drm/msm: fix use-after-free on probe deferral

The bridge counter was never reset when tearing down the DRM device so
that stale pointers to deallocated structures would be accessed on the
next tear down (e.g. after a second late bind deferral).

Given enough bridges and a few probe deferrals this could currently also
lead to data beyond the bridge array being corrupted.

Fixes: d28ea556267c ("drm/msm: properly add and remove internal bridges")
Fixes: a3376e3ec81c ("drm/msm: convert to drm_bridge")
Cc: stable@vger.kernel.org      # 3.12
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/502665/
Link: https://lore.kernel.org/r/20220913085320.8577-2-johan+linaro@kernel.org
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 07f6641..fec6d44 100644 (file)
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -247,6 +247,7 @@ static int msm_drm_uninit(struct device *dev)
 
        for (i = 0; i < priv->num_bridges; i++)
                drm_bridge_remove(priv->bridges[i]);
+       priv->num_bridges = 0;
 
        pm_runtime_get_sync(dev);
        msm_irq_uninstall(ddev);