Re: [PATCH 1/2] drm/ttm: set ttm_buffer_object pointer as null after it's freed

[Huang Rui <ray.huang-5C7GfCeVMHo@public.gmane.org>]

On Mon, Sep 10, 2018 at 11:00:04AM +0200, Christian König wrote:
> Hi Ray,
> 
> well those patches doesn't make sense, the pointer is only local to
> the function.

You're right.
I narrowed it with gdb dump from ttm_bo_bulk_move_lru_tail+0x2b, the
use-after-free should be in below codes: 

man = &bulk->tt[i].first->bdev->man[TTM_PL_TT];
ttm_bo_bulk_move_helper(&bulk->tt[i], &man->lru[i], false);

Is there a case, when orignal bo is destroyed in the bulk pos, but it
doesn't update pos->first pointer, then we still use it during the bulk
moving?

Thanks,
Ray

> 
> Regards,
> Christian.
> 
> Am 10.09.2018 um 10:57 schrieb Huang Rui:
> >It avoids to be refered again after freed.
> >
> >Signed-off-by: Huang Rui <ray.huang@amd.com>
> >Cc: Christian König <christian.koenig@amd.com>
> >Cc: Tom StDenis <Tom.StDenis@amd.com>
> >---
> >  drivers/gpu/drm/ttm/ttm_bo.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> >diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> >index 138c989..d3ef5f8 100644
> >--- a/drivers/gpu/drm/ttm/ttm_bo.c
> >+++ b/drivers/gpu/drm/ttm/ttm_bo.c
> >@@ -54,6 +54,7 @@ static struct attribute ttm_bo_count = {
> >  static void ttm_bo_default_destroy(struct ttm_buffer_object *bo)
> >  {
> >  	kfree(bo);
> >+	bo = NULL;
> >  }
> >  static inline int ttm_mem_type_from_place(const struct ttm_place *place,
> 
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