The function disable_outputs() and
drm_atomic_helper_commit_modeset_enables() tries to retrieve
helper_private from the target CRTC, for dereferencing some operations.
However, the current implementation does not check whether
helper_private is null and, if not, if it has a valid pointer to a dpms
and commit functions. This commit adds pointer validations before
trying to dereference the dpms and commit function.

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiram...@gmail.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 30 ++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c 
b/drivers/gpu/drm/drm_atomic_helper.c
index 540a77a2ade9..fbeef7c461fc 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1028,14 +1028,16 @@ disable_outputs(struct drm_device *dev, struct 
drm_atomic_state *old_state)
 
 
                /* Right function depends upon target state. */
-               if (new_crtc_state->enable && funcs->prepare)
-                       funcs->prepare(crtc);
-               else if (funcs->atomic_disable)
-                       funcs->atomic_disable(crtc, old_crtc_state);
-               else if (funcs->disable)
-                       funcs->disable(crtc);
-               else
-                       funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
+               if (funcs) {
+                       if (new_crtc_state->enable && funcs->prepare)
+                               funcs->prepare(crtc);
+                       else if (funcs->atomic_disable)
+                               funcs->atomic_disable(crtc, old_crtc_state);
+                       else if (funcs->disable)
+                               funcs->disable(crtc);
+                       else if (funcs->dpms)
+                               funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
+               }
 
                if (!(dev->irq_enabled && dev->num_crtcs))
                        continue;
@@ -1277,11 +1279,13 @@ void drm_atomic_helper_commit_modeset_enables(struct 
drm_device *dev,
                if (new_crtc_state->enable) {
                        DRM_DEBUG_ATOMIC("enabling [CRTC:%d:%s]\n",
                                         crtc->base.id, crtc->name);
-
-                       if (funcs->atomic_enable)
-                               funcs->atomic_enable(crtc, old_crtc_state);
-                       else
-                               funcs->commit(crtc);
+                       if (funcs) {
+                               if (funcs->atomic_enable)
+                                       funcs->atomic_enable(crtc,
+                                                            old_crtc_state);
+                               else if (funcs->atomic_enable)
+                                       funcs->commit(crtc);
+                       }
                }
        }
 
-- 
2.21.0
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