Cooperative regenerating codes are a kind of erasure codes which are optimal in terms of minimizing the repair bandwidth. An (n,k,d,r)-cooperative regenerating code has n storage nodes, where k arbitrary nodes are enough to reconstruct original data, and r failed nodes can be repaired cooperatively with the help of d arbitrary surviving nodes. In the regenerating-code framework, there exists a tradeoff between the storage capacity and the repair bandwidth, but the problem of specifying the optimal storage-bandwidth tradeoff of the exact-repair cooperative regenerating codes remains open. We propose an outer bound on the storage-bandwidth tradeoff of exact-repair and linear cooperative regenerating codes.