[PATCH] thermal/drivers/rcar_thermal: fix list_first_entry on possibly empty sensor list in suspend/resume

[Li Ximo <lixicaicai@gmail.com>]

From: Wang Haoran <haoranwangsec@gmail.com>

rcar_thermal_suspend() and rcar_thermal_resume() call
list_first_entry(&common->head, ...) without checking whether the list
is empty. list_first_entry() does not return NULL for an empty list; it
returns the container_of() of the list head pointer, i.e. a wild pointer
into struct rcar_thermal_common. Dereferencing it at
priv->chip->needs_suspend_resume (and the MMIO accesses through
priv->base that follow) is undefined behavior and can corrupt memory or
crash the kernel.

The list can indeed be empty: rcar_thermal_probe() only adds a sensor to
common->head after platform_get_resource() succeeds, and it returns
success even when zero sensors were probed (no i == 0 check before
"return 0"). With a malformed DT node (no MEM resource) the driver binds
successfully with an empty list, and the PM core then unconditionally
invokes the suspend/resume callbacks. This was found by code audit; we
do not have R-Car hardware to reproduce it at runtime.

Fix both callbacks by switching to list_first_entry_or_null() and
returning 0 early when the sensor list is empty. This matches how the
rest of the driver already tolerates an empty list via the
list_for_each_entry()-based rcar_thermal_for_each_priv() iterator used
in remove and IRQ handling, and does not change behavior on the normal
non-empty path.

Reported-by: Wang Haoran <haoranwangsec@gmail.com>
Reported-by: Li Ximo <lixicaicai@gmail.com>
Signed-off-by: Wang Haoran <haoranwangsec@gmail.com>
---
 drivers/thermal/renesas/rcar_thermal.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/thermal/renesas/rcar_thermal.c b/drivers/thermal/renesas/rcar_thermal.c
index 9a9038671..65dba6354 100644
--- a/drivers/thermal/renesas/rcar_thermal.c
+++ b/drivers/thermal/renesas/rcar_thermal.c
@@ -530,8 +530,11 @@ static int rcar_thermal_probe(struct platform_device *pdev)
 static int rcar_thermal_suspend(struct device *dev)
 {
 	struct rcar_thermal_common *common = dev_get_drvdata(dev);
-	struct rcar_thermal_priv *priv = list_first_entry(&common->head,
-							  typeof(*priv), list);
+	struct rcar_thermal_priv *priv = list_first_entry_or_null(&common->head,
+								  typeof(*priv), list);
+
+	if (!priv)
+		return 0;
 
 	if (priv->chip->needs_suspend_resume) {
 		rcar_thermal_common_write(common, ENR, 0);
@@ -545,10 +548,13 @@ static int rcar_thermal_suspend(struct device *dev)
 static int rcar_thermal_resume(struct device *dev)
 {
 	struct rcar_thermal_common *common = dev_get_drvdata(dev);
-	struct rcar_thermal_priv *priv = list_first_entry(&common->head,
-							  typeof(*priv), list);
+	struct rcar_thermal_priv *priv = list_first_entry_or_null(&common->head,
+								  typeof(*priv), list);
 	int ret;
 
+	if (!priv)
+		return 0;
+
 	if (priv->chip->needs_suspend_resume) {
 		ret = rcar_thermal_update_temp(priv);
 		if (ret < 0)
-- 
2.30.2