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 da385187 for ; Wed, 22 Jan 2020 15:33:08 +0000 (UTC) Received: (qmail 9493 invoked by uid 550); 22 Jan 2020 15:33:07 -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 9472 invoked from network); 22 Jan 2020 15:33:06 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579707174; 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=lukizSyFTkoCgu6xnxIGPXbkU9xyLUCT9IWiVqolSxo=; b=YFW4T6nL1+y4QP2n46Fo4JV9/xsMLvKDcv1PcS36eh2YS4gmWtj5g3KX1f2/6MlGKJ/F6q /4VKBkjRZhP25X8OkNTZPW7k38aduUJMrugdcORwQjfH+IRnIG0/zZLJNUEg00MAUzfoCj XeQLodIT/Nn4yj9YDD55++6wXcrRX8Y= 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> <87a76fjzpx.fsf@oldenburg2.str.redhat.com> <20200122151507.GB30412@brightrain.aerifal.cx> Date: Wed, 22 Jan 2020 16:32:45 +0100 In-Reply-To: <20200122151507.GB30412@brightrain.aerifal.cx> (Rich Felker's message of "Wed, 22 Jan 2020 10:15:07 -0500") Message-ID: <87zhefik0y.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 2.79 on 10.5.11.13 X-MC-Unique: kv-JYc7_ODix7BwjkEwkxg-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 04:08:26PM +0100, Florian Weimer wrote: >> * Rich Felker: >>=20 >> > 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. >>=20 >> 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. > > Yes, I understood that. I was going into why there should be a real > implementation, but didn't make it clear that that was what I was > doing. Ah, yes, there should be a real implementation if we can get full lchmod/AT_SYMLINK_NOFOLLOW behavior on file systems that support it. If we can't, I'm not sure if there is a point to it. >> 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. > > Emulations in userspace that are approximate, have race conditions, > etc. are bad. Ones that are rigorous are good, though. Is there a reason for the S_ISLNK check in the musl implementation? With current kernels, chmod on the proc pseudo-file will not traverse the symbolic link, but I have yet to check if this has always been the case. Thanks, Florian