom-killer can't account the memory populated by get_arg_page() in bprm->mm. > I couldn't find any place where the argc/envc > pointers were being included in the count, But why??? To clarify, size += ptr_size; after acct_arg_size() is clear and correct, we are going to check rlim_stack and thus the size should include the pointers we will add in create_elf_tables(). But acct_arg_size() should only account the pages we allocate for bprm->mm, nothing more. create_elf_tables() does not allocate the memory when it populates arg_start/arg_end/env_start/env_end. Plus at this time the process has already switched to bprm->mm. > > Not to mention that ptr_size/PAGE_SIZE doesn't look right in any case... > > Hm? acct_arg_size() takes pages, not bytes. I think this is correct? > What doesn't look right to you? Please forget. I meant that _if_ we actually wanted to account this additional memory in bprm->pages, than we would probably need something like acct_arg_size(size/PAGE_SIZE + DIV_ROUND_UP(ptr_size, PAGE_SIZE)). > > In short. Am I totally confused or the patch below makes sense? This way we do > > not need the fat comment. > > Even if I'm wrong about acct_arg_size(), we need to keep the comment I won't argue, but to me evrything looks obvious as long as we don't pass ptr_size acct_arg_size(). Oleg.