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 [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id A81483836F8D for ; Wed, 13 Jul 2022 14:01:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A81483836F8D 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-656-tq72ViOHP66xS-7ZHWafJg-1; Wed, 13 Jul 2022 10:01:12 -0400 X-MC-Unique: tq72ViOHP66xS-7ZHWafJg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D53C41C068CB; Wed, 13 Jul 2022 14:01:11 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.60]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7EEA640CFD0A; Wed, 13 Jul 2022 14:01:10 +0000 (UTC) From: Florian Weimer To: David Malcolm Cc: Szabolcs Nagy via Gcc , Szabolcs Nagy , libc-alpha@sourceware.org, Mir Immad Subject: Re: Adding file descriptor attribute(s) to gcc and glibc References: <260f0b41c663133cea96eb64bd85e8ba16d8a936.camel@redhat.com> <5769682d0d17579cbd72f72a4001bfa8444b80a8.camel@redhat.com> <877d4h1alh.fsf@oldenburg.str.redhat.com> <6460438cc9e634d0b5e40a1438038c9adce151bb.camel@redhat.com> Date: Wed, 13 Jul 2022 16:01:08 +0200 In-Reply-To: <6460438cc9e634d0b5e40a1438038c9adce151bb.camel@redhat.com> (David Malcolm's message of "Wed, 13 Jul 2022 09:33:28 -0400") Message-ID: <87tu7lyuvv.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-5.5 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 X-BeenThere: gcc@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 13 Jul 2022 14:01:17 -0000 * David Malcolm: > On Wed, 2022-07-13 at 14:05 +0200, Florian Weimer wrote: >> * Szabolcs Nagy via Gcc: > > [adding Immad back to the CC list] > >>=20 >> > to be honest, i'd expect interesting fd bugs to be >> > dynamic and not easy to statically analyze. >> > the use-after-unchecked-open maybe useful. i would >> > not expect the access direction to catch many bugs. >>=20 >> You might be right.=C2=A0 But I think the annotations could help to catc= h >> use-after-close errors. >>=20 >> By the way, I think it would help us if we didn't have to special- >> case >> AT_FDCWD using inline wrappers. > > Florian: I confess I wasn't familiar with AT_FDCWD until I read your > email and did a little reading a few minutes ago; it seems to be a > "magic number" for an FD that has special meaning; on my system it has > the value -100. > > GCC's current implementation of the various -Wanalyzer-fd-* warnings > will track state for constant integer values as well as symbolic > values; it doesn't have any special meanings for specific integer > values. So e.g. it doesn't assume that 0, 1, and 2 have specific > meaning or are opened with specific flags (the analysis doesn't > necessarily begin its execution path at the start of "main", so there's > no guarantee that the standard FDs have their standard meaning). Ahh. It might be useful to detect close (-1) etc. as a form of double-close, and ther AT_FDCWD is exceptional. > Presumably if someone attempts > close (AT_FDCWD); > they'll get -1 and errno set to EBADFD, right? Correct > I don't think GCC's -fanalyzer needs to check for that. Not sure =E2=80=A6 > -fanalyzer's filedescriptor support doesn't yet have a concept of > "directory filedescriptors". Should it? (similarly, it doesn't yet > know about sockets) > > A possible way to annotate "openat": > > int openat(int dirfd, const char *pathname, int flags) > __attr_fd_arg(1); openat is not the most general interface in this regard. We have other *at functions which accept an O_PATH descriptor (or maybe even a different kind of non-directory descriptor) with pathname =3D=3D "" and AT_EMPTY_PATH. I'm not sure if modeling all this is beneficial. Thanks, Florian