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

From: Li Tuo
Date: Sun Aug 01 2021 - 22:48:25 EST

Thanks for your feedback! We will remove the null tests according to your advice and prepare a V2 patch.

Best wishes,
Tuo Li

On 2021/8/2 1:19, Christian König wrote:
Am 31.07.21 um 10:04 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_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.

NAK, the NULL test is just a leftover from when the objects where distinct.

Please remove the NULL test instead.


Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>
Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
  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;