hwmon: (nct6775) Fix crash in clear_caseopen

Paweł Marciniak reports the following crash, observed when clearing
the chassis intrusion alarm.

BUG: kernel NULL pointer dereference, address: 0000000000000028
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 3 PID: 4815 Comm: bash Tainted: G S                5.16.2-200.fc35.x86_64 #1
Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./Z97 Extreme4, BIOS P2.60A 05/03/2018
RIP: 0010:clear_caseopen+0x5a/0x120 [nct6775]
Code: 68 70 e8 e9 32 b1 e3 85 c0 0f 85 d2 00 00 00 48 83 7c 24 ...
RSP: 0018:ffffabcb02803dd8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: ffff8e8808192880 RSI: 0000000000000000 RDI: ffff8e87c7509a68
RBP: 0000000000000000 R08: 0000000000000001 R09: 000000000000000a
R10: 000000000000000a R11: f000000000000000 R12: 000000000000001f
R13: ffff8e87c7509828 R14: ffff8e87c7509a68 R15: ffff8e88494527a0
FS:  00007f4db9151740(0000) GS:ffff8e8ebfec0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000028 CR3: 0000000166b66001 CR4: 00000000001706e0
Call Trace:
 <TASK>
 kernfs_fop_write_iter+0x11c/0x1b0
 new_sync_write+0x10b/0x180
 vfs_write+0x209/0x2a0
 ksys_write+0x4f/0xc0
 do_syscall_64+0x3b/0x90
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The problem is that the device passed to clear_caseopen() is the hwmon
device, not the platform device, and the platform data is not set in the
hwmon device. Store the pointer to sio_data in struct nct6775_data and
get if from there if needed.

Fixes: 2e7b988 ("hwmon: (nct6775) Use superio_*() function pointers in sio_data.")
Cc: Denis Pauk <[email protected]>
Cc: Bernhard Seibold <[email protected]>
Reported-by: Paweł Marciniak <[email protected]>
Tested-by: Denis Pauk <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>

Author: groeck

drivers/hwmon/nct6775.c

@@ -1175,7 +1175,7 @@ static inline u8 in_to_reg(u32 val, u8 nr)
 
 struct nct6775_data {
 	int addr;	/* IO base of hw monitor block */
-	int sioreg;	/* SIO register address */
+	struct nct6775_sio_data *sio_data;
 	enum kinds kind;
 	const char *name;
 
@@ -3559,7 +3559,7 @@ clear_caseopen(struct device *dev, struct device_attribute *attr,
 	       const char *buf, size_t count)
 {
 	struct nct6775_data *data = dev_get_drvdata(dev);
-	struct nct6775_sio_data *sio_data = dev_get_platdata(dev);
+	struct nct6775_sio_data *sio_data = data->sio_data;
 	int nr = to_sensor_dev_attr(attr)->index - INTRUSION_ALARM_BASE;
 	unsigned long val;
 	u8 reg;
@@ -3967,7 +3967,7 @@ static int nct6775_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	data->kind = sio_data->kind;
-	data->sioreg = sio_data->sioreg;
+	data->sio_data = sio_data;
 
 	if (sio_data->access == access_direct) {
 		data->addr = res->start;