thermal/core: Add NULL pointer check before using cooling device stats

stable inclusion
from stable-5.10.28
commit 1e2a75c24a487a1fc713c4b78749c2b8a3a8d387
bugzilla: 51779

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

[ Upstream commit 2046a24a ]

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 sysfs can 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>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1607367181-24589-1-git-send-email-manafm@codeaurora.org


Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by:   Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>