From: Geliang Tang <tanggeliang@kylinos.cn>

KF_TRUSTED_ARGS flag is used for bpf_iter_mptcp_subflow_new, it indicates
that the all pointer arguments are valid. It's necessary to add a
KF_ACQUIRE helper to get valid "msk".

This patch adds bpf_mptcp_sock_acquire() and bpf_mptcp_sock_release()
helpers for this. Increase sk->sk_refcnt in _acquire() and decrease it
in _release(). Register them with KF_ACQUIRE flag and KF_RELEASE flag.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/bpf.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 31bb2a869d34..f5700dbe2024 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -243,6 +243,22 @@ __bpf_kfunc void bpf_iter_mptcp_subflow_destroy(struct bpf_iter_mptcp_subflow *i
 {
 }
 
+__bpf_kfunc struct mptcp_sock *bpf_mptcp_sock_acquire(struct mptcp_sock *msk)
+{
+	struct sock *sk = (struct sock *)msk;
+
+	if (sk && refcount_inc_not_zero(&sk->sk_refcnt))
+		return msk;
+	return NULL;
+}
+
+__bpf_kfunc void bpf_mptcp_sock_release(struct mptcp_sock *msk)
+{
+	struct sock *sk = (struct sock *)msk;
+
+	WARN_ON_ONCE(!sk || !refcount_dec_not_one(&sk->sk_refcnt));
+}
+
 __bpf_kfunc struct mptcp_subflow_context *
 bpf_mptcp_subflow_ctx_by_pos(const struct mptcp_sched_data *data, unsigned int pos)
 {
@@ -264,6 +280,8 @@ BTF_ID_FLAGS(func, mptcp_subflow_set_scheduled)
 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)
+BTF_ID_FLAGS(func, bpf_mptcp_sock_acquire, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_mptcp_sock_release, KF_RELEASE)
 BTF_KFUNCS_END(bpf_mptcp_common_kfunc_ids)
 
 static const struct btf_kfunc_id_set bpf_mptcp_common_kfunc_set = {
-- 
2.43.0