bug#42673: 26.3; Return value of XGetIMValues not checked in xim_open_dpy (src/xterm.c)

[Yichao Yu]

The call in question is at
https://git.savannah.gnu.org/cgit/emacs.git/tree/src/xterm.c?id=9fe2bdb88a4ebd4b2286c1c2a2a2ba7411af01b6#n10316
Since the return value isn't checked, a failure to initialize here can
cause `dpyinfo->xim_styles` to be `NULL` which intern cause readers
like 
https://git.savannah.gnu.org/cgit/emacs.git/tree/src/xfns.c?id=9fe2bdb88a4ebd4b2286c1c2a2a2ba7411af01b6#n2659
to pass a `NULL` pointer to `best_xim_style` and crash.

The fix is to check if the return value of `XGetIMValues` is not
`NULL` and if it is not `NULL`, disable XIM.

It currently triggers due to
https://gitlab.freedesktop.org/xorg/lib/libx11/-/issues/116 but this
function can also fail for other reasons including bugs on the input
method side. It's not guaranteed to success and a failure in this
function should not cause emacs itself to crash...

In GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.21)

of 2020-07-29 built on yyc.yyc-arch.org

Repository revision: d9eea1ad1bca16406a6d4c9bd0daa57a9d0a531f

System Description: Arch Linux


Recent messages:

For information about GNU Emacs and the GNU system, type C-h C-a.

user-error: Beginning of history; no preceding item [2 times]

Making completion list...

Quit

C-x C-g is undefined


Configured using:

'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib

--localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int

--with-modules 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt

-g -fvar-tracking-assignments

-fdebug-prefix-map=/home/yuyichao/projects/arch-pkg/pkg/tmp/emacs/repos/extra-x86_64/src=/usr/src/debug

-ggdb3 -O0 -DDEBUG_XIC_FONTSET=1' CPPFLAGS=-D_FORTIFY_SOURCE=2

LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'


Configured features:

XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB

NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB

TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD LCMS2


Important settings:

value of $LANG: zh_CN.UTF-8

value of $XMODIFIERS: @im=fcitx

locale-coding-system: utf-8-unix


Major mode: Fundamental


Minor modes in effect:

tooltip-mode: t

global-eldoc-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

auto-composition-mode: t

auto-encryption-mode: t

auto-compression-mode: t

buffer-read-only: t

line-number-mode: t

transient-mark-mode: t


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/usr/share/emacs/site-lisp/org/ob hides /usr/share/emacs/26.3/lisp/org/ob

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Features:

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format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg

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ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win

term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe

tabulated-list replace newcomment text-mode elisp-mode lisp-mode

prog-mode register page menu-bar rfn-eshadow isearch timer select

scroll-bar mouse jit-lock font-lock syntax facemenu font-core

term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang

vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932

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help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs

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base64 format env code-pages mule custom widget hashtable-print-readable

backquote threads dbusbind inotify lcms2 dynamic-setting

system-font-setting font-render-setting move-toolbar gtk x-toolkit x

multi-tty make-network-process emacs)


Memory information:

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