From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id E4AE73858D28 for ; Tue, 30 May 2023 11:50:32 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org E4AE73858D28 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685447432; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=niUi8cSdDXsnXyO6s+zhwKk/e25N3d4R95ZneFs6U2I=; b=a1CoSf9iZj9+zPbVa9Gd0nj/5bLheJzcpQzueG8p3/DzFv8CR0g5l5gMmiEKqYjzfGB7cR QzQpi9JUKRlx8qYrAZa0FWnBN0ugJa0a2mIHbHapJyTxMTYlHluhTQ4cjIZkJML7wfKgZL zV6cJFWAnNMhkqRMtCxqGXuEChP7LcI= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-167-bA0YclRePF61sr3BfiMYog-1; Tue, 30 May 2023 07:50:29 -0400 X-MC-Unique: bA0YclRePF61sr3BfiMYog-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DD73D2814240; Tue, 30 May 2023 11:50:28 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.38]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F1113492B0A; Tue, 30 May 2023 11:50:27 +0000 (UTC) From: Florian Weimer To: Sergey Bugaev Cc: Siddhesh Poyarekar , libc-alpha@sourceware.org Subject: Re: [PATCH v2 0/3] fcntl fortification References: <20230528172013.73111-1-bugaevc@gmail.com> <87wn0qw88m.fsf@oldenburg.str.redhat.com> <878rd6uleb.fsf@oldenburg.str.redhat.com> Date: Tue, 30 May 2023 13:50:26 +0200 In-Reply-To: (Sergey Bugaev's message of "Tue, 30 May 2023 14:34:45 +0300") Message-ID: <87zg5mt4vx.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-4.9 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: * Sergey Bugaev: >> Oh, I'm not sure if the run-time check is really that useful. >> >> There's no vfcntl function, so I expect that we will have accurate type >> information at the callsite in most cases, and the compile-time check >> works. > > I see. Well, I copied what the open () fortification was doing, and I > see that many other fortifications have a runtime-checked version in > addition to compile-time checks. > > There is no vopen either, but it's not hard to imagine someone doing > > open (path, O_WRITE | O_CREAT | (cloexec ? O_CLOEXEC : 0)) > > and similarly > > fcntl (fd, cloexec ? F_DUPFD_CLOEXEC : F_DUPFD) > > in both cases __builtin_constant_p will be false, and the user will > miss out on the fortification, and won't notice they forgot the > required 3rd argument. That suggests that we should apply __builtin_constant_p to the result of the cmd check, and not the cmd value. So something like (__builtin_constant_p ((cmd) == F_DUPFD || (cmd) == F_DUPFD_CLOEXEC) && ((cmd) == F_DUPFD || (cmd) == F_DUPFD_CLOEXEC)) with a potential guard against evaluating cmd multiple times. Thanks, Florian