archive mirror
 help / color / mirror / Atom feed
Subject: [PATCH 3/4] mptcp: fix syncookie process if mptcp can not_accept new subflow
Date: Fri, 11 Jun 2021 15:34:41 +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.

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 75ed530..6d98e19 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -224,6 +224,8 @@ 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,
@@ -263,9 +265,7 @@ 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:[~2021-06-11  7:35 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-11  7:34 [PATCH v3 0/4] Fix some mptcp syncookie process bugs wujianguo106
2021-06-11  7:34 ` [PATCH 1/4] mptcp: fix warning in __skb_flow_dissect() when do syn cookie for subflow join wujianguo106
2021-06-11  7:34 ` [PATCH 2/4] mptcp: remove redundant req destruct in subflow_check_req() wujianguo106
2021-06-11  7:34 ` wujianguo106 [this message]
2021-06-11  7:34 ` [PATCH 4/4] mptcp: avoid processing packet if a subflow reset wujianguo106

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \
    --subject='Re: [PATCH 3/4] mptcp: fix syncookie process if mptcp can not_accept new subflow' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).