HID: ft260: check data size in ft260_smbus_write()

The SMbus block transaction limits the number of bytes transferred to 32,
but nothing prevents a user from specifying via ioctl a larger data size
than the ft260 can handle in a single transfer.

i2cdev_ioctl_smbus()
   --> i2c_smbus_xfer
       --> __i2c_smbus_xfer
           --> ft260_smbus_xfer
               --> ft260_smbus_write

This patch adds data size checking in the ft260_smbus_write().

Fixes: 98189a0adfa0 ("HID: ft260: add usb hid to i2c host bridge driver")
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-ft260.c

@@ -201,7 +201,7 @@ struct ft260_i2c_write_request_report {
 	u8 address;		/* 7-bit I2C address */
 	u8 flag;		/* I2C transaction condition */
 	u8 length;		/* data payload length */
-	u8 data[60];		/* data payload */
+	u8 data[FT260_WR_DATA_MAX]; /* data payload */
 } __packed;
 
 struct ft260_i2c_read_request_report {
@@ -429,6 +429,9 @@ static int ft260_smbus_write(struct ft260_device *dev, u8 addr, u8 cmd,
 	struct ft260_i2c_write_request_report *rep =
 		(struct ft260_i2c_write_request_report *)dev->write_buf;
 
+	if (data_len >= sizeof(rep->data))
+		return -EINVAL;
+
 	rep->address = addr;
 	rep->data[0] = cmd;
 	rep->length = data_len + 1;