mptcp: decrement subflows counter on failed passive join

mptcp_pm_allow_new_subflow() increments extra_subflows before
__mptcp_finish_join() on the passive MP_JOIN path.

In case of race conditions, the subflow is dropped without calling
mptcp_close_ssk(), so the counter is not rolled back.

Call mptcp_pm_close_subflow() when the join completion fails to
decrement the subflows counter.

Fixes: 10f6d46c943d ("mptcp: fix race between MP_JOIN and close")
Cc: stable@vger.kernel.org
Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260722-net-mptcp-misc-fixes-7-2-rc5-v1-1-6fb595bc86ef@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index cb9515f505aa4e019d2390070929d9057aa0e518..b32f0cd262a72cf25ae1e93c2d55e15b6bbdc10b 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3907,6 +3907,7 @@ bool mptcp_finish_join(struct sock *ssk)
        mptcp_data_unlock(parent);
 
        if (!ret) {
+               mptcp_pm_close_subflow(msk);
 err_prohibited:
                subflow->reset_reason = MPTCP_RST_EPROHIBIT;
                return false;