linux-kernel - [PATCH] drm/atomic-helper: Validate pointer before dereference

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Date:   Mon, 11 Mar 2019 18:01:20 -0300
From:   Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/atomic-helper: Validate pointer before dereference

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 <rodrigosiqueiramelo@...il.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