[PATCH] drm/ttm: fix null-ptr-deref in radeon_ttm_tt_populate()

[Nikita Zhandarovich]

Currently, drm_prime_sg_to_page_addr_arrays() dereferences 'gtt->ttm'
without ensuring that 'gtt' (and therefore 'gtt->tmm') is not NULL.

Fix this by testing 'gtt' for NULL value before dereferencing.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 40f5cf996991 ("drm/radeon: add PRIME support (v2)")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich at fintech.ru>
---
 drivers/gpu/drm/radeon/radeon_ttm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 1e8e287e113c..33d01c3bdee4 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -553,7 +553,7 @@ static int radeon_ttm_tt_populate(struct ttm_device *bdev,
 		return 0;
 	}
 
-	if (slave && ttm->sg) {
+	if (gtt && slave && ttm->sg) {
 		drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
 					       ttm->num_pages);
 		return 0;
-- 
2.25.1