[PATCH 5.8 011/633] net: mptcp: make DACK4/DACK8 usage consistent among all subflows

Greg Kroah-Hartman
2020-10-27T17:10:40Z

From: Davide Caratti <dcaratti@redhat.com>

[ 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>
---
net/mptcp/options.c | 2 +-
net/mptcp/protocol.h | 2 +-
net/mptcp/subflow.c | 3 +--
3 files changed, 3 insertions(+), 4 deletions(-)

--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -517,7 +517,7 @@ static bool mptcp_established_options_ds
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;
--- 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;
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -682,12 +682,11 @@ static enum mapping_status get_mapping_s
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 */