[PATCH v2] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

[PATCH v2] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

[Qasim Ijaz]

_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.
 
Fixes: 8144d17a81d9 ("drm/msm/dpu: Skip trigger flush and start for CWB")
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
v2:
- Moved Signed-off tag below Fixes tag
- Moved dpu_enc declaration to the top and initialisation below sanity checks

 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
index 0eed93a4d056..0bd1f2bfaaff 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
@@ -1667,7 +1667,7 @@ 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);
+	struct dpu_encoder_virt *dpu_enc;
 
 	if (!phys) {
 		DPU_ERROR("invalid argument(s)\n");
@@ -1678,6 +1678,8 @@ static void _dpu_encoder_trigger_start(struct dpu_encoder_phys *phys)
 		DPU_ERROR("invalid pingpong hw\n");
 		return;
 	}
+
+	dpu_enc = to_dpu_encoder_virt(phys->parent);
 
 	if (phys->parent->encoder_type == DRM_MODE_ENCODER_VIRTUAL &&
 	    dpu_enc->cwb_mask) {
-- 
2.39.5

Re: [PATCH v2] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

[Dmitry Baryshkov]

On Sun, Mar 09, 2025 at 09:55:25AM +0000, Qasim Ijaz wrote:
> _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.
>  
> Fixes: 8144d17a81d9 ("drm/msm/dpu: Skip trigger flush and start for CWB")
> Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
> ---
> v2:
> - Moved Signed-off tag below Fixes tag
> - Moved dpu_enc declaration to the top and initialisation below sanity checks
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
-- 
With best wishes
Dmitry

Re: [PATCH v2] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

[Markus Elfring]

…
> Fix this by reordering the dereference after the sanity checks.

Can another wording approach (like the following) be more appropriate?

  Thus move the assignment of the variable “dpu_enc” behind …


Would an other summary phrase become nicer?

Regards,
Markus