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=-3.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 597DFC2BA1B for ; Wed, 8 Apr 2020 21:29:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21DDA206F7 for ; Wed, 8 Apr 2020 21:29:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="MowKziS/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730486AbgDHV3k (ORCPT ); Wed, 8 Apr 2020 17:29:40 -0400 Received: from mail-ed1-f66.google.com ([209.85.208.66]:39860 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730452AbgDHV3k (ORCPT ); Wed, 8 Apr 2020 17:29:40 -0400 Received: by mail-ed1-f66.google.com with SMTP id a43so10628845edf.6; Wed, 08 Apr 2020 14:29:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:reply-to:from:date:message-id :subject:to:cc:content-transfer-encoding; bh=A//Ihtk8E6tGXssdeUVjq+HsfLF2Kwp1UsiAdKMAPC0=; b=MowKziS/aP0dLyQZfm3LH2OOVnSziB5+YdNABqp5DaO6phZMONdWTHrVb68lnPg/xo kU7SNyJ55ozs6l8SVZQ4sTKHnKMiU7K1trC42DZ8nQv+XCBy3tJRNa7MlUi3CFG85uuy DHrwLeRL96bm0aApoHpe1wE7oNoDwkk88NOE5rYA46ujRbnXR6PeVbnwXmeCYctS2JE8 zaUbA8cWy1HyIiCWsFipHTdTn58SLJpHd8btcG80FrOTsa5FPNgR5zmzR9+JEE64Nvsb 1FSlURpgnIhGlgrhr8hPuLihnQzuIgEdiwHzcLxmg9fHMgCdU4R9OGUM9ukHQJTMivP3 jOVw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:reply-to :from:date:message-id:subject:to:cc:content-transfer-encoding; bh=A//Ihtk8E6tGXssdeUVjq+HsfLF2Kwp1UsiAdKMAPC0=; b=cjevSeseNfmcJXrgH6+q0dxEjNx3UJMrHrguerhvMrOmvS3lDhPomwjfAMS3YWw5Dr KEWcEaHYFR7uRrHhCedEyroH3yLeD5oxepBHDp/pOp9yAtjH0aY1V2YEdwODr3eokfBq NLReOddEafYWjgx9cpnJDiOUC5tW6HoNk0w2a+zcIpB/k5NZTt7ssONEuMb4dfmVg6e/ o4eyhi6NaZzb/GGJftNHGi9crc4ktekbmmqgUbuToiZ50+Awhb1M8YwfwRxCMJhh2Nt2 HCtGVZQvF1iaa5KLuF9rB6N7J2ihL4vGv+8jZcI3cMpUykjv6IyMXw1USlPMdpAD2azI NTiA== X-Gm-Message-State: AGi0PuZxf3wrC1s/+jvNeTNDeUtlD/tJAlPcA9sImISi2j1YfXCZvaT7 W9niv41zW7xK5acl1+Ja47hXtU2STvgZY/thvCo= X-Google-Smtp-Source: APiQypIcLuUPcM7dpcYmVLN0FYDPTb1IWXC7Gx88nUJmVVsFuobNJPDrfewiy+GojX6YPVRfdLX7XRnOLG2Q2pY9QhQ= X-Received: by 2002:a05:6402:30b2:: with SMTP id df18mr8251337edb.149.1586381377148; Wed, 08 Apr 2020 14:29:37 -0700 (PDT) MIME-Version: 1.0 References: <20200202151907.23587-1-cyphar@cyphar.com> <20200202151907.23587-3-cyphar@cyphar.com> <1567baea-5476-6d21-4f03-142def0f62e3@gmail.com> <20200331143911.lokfoq3lqfri2mgy@yavin.dot.cyphar.com> In-Reply-To: Reply-To: mtk.manpages@gmail.com From: "Michael Kerrisk (man-pages)" Date: Wed, 8 Apr 2020 23:29:25 +0200 Message-ID: Subject: Re: [PATCH man-pages v2 2/2] openat2.2: document new openat2(2) syscall To: Aleksa Sarai Cc: Al Viro , Christian Brauner , Aleksa Sarai , linux-man , Linux API , "linux-fsdevel@vger.kernel.org" , lkml Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-man-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org Hi Aleksa, Ping! Cheers, Michael On Wed, 1 Apr 2020 at 08:38, Michael Kerrisk (man-pages) wrote: > > Hello Aleksa, > > On 3/31/20 4:39 PM, Aleksa Sarai wrote: > > On 2020-03-30, Michael Kerrisk (man-pages) wro= te: > >> Hello Aleksa, > >> > >> On 2/2/20 4:19 PM, Aleksa Sarai wrote: > >>> Rather than trying to merge the new syscall documentation into open.2 > >>> (which would probably result in the man-page being incomprehensible), > >>> instead the new syscall gets its own dedicated page with links betwee= n > >>> open(2) and openat2(2) to avoid duplicating information such as the l= ist > >>> of O_* flags or common errors. > >>> > >>> In addition to describing all of the key flags, information about the > >>> extensibility design is provided so that users can better understand = why > >>> they need to pass sizeof(struct open_how) and how their programs will > >>> work across kernels. After some discussions with David Laight, I also > >>> included explicit instructions to zero the structure to avoid issues > >>> when recompiling with new headers. > >>> > >>> Signed-off-by: Aleksa Sarai > >> > >> Thanks. I've applied this patch, but also done quite a lot of > >> editing of the page. The current draft is below (and also pushed > >> to Git). Could I ask you to review the page, to see if I injected > >> any error during my edits. > > > > Looks good to me. > > > >> In addition, I've added a number of FIXMEs in comments > >> in the page source. Can you please check these, and let me > >> know your thoughts. > > > > Will do, see below. > > > >> .\" FIXME I find the "previously-functional systems" in the previous > >> .\" sentence a little odd (since openat2() ia new sysycall), so I woul= d > >> .\" like to clarify a little... > >> .\" Are you referring to the scenario where someone might take an > >> .\" existing application that uses openat() and replaces the uses > >> .\" of openat() with openat2()? In which case, is it correct to > >> .\" understand that you mean that one should not just indiscriminately > >> .\" add the RESOLVE_NO_XDEV flag to all of the openat2() calls? > >> .\" If I'm not on the right track, could you point me in the right > >> .\" direction please. > > > > This is mostly meant as a warning to hopefully avoid applications > > because the developer didn't realise that system paths may contain > > symlinks or bind-mounts. For an application which has switched to > > openat2() and then uses RESOLVE_NO_SYMLINKS for a non-security reason, > > it's possible that on some distributions (or future versions of a > > distribution) that their application will stop working because a system > > path suddenly contains a symlink or is a bind-mount. > > > > This was a concern which was brought up on LWN some time ago. If you ca= n > > think of a phrasing that makes this more clear, I'd appreciate it. > > Thanks. I've made the text: > > Applications that employ the RESOLVE_NO_XDEV flag > are encouraged to make its use configurable (unless > it is used for a specific security purpose), as bind > mounts are widely used by end-users. Setting this > flag indiscriminately=E2=80=94i.e., for purposes not= specif=E2=80=90 > ically related to security=E2=80=94for all uses of o= penat2() > may result in spurious errors on previously-func= =E2=80=90 > tional systems. This may occur if, for example, a > system pathname that is used by an application is > modified (e.g., in a new distribution release) so > that a pathname component (now) contains a bind > mount. > > Okay? > > >> .\" FIXME: what specific details in symlink(7) are being referred > >> .\" by the following sentence? It's not clear. > > > > The section on magic-links, but you're right that the sentence ordering > > is a bit odd. It should probably go after the first sentence. > > I must admit that I'm still confused. There's only the briefest of > mentions of magic links in symlink(7). Perhaps that needs to be fixed? > > And, while I think of it, the text just preceding that FIXME says: > > Due to the potential danger of unknowingly opening > these magic links, it may be preferable for users to > disable their resolution entirely. > > This sentence reads a little strangely. Could you please give me some > concrete examples, and I will try rewording that sentence a bit. > > >> .\" FIXME I found the following hard to understand (in particular, the > >> .\" meaning of "scoped" is unclear) , and reworded as below. Is it oka= y? > >> .\" Absolute symbolic links and ".." path components will be scope= d to > >> .\" .IR dirfd . > > > > Scoped does broadly mean "interpreted relative to", though the > > difference is mainly that when I said scoped it's meant to be more of a= n > > assertive claim ("the kernel promises to always treat this path inside > > dirfd"). But "interpreted relative to" is a clearer way of phrasing the > > semantics, so I'm okay with this change. > > Okay. > > >> .\" FIXME The next piece is unclear (to me). What kind of ".." escape > >> .\" attempts does chroot() not detect that RESOLVE_IN_ROOT does? > > > > If the root is moved, you can escape from a chroot(2). But this sentenc= e > > might not really belong in a man-page since it's describing (important) > > aspects of the implementation and not the semantics. > > So, should I just remove the sentence? > > Thanks, > > Michael > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ --=20 Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/