mptcp: fix 'use_ack' option access.

The mentioned RX option field is initialized only for DSS
packet, we must access it only if 'dss' is set too, or
the subflow will end-up in a bad status, leading to
RFC violations.

Fixes: d22f4988ffec ("mptcp: process MP_CAPABLE data option")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index ecf41d5..9486720 100644 (file)
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -695,7 +695,7 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *sk,
        if (TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1)
                return subflow->mp_capable;
 
-       if (mp_opt->use_ack) {
+       if (mp_opt->dss && mp_opt->use_ack) {
                /* subflows are fully established as soon as we get any
                 * additional ack.
                 */