bug#59104: 28.2; Uninitialized field command_modes in Lisp_Module_Function

bug#59104: 28.2; Uninitialized field command_modes in Lisp_Module_Function

[Richard Copley]

1. Save the "next-prime" sample C program in section E.8.3 "Module
Values" of the Elisp manual to file "sample.c"

2. Add these three lines before "return 0;" in function
"emacs_module_init" at the end of the file:

        const char s[] = "nInteger: ";
        emacs_value spec = env->make_string(env, s, sizeof s - 1);
        env->make_interactive (env, func, spec);

3. Save and compile (compile-command: "gcc --shared -o ~/sample.so
sample.c -lgmp").

4. (Dangerous) Load the module and attempt to access the command_modes
field of the Lisp_Module_Function object for the next-prime command.

        emacs --batch -eval "(load-library \"~/sample.so\")" -eval
"(print (command-modes 'next-prime))"

The command_modes field seems to be uninitialized. This might print a
random integer, print a randomly selected lisp object from memory, or
segfault.


In GNU Emacs 28.2 (build 2, x86_64-w64-mingw32)
 of 2022-10-11 built on fv-az365-328
Repository revision: b35f9af313a5d5c42988eb5a7751209b4234a67e
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 10.0.19045
System Description: Microsoft Windows 10 Pro (v10.0.2009.19045.2130)

Configured using:
 'configure --prefix=/mingw64 --host=x86_64-w64-mingw32
 --build=x86_64-w64-mingw32 --with-modules --without-dbus
 --without-compress-install --with-native-compilation
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe'
 CPPFLAGS=-D__USE_MINGW_ANSI_STDIO=1 LDFLAGS=-pipe'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LIBXML2 MODULES NATIVE_COMP NOTIFY
W32NOTIFY PDUMPER PNG RSVG SOUND THREADS TIFF TOOLKIT_SCROLL_BARS XPM
ZLIB

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec epa
derived epg rfc6068 epg-config gnus-util rmail rmail-loaddefs
auth-source eieio eieio-core eieio-loaddefs password-cache json map
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils time-date misearch multi-isearch shell pcomplete compile
text-property-search comint ansi-color ring vc-git diff-mode easy-mmode
vc-dispatcher cc-mode cc-fonts cc-guess cc-menus cc-cmds cc-styles
cc-align cc-engine cc-vars cc-defs dired-aux dired comp comp-cstr
warnings subr-x rx cl-seq cl-macs cl-extra help-mode seq byte-opt gv
cl-loaddefs cl-lib bytecomp byte-compile cconv dired-loaddefs iso-transl
tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel dos-w32 ls-lisp disp-table
term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice
button loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads w32notify w32 multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 166842 11642)
 (symbols 48 11063 1)
 (strings 32 38698 2749)
 (string-bytes 1 1480785)
 (vectors 16 24357)
 (vector-slots 8 430076 60478)
 (floats 8 42 269)
 (intervals 56 2483 0)
 (buffers 992 18))

bug#59104: 28.2; Uninitialized field command_modes in Lisp_Module_Function

[Richard Copley]

> The command_modes field seems to be uninitialized. This might print a
> random integer, print a randomly selected lisp object from memory, or
> segfault.

I can confirm that changing the 'field' argument from "interactive_form" 
to "command_modes", in the invocation of ALLOCATE_PSEUDOVECTOR in 
allocate_module_function (), fixes the problem. See "emacs-module.c", 
line 564.

bug#59104: 28.2; Uninitialized field command_modes in Lisp_Module_Function

[Eli Zaretskii]

> Date: Wed, 9 Nov 2022 16:24:35 +0000
> From: Richard Copley <rcopley@gmail.com>
> 
> > The command_modes field seems to be uninitialized. This might print a
> > random integer, print a randomly selected lisp object from memory, or
> > segfault.
> 
> I can confirm that changing the 'field' argument from "interactive_form" 
> to "command_modes", in the invocation of ALLOCATE_PSEUDOVECTOR in 
> allocate_module_function (), fixes the problem. See "emacs-module.c", 
> line 564.

Thanks, I think this is the right fix, so I've now installed this on
the master branch, and I'm closing the bug.