watchdog: sbc_fitpc2_wdt: add __user annotations

After a change to the put_user() macro on x86, kernel test robot has
started sending me complaints (from sparse) about passing kernel
pointers to put_user(). So add the __user annotations to the various
casts in fitpc2_wdt_ioctl(), and while in here, also make the write
method actually match the prototype of file_operations::write.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Guenter Roeck <inux@roeck-us.net>
Link: https://lore.kernel.org/r/20201025124518.31647-1-linux@rasmusvillemoes.dkSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/sbc_fitpc2_wdt.c

@@ -78,7 +78,7 @@ static int fitpc2_wdt_open(struct inode *inode, struct file *file)
 	return stream_open(inode, file);
 }
 
-static ssize_t fitpc2_wdt_write(struct file *file, const char *data,
+static ssize_t fitpc2_wdt_write(struct file *file, const char __user *data,
 						size_t len, loff_t *ppos)
 {
 	size_t i;
@@ -125,16 +125,16 @@ static long fitpc2_wdt_ioctl(struct file *file, unsigned int cmd,
 
 	switch (cmd) {
 	case WDIOC_GETSUPPORT:
-		ret = copy_to_user((struct watchdog_info *)arg, &ident,
+		ret = copy_to_user((struct watchdog_info __user *)arg, &ident,
 				   sizeof(ident)) ? -EFAULT : 0;
 		break;
 
 	case WDIOC_GETSTATUS:
-		ret = put_user(0, (int *)arg);
+		ret = put_user(0, (int __user *)arg);
 		break;
 
 	case WDIOC_GETBOOTSTATUS:
-		ret = put_user(0, (int *)arg);
+		ret = put_user(0, (int __user *)arg);
 		break;
 
 	case WDIOC_KEEPALIVE:
@@ -143,7 +143,7 @@ static long fitpc2_wdt_ioctl(struct file *file, unsigned int cmd,
 		break;
 
 	case WDIOC_SETTIMEOUT:
-		ret = get_user(time, (int *)arg);
+		ret = get_user(time, (int __user *)arg);
 		if (ret)
 			break;
 
@@ -157,7 +157,7 @@ static long fitpc2_wdt_ioctl(struct file *file, unsigned int cmd,
 		fallthrough;
 
 	case WDIOC_GETTIMEOUT:
-		ret = put_user(margin, (int *)arg);
+		ret = put_user(margin, (int __user *)arg);
 		break;
 	}