Re: [PATCH] drm/amdgpu: fix possible null-pointer dereference in amdgpu_ttm_tt_unpopulate()

[Christian König]

Am 31.07.21 um 10:13 schrieb Tuo Li:
The variable ttm is assigned to the variable gtt, and the variable gtt
is checked in:
   if (gtt && gtt->userptr)
This indicates that both ttm and gtt can be NULL.
If so, a null-pointer dereference will occur:
   if (ttm->page_flags & TTM_PAGE_FLAG_SG)

Also, some null-pointer dereferences will occur in the function
ttm_pool_free() which is called in:
   return ttm_pool_free(&adev->mman.bdev.pool, ttm);

To fix these possible null-pointer dereferences, the function returns
when ttm is NULL.

NAK, same as with the other patch.

The ttm object is mandatory, asking the driver to destroy a ttm object 
which doesn't exists makes no sense at all and is a bug in the upper layer.

The NULL check is just a leftover from when the gtt and ttm objects 
where distinct. Please remove that one instead.

BTW: Bonus points for changing the (void *) cast into a much cleaner 
container_of().

Thanks,
Christian.


Reported-by: TOTE Robot <os...@tsinghua.edu.cn>
Signed-off-by: Tuo Li <isli...@gmail.com>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 3a55f08e00e1..0216ca085f11 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1146,7 +1146,10 @@ static void amdgpu_ttm_tt_unpopulate(struct ttm_device 
*bdev,
        struct amdgpu_ttm_tt *gtt = (void *)ttm;
        struct amdgpu_device *adev;
  
-	if (gtt && gtt->userptr) {
+       if (ttm == NULL)
+               return;
+
+       if (gtt->userptr) {
                amdgpu_ttm_tt_set_user_pages(ttm, NULL);
                kfree(ttm->sg);
                ttm->sg = NULL;