mptcp: subflow: add mptcp_subflow_init_cookie_req helper

Will be used to initialize the mptcp request socket when a MP_CAPABLE
request was handled in syncookie mode, i.e. when a TCP ACK containing a
MP_CAPABLE option is a valid syncookie value.

Normally (non-cookie case), MPTCP will generate a unique 32 bit connection
ID and stores it in the MPTCP token storage to be able to retrieve the
mptcp socket for subflow joining.

In syncookie case, we do not want to store any state, so just generate the
unique ID and use it in the reply.

This means there is a small window where another connection could generate
the same token.

When Cookie ACK comes back, we check that the token has not been registered
in the mean time.  If it was, the connection needs to fall back to TCP.

Changes in v2:
 - use req->syncookie instead of passing 'want_cookie' arg to ->init_req()
   (Eric Dumazet)

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 0 deletions

diff --git a/net/mptcp/token.c b/net/mptcp/token.c
index f82410c54653..8b47c4bb1c6b 100644
--- a/net/mptcp/token.c
+++ b/net/mptcp/token.c
@@ -204,6 +204,32 @@ void mptcp_token_accept(struct mptcp_subflow_request_sock *req,
 	spin_unlock_bh(&bucket->lock);
 }
 
+bool mptcp_token_exists(u32 token)
+{
+	struct hlist_nulls_node *pos;
+	struct token_bucket *bucket;
+	struct mptcp_sock *msk;
+	struct sock *sk;
+
+	rcu_read_lock();
+	bucket = token_bucket(token);
+
+again:
+	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
+		msk = mptcp_sk(sk);
+		if (READ_ONCE(msk->token) == token)
+			goto found;
+	}
+	if (get_nulls_value(pos) != (token & token_mask))
+		goto again;
+
+	rcu_read_unlock();
+	return false;
+found:
+	rcu_read_unlock();
+	return true;
+}
+
 /**
  * mptcp_token_get_sock - retrieve mptcp connection sock using its token
  * @token: token of the mptcp connection to retrieve