[PATCH] thermal: Add a sanity check for invalid state at stats update

[Takashi Iwai]

The thermal sysfs handler keeps the statistics table with the fixed
size that was determined from the initial max_states() call, and the
table entry is updated at each sysfs cur_state write call.  And, when
the driver's set_cur_state() ops accepts the value given from
user-space, the thermal sysfs core blindly applies it to the
statistics table entry, which may overflow and cause an Oops.
Although it's rather a bug in the driver's ops implementations, we
shouldn't crash but rather give a proper warning instead.

This patch adds a sanity check for avoiding such an OOB access and
warns with a stack trace to show the suspicious device in question.

Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---

We've hit some crash by stress tests, and this patch at least works
around the crash itself.  While the actual bug fix of the buggy driver
is still being investigated, I submit the hardening in the core side
at first.

 drivers/thermal/thermal_sysfs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index aa99edb4dff7..a23c4e701d63 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -772,6 +772,11 @@ void thermal_cooling_device_stats_update(struct thermal_cooling_device *cdev,
 
 	spin_lock(&stats->lock);
 
+	if (dev_WARN_ONCE(&cdev->device, new_state >= stats->max_states,
+			  "new state %ld exceeds max_state %ld",
+			  new_state, stats->max_states))
+		goto unlock;
+
 	if (stats->state == new_state)
 		goto unlock;
 
-- 
2.16.4