From: Wyatt Feng Date: Mon, 3 Aug 2026 16:16:39 +0000 (+0200) Subject: mptcp: fastopen: only mark MPTFO subflows with SYN data X-Git-Tag: v7.2-rc7~27^2~14^2~1 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e00b63056fb4f261455b3e5df5268a1f8ce47a87;p=thirdparty%2Flinux.git mptcp: fastopen: only mark MPTFO subflows with SYN data Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty. mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established(). Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty. Note that mptcp_subflow_context's is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really "doing TFO". Fixes: 36b122baf6a8 ("mptcp: add subflow_v(4,6)_send_synack()") Cc: stable@vger.kernel.org Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Zhengchuan Liang Reported-by: Xin Liu Signed-off-by: Wyatt Feng Signed-off-by: Ren Wei Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-7-b8f496d71664@kernel.org Signed-off-by: Jakub Kicinski --- diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c index 082c46c0f50e..f717750906ff 100644 --- a/net/mptcp/fastopen.c +++ b/net/mptcp/fastopen.c @@ -24,12 +24,13 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf sk = subflow->conn; tp = tcp_sk(ssk); - subflow->is_mptfo = 1; - + /* A valid TFO cookie does not guarantee SYN data. */ skb = skb_peek(&ssk->sk_receive_queue); - if (WARN_ON_ONCE(!skb)) + if (!skb) return; + subflow->is_mptfo = 1; + /* dequeue the skb from sk receive queue */ __skb_unlink(skb, &ssk->sk_receive_queue); skb_ext_reset(skb);