Fixed bug 3544 - Memory freeing bug in SDL_DestroyRenderer/SDL_DestroyTexture

felix

Here's a snippet of SDL_DestroyRenderer from hg revision 10746:7540ff5d0e0e:

    SDL_Texture *texture = NULL;
    SDL_Texture *nexttexture = NULL;
    /* ... */
    for (texture = renderer->textures; texture; texture = nexttexture) {
        nexttexture = texture->next;
        SDL_DestroyTexture(texture);
    }

SDL_DestroyTexture removes the texture from the linked list pointed to by the renderer and ends up calling SDL_DestroyTextureInternal, which contains this:

    if (texture->native) {
        SDL_DestroyTexture(texture->native);
    }

If it happens that texture->native is an alias of nexttexture two stack frames up, SDL_DestroyRenderer will end up trying to destroy an already freed texture. I've had this very situation happen in dosemu2.

Bug introduced in revision 10650:a8253d439914, which has a somewhat ironic description of "Fixed all known static analysis bugs"...

src/render/SDL_render.c

@@ -1951,11 +1951,9 @@ SDL_DestroyRenderer(SDL_Renderer * renderer)
     /* Free existing textures for this renderer */
     SDL_SetRenderTarget(renderer, NULL);
 
-    for (texture = renderer->textures; texture; texture = nexttexture) {
-        nexttexture = texture->next;
-        SDL_DestroyTexture(texture);
+    while (renderer->textures) {
+        SDL_DestroyTexture(renderer->textures);
     }
-    renderer->textures = NULL;
 
     if (renderer->window) {
         SDL_SetWindowData(renderer->window, SDL_WINDOWRENDERDATA, NULL);