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Subject: [PATCH mptcp-net v7 3/5] mptcp: fix syncookie process if mptcp can not_accept new subflow
Date: Fri, 25 Jun 2021 16:25:57 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

From: Jianguo Wu <>

Lots of "TCP: tcp_fin: Impossible, sk->sk_state=7" in client side
when doing stress testing using wrk and webfsd.

There are at least two cases may trigger this warning:
1.mptcp is in syncookie, and server recv MP_JOIN SYN request,
  in subflow_check_req(), the mptcp_can_accept_new_subflow()
  return false, so subflow_init_req_cookie_join_save() isn't
  called, i.e. not store the data present in the MP_JOIN syn
  request and the random nonce in hash table - join_entries[],
  but still send synack. When recv 3rd-ack,
  mptcp_token_join_cookie_init_state() will return false, and
  3rd-ack is dropped, then if mptcp conn is closed by client,
  client will send a DATA_FIN and a MPTCP FIN, the DATA_FIN
  doesn't have MP_CAPABLE or MP_JOIN,
  so mptcp_subflow_init_cookie_req() will return 0, and pass
  the cookie check, MP_JOIN request is fallback to normal TCP.
  Server will send a TCP FIN if closed, in client side,
  when process TCP FIN, it will do reset, the code path is:
  mptcp_subflow_reset() will set sock state to TCP_CLOSE,
  so tcp_fin will hit TCP_CLOSE, and print the warning.
2.mptcp is in syncookie, and server recv 3rd-ack, in
  mptcp_subflow_init_cookie_req(), mptcp_can_accept_new_subflow()
  return false, and subflow_req->mp_join is not set to 1,
  so in subflow_syn_recv_sock() will not reset the MP_JOIN
  subflow, but fallback to normal TCP, and then the same thing
  happens when server will send a TCP FIN if closed.

For case1, subflow_check_req() return -EPERM,
then tcp_conn_request() will drop MP_JOIN SYN.

For case2, let subflow_syn_recv_sock() call mptcp_can_accept_new_subflow(),
and do fatal fallback, send reset.

Fixes: 9466a1ccebbe("mptcp: enable JOIN requests even if cookies are in use")
Signed-off-by: Jianguo Wu <>
 net/mptcp/subflow.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 3a849fb..f3f1358 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -225,6 +225,8 @@ static int subflow_check_req(struct request_sock *req,
 		if (unlikely(req->syncookie)) {
 			if (mptcp_can_accept_new_subflow(subflow_req->msk))
 				subflow_init_req_cookie_join_save(subflow_req, skb);
+			else
+				return -EPERM;
 		pr_debug("token=%u, remote_nonce=%u msk=%p", subflow_req->token,
@@ -264,9 +266,7 @@ int mptcp_subflow_init_cookie_req(struct request_sock *req,
 		if (!mptcp_token_join_cookie_init_state(subflow_req, skb))
 			return -EINVAL;
-		if (mptcp_can_accept_new_subflow(subflow_req->msk))
-			subflow_req->mp_join = 1;
+		subflow_req->mp_join = 1;
 		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;

  parent reply	other threads:[~2021-06-25  8:26 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-25  8:25 [PATCH mptcp-net v7 0/5] Fix some mptcp syncookie process bugs wujianguo106
2021-06-25  8:25 ` [PATCH mptcp-net v7 1/5] mptcp: fix warning in __skb_flow_dissect() when do syn cookie for subflow join wujianguo106
2021-06-25  8:25 ` [PATCH mptcp-net v7 2/5] mptcp: remove redundant req destruct in subflow_check_req() wujianguo106
2021-06-25  8:25 ` wujianguo106 [this message]
2021-06-25  8:25 ` [PATCH mptcp-net v7 4/5] mptcp: avoid processing packet if a subflow reset wujianguo106
2021-06-25  8:58   ` Geliang Tang
2021-06-25  9:07   ` Matthieu Baerts
2021-06-25  9:46     ` Jianguo Wu
2021-06-26  1:07       ` Mat Martineau
2021-06-25 10:38   ` Paolo Abeni
2021-06-25 10:45   ` Paolo Abeni
2021-06-26  8:59     ` Jianguo Wu
2021-06-25  8:25 ` [PATCH mptcp-net v7 5/5] selftests: mptcp: fix case multiple subflows limited by server wujianguo106

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