In China, any type of work done by foreigners, for pay or for free (makes no difference if you are paid in money, goods or services, and / or work for free), to be done in a legal way you must have three documents, a work permit, a residence permit and an FEC.  Of course, whomever hires you must be authorized to hire foreigners.

As a student, the only type of work you may be legally perform is an internship sponsor by the college you attend, related to your field of study.  Anything else is playing Russians' roulette.

How are student's expected to survive then?