Re: emacs-29 3c1693d08b0: Fix Elisp code injection vulnerability in emacsclient-mail.desktop

[Ulrich Mueller]

>>>>> On Wed, 08 Mar 2023, Ulrich Mueller wrote:

> Sure, something like this (not yet tested):

> -Exec=bash -c "u=\\${1//\\\\\\\\/\\\\\\\\\\\\\\\\}; 
> u=\\${u//\\\\\\"/\\\\\\\\\\\\\\"}; exec emacsclient --alternate-editor= 
> --display=\\"\\$DISPLAY\\" --eval \\"(message-mailto \\\\\\"\\$u\\\\\\")\\"" 
> bash %u
> +Exec=sh -c "u=\\$\\(echo \\"\\$1\\" | sed 
> \\'s/[\\\\\\"]/\\\\\\\\\\&/g\\'\\); exec emacsclient --alternate-editor= 
> --display=\\"\\$DISPLAY\\" --eval \\"(message-mailto \\\\\\"\\$u\\\\\\")\\"" 
> sh %u

> Sorry, but it doesn't get less ugly. :) Also, it will now call _two_
> external programs. Is this acceptable, and is it guaranteed that sed
> will be available on users' systems?

In fact, only '"', '$', and '\' need to be backslash-escaped.
Patch included below, works fine here.

----- 8< -----
>From 1e1f128c5ca0c888dae4651bcb3d556737e3a207 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ulrich=20M=C3=BCller?= <ulm@gentoo.org>
Date: Wed, 8 Mar 2023 12:23:58 +0100
Subject: [PATCH] Avoid using bash in the emacsclient desktop file

* etc/emacsclient-mail.desktop (Exec): Use sh and sed instead
of bash, because the latter may not be available everywhere.
---
 etc/emacsclient-mail.desktop | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/etc/emacsclient-mail.desktop b/etc/emacsclient-mail.desktop
index 49c6f99f317..0a2420ddead 100644
--- a/etc/emacsclient-mail.desktop
+++ b/etc/emacsclient-mail.desktop
@@ -2,9 +2,9 @@
 Categories=Network;Email;
 Comment=GNU Emacs is an extensible, customizable text editor - and more
 # We want to pass the following commands to the shell wrapper:
-# u=${1//\\/\\\\}; u=${u//\"/\\\"}; exec emacsclient --alternate-editor= 
--display="$DISPLAY" --eval "(message-mailto \"$u\")"
+# u=$(echo "$1" | sed 's/[\"]/\\&/g'); exec emacsclient --alternate-editor= 
--display="$DISPLAY" --eval "(message-mailto \"$u\")"
 # Special chars '"', '$', and '\' must be escaped as '\\"', '\\$', and '\\\\'.
-Exec=bash -c "u=\\${1//\\\\\\\\/\\\\\\\\\\\\\\\\}; 
u=\\${u//\\\\\\"/\\\\\\\\\\\\\\"}; exec emacsclient --alternate-editor= 
--display=\\"\\$DISPLAY\\" --eval \\"(message-mailto \\\\\\"\\$u\\\\\\")\\"" 
bash %u
+Exec=sh -c "u=\\$(echo \\"\\$1\\" | sed 's/[\\\\\\"]/\\\\\\\\&/g'); exec 
emacsclient --alternate-editor= --display=\\"\\$DISPLAY\\" --eval 
\\"(message-mailto \\\\\\"\\$u\\\\\\")\\"" sh %u
 Icon=emacs
 Name=Emacs (Mail, Client)
 MimeType=x-scheme-handler/mailto;
@@ -16,7 +16,7 @@ Actions=new-window;new-instance;
 
 [Desktop Action new-window]
 Name=New Window
-Exec=bash -c "u=\\${1//\\\\\\\\/\\\\\\\\\\\\\\\\}; 
u=\\${u//\\\\\\"/\\\\\\\\\\\\\\"}; exec emacsclient --alternate-editor= 
--create-frame --eval \\"(message-mailto \\\\\\"\\$u\\\\\\")\\"" bash %u
+Exec=sh -c "u=\\$(echo \\"\\$1\\" | sed 's/[\\\\\\"]/\\\\\\\\&/g'); exec 
emacsclient --alternate-editor= --create-frame --eval \\"(message-mailto 
\\\\\\"\\$u\\\\\\")\\"" sh %u
 
 [Desktop Action new-instance]
 Name=New Instance
-- 
2.39.2