In this paper, we investigate the physical layer security issue in a cellular network with a full-duplex (FD) base station and multiple uplinks and downlinks. We provide a novel cooperative jamming mechanism in order to enhance the secrecy performance for the investigated scenario. The total bandwidth is divided into multiple resource blocks (RBs). In our investigation, each uplink or downlink can acquire at most one RB, and each RB can only be assigned to one uplink and one downlink. We formulate the secrecy capacity maximization problem as a joint RB assignment and power allocation problem, and then propose a bipartite graph based propose-and-decide algorithm (BGPDA) to solve this problem effectively and efficiently. The numerical simulations verify the efficiency of our proposed algorithm.