Re: KASAN: use-after-free Read in drm_gem_object_release

[butt3rflyh4ck <butterflyhuangxx@gmail.com>]

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Thank you for pointing out my spelling error. ok, I upload a PoC and
compile it to a binary. you can test it.

regards,
  butt3rflyh4ck.

On Fri, Jul 10, 2020 at 7:53 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Fri, Jul 10, 2020 at 04:24:03PM +0800, butt3rflyh4ck wrote:
> > I report a bug (in linux-5.8.0-rc4) found by syzkaller.
> >
> > kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.8.0-rc4.config
> >
> > I test the reproducer and crash too.
> >
> > In the drm_em_vram_t() function,  ttm_bo_init() function call
>          ^^^^^^^^^^^^^
> This a typo.  The function name is drm_gem_vram_init().
>
> > ttm_bo_init_reserved(),
> > the ttm_bo_init_reserved() function  call ttm_bo_put(), it will free
> > gbo->bo that is struct ttm_buffer_object.
> >
> > then, goto the err_drm_gem_object_release lable,
> > drm_gem_object_release() function will free gbo->bo.base, so cause use
> > after free.
> >
>
> There is a third free in drm_gem_vram_create().  This is a triple free
> bug.  The correct place to free this is in drm_gem_vram_create() because
> that's where it was allocated.
>
> This code is quite subtle so I'm not going to attempt to fix it because
> I can't test it.
>
> regards,
> dan carpenter
>

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