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

[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_alloc() which is called in:
  return ttm_pool_alloc(&adev->mman.bdev.pool, ttm, ctx);

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

Reported-by: TOTE Robot <oslab at tsinghua.edu.cn>
Signed-off-by: Tuo Li <islituo at 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..80440f799c09 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1120,8 +1120,11 @@ static int amdgpu_ttm_tt_populate(struct ttm_device *bdev,
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bdev);
 	struct amdgpu_ttm_tt *gtt = (void *)ttm;
 
+	if (ttm == NULL)
+		return -EINVAL;
+
 	/* user pages are bound by amdgpu_ttm_tt_pin_userptr() */
-	if (gtt && gtt->userptr) {
+	if (gtt->userptr) {
 		ttm->sg = kzalloc(sizeof(struct sg_table), GFP_KERNEL);
 		if (!ttm->sg)
 			return -ENOMEM;
-- 
2.25.1