netdev - [PATCH net-next 6/8] subflow: explicitly check for plain tcp rsk

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Date:   Thu, 23 Jul 2020 13:02:34 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>, mptcp@...ts.01.org
Subject: [PATCH net-next 6/8] subflow: explicitly check for plain tcp rsk

When syncookie are in use, the TCP stack may feed into
subflow_syn_recv_sock() plain TCP request sockets. We can't
access mptcp_subflow_request_sock-specific fields on such
sockets. Explicitly check the rsk ops to do safe accesses.

Reviewed-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
Tested-by: Christoph Paasch <cpaasch@...le.com>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/mptcp/subflow.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 7f3ef1840df5..3ef445f59556 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -415,7 +415,7 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,

 	/* hopefully temporary handling for MP_JOIN+syncookie */
 	subflow_req = mptcp_subflow_rsk(req);
-	fallback_is_fatal = subflow_req->mp_join;
+	fallback_is_fatal = tcp_rsk(req)->is_mptcp && subflow_req->mp_join;
 	fallback = !tcp_rsk(req)->is_mptcp;
 	if (fallback)
 		goto create_child;
-- 
2.26.2