This is a note to let you know that I've just added the patch titled [PATCH stable 5.9 13/24] net: mptcp: make DACK4/DACK8 usage consistent among all subflows to the 5.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-mptcp-make-dack4-dack8-usage-consistent-among-all-subflows.patch and it can be found in the queue-5.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Sat Oct 17 08:52:03 AM CEST 2020 From: Davide Caratti <dcaratti@xxxxxxxxxx> Date: Tue, 6 Oct 2020 18:26:17 +0200 Subject: [PATCH stable 5.9 13/24] net: mptcp: make DACK4/DACK8 usage consistent among all subflows From: Davide Caratti <dcaratti@xxxxxxxxxx> [ 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@xxxxxxxxxx> Signed-off-by: Davide Caratti <dcaratti@xxxxxxxxxx> Reviewed-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -516,7 +516,7 @@ 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 = READ_ONCE(msk->ack_seq); opts->ext_copy.ack64 = 1; --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -203,6 +203,7 @@ 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; @@ -295,7 +296,6 @@ 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; --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -781,12 +781,11 @@ 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 */ Patches currently in stable-queue which might be from dcaratti@xxxxxxxxxx are queue-5.9/net-mptcp-make-dack4-dack8-usage-consistent-among-all-subflows.patch