mptcp: always include dack if possible. (2398e399) · Commits · 戴 / test

Currently passive MPTCP socket can skip including the DACK option - if the peer sends data before accept() completes. The above happens because the msk 'can_ack' flag is set only after the accept() call. Such missing DACK option may cause - as per RFC spec - unwanted fallback to TCP. This change addresses the issue using the key material available in the current subflow, if any, to create a suitable dack option when msk ack seq is not yet available. v1 -> v2: - adavance the generated ack after the initial MPC packet Fixes: ("mptcp: process MP_CAPABLE data option") Signed-off-by:

Paolo Abeni <pabeni@redhat.com> Reviewed-by:

Mat Martineau <mathew.j.martineau@linux.intel.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/mptcp/options.c

+17 −2

Original line number	Diff line number	Diff line
		@@ -334,6 +334,8 @@ static bool mptcp_established_options_dss(struct sock sk, struct sk_buff skb,
		struct mptcp_sock *msk;
		unsigned int ack_size;
		bool ret = false;
		bool can_ack;
		u64 ack_seq;
		u8 tcp_fin;

		if (skb) {
		@@ -360,9 +362,22 @@ static bool mptcp_established_options_dss(struct sock sk, struct sk_buff skb,
		ret = true;
		}

		/* passive sockets msk will set the 'can_ack' after accept(), even
		* if the first subflow may have the already the remote key handy
		*/
		can_ack = true;
		opts->ext_copy.use_ack = 0;
		msk = mptcp_sk(subflow->conn);
		if (!msk \|\| !READ_ONCE(msk->can_ack)) {
		if (likely(msk && READ_ONCE(msk->can_ack))) {
		ack_seq = msk->ack_seq;
		} else if (subflow->can_ack) {
		mptcp_crypto_key_sha(subflow->remote_key, NULL, &ack_seq);
		ack_seq++;
		} else {
		can_ack = false;
		}

		if (unlikely(!can_ack)) {
		*size = ALIGN(dss_size, 4);
		return ret;
		}
		@@ -375,7 +390,7 @@ static bool mptcp_established_options_dss(struct sock sk, struct sk_buff skb,

		dss_size += ack_size;

		opts->ext_copy.data_ack = msk->ack_seq;
		opts->ext_copy.data_ack = ack_seq;
		opts->ext_copy.ack64 = 1;
		opts->ext_copy.use_ack = 1;

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