Squash to "bpf: Register mptcp common kfunc set"

Address Martin's comments in v1:

- check IPPROTO_MPTCP in bpf_mptcp_sk.
- add null-checks for the wrappers.
- add more BPF flags for the wrappers.
- register this kfunc set to BPF_PROG_TYPE_CGROUP_SOCKOPT only,
  not BPF_PROG_TYPE_UNSPEC.

Signed-off-by: Geliang Tang <[email protected]>

net/mptcp/bpf.c

@@ -218,18 +218,27 @@ __bpf_kfunc_start_defs();
 
 __bpf_kfunc static struct mptcp_sock *bpf_mptcp_sk(struct sock *sk)
 {
+	if (!sk || sk->sk_protocol != IPPROTO_MPTCP)
+		return NULL;
+
 	return mptcp_sk(sk);
 }
 
 __bpf_kfunc static struct mptcp_subflow_context *
 bpf_mptcp_subflow_ctx(const struct sock *sk)
 {
+	if (!sk)
+		return NULL;
+
 	return mptcp_subflow_ctx(sk);
 }
 
 __bpf_kfunc static struct sock *
 bpf_mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow)
 {
+	if (!subflow)
+		return NULL;
+
 	return mptcp_subflow_tcp_sock(subflow);
 }
 
@@ -299,9 +308,9 @@ __bpf_kfunc static bool bpf_mptcp_subflow_queues_empty(struct sock *sk)
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(bpf_mptcp_common_kfunc_ids)
-BTF_ID_FLAGS(func, bpf_mptcp_sk)
-BTF_ID_FLAGS(func, bpf_mptcp_subflow_ctx)
-BTF_ID_FLAGS(func, bpf_mptcp_subflow_tcp_sock)
+BTF_ID_FLAGS(func, bpf_mptcp_sk, KF_TRUSTED_ARGS | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_mptcp_subflow_ctx, KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_mptcp_subflow_tcp_sock, KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_mptcp_subflow_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_iter_mptcp_subflow_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_mptcp_subflow_destroy, KF_ITER_DESTROY)
@@ -335,7 +344,7 @@ static int __init bpf_mptcp_kfunc_init(void)
 	int ret;
 
 	ret = register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
-	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC,
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCKOPT,
 					       &bpf_mptcp_common_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
 					       &bpf_mptcp_sched_kfunc_set);