[bug report] drm/ttm: Fix dummy res NULL ptr deref bug

[Arunpravin Paneer Selvam]

Hi Dan,

On 8/11/2022 5:26 PM, Dan Carpenter wrote:
> On Thu, Aug 11, 2022 at 04:36:33PM +0530, Arunpravin Paneer Selvam wrote:
>> Hi Dan,
>>
>> drm-misc-fixes doesn't have the updated ttm_bo.c file, we have the updated
>> ttm_bo.c version in
>> drm-misc-next branch. Please find below for the line number 907.
>>
>> On 8/11/2022 3:25 PM, Dan Carpenter wrote:
>>> Hello Arunpravin Paneer Selvam,
>>>
>>> This is a semi-automatic email about new static checker warnings.
>>>
>>> The patch cf4b7387c0a8: "drm/ttm: Fix dummy res NULL ptr deref bug"
>>> from Aug 9, 2022, leads to the following Smatch complaint:
>>>
>>>       drivers/gpu/drm/ttm/ttm_bo.c:915 ttm_bo_validate()
>>>       warn: variable dereferenced before check 'bo->resource' (see line 907)
>>>
>>> drivers/gpu/drm/ttm/ttm_bo.c
>>>      906		 */
>>>      907		if (!ttm_resource_compat(bo->resource, placement)) {
>>>                                            ^^^^^^^^^^^^
>>> Unchecked dereference here inside the function.
>> |if (!bo->resource || !ttm_resource_compat(bo->resource, placement)) { we
>> have this version in drm-misc-next Regards, Arun |
>>
> Huh...  That's very interesting.  It appears there was a bug in
> drm-misc-next, we applied the fix to the wrong tree, and now both trees
> are wrong.  The drm-misc-next tree still has the bug and the other tree
> has a static checker warning about nonsensical NULL checks.
>
> Eventually drm-misc-next will get merged and everything will work.  Is
> it too late to remove the bogus "CC: stable at vger.kernel.org"?
I will look into this problem.
> This could have been avoided if the NULL dereference fix had a Fixes tag.
I should have added the below tag
Fixes: 347987a2cf0d ("drm/ttm: rename and cleanup ttm_bo_init")

I will check on this.

Thanks,
Arun
>
> regards,
> dan carpenter
>