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

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

In malidp_mw_connector_reset, new memory is allocated with kzalloc, but 
no check is performed. In order to prevent null pointer dereferencing, 
ensure that mw_state is checked before calling 
__drm_atomic_helper_connector_reset.

Fixes: 8cbc5caf36ef ("drm: mali-dp: Add writeback connector")
Signed-off-by: Huai-Yuan Liu <qq810974084@gmail.com>
---
V2:
* In patch V2, we additionally set connector->state to NULL. In this way
we can ensure that there is no state pointing to freed memory.
  Thanks to Liviu Dudau for helpful suggestion.
---
 drivers/gpu/drm/arm/malidp_mw.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/arm/malidp_mw.c b/drivers/gpu/drm/arm/malidp_mw.c
index 626709bec6f5..2577f0cef8fc 100644
--- a/drivers/gpu/drm/arm/malidp_mw.c
+++ b/drivers/gpu/drm/arm/malidp_mw.c
@@ -72,7 +72,10 @@ static void malidp_mw_connector_reset(struct drm_connector *connector)
 		__drm_atomic_helper_connector_destroy_state(connector->state);
 
 	kfree(connector->state);
-	__drm_atomic_helper_connector_reset(connector, &mw_state->base);
+	connector->state = NULL;
+
+	if (mw_state)
+		__drm_atomic_helper_connector_reset(connector, &mw_state->base);
 }
 
 static enum drm_connector_status
-- 
2.34.1