[PATCH net v2 4/5] mptcp: fix 'use_ack' option access.

[Paolo Abeni]

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 <pab...@redhat.com>
---
 net/mptcp/options.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index ecf41d52d2fc..9486720c3256 100644
--- 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.
                 */
-- 
2.21.1