[PATCH net-next 4/5] mptcp: move first subflow allocation at mpc access time

[Matthieu Baerts]

From: Paolo Abeni <pabeni@xxxxxxxxxx>

In the long run this will simplify the mptcp code and will
allow for more consistent behavior. Move the first subflow
allocation out of the sock->init ops into the __mptcp_nmpc_socket()
helper.

Since the first subflow creation can now happen after the first
setsockopt() we additionally need to invoke mptcp_sockopt_sync()
on it.

Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Reviewed-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx>
Signed-off-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx>
---
 net/mptcp/pm_netlink.c |  4 ++--
 net/mptcp/protocol.c   | 61 ++++++++++++++++++++++++++++++--------------------
 net/mptcp/protocol.h   |  2 +-
 net/mptcp/sockopt.c    | 24 +++++++++++---------
 4 files changed, 54 insertions(+), 37 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 1c42bebca39e..bc343dab5e3f 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1035,8 +1035,8 @@ static int mptcp_pm_nl_create_listen_socket(struct sock *sk,
 	lock_sock(newsk);
 	ssock = __mptcp_nmpc_socket(mptcp_sk(newsk));
 	release_sock(newsk);
-	if (!ssock)
-		return -EINVAL;
+	if (IS_ERR(ssock))
+		return PTR_ERR(ssock);
 
 	mptcp_info2sockaddr(&entry->addr, &addr, entry->addr.family);
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 22e073b373af..a676ac1bb9f1 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -49,18 +49,6 @@ static void __mptcp_check_send_data_fin(struct sock *sk);
 DEFINE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
 static struct net_device mptcp_napi_dev;
 
-/* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not
- * completed yet or has failed, return the subflow socket.
- * Otherwise return NULL.
- */
-struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk)
-{
-	if (!msk->subflow || READ_ONCE(msk->can_ack))
-		return NULL;
-
-	return msk->subflow;
-}
-
 /* Returns end sequence number of the receiver's advertised window */
 static u64 mptcp_wnd_end(const struct mptcp_sock *msk)
 {
@@ -116,6 +104,31 @@ static int __mptcp_socket_create(struct mptcp_sock *msk)
 	return 0;
 }
 
+/* If the MPC handshake is not started, returns the first subflow,
+ * eventually allocating it.
+ */
+struct socket *__mptcp_nmpc_socket(struct mptcp_sock *msk)
+{
+	struct sock *sk = (struct sock *)msk;
+	int ret;
+
+	if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
+		return ERR_PTR(-EINVAL);
+
+	if (!msk->subflow) {
+		if (msk->first)
+			return ERR_PTR(-EINVAL);
+
+		ret = __mptcp_socket_create(msk);
+		if (ret)
+			return ERR_PTR(ret);
+
+		mptcp_sockopt_sync(msk, msk->first);
+	}
+
+	return msk->subflow;
+}
+
 static void mptcp_drop(struct sock *sk, struct sk_buff *skb)
 {
 	sk_drops_add(sk, skb);
@@ -1667,6 +1680,7 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
 {
 	unsigned int saved_flags = msg->msg_flags;
 	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct socket *ssock;
 	struct sock *ssk;
 	int ret;
 
@@ -1676,8 +1690,11 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
 	 * Since the defer_connect flag is cleared after the first succsful
 	 * fastopen attempt, no need to check for additional subflow status.
 	 */
-	if (msg->msg_flags & MSG_FASTOPEN && !__mptcp_nmpc_socket(msk))
-		return -EINVAL;
+	if (msg->msg_flags & MSG_FASTOPEN) {
+		ssock = __mptcp_nmpc_socket(msk);
+		if (IS_ERR(ssock))
+			return PTR_ERR(ssock);
+	}
 	if (!msk->first)
 		return -EINVAL;
 
@@ -2740,10 +2757,6 @@ static int mptcp_init_sock(struct sock *sk)
 	if (unlikely(!net->mib.mptcp_statistics) && !mptcp_mib_alloc(net))
 		return -ENOMEM;
 
-	ret = __mptcp_socket_create(mptcp_sk(sk));
-	if (ret)
-		return ret;
-
 	set_bit(SOCK_CUSTOM_SOCKOPT, &sk->sk_socket->flags);
 
 	/* fetch the ca name; do it outside __mptcp_init_sock(), so that clone will
@@ -3563,8 +3576,8 @@ static int mptcp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	int err = -EINVAL;
 
 	ssock = __mptcp_nmpc_socket(msk);
-	if (!ssock)
-		return -EINVAL;
+	if (IS_ERR(ssock))
+		return PTR_ERR(ssock);
 
 	mptcp_token_destroy(msk);
 	inet_sk_state_store(sk, TCP_SYN_SENT);
@@ -3652,8 +3665,8 @@ static int mptcp_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 
 	lock_sock(sock->sk);
 	ssock = __mptcp_nmpc_socket(msk);
-	if (!ssock) {
-		err = -EINVAL;
+	if (IS_ERR(ssock)) {
+		err = PTR_ERR(ssock);
 		goto unlock;
 	}
 
@@ -3689,8 +3702,8 @@ static int mptcp_listen(struct socket *sock, int backlog)
 
 	lock_sock(sk);
 	ssock = __mptcp_nmpc_socket(msk);
-	if (!ssock) {
-		err = -EINVAL;
+	if (IS_ERR(ssock)) {
+		err = PTR_ERR(ssock);
 		goto unlock;
 	}
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index a9eb0e428a6b..21eda9cd0c52 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -627,7 +627,7 @@ void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 void __mptcp_subflow_send_ack(struct sock *ssk);
 void mptcp_subflow_reset(struct sock *ssk);
 void mptcp_sock_graft(struct sock *sk, struct socket *parent);
-struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk);
+struct socket *__mptcp_nmpc_socket(struct mptcp_sock *msk);
 bool __mptcp_close(struct sock *sk, long timeout);
 void mptcp_cancel_work(struct sock *sk);
 void mptcp_set_owner_r(struct sk_buff *skb, struct sock *sk);
diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index b655cebda0f3..d4258869ac48 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -301,9 +301,9 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
 	case SO_BINDTOIFINDEX:
 		lock_sock(sk);
 		ssock = __mptcp_nmpc_socket(msk);
-		if (!ssock) {
+		if (IS_ERR(ssock)) {
 			release_sock(sk);
-			return -EINVAL;
+			return PTR_ERR(ssock);
 		}
 
 		ret = sock_setsockopt(ssock, SOL_SOCKET, optname, optval, optlen);
@@ -396,9 +396,9 @@ static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname,
 	case IPV6_FREEBIND:
 		lock_sock(sk);
 		ssock = __mptcp_nmpc_socket(msk);
-		if (!ssock) {
+		if (IS_ERR(ssock)) {
 			release_sock(sk);
-			return -EINVAL;
+			return PTR_ERR(ssock);
 		}
 
 		ret = tcp_setsockopt(ssock->sk, SOL_IPV6, optname, optval, optlen);
@@ -693,9 +693,9 @@ static int mptcp_setsockopt_sol_ip_set_transparent(struct mptcp_sock *msk, int o
 	lock_sock(sk);
 
 	ssock = __mptcp_nmpc_socket(msk);
-	if (!ssock) {
+	if (IS_ERR(ssock)) {
 		release_sock(sk);
-		return -EINVAL;
+		return PTR_ERR(ssock);
 	}
 
 	issk = inet_sk(ssock->sk);
@@ -762,13 +762,15 @@ static int mptcp_setsockopt_first_sf_only(struct mptcp_sock *msk, int level, int
 {
 	struct sock *sk = (struct sock *)msk;
 	struct socket *sock;
-	int ret = -EINVAL;
+	int ret;
 
 	/* Limit to first subflow, before the connection establishment */
 	lock_sock(sk);
 	sock = __mptcp_nmpc_socket(msk);
-	if (!sock)
+	if (IS_ERR(sock)) {
+		ret = PTR_ERR(sock);
 		goto unlock;
+	}
 
 	ret = tcp_setsockopt(sock->sk, level, optname, optval, optlen);
 
@@ -861,7 +863,7 @@ static int mptcp_getsockopt_first_sf_only(struct mptcp_sock *msk, int level, int
 {
 	struct sock *sk = (struct sock *)msk;
 	struct socket *ssock;
-	int ret = -EINVAL;
+	int ret;
 	struct sock *ssk;
 
 	lock_sock(sk);
@@ -872,8 +874,10 @@ static int mptcp_getsockopt_first_sf_only(struct mptcp_sock *msk, int level, int
 	}
 
 	ssock = __mptcp_nmpc_socket(msk);
-	if (!ssock)
+	if (IS_ERR(ssock)) {
+		ret = PTR_ERR(ssock);
 		goto out;
+	}
 
 	ret = tcp_getsockopt(ssock->sk, level, optname, optval, optlen);
 

-- 
2.39.2