Received: (at 39236) by debbugs.gnu.org; 22 Jan 2020 16:19:14 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 11:19:14 2020 Received: from localhost ([127.0.0.1]:51204 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuIio-0004wl-Eq for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 11:19:14 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:24421 helo=us-smtp-delivery-1.mimecast.com) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <fweimer@HIDDEN>) id 1iuIim-0004wd-JR for 39236 <at> debbugs.gnu.org; Wed, 22 Jan 2020 11:19:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579709951; 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=zeQORNwkm9Y5eAZO0NO+SYMTGlLa/12TJHMX7xt/F84=; b=iiianIymwP5cjBPIevQVx+x9ek26VbtH/3Id4z5JwKNAHzWICNP20F+18ruBAG8GSOz33u XtWRj8Idz5+dYgW/BjMIE5+OKrY2OEY9pbAhcaW92tKUwjI0nfH7NAb7/rJ7ZghkeC4lFv Sbh4BwtTMUTteYq/9G++awXuOFphaBY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-156-pAF230loNzq0cTwbCCBKbQ-1; Wed, 22 Jan 2020 11:19:09 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4DF601005512; Wed, 22 Jan 2020 16:19:08 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-227.str.redhat.com [10.33.192.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 690711001B03; Wed, 22 Jan 2020 16:19:07 +0000 (UTC) From: Florian Weimer <fweimer@HIDDEN> To: Rich Felker <dalias@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod References: <20200122141557.GA8157@HIDDEN> <87ftg7k1at.fsf@HIDDEN> <20200122144243.GZ30412@HIDDEN> <87a76fjzpx.fsf@HIDDEN> <20200122151507.GB30412@HIDDEN> <87zhefik0y.fsf@HIDDEN> <20200122160743.GC30412@HIDDEN> Date: Wed, 22 Jan 2020 17:19:05 +0100 In-Reply-To: <20200122160743.GC30412@HIDDEN> (Rich Felker's message of "Wed, 22 Jan 2020 11:07:43 -0500") Message-ID: <87v9p3ihvq.fsf@HIDDEN> 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: pAF230loNzq0cTwbCCBKbQ-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 39236 Cc: musl@HIDDEN, 39236 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.0 (-) * Rich Felker: > On Wed, Jan 22, 2020 at 04:32:45PM +0100, Florian Weimer wrote: >> * Rich Felker: >>=20 >> > 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, wh= ich 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 kn= ow 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* followi= ng >> >> > the link and thereby unwantedly changing the permissions of the lin= k >> >> > target. But, fchmodat with AT_SYMLINK_NOFOLLOW works just as well a= nd >> >> > is standard, and that's really what coreutils should be using. >> >>=20 >> >> I think you misread what I wrote: lchmod *always* returns ENOSYS. Ev= en >> >> 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. >>=20 >> 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 point is to fail when the target is a symlink, rather than > (erroneously and possibly dangerously) applying the chmod to the link > target. Actually supporting link modes is useless. It's the "not > modifying the target" that's important. The kernel supports it on some file systems, though: $ ls -l /tmp/x l---------. 1 fweimer fweimer 6 Jan 22 15:27 /tmp/x -> /tmp/x Although mode 0 curiously does not prevent readlink calls. > It's explained in the bz you just replied on, > https://sourceware.org/bugzilla/show_bug.cgi?id=3D14578 > > The point of the S_ISLNK check is to fail out early with the ENOTSUPP, > which the caller should treat as "success-like", in the non-racing > condition, without the need to open a fd (which may fail with > ENFILE/EMFILE) and without the need for /proc to be mounted. > Otherwise, a different error will be produced when one of those cases > is hit, and the caller will treat it as a real error. Hmm. The way I read the musl code, the O_PATH descriptor already exists. At this point, you can just chmod the O_PATH descriptor, and have the kernel report EOPNOTSUPP if the file system does not support that. Thanks, Florian
bug-coreutils@HIDDEN:bug#39236; Package coreutils.
Full text available.Received: (at 39236) by debbugs.gnu.org; 22 Jan 2020 16:08:00 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 11:08:00 2020 Received: from localhost ([127.0.0.1]:51182 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuIXw-0002eU-57 for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 11:08:00 -0500 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:54460 helo=brightrain.aerifal.cx) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <dalias@HIDDEN>) id 1iuIXu-0002eM-Ls for 39236 <at> debbugs.gnu.org; Wed, 22 Jan 2020 11:07:59 -0500 Received: from dalias by brightrain.aerifal.cx with local (Exim 3.15 #2) id 1iuIXf-0002Ra-00; Wed, 22 Jan 2020 16:07:43 +0000 Date: Wed, 22 Jan 2020 11:07:43 -0500 From: Rich Felker <dalias@HIDDEN> To: Florian Weimer <fweimer@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod Message-ID: <20200122160743.GC30412@HIDDEN> References: <20200122141557.GA8157@HIDDEN> <87ftg7k1at.fsf@HIDDEN> <20200122144243.GZ30412@HIDDEN> <87a76fjzpx.fsf@HIDDEN> <20200122151507.GB30412@HIDDEN> <87zhefik0y.fsf@HIDDEN> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87zhefik0y.fsf@HIDDEN> User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-Score: 0.6 (/) X-Debbugs-Envelope-To: 39236 Cc: musl@HIDDEN, 39236 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -0.4 (/) On Wed, Jan 22, 2020 at 04:32:45PM +0100, Florian Weimer wrote: > * Rich Felker: > > > On Wed, Jan 22, 2020 at 04:08:26PM +0100, Florian Weimer wrote: > >> * Rich Felker: > >> > >> > On Wed, Jan 22, 2020 at 03:34:18PM +0100, Florian Weimer wrote: > >> >> * Rich Felker: > >> >> > >> >> > 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. > >> >> > >> >> 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. > > > > 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 point is to fail when the target is a symlink, rather than (erroneously and possibly dangerously) applying the chmod to the link target. Actually supporting link modes is useless. It's the "not modifying the target" that's important. > >> 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. It's explained in the bz you just replied on, https://sourceware.org/bugzilla/show_bug.cgi?id=14578 The point of the S_ISLNK check is to fail out early with the ENOTSUPP, which the caller should treat as "success-like", in the non-racing condition, without the need to open a fd (which may fail with ENFILE/EMFILE) and without the need for /proc to be mounted. Otherwise, a different error will be produced when one of those cases is hit, and the caller will treat it as a real error. Rich
bug-coreutils@HIDDEN:bug#39236; Package coreutils.
Full text available.Received: (at 39236) by debbugs.gnu.org; 22 Jan 2020 16:00:03 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 11:00:03 2020 Received: from localhost ([127.0.0.1]:51160 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuIQE-0002Qd-QK for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 11:00:03 -0500 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:54454 helo=brightrain.aerifal.cx) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <dalias@HIDDEN>) id 1iuHit-0001II-5S for 39236 <at> debbugs.gnu.org; Wed, 22 Jan 2020 10:15:16 -0500 Received: from dalias by brightrain.aerifal.cx with local (Exim 3.15 #2) id 1iuHil-0002IE-00; Wed, 22 Jan 2020 15:15:07 +0000 Date: Wed, 22 Jan 2020 10:15:07 -0500 From: Rich Felker <dalias@HIDDEN> To: Florian Weimer <fweimer@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod Message-ID: <20200122151507.GB30412@HIDDEN> References: <20200122141557.GA8157@HIDDEN> <87ftg7k1at.fsf@HIDDEN> <20200122144243.GZ30412@HIDDEN> <87a76fjzpx.fsf@HIDDEN> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a76fjzpx.fsf@HIDDEN> User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-Score: 0.6 (/) X-Debbugs-Envelope-To: 39236 X-Mailman-Approved-At: Wed, 22 Jan 2020 11:00:00 -0500 Cc: musl@HIDDEN, 39236 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -0.4 (/) On Wed, Jan 22, 2020 at 04:08:26PM +0100, Florian Weimer wrote: > * Rich Felker: > > > On Wed, Jan 22, 2020 at 03:34:18PM +0100, Florian Weimer wrote: > >> * Rich Felker: > >> > >> > 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. > >> > >> 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. 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. > 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. Rich
bug-coreutils@HIDDEN:bug#39236; Package coreutils.
Full text available.Received: (at submit) by debbugs.gnu.org; 22 Jan 2020 16:00:03 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 11:00:02 2020 Received: from localhost ([127.0.0.1]:51158 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuIQE-0002QV-7E for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 11:00:02 -0500 Received: from lists.gnu.org ([209.51.188.17]:35756) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <dalias@HIDDEN>) id 1iuHDm-0008U7-C4 for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 09:43:06 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33381) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from <dalias@HIDDEN>) id 1iuHDl-0005FV-BP for bug-coreutils@HIDDEN; Wed, 22 Jan 2020 09:43:06 -0500 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on eggs.gnu.org X-Spam-Level: ** X-Spam-Status: No, score=2.1 required=5.0 tests=BAYES_50,KHOP_HELO_FCRDNS, RDNS_DYNAMIC autolearn=disabled version=3.3.2 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from <dalias@HIDDEN>) id 1iuHDk-00050T-Fe for bug-coreutils@HIDDEN; Wed, 22 Jan 2020 09:43:05 -0500 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:45894 helo=brightrain.aerifal.cx) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from <dalias@HIDDEN>) id 1iuHDk-0004zE-As for bug-coreutils@HIDDEN; Wed, 22 Jan 2020 09:43:04 -0500 Received: from dalias by brightrain.aerifal.cx with local (Exim 3.15 #2) id 1iuHDP-0002CP-00; Wed, 22 Jan 2020 14:42:43 +0000 Date: Wed, 22 Jan 2020 09:42:43 -0500 From: Rich Felker <dalias@HIDDEN> To: Florian Weimer <fweimer@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod Message-ID: <20200122144243.GZ30412@HIDDEN> References: <20200122141557.GA8157@HIDDEN> <87ftg7k1at.fsf@HIDDEN> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ftg7k1at.fsf@HIDDEN> User-Agent: Mutt/1.5.21 (2010-09-15) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 216.12.86.13 X-Spam-Score: -1.4 (-) X-Debbugs-Envelope-To: submit X-Mailman-Approved-At: Wed, 22 Jan 2020 11:00:00 -0500 Cc: musl@HIDDEN, bug-coreutils@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.4 (--) On Wed, Jan 22, 2020 at 03:34:18PM +0100, Florian Weimer wrote: > * Rich Felker: > > > 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. > > 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. Rich
bug-coreutils@HIDDEN:bug#39236; Package coreutils.
Full text available.Received: (at 39236) by debbugs.gnu.org; 22 Jan 2020 15:33:00 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 10:33:00 2020 Received: from localhost ([127.0.0.1]:51122 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuI04-0001kt-2S for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 10:33:00 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:47420 helo=us-smtp-delivery-1.mimecast.com) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <fweimer@HIDDEN>) id 1iuI02-0001kf-H3 for 39236 <at> debbugs.gnu.org; Wed, 22 Jan 2020 10:32:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579707172; 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=PDWOvsRcLwvMkTLRDh4cGrxGBOlQpOAfwfR/9xzoJiQre+vg4QXjhrjvm7u7DLsxAiBUfX 58s5tj5NkzaOsSkSZnSr4i+WdyjXsVFHVc9EUCn3DJkWpkbEKSuXXiLl4GqMXzJMuLu8MC skiiXF2WYXgSRrWF5COyHcX9O+CTx/k= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-39-kv-JYc7_ODix7BwjkEwkxg-1; Wed, 22 Jan 2020 10:32:49 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 715A7132908; Wed, 22 Jan 2020 15:32:47 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-227.str.redhat.com [10.33.192.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9E2A98BE19; Wed, 22 Jan 2020 15:32:46 +0000 (UTC) From: Florian Weimer <fweimer@HIDDEN> To: Rich Felker <dalias@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod References: <20200122141557.GA8157@HIDDEN> <87ftg7k1at.fsf@HIDDEN> <20200122144243.GZ30412@HIDDEN> <87a76fjzpx.fsf@HIDDEN> <20200122151507.GB30412@HIDDEN> Date: Wed, 22 Jan 2020 16:32:45 +0100 In-Reply-To: <20200122151507.GB30412@HIDDEN> (Rich Felker's message of "Wed, 22 Jan 2020 10:15:07 -0500") Message-ID: <87zhefik0y.fsf@HIDDEN> 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 X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 39236 Cc: musl@HIDDEN, 39236 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.0 (-) * 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
bug-coreutils@HIDDEN:bug#39236; Package coreutils.
Full text available.Received: (at 39236) by debbugs.gnu.org; 22 Jan 2020 15:08:41 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 10:08:41 2020 Received: from localhost ([127.0.0.1]:51085 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuHcW-00017l-UP for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 10:08:41 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:46086 helo=us-smtp-1.mimecast.com) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <fweimer@HIDDEN>) id 1iuHcV-00017Y-42 for 39236 <at> debbugs.gnu.org; Wed, 22 Jan 2020 10:08:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579705713; 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=SNVKfuTd9kTB3aAoEoMzbzo7lN8JnjBmcASMweQ80AARsR7qf2wXuHyTECC1Zlz8PuvAFk 7N+QbWRi0usw9vZbx30a/r+ffCiongU1XBgc9leP/NQC0Bq5K0NNg8/MgSk36wngai7vmj C8wGwqGAUkndGW6zg+qe+vfGaPSenQs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-177-c8t5ySplPmmDUBal30tzFg-1; Wed, 22 Jan 2020 10:08:30 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B11EA18AAFA2; Wed, 22 Jan 2020 15:08:28 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-227.str.redhat.com [10.33.192.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CD1E11001B35; Wed, 22 Jan 2020 15:08:27 +0000 (UTC) From: Florian Weimer <fweimer@HIDDEN> To: Rich Felker <dalias@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod References: <20200122141557.GA8157@HIDDEN> <87ftg7k1at.fsf@HIDDEN> <20200122144243.GZ30412@HIDDEN> Date: Wed, 22 Jan 2020 16:08:26 +0100 In-Reply-To: <20200122144243.GZ30412@HIDDEN> (Rich Felker's message of "Wed, 22 Jan 2020 09:42:43 -0500") Message-ID: <87a76fjzpx.fsf@HIDDEN> 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 X-Spam-Score: -0.0 (/) X-Debbugs-Envelope-To: 39236 Cc: musl@HIDDEN, 39236 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.0 (-) * 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
bug-coreutils@HIDDEN:bug#39236; Package coreutils.
Full text available.Received: (at submit) by debbugs.gnu.org; 22 Jan 2020 14:35:40 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Jan 22 09:35:40 2020 Received: from localhost ([127.0.0.1]:49307 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1iuH6Z-0008IG-W0 for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 09:35:40 -0500 Received: from lists.gnu.org ([209.51.188.17]:41002) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <fweimer@HIDDEN>) id 1iuH6X-0008I9-6M for submit <at> debbugs.gnu.org; Wed, 22 Jan 2020 09:35:38 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60667) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from <fweimer@HIDDEN>) id 1iuH6V-0001e8-Ov for bug-coreutils@HIDDEN; Wed, 22 Jan 2020 09:35:36 -0500 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on eggs.gnu.org X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_NONE autolearn=disabled version=3.3.2 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from <fweimer@HIDDEN>) id 1iuH6T-00085p-Sk for bug-coreutils@HIDDEN; Wed, 22 Jan 2020 09:35:35 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:49757 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from <fweimer@HIDDEN>) id 1iuH6T-00084a-ML for bug-coreutils@HIDDEN; Wed, 22 Jan 2020 09:35:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579703731; 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=fa+uvWeqANcSMjzzWVClZJdS/OnErGIq9duycYoIYnE=; b=TkkVgjxCJz+564g7gdknpTcggAQ+Euu3D1yPmBH8gXMUDvK5djTm9p7bUw2DqdZFjCQY02 vZsUlgs3+CU3qe4/GLSrh+IBdbyoqVMtNNK8SWLomd884NKVuk2ffuGcOqXP9o52Yq0TzH Urr9jrDio1JTu+FlPqTWxnB492S5/nA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-258-D7e9fOYjOwawhIimdHGfIQ-1; Wed, 22 Jan 2020 09:34:22 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3F848100550E; Wed, 22 Jan 2020 14:34:21 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-227.str.redhat.com [10.33.192.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 55B5D100EA05; Wed, 22 Jan 2020 14:34:20 +0000 (UTC) From: Florian Weimer <fweimer@HIDDEN> To: Rich Felker <dalias@HIDDEN> Subject: Re: [musl] coreutils cp mishandles error return from lchmod References: <20200122141557.GA8157@HIDDEN> Date: Wed, 22 Jan 2020 15:34:18 +0100 In-Reply-To: <20200122141557.GA8157@HIDDEN> (Rich Felker's message of "Wed, 22 Jan 2020 09:15:57 -0500") Message-ID: <87ftg7k1at.fsf@HIDDEN> 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: D7e9fOYjOwawhIimdHGfIQ-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-Spam-Score: -1.4 (-) X-Debbugs-Envelope-To: submit Cc: musl@HIDDEN, bug-coreutils@HIDDEN X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -2.4 (--) * Rich Felker: > 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. 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. Thanks, Florian
Florian Weimer <fweimer@HIDDEN>:bug-coreutils@HIDDEN.
Full text available.bug-coreutils@HIDDEN:bug#39236; Package coreutils.
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