The RFC 8684 mandates that no-data DATA FIN packets should carry a DSS with 0 sequence number and data len equal to 1. Currently, on FIN retransmission we re-use the existing mapping; if the previous fin transmission was part of a partially acked data packet, we could end-up writing in the egress packet a non-compliant DSS. The above will be detected by a "Bad mapping" warning on the receiver side. This change addresses the issue explicitly checking for 0 len packet when adding the DATA_FIN option. Fixes: 6d0060f600ad ("mptcp: Write MPTCP DSS headers to outgoing data packets") Signed-off-by: Paolo Abeni --- net/mptcp/options.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- this should go on "top" of export branch, just before the "DO NOT MERGE" changes. Hopefully should not conflict with others diff --git a/net/mptcp/options.c b/net/mptcp/options.c index f464f8669dfc..46470194b8ca 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -451,9 +451,9 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb, } static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow, - struct mptcp_ext *ext) + struct sk_buff *skb, struct mptcp_ext *ext) { - if (!ext->use_map) { + if (!ext->use_map || !skb->len) { /* RFC6824 requires a DSS mapping with specific values * if DATA_FIN is set but no data payload is mapped */ @@ -505,7 +505,7 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb, opts->ext_copy = *mpext; if (skb && tcp_fin && subflow->data_fin_tx_enable) - mptcp_write_data_fin(subflow, &opts->ext_copy); + mptcp_write_data_fin(subflow, skb, &opts->ext_copy); ret = true; } -- 2.26.2