netdev - [PATCH net] net: mptcp: make DACK4/DACK8 usage consistent among all subflows

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Date:   Tue,  6 Oct 2020 18:26:17 +0200
From:   Davide Caratti <dcaratti@...hat.com>
To:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc:     mptcp@...ts.01.org, Christoph Paasch <cpaasch@...le.com>,
        pabeni@...hat.com, Matthieu Baerts <matthieu.baerts@...sares.net>
Subject: [PATCH net] net: mptcp: make DACK4/DACK8 usage consistent among all subflows

using packetdrill it's possible to observe the same MPTCP DSN being acked
by different subflows with DACK4 and DACK8. This is in contrast with what
specified in RFC8684 §3.3.2: if an MPTCP endpoint transmits a 64-bit wide
DSN, it MUST be acknowledged with a 64-bit wide DACK. Fix 'use_64bit_ack'
variable to make it a property of MPTCP sockets, not TCP subflows.

Fixes: a0c1d0eafd1e ("mptcp: Use 32-bit DATA_ACK when possible")
Acked-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 net/mptcp/options.c  | 2 +-
 net/mptcp/protocol.h | 2 +-
 net/mptcp/subflow.c  | 3 +--
 3 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 888bbbbb3e8a..9d7fa93fe0cf 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -516,7 +516,7 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 		return ret;
 	}
 
-	if (subflow->use_64bit_ack) {
+	if (READ_ONCE(msk->use_64bit_ack)) {
 		ack_size = TCPOLEN_MPTCP_DSS_ACK64;
 		opts->ext_copy.data_ack = READ_ONCE(msk->ack_seq);
 		opts->ext_copy.ack64 = 1;
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 20f04ac85409..285dd8b2b43a 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -202,6 +202,7 @@ struct mptcp_sock {
 	bool		fully_established;
 	bool		rcv_data_fin;
 	bool		snd_data_fin_enable;
+	bool		use_64bit_ack; /* Set when we received a 64-bit DSN */
 	spinlock_t	join_list_lock;
 	struct work_struct work;
 	struct list_head conn_list;
@@ -294,7 +295,6 @@ struct mptcp_subflow_context {
 		backup : 1,
 		data_avail : 1,
 		rx_eof : 1,
-		use_64bit_ack : 1, /* Set when we received a 64-bit DSN */
 		can_ack : 1;	    /* only after processing the remote a key */
 	u32	remote_nonce;
 	u64	thmac;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 6f035af1c9d2..91bef7bfffa6 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -769,12 +769,11 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 	if (!mpext->dsn64) {
 		map_seq = expand_seq(subflow->map_seq, subflow->map_data_len,
 				     mpext->data_seq);
-		subflow->use_64bit_ack = 0;
 		pr_debug("expanded seq=%llu", subflow->map_seq);
 	} else {
 		map_seq = mpext->data_seq;
-		subflow->use_64bit_ack = 1;
 	}
+	WRITE_ONCE(mptcp_sk(subflow->conn)->use_64bit_ack, !!mpext->dsn64);
 
 	if (subflow->map_valid) {
 		/* Allow replacing only with an identical map */
-- 
2.26.2