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.