[hamiltont]

You've got it backwards - the DB server can pipe an arbitrary file from the client. So it is considered the fault of the client - it should not allow that. Since the mysql client is the one receiving the request and it should apply standard security practices by not blindly trusting an incoming request and instead validating that the path is equal to an earlier client load request sent to the server. (Although a better approach IMO would be to modify the wire protocol so the server "request" does not use the file name, but instead uses an ID from the earlier client request)