[PATCH] drm/msm: Fix NULL deref on bind/probe deferral

[PATCH] drm/msm: Fix NULL deref on bind/probe deferral

[Sean Paul]

This patch avoids dereferencing msm_host->dev when it is NULL.

If we find ourselves tearing down dsi before calling
(mdp4|mdp5|dpu)_kms_init(), we'll end up in a state where the dev
pointer is NULL and trying to extract priv from it will fail.

This was introduced in a seemingly innocuous commit to ensure the
arguments to msm_gem_put_iova() are correct (even though that
function has been a stub for ~5 years). Correctness FTW! \o/

Fixes: b01884a286b0 drm/msm: use correct aspace pointer in msm_gem_put_iova()
Cc: Daniel Mack <daniel@zonque.org>
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index b916f464f4ec..2f1a2780658a 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1066,8 +1066,18 @@ static int dsi_tx_buf_alloc(struct msm_dsi_host *msm_host, int size)
 static void dsi_tx_buf_free(struct msm_dsi_host *msm_host)
 {
 	struct drm_device *dev = msm_host->dev;
-	struct msm_drm_private *priv = dev->dev_private;
+	struct msm_drm_private *priv;
+
+	/*
+	 * This is possible if we're tearing down before we've had a chance to
+	 * fully initialize. A very real possibility if our probe is deferred,
+	 * in which case we'll hit msm_dsi_host_destroy() without having run
+	 * through the dsi_tx_buf_alloc().
+	 */
+	if (!dev)
+		return;
 
+	priv = dev->dev_private;
 	if (msm_host->tx_gem_obj) {
 		msm_gem_put_iova(msm_host->tx_gem_obj, priv->kms->aspace);
 		drm_gem_object_put_unlocked(msm_host->tx_gem_obj);
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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Re: [PATCH] drm/msm: Fix NULL deref on bind/probe deferral

[abhinavk-sgV2jX0FEOL9JmXXK+q4OQ]

On 2018-05-31 11:48, Sean Paul wrote:
> This patch avoids dereferencing msm_host->dev when it is NULL.
> 
> If we find ourselves tearing down dsi before calling
> (mdp4|mdp5|dpu)_kms_init(), we'll end up in a state where the dev
> pointer is NULL and trying to extract priv from it will fail.
> 
> This was introduced in a seemingly innocuous commit to ensure the
> arguments to msm_gem_put_iova() are correct (even though that
> function has been a stub for ~5 years). Correctness FTW! \o/
> 
> Fixes: b01884a286b0 drm/msm: use correct aspace pointer in 
> msm_gem_put_iova()
> Cc: Daniel Mack <daniel@zonque.org>
> Cc: Rob Clark <robdclark@gmail.com>
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c
> b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index b916f464f4ec..2f1a2780658a 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1066,8 +1066,18 @@ static int dsi_tx_buf_alloc(struct msm_dsi_host
> *msm_host, int size)
>  static void dsi_tx_buf_free(struct msm_dsi_host *msm_host)
>  {
>  	struct drm_device *dev = msm_host->dev;
> -	struct msm_drm_private *priv = dev->dev_private;
> +	struct msm_drm_private *priv;
> +
> +	/*
> +	 * This is possible if we're tearing down before we've had a chance 
> to
> +	 * fully initialize. A very real possibility if our probe is 
> deferred,
> +	 * in which case we'll hit msm_dsi_host_destroy() without having run
> +	 * through the dsi_tx_buf_alloc().
> +	 */
> +	if (!dev)
> +		return;
> 
> +	priv = dev->dev_private;
>  	if (msm_host->tx_gem_obj) {
>  		msm_gem_put_iova(msm_host->tx_gem_obj, priv->kms->aspace);
>  		drm_gem_object_put_unlocked(msm_host->tx_gem_obj);
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