[PATCH 4.19 147/148] drm/rockchip: psr: do not dereference encoder before it is null checked.

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>

commit 4eda776c3cefcb1f01b2d85bd8753f67606282b5 upstream.

'encoder' is dereferenced before it is null sanity checked, hence we
potentially have a null pointer dereference bug. Instead, initialise
drm_drv from encoder->dev->dev_private after we are sure 'encoder' is
not null.

Fixes: 5182c1a556d7f ("drm/rockchip: add an common abstracted PSR driver")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
Signed-off-by: Heiko Stuebner <heiko@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20181013105654.11827-1-enric.balletbo@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/rockchip/rockchip_drm_psr.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
@@ -189,12 +189,14 @@ EXPORT_SYMBOL(rockchip_drm_psr_flush_all
 int rockchip_drm_psr_register(struct drm_encoder *encoder,
 			int (*psr_set)(struct drm_encoder *, bool enable))
 {
-	struct rockchip_drm_private *drm_drv = encoder->dev->dev_private;
+	struct rockchip_drm_private *drm_drv;
 	struct psr_drv *psr;
 
 	if (!encoder || !psr_set)
 		return -EINVAL;
 
+	drm_drv = encoder->dev->dev_private;
+
 	psr = kzalloc(sizeof(struct psr_drv), GFP_KERNEL);
 	if (!psr)
 		return -ENOMEM;