[PATCH V2] drm/tegra: fix a possible null pointer dereference

[Huai-Yuan Liu <qq810974084@gmail.com>]

In malidp_tegra_crtc_reset, new memory is allocated with kzalloc, but
no check is performed. Before calling __drm_atomic_helper_crtc_reset,
mw_state should be checked to prevent possible null pointer dereference.

Fixes: b7e0b04ae450 ("drm/tegra: Convert to using __drm_atomic_helper_crtc_reset() for reset.")
Signed-off-by: Huai-Yuan Liu <qq810974084@gmail.com>
---
V2:
* In patch V2, we call __drm_atomic_helper_crtc_reset(crtc, NULL) when
state is null.
  Thanks to Thierry Reding for helpful suggestion.
---
 drivers/gpu/drm/tegra/dc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index be61c9d1a4f0..afa7c269c29a 100644
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/drivers/gpu/drm/tegra/dc.c
@@ -1388,7 +1388,10 @@ static void tegra_crtc_reset(struct drm_crtc *crtc)
 	if (crtc->state)
 		tegra_crtc_atomic_destroy_state(crtc, crtc->state);
 
-	__drm_atomic_helper_crtc_reset(crtc, &state->base);
+	if (state)
+		__drm_atomic_helper_crtc_reset(crtc, &state->base);
+	else
+		__drm_atomic_helper_crtc_reset(crtc, NULL);
 }
 
 static struct drm_crtc_state *
-- 
2.34.1