From: Geliang Tang <tanggeliang@kylinos.cn>

The 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>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/bpf.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index d107c2865e97e6ccffb9e0720dfbbd232b63a3b8..5bd04548e846b4dc120dbc83725a604821fac772 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -90,6 +90,23 @@ bpf_iter_mptcp_subflow_destroy(struct bpf_iter_mptcp_subflow *it)
 {
 }
 
+__bpf_kfunc static 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 static 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_end_defs();
 
 BTF_KFUNCS_START(bpf_mptcp_common_kfunc_ids)
@@ -99,6 +116,8 @@ BTF_ID_FLAGS(func, bpf_mptcp_subflow_tcp_sock)
 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 = {

-- 
2.45.2