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From:   Tuo Li <islituo@gmail.com>
To:     alexander.deucher@amd.com, christian.koenig@amd.com,
        Xinhui.Pan@amd.com, airlied@linux.ie, daniel@ffwll.ch,
        sumit.semwal@linaro.org, airlied@redhat.com,
        Felix.Kuehling@amd.com, Oak.Zeng@amd.com, nirmoy.das@amd.com,
        tzimmermann@suse.de, Philip.Yang@amd.com
Cc:     amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        linaro-mm-sig@lists.linaro.org, baijiaju1990@gmail.com,
        Tuo Li <islituo@gmail.com>, TOTE Robot <oslab@tsinghua.edu.cn>
Subject: [PATCH] drm/amdgpu: fix possible null-pointer dereference in amdgpu_ttm_tt_unpopulate()
Date:   Sat, 31 Jul 2021 01:13:06 -0700
Message-Id: <20210731081306.86523-1-islituo@gmail.com>
MIME-Version: 1.0
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Precedence: bulk

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.

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Tuo Li <islituo@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;
-- 
2.25.1