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[209.132.180.67]) by mx.google.com with ESMTP id p14si1912364pgh.566.2019.08.29.06.20.35; Thu, 29 Aug 2019 06:20:54 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727242AbfH2NTm (ORCPT + 99 others); Thu, 29 Aug 2019 09:19:42 -0400 Received: from mx2.mailbox.org ([80.241.60.215]:52156 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726283AbfH2NTl (ORCPT ); Thu, 29 Aug 2019 09:19:41 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [80.241.60.241]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx2.mailbox.org (Postfix) with ESMTPS id C76B2A10EE; Thu, 29 Aug 2019 15:19:33 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by spamfilter05.heinlein-hosting.de (spamfilter05.heinlein-hosting.de [80.241.56.123]) (amavisd-new, port 10030) with ESMTP id YERUiiJJutp0; Thu, 29 Aug 2019 15:19:27 +0200 (CEST) Date: Thu, 29 Aug 2019 23:19:04 +1000 From: Aleksa Sarai To: Rasmus Villemoes Cc: Daniel Colascione , Al Viro , Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Christian Brauner , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , David Drysdale , Chanho Min , Oleg Nesterov , Aleksa Sarai , Linus Torvalds , containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org, Linux API , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Linux FS Devel , linux-ia64@vger.kernel.org, linux-kernel , "open list:KERNEL SELFTEST FRAMEWORK" , linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: Re: [PATCH RESEND v11 7/8] open: openat2(2) syscall Message-ID: <20190829131904.bkbalbtqt6j3gwcp@yavin> References: <20190820033406.29796-1-cyphar@cyphar.com> <20190820033406.29796-8-cyphar@cyphar.com> <20190829121527.u2uvdyeatme5cgkb@yavin> <899401fa-ff0a-2ce9-8826-09904efab2d2@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="itirvnprc6jjrbl3" Content-Disposition: inline In-Reply-To: <899401fa-ff0a-2ce9-8826-09904efab2d2@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --itirvnprc6jjrbl3 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-08-29, Rasmus Villemoes wrote: > On 29/08/2019 14.15, Aleksa Sarai wrote: > > On 2019-08-24, Daniel Colascione wrote: >=20 > >> Why pad the structure when new functionality (perhaps accommodated via > >> a larger structure) could be signaled by passing a new flag? Adding > >> reserved fields to a structure with a size embedded in the ABI makes a > >> lot of sense --- e.g., pthread_mutex_t can't grow. But this structure > >> can grow, so the reservation seems needless to me. > >=20 > > Quite a few folks have said that ->reserved is either unnecessary or > > too big. I will be changing this, though I am not clear what the best > > way of extending the structure is. If anyone has a strong opinion on > > this (or an alternative to the ones listed below), please chime in. I > > don't have any really strong attachment to this aspect of the API. > >=20 > > There appear to be a few ways we can do it (that all have precedence > > with other syscalls): > >=20 > > 1. Use O_* flags to indicate extensions. > > 2. A separate "version" field that is incremented when we change. > > 3. Add a size_t argument to openat2(2). > > 4. Reserve space (as in this patchset). > >=20 > > (My personal preference would be (3), followed closely by (2).) >=20 > 3, definitely, and instead of having to invent a new scheme for every > new syscall, make that the default pattern by providing a helper Sure (though hopefully I don't need to immediately go and refactor all the existing size_t syscalls). I will be presenting about this patchset at the containers microconference at LPC (in a few weeks), so I'll hold of on any API-related rewrites until after that. > int __copy_abi_struct(void *kernel, size_t ksize, const void __user > *user, size_t usize) > { > size_t copy =3D min(ksize, usize); >=20 > if (copy_from_user(kernel, user, copy)) > return -EFAULT; >=20 > if (usize > ksize) { > /* maybe a separate "return user_is_zero(user + ksize, usize - > ksize);" helper */ > char c; > user +=3D ksize; > usize -=3D ksize; > while (usize--) { > if (get_user(c, user++)) > return -EFAULT; > if (c) > return -EINVAL; This part would probably be better done with memchr_inv() and copy_from_user() (and probably should put an upper limit on usize), but I get what you mean. > } > } else if (ksize > usize) { > memset(kernel + usize, 0, ksize - usize); > } > return 0; > } > #define copy_abi_struct(kernel, user, usize) \ > __copy_abi_struct(kernel, sizeof(*kernel), user, usize) > > > Both (1) and (2) have the problem that the "struct version" is inside > > the struct so we'd need to copy_from_user() twice. This isn't the end of > > the world, it just feels a bit less clean than is ideal. (3) fixes that > > problem, at the cost of making the API slightly more cumbersome to use > > directly (though again glibc could wrap that away). >=20 > I don't see how 3 is cumbersome to use directly. Userspace code does > struct openat_of_the_day args =3D {.field1 =3D x, .field3 =3D y} and pass= es > &args, sizeof(args). What does glibc need to do beyond its usual munging > of the userspace ABI registers to the syscall ABI registers? I'd argue that ret =3D openat2(AT_FDCWD, "foo", &how, sizeof(how)); // (3) is slightly less pretty than ret =3D openat2(AT_FDCWD, "foo", &how); // (1), (2), (4) But it's not really that bad. Forget I said anything. --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --itirvnprc6jjrbl3 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXWfQxQAKCRCdlLljIbnQ EoMSAP9J0uy3xcD3flC3cANph5LKQ2g0JWnMb61ew5LWDORVogD/UGWciY+tdPiy YNHs2UcBt9SEH1MNpEIgf2GN6RoyaQI= =ne2z -----END PGP SIGNATURE----- --itirvnprc6jjrbl3--