ACPI / EC: access user space with get_user()/put_user()

User space pointer may not be dereferenced. Use get_user()/put_user()
instead and check their return codes.

Signed-off-by: Vasiliy Kulikov <[e-mail]>
Signed-off-by: Thomas Renninger <[e-mail]>
Signed-off-by: Jiri Slaby <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/ec_sys.c

···
 #include <linux/acpi.h>
 #include <linux/debugfs.h>
 #include <linux/module.h>
+#include <linux/uaccess.h>
 #include "internal.h"
 
 MODULE_AUTHOR("Thomas Renninger <[e-mail]>");
···
 	 * struct acpi_ec *ec = ((struct seq_file *)f->private_data)->private;
 	 */
 	unsigned int size = EC_SPACE_SIZE;
-	u8 *data = (u8 *) buf;
 	loff_t init_off = *off;
 	int err = 0;
 
···
 		size = count;
 
 	while (size) {
-		err = ec_read(*off, &data[*off - init_off]);
+		u8 byte_read;
+		err = ec_read(*off, &byte_read);
 		if (err)
 			return err;
+		if (put_user(byte_read, buf + *off - init_off)) {
+			if (*off - init_off)
+				return *off - init_off; /* partial read */
+			return -EFAULT;
+		}
 		*off += 1;
 		size--;
 	}
···
 
 	unsigned int size = count;
 	loff_t init_off = *off;
-	u8 *data = (u8 *) buf;
 	int err = 0;
 
 	if (*off >= EC_SPACE_SIZE)
···
 	}
 
 	while (size) {
-		u8 byte_write = data[*off - init_off];
+		u8 byte_write;
+		if (get_user(byte_write, buf + *off - init_off)) {
+			if (*off - init_off)
+				return *off - init_off; /* partial write */
+			return -EFAULT;
+		}
 		err = ec_write(*off, byte_write);
 		if (err)
 			return err;