From: Paolo Abeni <pabeni@redhat.com>

mptcp_disconnect() clears the fallback bit unconditionally, without
touching the associated flags.

The bit clear is safe, as no fallback operation can race with that --
all subflow are already in TCP_CLOSE status thanks to the previous
FASTCLOSE -- but we need to consistently reset all the fallback related
status.

Also acquire the relevant lock, to avoid fouling static analyzers.

Fixes: b29fcfb54cd7 ("mptcp: full disconnect implementation")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index bf92cee9b5cee39e2b0831b6f7e06ce013fb6913..6a817a13b1549c3397e8fa2e315448ce2770e195 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3142,7 +3142,16 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 	 * subflow
 	 */
 	mptcp_destroy_common(msk, MPTCP_CF_FASTCLOSE);
+
+	/* The first subflow is already in TCP_CLOSE status, the following
+	 * can't overlap with a fallback anymore
+	 */
+	spin_lock_bh(&msk->fallback_lock);
+	msk->allow_subflows = true;
+	msk->allow_infinite_fallback = true;
 	WRITE_ONCE(msk->flags, 0);
+	spin_unlock_bh(&msk->fallback_lock);
+
 	msk->cb_flags = 0;
 	msk->recovery = false;
 	WRITE_ONCE(msk->can_ack, false);

-- 
2.48.1