drm/imx: fix use after free

Component driver structures allocated with devm_kmalloc() in bind() are
freed automatically after unbind(). Since the contained drm structures
are accessed afterwards in drm_mode_config_cleanup(), move the
allocation into probe() to extend the driver structure's lifetime to the
lifetime of the device. This should eventually be changed to use drm
resource managed allocations with lifetime of the drm device.

We also need to ensure that all componets are available during the
unbind() so we need to call component_unbind_all() before we free
non-devres resources like planes.

Note this patch fixes the the use after free bug but introduces a
possible boot loop issue. The issue is triggered if the HDMI support is
enabled and a component driver always return -EPROBE_DEFER, see
discussion [1] for more details.

[1] https://lkml.org/lkml/2020/3/24/1467

Fixes: 17b5001b5143 ("imx-drm: convert to componentised device support")
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
[m.felsch@pengutronix: fix imx_tve_probe()]
[m.felsch@pengutronix: resort component_unbind_all())
[m.felsch@pengutronix: adapt commit message]
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/gpu/drm/imx/imx-drm-core.c b/drivers/gpu/drm/imx/imx-drm-core.c
index 2e38f1a5cf8d..3421043a558d 100644
--- a/drivers/gpu/drm/imx/imx-drm-core.c
+++ b/drivers/gpu/drm/imx/imx-drm-core.c
@@ -275,9 +275,10 @@ static void imx_drm_unbind(struct device *dev)
 
 	drm_kms_helper_poll_fini(drm);
 
+	component_unbind_all(drm->dev, drm);
+
 	drm_mode_config_cleanup(drm);
 
-	component_unbind_all(drm->dev, drm);
 	dev_set_drvdata(dev, NULL);
 
 	drm_dev_put(drm);