video: Update self-referential pointers when reallocating the display list

The display list can contain self-referential pointers if the current mode pointer points to the desktop mode or a fullscreen mode array element, and reallocating the display or fullscreen mode lists without updating the current mode pointer in these cases can leave them pointing to freed memory or garbage data. Manually copy the list items and update the self-referential pointers if necessary.

src/video/SDL_video.c

@@ -630,10 +630,21 @@ SDL_DisplayID SDL_AddVideoDisplay(const SDL_VideoDisplay *display, SDL_bool send
     SDL_VideoDisplay *displays, *new_display;
     SDL_DisplayID id = 0;
 
-    displays = (SDL_VideoDisplay *)SDL_realloc(_this->displays, (_this->num_displays + 1) * sizeof(*displays));
+    displays = (SDL_VideoDisplay *)SDL_malloc((_this->num_displays + 1) * sizeof(*displays));
     if (displays) {
         int i;
+
+        /* The display list may contain self-referential pointers to the desktop mode. */
+        SDL_memcpy(displays, _this->displays, _this->num_displays * sizeof(*displays));
+        for (i = 0; i < _this->num_displays; ++i) {
+            if (displays[i].current_mode == &_this->displays[i].desktop_mode) {
+                displays[i].current_mode = &displays[i].desktop_mode;
+            }
+        }
+
+        SDL_free(_this->displays);
         _this->displays = displays;
+
         id = _this->next_object_id++;
         new_display = &displays[_this->num_displays++];
 
@@ -938,10 +949,20 @@ SDL_bool SDL_AddFullscreenDisplayMode(SDL_VideoDisplay *display, const SDL_Displ
 
     /* Go ahead and add the new mode */
     if (nmodes == display->max_fullscreen_modes) {
-        modes = (SDL_DisplayMode *)SDL_realloc(modes, (display->max_fullscreen_modes + 32) * sizeof(*modes));
+        modes = (SDL_DisplayMode *)SDL_malloc((display->max_fullscreen_modes + 32) * sizeof(*modes));
         if (modes == NULL) {
             return SDL_FALSE;
         }
+
+        /* Copy the list and update the current mode pointer, if necessary. */
+        SDL_memcpy(modes, display->fullscreen_modes, nmodes * sizeof(*modes));
+        for (i = 0; i < nmodes; ++i) {
+            if (display->current_mode == &display->fullscreen_modes[i]) {
+                display->current_mode = &modes[i];
+            }
+        }
+
+        SDL_free(display->fullscreen_modes);
         display->fullscreen_modes = modes;
         display->max_fullscreen_modes += 32;
     }