[PATCH mptcp-next RFC v5 3/3] mptcp: reject new subflows after fallback

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

From: Chenguang Zhao <zhaochenguang@kylinos.cn>

Check FALLBACK_DONE in mptcp_can_accept_new_subflow() so that
MP_JOIN is rejected after the connection has fallen back to TCP.

Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
---
 net/mptcp/subflow.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index af81ad5e699d..c35f3bfda535 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -61,6 +61,7 @@ static void subflow_generate_hmac(u64 key1, u64 key2, u32 nonce1, u32 nonce2,
 static bool mptcp_can_accept_new_subflow(const struct mptcp_sock *msk)
 {
 	return mptcp_is_fully_established((void *)msk) &&
+		!__mptcp_check_fallback(msk) &&
 		((mptcp_pm_is_userspace(msk) &&
 		  mptcp_userspace_pm_active(msk)) ||
 		 READ_ONCE(msk->pm.accept_subflow));
-- 
2.25.1