Fix random segfault on GTK icon functions

The segfaults were happening on GTK icon theme functions, which are
called via the C++ interface functions such as Gtk::IconTheme::has_icon.

There are multiple modules and threads using this functions on the default
icon theme by calling Gtk::IconTheme::get_default(), which returns the same
object for all callers, and was causing concurrent access to the same internal
data structures on the GTK lib. Even a seemingly read-only function such as
has_icon can cause writes due to the internal icon cache being updated.

To avoid this issues, a program wide global mutex must be used to ensure
a single thread is accessing the default icon theme instance.

This commit implements wrappers for the existing IconTheme function calls,
ensuring the global lock is held while calling the underling GTK functions.

include/util/gtk_icon.hpp

@@ -0,0 +1,12 @@
+#pragma once
+#include <string>
+#include <mutex>
+#include <gtkmm/icontheme.h>
+
+class DefaultGtkIconThemeWrapper {
+  private:
+    static std::mutex default_theme_mutex;
+  public:
+    static bool has_icon(const std::string&);
+    static Glib::RefPtr<Gdk::Pixbuf> load_icon(const char*, int, Gtk::IconLookupFlags);
+};

meson.build

@@ -173,7 +173,8 @@ src_files = files(
     'src/util/prepare_for_sleep.cpp',
     'src/util/ustring_clen.cpp',
     'src/util/sanitize_str.cpp',
-    'src/util/rewrite_string.cpp'
+    'src/util/rewrite_string.cpp',
+    'src/util/gtk_icon.cpp'
 )
 
 inc_dirs = ['include']

src/modules/gamemode.cpp

@@ -16,10 +16,11 @@
 #include "glibmm/ustring.h"
 #include "glibmm/variant.h"
 #include "glibmm/varianttype.h"
-#include "gtkmm/icontheme.h"
 #include "gtkmm/label.h"
 #include "gtkmm/tooltip.h"
 
+#include "util/gtk_icon.hpp"
+
 namespace waybar::modules {
 Gamemode::Gamemode(const std::string& id, const Json::Value& config)
     : AModule(config, "gamemode", id), box_(Gtk::ORIENTATION_HORIZONTAL, 0), icon_(), label_() {
@@ -224,7 +225,7 @@ auto Gamemode::update() -> void {
   label_.set_markup(str);
 
   if (useIcon) {
-    if (!Gtk::IconTheme::get_default()->has_icon(iconName)) {
+    if (!DefaultGtkIconThemeWrapper::has_icon(iconName)) {
       iconName = DEFAULT_ICON_NAME;
     }
     icon_.set_from_icon_name(iconName, Gtk::ICON_SIZE_INVALID);

src/modules/sni/item.cpp

@@ -9,6 +9,7 @@
 #include <map>
 
 #include "util/format.hpp"
+#include "util/gtk_icon.hpp"
 
 template <>
 struct fmt::formatter<Glib::VariantBase> : formatter<std::string> {
@@ -379,10 +380,8 @@ Glib::RefPtr<Gdk::Pixbuf> Item::getIconByName(const std::string& name, int reque
     return icon_theme->load_icon(name.c_str(), tmp_size,
                                  Gtk::IconLookupFlags::ICON_LOOKUP_FORCE_SIZE);
   }
-  Glib::RefPtr<Gtk::IconTheme> default_theme = Gtk::IconTheme::get_default();
-  default_theme->rescan_if_needed();
-  return default_theme->load_icon(name.c_str(), tmp_size,
-                                  Gtk::IconLookupFlags::ICON_LOOKUP_FORCE_SIZE);
+  return DefaultGtkIconThemeWrapper::load_icon(name.c_str(), tmp_size,
+                                               Gtk::IconLookupFlags::ICON_LOOKUP_FORCE_SIZE);
 }
 
 double Item::getScaledIconSize() {

src/modules/sway/window.cpp

@@ -5,7 +5,6 @@
 #include <glibmm/keyfile.h>
 #include <glibmm/miscutils.h>
 #include <gtkmm/enums.h>
-#include <gtkmm/icontheme.h>
 #include <spdlog/spdlog.h>
 
 #include <filesystem>
@@ -13,6 +12,7 @@
 #include <string>
 
 #include "util/rewrite_string.hpp"
+#include "util/gtk_icon.hpp"
 
 namespace waybar::modules::sway {
 
@@ -81,13 +81,12 @@ std::optional<Glib::ustring> getIconName(const std::string& app_id, const std::s
   if (!desktop_file_path.has_value()) {
     // Try some heuristics to find a matching icon
 
-    const auto default_icon_theme = Gtk::IconTheme::get_default();
-    if (default_icon_theme->has_icon(app_id)) {
+    if (DefaultGtkIconThemeWrapper::has_icon(app_id)) {
       return app_id;
     }
 
     const auto app_id_desktop = app_id + "-desktop";
-    if (default_icon_theme->has_icon(app_id_desktop)) {
+    if (DefaultGtkIconThemeWrapper::has_icon(app_id_desktop)) {
       return app_id_desktop;
     }
 
@@ -101,7 +100,7 @@ std::optional<Glib::ustring> getIconName(const std::string& app_id, const std::s
     const auto first_space = app_id.find_first_of(' ');
     if (first_space != std::string::npos) {
       const auto first_word = to_lower(app_id.substr(0, first_space));
-      if (default_icon_theme->has_icon(first_word)) {
+      if (DefaultGtkIconThemeWrapper::has_icon(first_word)) {
         return first_word;
       }
     }
@@ -109,7 +108,7 @@ std::optional<Glib::ustring> getIconName(const std::string& app_id, const std::s
     const auto first_dash = app_id.find_first_of('-');
     if (first_dash != std::string::npos) {
       const auto first_word = to_lower(app_id.substr(0, first_dash));
-      if (default_icon_theme->has_icon(first_word)) {
+      if (DefaultGtkIconThemeWrapper::has_icon(first_word)) {
         return first_word;
       }
     }

src/modules/upower/upower.cpp

@@ -5,9 +5,10 @@
 #include <cstring>
 #include <string>
 
-#include "gtkmm/icontheme.h"
 #include "gtkmm/tooltip.h"
 
+#include "util/gtk_icon.hpp"
+
 namespace waybar::modules::upower {
 UPower::UPower(const std::string& id, const Json::Value& config)
     : AModule(config, "upower", id),
@@ -372,7 +373,7 @@ auto UPower::update() -> void {
   label_.set_markup(onlySpaces ? "" : label_format);
 
   // Set icon
-  if (icon_name == NULL || !Gtk::IconTheme::get_default()->has_icon(icon_name)) {
+  if (icon_name == NULL || !DefaultGtkIconThemeWrapper::has_icon(icon_name)) {
     icon_name = (char*)"battery-missing-symbolic";
   }
   icon_.set_from_icon_name(icon_name, Gtk::ICON_SIZE_INVALID);

src/modules/upower/upower_tooltip.cpp

@@ -2,10 +2,11 @@
 
 #include "gtkmm/box.h"
 #include "gtkmm/enums.h"
-#include "gtkmm/icontheme.h"
 #include "gtkmm/image.h"
 #include "gtkmm/label.h"
 
+#include "util/gtk_icon.hpp"
+
 namespace waybar::modules::upower {
 UPowerTooltip::UPowerTooltip(uint iconSize_, uint tooltipSpacing_, uint tooltipPadding_)
     : Gtk::Window(),
@@ -62,7 +63,7 @@ uint UPowerTooltip::updateTooltip(Devices& devices) {
     std::string deviceIconName = getDeviceIcon(kind);
     Gtk::Image* deviceIcon = new Gtk::Image();
     deviceIcon->set_pixel_size(iconSize);
-    if (!Gtk::IconTheme::get_default()->has_icon(deviceIconName)) {
+    if (!DefaultGtkIconThemeWrapper::has_icon(deviceIconName)) {
       deviceIconName = "battery-missing-symbolic";
     }
     deviceIcon->set_from_icon_name(deviceIconName, Gtk::ICON_SIZE_INVALID);
@@ -79,7 +80,7 @@ uint UPowerTooltip::updateTooltip(Devices& devices) {
     // Set icon
     Gtk::Image* icon = new Gtk::Image();
     icon->set_pixel_size(iconSize);
-    if (icon_name == NULL || !Gtk::IconTheme::get_default()->has_icon(icon_name)) {
+    if (icon_name == NULL || !DefaultGtkIconThemeWrapper::has_icon(icon_name)) {
       icon_name = (char*)"battery-missing-symbolic";
     }
     icon->set_from_icon_name(icon_name, Gtk::ICON_SIZE_INVALID);

src/util/gtk_icon.cpp

@@ -0,0 +1,26 @@
+#include "util/gtk_icon.hpp"
+
+/* We need a global mutex for accessing the object returned by Gtk::IconTheme::get_default()
+ * because it always returns the same object across different threads, and concurrent
+ * access can cause data corruption and lead to invalid memory access and crashes.
+ * Even concurrent calls that seem read only such as has_icon can cause issues because
+ * the GTK lib may update the internal icon cache on this calls.
+*/
+
+std::mutex DefaultGtkIconThemeWrapper::default_theme_mutex;
+
+bool DefaultGtkIconThemeWrapper::has_icon(const std::string& value) {
+
+  const std::lock_guard<std::mutex> lock(default_theme_mutex);
+
+  return Gtk::IconTheme::get_default()->has_icon(value);
+}
+
+Glib::RefPtr<Gdk::Pixbuf> DefaultGtkIconThemeWrapper::load_icon(const char *name, int tmp_size, Gtk::IconLookupFlags flags) {
+
+  const std::lock_guard<std::mutex> lock(default_theme_mutex);
+
+  auto default_theme = Gtk::IconTheme::get_default();
+  default_theme->rescan_if_needed();
+  return default_theme->load_icon(name, tmp_size, flags);
+}