[PATCH] drivers: thermal: Add NULL pointer check before using cooling device stats

[Manaf Meethalavalappu Pallikunhi <manafm@codeaurora.org>]

There is a possible chance that some cooling device stats buffer
allocation fails due to very high cooling device max state value.
Later cooling device update or cooling stats sysfs will try to
access stats data for the same cooling device. It will lead to
NULL pointer dereference issue.

Add a NULL pointer check before accessing thermal cooling device
stats data. It fixes the following bug

[ 26.812833] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
[ 27.122960] Call trace:
[ 27.122963] do_raw_spin_lock+0x18/0xe8
[ 27.122966] _raw_spin_lock+0x24/0x30
[ 27.128157] thermal_cooling_device_stats_update+0x24/0x98
[ 27.128162] cur_state_store+0x88/0xb8
[ 27.128166] dev_attr_store+0x40/0x58
[ 27.128169] sysfs_kf_write+0x50/0x68
[ 27.133358] kernfs_fop_write+0x12c/0x1c8
[ 27.133362] __vfs_write+0x54/0x160
[ 27.152297] vfs_write+0xcc/0x188
[ 27.157132] ksys_write+0x78/0x108
[ 27.162050] ksys_write+0xf8/0x108
[ 27.166968] __arm_smccc_hvc+0x158/0x4b0
[ 27.166973] __arm_smccc_hvc+0x9c/0x4b0
[ 27.186005] el0_svc+0x8/0xc

Signed-off-by: Manaf Meethalavalappu Pallikunhi <manafm@codeaurora.org>
---
 drivers/thermal/thermal_sysfs.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index 473449b..a5e4855 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -827,6 +827,9 @@ void thermal_cooling_device_stats_update(struct thermal_cooling_device *cdev,
 {
 	struct cooling_dev_stats *stats = cdev->stats;
 
+	if (!stats)
+		return;
+
 	spin_lock(&stats->lock);
 
 	if (stats->state == new_state)
@@ -848,6 +851,9 @@ static ssize_t total_trans_show(struct device *dev,
 	struct cooling_dev_stats *stats = cdev->stats;
 	int ret;
 
+	if (!stats)
+		return -ENODEV;
+
 	spin_lock(&stats->lock);
 	ret = sprintf(buf, "%u\n", stats->total_trans);
 	spin_unlock(&stats->lock);
@@ -864,6 +870,9 @@ time_in_state_ms_show(struct device *dev, struct device_attribute *attr,
 	ssize_t len = 0;
 	int i;
 
+	if (!stats)
+		return -ENODEV;
+
 	spin_lock(&stats->lock);
 	update_time_in_state(stats);
 
@@ -882,8 +891,12 @@ reset_store(struct device *dev, struct device_attribute *attr, const char *buf,
 {
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
 	struct cooling_dev_stats *stats = cdev->stats;
-	int i, states = stats->max_states;
+	int i, states;
+
+	if (!stats)
+		return -ENODEV;
 
+	states = stats->max_states;
 	spin_lock(&stats->lock);
 
 	stats->total_trans = 0;
@@ -907,6 +920,9 @@ static ssize_t trans_table_show(struct device *dev,
 	ssize_t len = 0;
 	int i, j;
 
+	if (!stats)
+		return -ENODEV;
+
 	len += snprintf(buf + len, PAGE_SIZE - len, " From  :    To\n");
 	len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
 	for (i = 0; i < stats->max_states; i++) {
-- 
2.7.4