Most universities allow you to double major in CS and math (other than a few that limit you to a single major, or the ones that house the two departments in different schools/colleges and don’t allow students to double major from two different schools/colleges). For these universities, double major in CS and math is relatively easily achievable because some of required and elective math courses for the CS major can satisfy some of the requirements for the math major. If you pick a CS discipline that requires a lot of math and do well, no one (graduate schools or employers) will care whether you have a secondary math major/minor.