net: mptcp: make DACK4/DACK8 usage consistent among all subflows

[ Upstream commit 37198e93ced70733f0b993dff28b7c33857e254f ]

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@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 8f940be42f98a567b84a26d398200d3627d5efbc..77d46cc8165bc8148751f014a75ce5705d53fc42 100644 (file)
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -517,7 +517,7 @@ 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 = msk->ack_seq;
                opts->ext_copy.ack64 = 1;

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index c6eeaf3e8dcb7f786ba9cb0f672add43092f67f3..4675a7bbebb1532b3a298ad85200e3685f5ebda9 100644 (file)
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -199,6 +199,7 @@ struct mptcp_sock {
        u32             token;
        unsigned long   flags;
        bool            can_ack;
+       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;
@@ -285,7 +286,6 @@ struct mptcp_subflow_context {
                data_avail : 1,
                rx_eof : 1,
                data_fin_tx_enable : 1,
-               use_64bit_ack : 1, /* Set when we received a 64-bit DSN */
                can_ack : 1;        /* only after processing the remote a key */
        u64     data_fin_tx_seq;
        u32     remote_nonce;

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 3838a0b3a21ffd122c358dc3700ba2fc48547433..2e145b53b81f4380fc4d6672fc1b784653cb623f 100644 (file)
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -682,12 +682,11 @@ 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 */