Only when configured, grant root access to the X11 display (#776437)

GParted fails to display when run under Wayland [1][2][3].  This is
because by intentional design Wayland doesn't allow applications with
root privileges access to the display [4].

As an interim workaround make the gparted shell wrapper use xhost to
grant root access to the X11 server if root doesn't already have access,
but only when configured.  Granting root access must be explicitly
enabled when building GParted like this:
    ./configure --enable-xhost-root
It defaults to disabled.  When gpartedbin binary ends the shell wrapper
revokes root access only if it granted such access.

[1] GNOME Bug 776437 - GParted fails to run as root under Wayland
    https://bugzilla.gnome.org/show_bug.cgi?id=776437

[2] Ubuntu Bug 1652282 - GParted does not work in GNOME on Wayland
    https://bugs.launchpad.net/ubuntu/+source/gparted/+bug/1652282

[3] Fedora Bug 1397103 - gparted not working under Wayland
    https://bugzilla.redhat.com/show_bug.cgi?id=1397103

[4] Common Fedora 25 bugs
    Running graphical apps with root privileges (e.g. gparted) does not
    work on Wayland
    https://fedoraproject.org/wiki/Common_F25_bugs#wayland-root-apps

Bug 776437 - GParted fails to run as root under Wayland

Makefile.am

@@ -34,7 +34,8 @@ CLEANFILES = $(bin_SCRIPTS) $(DESKTOP_IN_FILES) $(polkit_action_in_FILES)
 
 do_subst = sed -e 's,[@]sbindir[@],$(sbindir),g' \
 	-e 's,[@]bindir[@],$(bindir),g' \
-	-e 's,[@]gksuprog[@],$(GKSUPROG),g'
+	-e 's,[@]gksuprog[@],$(GKSUPROG),g' \
+	-e 's,[@]enable_xhost_root[@],$(ENABLE_XHOST_ROOT),g'
 
 gparted.desktop.in:  gparted.desktop.in.in Makefile
 	$(do_subst) < $(srcdir)/gparted.desktop.in.in > gparted.desktop.in

README

@@ -145,6 +145,11 @@ b. Building from Source
               specifically enabled with the --enable-online-resize flag:
                 E.g., ./configure --enable-online-resize
 
+   If you wish to build GParted to allow it to use xhost to grant root
+   access to the X11 server use the --enable-xhost-root flag.  This is
+   required to allow GParted to display under Wayland.
+      ./configure --enable-xhost-root
+
    Please note that more than one configure flag can be used:
       E.g., ./configure --disable-doc --enable-libparted-dmraid
 
@@ -332,4 +337,6 @@ system.  These commands include:
    udevinfo        - used in dmraid to query udev name
    udevadm         - used in dmraid to query udev name
    yelp            - used to display help manual
+   xhost           - used to grant root access to the X11 server, only
+                     when configured to do so
 

configure.ac

@@ -392,6 +392,25 @@ else
 fi
 
 
+dnl Check whether to explicitly grant root access to the display.
+AC_ARG_ENABLE(
+	[xhost-root],
+	AS_HELP_STRING(
+		[--enable-xhost-root],
+		[enable explicitly granting root access to the display @<:@default=disabled@:>@]),
+	[enable_xhost_root=$enableval],
+	[enable_xhost_root=no]
+)
+
+AC_MSG_CHECKING([whether to explicitly grant root access to the display])
+if test "x$enable_xhost_root" = 'xyes'; then
+	AC_MSG_RESULT([yes])
+else
+	AC_MSG_RESULT([no])
+fi
+AC_SUBST([ENABLE_XHOST_ROOT], $enable_xhost_root)
+
+
 AC_CONFIG_FILES([
 Makefile
 compose/Makefile
@@ -422,6 +441,8 @@ echo "                      Build help documentation?  :  $enable_doc"
 echo ""
 echo "           Use native libparted dmraid support?  :  $enable_libparted_dmraid"
 echo ""
+echo "   Explicitly grant root access to the display?  :  $enable_xhost_root"
+echo ""
 echo "       --- Features Based On Libparted Version ---"
 echo "       Need delete old partitions before"
 echo "              creating a loop table workaround?  :  $need_loop_delete_old_ptns_workaround"

gparted.in

@@ -56,8 +56,35 @@ if test "x`id -u`" != "x0"; then
 		exit 1
 	fi
 
+	#
+	# Interim workaround to allow GParted run by root access to the
+	# X11 display server under Wayland.  If configured with
+	# './configure --enable-xhost-root', the xhost command is
+	# available and root has not been granted access to the X11
+	# display via xhost, then grant access.
+	#
+	ENABLE_XHOST_ROOT=@enable_xhost_root@
+	GRANTED_XHOST_ROOT=no
+	if test "x$ENABLE_XHOST_ROOT" = 'xyes' && xhost 1> /dev/null 2>&1; then
+		if ! xhost | grep -qi 'SI:localuser:root$'; then
+			xhost +SI:localuser:root
+			GRANTED_XHOST_ROOT=yes
+		fi
+	fi
+
+	#
+	# Run gparted as root.
+	#
 	@gksuprog@ '@bindir@/gparted' "$@"
-	exit $?
+	status=$?
+
+	#
+	# Revoke root access to the X11 display, only if we granted it.
+	#
+	if test "x$GRANTED_XHOST_ROOT" = 'xyes'; then
+		xhost -SI:localuser:root
+	fi
+	exit $status
 fi
 
 #