uaccess: fix integer overflow on access_ok()

In the Linux kernel, the following vulnerability has been resolved: uaccess: fix integer overflow on access_ok() Three architectures check the end of a user access against the address limit without taking a possible overflow into account. Passing a negative length or another overflow in here returns success when it should not. Use the most common correct implementation here, which optimizes for a constant 'size' argument, and turns the common case into a single comparison.