mptcp: refactor passive socket initialization

After commit 30e51b923e43 ("mptcp: fix unreleased socket in accept queue")
unaccepted msk sockets go throu complete shutdown, we don't need anymore
to delay inserting the first subflow into the subflow lists.

The reference counting deserve some extra care, as __mptcp_close() is
unaware of the request socket linkage to the first subflow.

Please note that this is more a refactoring than a fix but because this
modification is needed to include other corrections, see the following
commits. Then a Fixes tag has been added here to help the stable team.

Fixes: 30e51b923e43 ("mptcp: fix unreleased socket in accept queue")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Tested-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 21 insertions, 6 deletions

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 5070dc33675d..a631a5e6fc7b 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -397,6 +397,12 @@ void mptcp_subflow_reset(struct sock *ssk)
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	struct sock *sk = subflow->conn;
 
+	/* mptcp_mp_fail_no_response() can reach here on an already closed
+	 * socket
+	 */
+	if (ssk->sk_state == TCP_CLOSE)
+		return;
+
 	/* must hold: tcp_done() could drop last reference on parent */
 	sock_hold(sk);
 
@@ -750,6 +756,7 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 	struct mptcp_options_received mp_opt;
 	bool fallback, fallback_is_fatal;
 	struct sock *new_msk = NULL;
+	struct mptcp_sock *owner;
 	struct sock *child;
 
 	pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);
@@ -824,6 +831,8 @@ create_child:
 		ctx->setsockopt_seq = listener->setsockopt_seq;
 
 		if (ctx->mp_capable) {
+			owner = mptcp_sk(new_msk);
+
 			/* this can't race with mptcp_close(), as the msk is
 			 * not yet exposted to user-space
 			 */
@@ -832,14 +841,14 @@ create_child:
 			/* record the newly created socket as the first msk
 			 * subflow, but don't link it yet into conn_list
 			 */
-			WRITE_ONCE(mptcp_sk(new_msk)->first, child);
+			WRITE_ONCE(owner->first, child);
 
 			/* new mpc subflow takes ownership of the newly
 			 * created mptcp socket
 			 */
 			mptcp_sk(new_msk)->setsockopt_seq = ctx->setsockopt_seq;
-			mptcp_pm_new_connection(mptcp_sk(new_msk), child, 1);
-			mptcp_token_accept(subflow_req, mptcp_sk(new_msk));
+			mptcp_pm_new_connection(owner, child, 1);
+			mptcp_token_accept(subflow_req, owner);
 			ctx->conn = new_msk;
 			new_msk = NULL;
 
@@ -847,15 +856,21 @@ create_child:
 			 * uses the correct data
 			 */
 			mptcp_copy_inaddrs(ctx->conn, child);
+			mptcp_propagate_sndbuf(ctx->conn, child);
+
+			mptcp_rcv_space_init(owner, child);
+			list_add(&ctx->node, &owner->conn_list);
+			sock_hold(child);
 
 			/* with OoO packets we can reach here without ingress
 			 * mpc option
 			 */
-			if (mp_opt.suboptions & OPTION_MPTCP_MPC_ACK)
+			if (mp_opt.suboptions & OPTION_MPTCP_MPC_ACK) {
 				mptcp_subflow_fully_established(ctx, &mp_opt);
+				mptcp_pm_fully_established(owner, child, GFP_ATOMIC);
+				ctx->pm_notified = 1;
+			}
 		} else if (ctx->mp_join) {
-			struct mptcp_sock *owner;
-
 			owner = subflow_req->msk;
 			if (!owner) {
 				subflow_add_reset_reason(skb, MPTCP_RST_EPROHIBIT);