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Bug 3544 - Memory freeing bug in SDL_DestroyRenderer/SDL_DestroyTexture
Summary: Memory freeing bug in SDL_DestroyRenderer/SDL_DestroyTexture
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: render (show other bugs)
Version: HG 2.0
Hardware: x86_64 Windows 7
: P2 blocker
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2017-01-04 22:14 UTC by felix
Modified: 2017-01-07 02:19 UTC (History)
1 user (show)

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Description felix 2017-01-04 22:14:40 UTC 
Here's a snippet of SDL_DestroyRenderer from hg revision 10746:95c57a177719:

    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:b6ec7005ca15, which has a somewhat ironic description of "Fixed all known static analysis bugs"...
Comment 1 Sam Lantinga 2017-01-06 08:32:26 UTC 
Fixed, thanks!
https://hg.libsdl.org/SDL/rev/703e501cd0a6
Comment 2 Ryan C. Gordon 2017-01-06 08:43:13 UTC 
(In reply to felix from comment #0)
> Bug introduced in revision 10650:b6ec7005ca15, which has a somewhat ironic
> description of "Fixed all known static analysis bugs"...

Sorry, that was my mistake; I didn't realize this called SDL_DestroyTexture internally, too.

--ryan.
Comment 3 Ryan C. Gordon 2017-01-07 02:19:28 UTC 
The static analysis concern is more properly fixed by https://hg.libsdl.org/SDL/rev/d8a4f8a929b2  ... it thinks we're reusing a variable that we just freed because it doesn't appear to understand that this is var is getting changed elsewhere, so we add an assert to tell it that it's definitely a different value each time through the loop.

--ryan.