Author :
Sam Lantinga
Date :
2017-08-11 19:42:39
Hash :79a846d4 Message :Fixed bug 3334 - SDL_ShowMessageBox uses wrong index and accesses un-allocated memory
romain.lacroix
For the windows implementation of SDL_ShowMessageBox() : ./src/video/windows/SDL_windowsmessagebox.c:345 WIN_ShowMessageBox()
The implementation in 2.0.4 uses "button index" for parameter "id" of function AddDialogButton().
It then expects the value provided in param wParam of function MessageBoxDialogProc() to be a valid index of a button.
It uses this value to index in the array of buttons when DialogBoxIndirect() returns (line 474 : *buttonid = buttons[which].buttonid;)
However, when dismissing this box with Escape, the return value of DialogBoxIndirect will be SDL_MESSAGEBOX_BUTTON_ESCAPEKEY_DEFAULT (=2) which is not always a valid index of array buttons.
When the array buttons has a length less or equal than 2, the memory access is invalid; I can see that the value written to *buttonId is uninitialized memory (random value).
The fix I propose : use value "buttonid" (field of button) for parameter "id" of AddDialogButton(), then copy return value of DialogBoxIndirect() in *buttonid. This way, we will not use an out-of-bounds index in array buttons.
Sam Lantinga