Hello Thomas,
On 5/9/22 20:32, Thomas Zimmermann wrote:
> Hi
>
> Am 09.05.22 um 18:33 schrieb Javier Martinez Canillas:
>> On 5/9/22 17:51, Andrzej Hajda wrote:
>>
>> [snip]
>>
>>>>>> +
>>>>> Regarding drm:
>>>>> What about drm_fb_helper_fini? It calls also framebuffer_release and is
>>>>> called often from _remove paths (checked intel/radeon/nouveau). I guess
>>>>> it should be fixed as well. Do you plan to fix it?
>>>>>
>>>> I think you are correct. Maybe we need something like the following?
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>>>> index d265a73313c9..b09598f7af28 100644
>>>> --- a/drivers/gpu/drm/drm_fb_helper.c
>>>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>>>> @@ -631,7 +631,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
>>>> if (info) {
>>>> if (info->cmap.len)
>>>> fb_dealloc_cmap(&info->cmap);
>>>> - framebuffer_release(info);
>
> After reviewing that code, drm_fb_helper_fini() appears to be called
> from .fb_destroy (see drm_fbdev_release). The code is hard to follow
> though. If there another way of releasing the framebuffer here?
>
Andrzej mentioned intel/radeon/nouveau as example, I only looked at i915
and the call chain is the following as far as I can tell:
struct pci_driver i915_pci_driver = {
...
.remove = i915_pci_remove,
...
};
i915_driver_remove
intel_modeset_driver_remove_noirq
intel_fbdev_fini
intel_fbdev_destroy
drm_fb_helper_fini
framebuffer_release
So my underdestanding is that if a program has the emulated fbdev device
opened and the i915 module is removed, then a use-after-free would be
triggered on drm_fbdev_fb_destroy() once the program closes the device:
drm_fbdev_fb_destroy
drm_fbdev_release(info->par); <-- info was already freed on .remove
--
Best regards,
Javier Martinez Canillas
Linux Engineering
Red Hat
