Received: (at 44627) by debbugs.gnu.org; 7 Jun 2022 10:44:42 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Tue Jun 07 06:44:42 2022 Received: from localhost ([127.0.0.1]:38327 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1nyWhW-0006gv-F2 for submit <at> debbugs.gnu.org; Tue, 07 Jun 2022 06:44:42 -0400 Received: from quimby.gnus.org ([95.216.78.240]:51518) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <larsi@HIDDEN>) id 1nyWhV-0006gh-1h for 44627 <at> debbugs.gnu.org; Tue, 07 Jun 2022 06:44:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=gnus.org; s=20200322; h=Content-Type:MIME-Version:Message-ID:In-Reply-To:Date: References:Subject:Cc:To:From:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=s0hnrMZTjyJ0RG9IYbPK14VY5AtI10JRsPet7tKZnlg=; b=YCsBlRjaRfFKsrhb4Eb3d42Qy1 S5/PTXqrk/Fg4zoc1C85580sjyG3j6sVEGnngwQ0tJpBQvUxswLwOPozqTl6gHVTeRTfGCJX9grry CaWw/f63pLK1IqgpEeYZZZUln1NlXBsIuft4AC7KuxF7GwHlUonf0cveRGIFy4phYJ2w=; Received: from [84.212.220.105] (helo=xo) by quimby.gnus.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from <larsi@HIDDEN>) id 1nyWhK-0001T8-MA; Tue, 07 Jun 2022 12:44:33 +0200 From: Lars Ingebrigtsen <larsi@HIDDEN> To: Michael Young <mwy-hsyzfo@HIDDEN> Subject: Re: bug#44627: 25.2; tempsetmodes handling does not update extended attributes References: <f86a6d7e-87c1-4854-6715-a9d4e0c73325@HIDDEN> X-Now-Playing: Blaine L. Reininger's _Commissions 2 (1)_: "The Master and Margarita" Date: Tue, 07 Jun 2022 12:44:30 +0200 In-Reply-To: <f86a6d7e-87c1-4854-6715-a9d4e0c73325@HIDDEN> (Michael Young's message of "Fri, 13 Nov 2020 23:50:28 -0500") Message-ID: <87pmjklpm9.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Spam-Report: Spam detection software, running on the system "quimby.gnus.org", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: Michael Young <mwy-hsyzfo@HIDDEN> writes: > Open a read-only file, toggle read-only mode, and modify the file. > Attempt to save the file. > Answer "yes" to the prompt > File <FILENAME> is write-protected; try to save anyway? (yes or no) > > [...] Content analysis details: (-2.9 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: 44627 Cc: 44627 <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: -3.3 (---) Michael Young <mwy-hsyzfo@HIDDEN> writes: > Open a read-only file, toggle read-only mode, and modify the file. > Attempt to save the file. > Answer "yes" to the prompt > File <FILENAME> is write-protected; try to save anyway? (yes or no) > > If the filesystem housing <FILENAME> supports extended attributes, > the attempt to temporarily change the file mode doesn't do anything, > and the subsequent attempt to write fails in basic-save-buffer-2: > Opening output file: Permission denied, <FILENAME> > > This section of files.el appears to be the problem: > https://github.com/emacs-mirror/emacs/blob/d408866ff2a0de7af5d8bb40d9c1c310573f1800/lisp/files.el#L5444 > > It retrieves the extended attributes, but then does not make any changes > to them before setting them. If the attempt to set the extended > attributes fails, it falls back on set-file-modes to set the > POSIX user write permission (128) -- that appears to work as intended. (I'm going through old bug reports that unfortunately weren't resolved at the time.) This bug report is about Emacs 25.2, but the code is still essentially the same today: ;; If file not writable, see if we can make it writable ;; temporarily while we write it. ;; But no need to do so if we have just backed it up ;; (setmodes is set) because that says we're superseding. (cond ((and tempsetmodes (not setmodes)) ;; Change the mode back, after writing. (setq setmodes (list (file-modes buffer-file-name) (file-extended-attributes buffer-file-name) buffer-file-name)) ;; If set-file-extended-attributes fails, fall back on ;; set-file-modes. (unless (with-demoted-errors "Error setting attributes: %s" (set-file-extended-attributes buffer-file-name (nth 1 setmodes))) (set-file-modes buffer-file-name (logior (car setmodes) 128))))) I.e., it's reading the extended attributes -- and then setting the extended attributes to exactly what they were, which seems nonsensical. Is this anything but a NOOP on any system? For this to work, Emacs would have to (as Michael points out) actually modify the extended attributes to allow writing, but does Emacs have any functions to do that? A brief poke around doesn't seem to reveal anything -- anybody know? -- (domestic pets only, the antidote for overdose, milk.) bloggy blog: http://lars.ingebrigtsen.no
bug-gnu-emacs@HIDDEN:bug#44627; Package emacs.
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From: Michael Young <mwy-hsyzfo@HIDDEN>
Subject: 25.2; tempsetmodes handling does not update extended attributes
To: bug-gnu-emacs@HIDDEN
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This bug report will be sent to the Bug-GNU-Emacs mailing list
and the GNU bug tracker at debbugs.gnu.org. Please check that
the From: line contains a valid email address. After a delay of up
to one day, you should receive an acknowledgment at that address.
Please write in English if possible, as the Emacs maintainers
usually do not have translators for other languages.
Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug. If you can, give a recipe
starting from 'emacs -Q':
Open a read-only file, toggle read-only mode, and modify the file.
Attempt to save the file.
Answer "yes" to the prompt
File <FILENAME> is write-protected; try to save anyway? (yes or no)
If the filesystem housing <FILENAME> supports extended attributes,
the attempt to temporarily change the file mode doesn't do anything,
and the subsequent attempt to write fails in basic-save-buffer-2:
Opening output file: Permission denied, <FILENAME>
This section of files.el appears to be the problem:
https://github.com/emacs-mirror/emacs/blob/d408866ff2a0de7af5d8bb40d9c1c310573f1800/lisp/files.el#L5444
It retrieves the extended attributes, but then does not make any changes
to them before setting them. If the attempt to set the extended
attributes fails, it falls back on set-file-modes to set the
POSIX user write permission (128) -- that appears to work as intended.
I'm not sure whether the right fix is to add the write bit in the extended-attributes
ACL entry somehow, or to execute the set-file-modes (with the 128 bit)
even when there are extended attirbutes. The description of
file-extended-attributes at the top of files.el says that they
are platform-specific metadata, so it's not clear to me how to
modify the ACL in a portable way, or if there is library support
for doing that.
I have encountered this behavior in several different versions of emacs,
including 25.2.2 and 27.1.
Let me know if you need any more information.
Thanks for your support!
If Emacs crashed, and you have the Emacs process in the gdb debugger,
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For information about GNU Emacs and the GNU system, type <f1> C-a.
Mark set
Note: file is write protected
Read-Only mode disabled in current buffer
‘toggle-read-only’ is an obsolete command (as of 24.3); use ‘read-only-mode’ instead.
Saving file /tmp/hi...
basic-save-buffer-2: Opening output file: Permission denied, /tmp/hi
Load-path shadows:
/usr/share/emacs/25.2/site-lisp/debian-startup hides /usr/share/emacs/site-lisp/debian-startup
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Memory information:
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(symbols 48 19842 0)
(miscs 40 48 135)
(strings 32 14416 4804)
(string-bytes 1 411539)
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Michael Young <mwy-hsyzfo@HIDDEN>:bug-gnu-emacs@HIDDEN.
Full text available.bug-gnu-emacs@HIDDEN:bug#44627; Package emacs.
Full text available.
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