[PATCH v2 mptcp-net 1/2] mptcp: do not fallback when OoO is present

[Paolo Abeni <pabeni@redhat.com>]

In case of DSS corruption, the MPTCP protocol tries to avoid the
subflow reset if fallback is possible. Such corruptions happen in
the receive path; to ensure fallback is possible the stack additionally
need to check for OoO data, otherwise the fallback will break the data
stream.

Fixes: e32d262c89e2 ("mptcp: handle consistently DSS corruption")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/598
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
Note: this does not avoid the WARN(), but fixes the inconsistend
read() behavior; the ingress data is OoO, we should not ack it
---
 net/mptcp/protocol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index d6b08e1de358..7b966f105f89 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -646,7 +646,8 @@ static void mptcp_check_data_fin(struct sock *sk)
 
 static void mptcp_dss_corruption(struct mptcp_sock *msk, struct sock *ssk)
 {
-	if (!mptcp_try_fallback(ssk, MPTCP_MIB_DSSCORRUPTIONFALLBACK)) {
+	if (!RB_EMPTY_ROOT(&msk->out_of_order_queue) ||
+	    !mptcp_try_fallback(ssk, MPTCP_MIB_DSSCORRUPTIONFALLBACK)) {
 		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSCORRUPTIONRESET);
 		mptcp_subflow_reset(ssk);
 	}
-- 
2.51.1