[PATCH export v3 2/4] mptcp: reject joins after fallback in mptcp_is_fully_established

[Chenguang Zhao <chenguang.zhao@linux.dev>]

From: Chenguang Zhao <zhaochenguang@kylinos.cn>

After fallback, treat the connection as not fully established so later
MP_JOIN attempts are rejected.

Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
---
 net/mptcp/protocol.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 7e168e450fb0..bf2483a7ed92 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -957,8 +957,11 @@ static inline void mptcp_start_tout_timer(struct sock *sk)
 
 static inline bool mptcp_is_fully_established(struct sock *sk)
 {
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
 	return inet_sk_state_load(sk) == TCP_ESTABLISHED &&
-	       READ_ONCE(mptcp_sk(sk)->fully_established);
+	       READ_ONCE(msk->fully_established) &&
+	       !test_bit(MPTCP_FALLBACK_DONE, &msk->flags);
 }
 
 static inline u64 mptcp_stamp(void)
-- 
2.25.1