RDMA/uverbs: Prevent integer overflow issue

In the Linux kernel, the following vulnerability has been resolved:

RDMA/uverbs: Prevent integer overflow issue

In the expression "cmd.wqe_size * cmd.wr_count", both variables are u32

values that come from the user so the multiplication can lead to integer

wrapping. Then we pass the result to uverbs_request_next_ptr() which also

could potentially wrap. The "cmd.sge_count * sizeof(struct ib_uverbs_sge)"

multiplication can also overflow on 32bit systems although it's fine on

64bit systems.

This patch does two things. First, I've re-arranged the condition in

uverbs_request_next_ptr() so that the use controlled variable "len" is on

one side of the comparison by itself without any math. Then I've modified

all the callers to use size_mul() for the multiplications.