drm/mediatek: fix OF sibling-node lookup

Use the new of_get_compatible_child() helper to lookup the sibling
instead of using of_find_compatible_node(), which searches the entire
tree from a given start node and thus can return an unrelated (i.e.
non-sibling) node.

This also addresses a potential use-after-free (e.g. after probe
deferral) as the tree-wide helper drops a reference to its first
argument (i.e. the parent device node).

While at it, also fix the related cec-node reference leak.

Fixes: 8f83f26891e1 ("drm/mediatek: Add HDMI support")
Cc: stable <stable@vger.kernel.org>     # 4.8
Cc: Junzhi Zhao <junzhi.zhao@mediatek.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: CK Hu <ck.hu@mediatek.com>
Cc: David Airlie <airlied@linux.ie>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
index 2d45d1dd9554..643f5edd68fe 100644
--- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
+++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
@@ -1446,8 +1446,7 @@ static int mtk_hdmi_dt_parse_pdata(struct mtk_hdmi *hdmi,
         }
 
         /* The CEC module handles HDMI hotplug detection */
-        cec_np = of_find_compatible_node(np->parent, NULL,
-                                         "mediatek,mt8173-cec");
+        cec_np = of_get_compatible_child(np->parent, "mediatek,mt8173-cec");
         if (!cec_np) {
                 dev_err(dev, "Failed to find CEC node\n");
                 return -EINVAL;
@@ -1457,8 +1456,10 @@ static int mtk_hdmi_dt_parse_pdata(struct mtk_hdmi *hdmi,
         if (!cec_pdev) {
                 dev_err(hdmi->dev, "Waiting for CEC device %pOF\n",
                         cec_np);
+                of_node_put(cec_np);
                 return -EPROBE_DEFER;
         }
+        of_node_put(cec_np);
         hdmi->cec_dev = &cec_pdev->dev;
 
         /*