From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.2 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by inbox.vuxu.org (OpenSMTPD) with SMTP id 488bd272 for ; Wed, 22 Jan 2020 15:08:45 +0000 (UTC) Received: (qmail 32433 invoked by uid 550); 22 Jan 2020 15:08:44 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 32415 invoked from network); 22 Jan 2020 15:08:43 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579705712; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IYAHJ29z0WQ1PTv+x2InhspzlPnZqmifdh8VCc9GoB0=; b=eCOYbM3/KLXxf9JHnUr0HzOe0LpGJYRquzKHQ+SCl0H2/dP4LAhu0S6XWaATy3x+gXghqy 94QB7nWKF5OdeZO1OPaJZF/smWc2uMinozVgv8XG036xDZvVhgWaNIhwCYjK/1VeeFgHUt j0pnfyyuCzX0CESTBO3SdrjjrPrhEJs= From: Florian Weimer To: Rich Felker Cc: 39236@debbugs.gnu.org, musl@lists.openwall.com References: <20200122141557.GA8157@brightrain.aerifal.cx> <87ftg7k1at.fsf@oldenburg2.str.redhat.com> <20200122144243.GZ30412@brightrain.aerifal.cx> Date: Wed, 22 Jan 2020 16:08:26 +0100 In-Reply-To: <20200122144243.GZ30412@brightrain.aerifal.cx> (Rich Felker's message of "Wed, 22 Jan 2020 09:42:43 -0500") Message-ID: <87a76fjzpx.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: c8t5ySplPmmDUBal30tzFg-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Subject: Re: [musl] coreutils cp mishandles error return from lchmod * Rich Felker: > On Wed, Jan 22, 2020 at 03:34:18PM +0100, Florian Weimer wrote: >> * Rich Felker: >>=20 >> > coreutils should be opting to use the system-provided lchmod, which is >> > safe, and correctly handling error returns (silently treating >> > EOPNOTSUPP as success) rather than as hard errors. >>=20 >> glibc's lchmod always returns ENOSYS (except on Hurd). I don't know how >> lchmod is used in coreutils, but I suspect it is not particularly >> useful. > > When preserving permissions (cp -p, archive extraction, etc.), you > want lchmod to work correctly just for the purpose of *not* following > the link and thereby unwantedly changing the permissions of the link > target. But, fchmodat with AT_SYMLINK_NOFOLLOW works just as well and > is standard, and that's really what coreutils should be using. I think you misread what I wrote: lchmod *always* returns ENOSYS. Even if the file is not a symbolic link. Likewise, fchmodat with AT_SYMLINK_NOFOLLOW *always* returns ENOTSUP. The reason for this is that the kernel does not provide a suitable system call to implement this, even though some file systems allow a mode change for symbolic links. I think we can do better, although I should note that each time we implement such emulation in userspace, it comes back to bite us eventually. Thanks, Florian