s390/vmcp: fix uaccess check and avoid undefined behavior
The vmcp device driver should return -EFAULT if get_user() fails, due to an invalid user space address. In addition the buffer size value from user space is passed unchecked to get_order(). The return value of get_order(0) undefined. Therefore explicitly test for zero before calling get_order() and also return -EFAULT if get_user() fails. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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