linux-kernel - [PATCH] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

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Message-Id: <20250308144839.33849-1-qasdev00@gmail.com>
Date: Sat,  8 Mar 2025 14:48:39 +0000
From: Qasim Ijaz <qasdev00@...il.com>
To: robdclark@...il.com,
	quic_abhinavk@...cinc.com,
	dmitry.baryshkov@...aro.org,
	sean@...rly.run,
	marijn.suijten@...ainline.org,
	airlied@...il.com,
	simona@...ll.ch,
	quic_jesszhan@...cinc.com
Cc: linux-arm-msm@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	freedreno@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

_dpu_encoder_trigger_start dereferences "struct dpu_encoder_phys *phys" 
before the sanity checks which can lead to a NULL pointer dereference if 
phys is NULL. 

Fix this by reordering the dereference after the sanity checks.

Signed-off-by: Qasim Ijaz <qasdev00@...il.com>
Fixes: 8144d17a81d9 ("drm/msm/dpu: Skip trigger flush and start for CWB")
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
index 0eed93a4d056..ba8b2a163232 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
@@ -1667,8 +1667,6 @@ static void _dpu_encoder_trigger_flush(struct drm_encoder *drm_enc,
  */
 static void _dpu_encoder_trigger_start(struct dpu_encoder_phys *phys)
 {
-	struct dpu_encoder_virt *dpu_enc = to_dpu_encoder_virt(phys->parent);
-
 	if (!phys) {
 		DPU_ERROR("invalid argument(s)\n");
 		return;
@@ -1679,6 +1677,8 @@ static void _dpu_encoder_trigger_start(struct dpu_encoder_phys *phys)
 		return;
 	}
 
+	struct dpu_encoder_virt *dpu_enc = to_dpu_encoder_virt(phys->parent);
+
 	if (phys->parent->encoder_type == DRM_MODE_ENCODER_VIRTUAL &&
 	    dpu_enc->cwb_mask) {
 		DPU_DEBUG("encoder %d CWB enabled, skipping\n", DRMID(phys->parent));
-- 
2.39.5