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Message-ID: <87wlqjzoxd.fsf@athena.silentflame.com>
Date: Wed, 11 Nov 2026 09:40:30 +0000
From: Sean Whitton <spwhitton@...hitton.name>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Cc: Eli Zaretskii <eliz@....org>, Stefan Monnier <monnier@....umontreal.ca>,
xeroday.sec@...il.com, 82213@...bugs.gnu.org
Subject: Emacs .dir-locals.el arbitrary code execution
X3r0Day discovered that Emacs 31.1 did not adequately validate the
contents of .dir-locals.el before executing code there.
Emacs 30.2 is unaffected.
A patch from Stefan Monnier is attached and will be included in our
upcoming 31.2 release.
For full details on the vulnerability please see
<https://debbugs.gnu.org/82213>.
-- >8 --
From: Stefan Monnier <monnier@....umontreal.ca>
diff --git a/lisp/files.el b/lisp/files.el
index 4cb1ac67629..eec547657d5 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3565,44 +3565,42 @@ magic-mode-regexp-match-limit
"Upper limit on `magic-mode-alist' regexp matches.
Also applies to `magic-fallback-mode-alist'.")
-(defun set-auto-mode--find-matching-alist-entry (alist name case-insensitive)
+(defun set-auto-mode--from-matching-alist-entry ( alist name case-insensitive
+ keep-mode-if-same dir-local)
"Find first matching entry in ALIST for file NAME.
If CASE-INSENSITIVE, the file system of file NAME is case-insensitive."
- (let (mode)
- (while name
- (let ((newmode
- (if case-insensitive
- ;; Filesystem is case-insensitive.
- (let ((case-fold-search t))
- (assoc-default name alist 'string-match))
- ;; Filesystem is case-sensitive.
- (or
- ;; First match case-sensitively.
- (let ((case-fold-search nil))
- (assoc-default name alist 'string-match))
- ;; Fallback to case-insensitive match.
- (and auto-mode-case-fold
- (let ((case-fold-search t))
- (assoc-default name alist 'string-match)))))))
- (when newmode
- (when mode
- ;; We had already found a mode but in a (REGEXP MODE t)
- ;; entry, so we still have to run MODE. Let's do it now.
- ;; FIXME: It's kind of ugly to run the function here.
- ;; An alternative could be to return a list of functions and
- ;; callers.
- (set-auto-mode-0 mode t))
- (setq mode newmode))
- (if (and newmode
- (not (functionp newmode))
- (consp newmode)
- (cadr newmode))
- ;; It's a (REGEXP MODE t): Keep looking but remember the MODE.
- (setq mode (car newmode)
- name (substring name 0 (match-beginning 0)))
- (setq name nil))))
- mode))
+ (let (was-set)
+ (while
+ (let* ((newmode
+ (if case-insensitive
+ ;; Filesystem is case-insensitive.
+ (let ((case-fold-search t))
+ (assoc-default name alist 'string-match))
+ ;; Filesystem is case-sensitive.
+ (or
+ ;; First match case-sensitively.
+ (let ((case-fold-search nil))
+ (assoc-default name alist 'string-match))
+ ;; Fallback to case-insensitive match.
+ (and auto-mode-case-fold
+ (let ((case-fold-search t))
+ (assoc-default name alist 'string-match))))))
+ ;; Extract MODE from (REGEXP MODE t) entries.
+ (mode-t (when (and (not (functionp newmode))
+ (consp newmode)
+ (cadr newmode))
+ (setq name (substring name 0 (match-beginning 0)))
+ (car newmode)))
+ (mode (or mode-t newmode)))
+ (when newmode
+ (if (and dir-local
+ (not (set-auto-mode--dir-local-valid-p mode)))
+ (message "Ignoring invalid mode `%S'" mode)
+ (set-auto-mode-0 mode keep-mode-if-same)
+ (setq was-set t))
+ mode-t)))
+ was-set))
(defun set-auto-mode--apply-alist (alist keep-mode-if-same dir-local)
"Helper function for `set-auto-mode'.
@@ -3614,8 +3612,7 @@ set-auto-mode--apply-alist
DIR-LOCAL non-nil means this call is via directory-locals, and
extra checks should be done."
(if buffer-file-name
- (let (mode
- (name buffer-file-name)
+ (let ((name buffer-file-name)
(remote-id (file-remote-p buffer-file-name))
(case-insensitive-p (file-name-case-insensitive-p
buffer-file-name)))
@@ -3625,15 +3622,8 @@ set-auto-mode--apply-alist
(when (and (stringp remote-id)
(string-match (regexp-quote remote-id) name))
(setq name (substring name (match-end 0))))
- (setq mode (set-auto-mode--find-matching-alist-entry
- alist name case-insensitive-p))
- (when (and dir-local mode
- (not (set-auto-mode--dir-local-valid-p mode)))
- (message "Ignoring invalid mode `%S'" mode)
- (setq mode nil))
- (when mode
- (set-auto-mode-0 mode keep-mode-if-same)
- t))))
+ (set-auto-mode--from-matching-alist-entry
+ alist name case-insensitive-p keep-mode-if-same dir-local))))
(defun set-auto-mode--dir-local-valid-p (mode)
"Say whether MODE can be used in a .dir-local.el `auto-mode-alist'."
--
Sean Whitton
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