drm/msm/dsi: fix memory corruption with too many bridges

commit 2e786eb upstream.

Add the missing sanity check on the bridge counter to avoid corrupting
data beyond the fixed-sized bridge array in case there are ever more
than eight bridges.

Fixes: a689554 ("drm/msm: Initial add DSI connector support")
Cc: [email protected]	# 4.1
Signed-off-by: Johan Hovold <[email protected]>
Tested-by: Kuogee Hsieh <[email protected]>
Reviewed-by: Kuogee Hsieh <[email protected]>
Reviewed-by: Dmitry Baryshkov <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/502668/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Abhinav Kumar <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: jhovold

drivers/gpu/drm/msm/dsi/dsi.c

@@ -212,6 +212,12 @@ int msm_dsi_modeset_init(struct msm_dsi *msm_dsi, struct drm_device *dev,
 		return -EINVAL;
 
 	priv = dev->dev_private;
+
+	if (priv->num_bridges == ARRAY_SIZE(priv->bridges)) {
+		DRM_DEV_ERROR(dev->dev, "too many bridges\n");
+		return -ENOSPC;
+	}
+
 	msm_dsi->dev = dev;
 
 	ret = msm_dsi_host_modeset_init(msm_dsi->host, dev);