[MPTCP] Re: [PATCH RFC 07/11] mptcp: subflow: add mptcp_subflow_init_cookie_req helper

[Christoph Paasch <cpaasch at apple.com>]

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On 07/14/20 - 20:25, Florian Westphal wrote:
> 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.
> 
> Signed-off-by: Florian Westphal <fw(a)strlen.de>
> ---
>  include/linux/tcp.h |  1 +
>  include/net/mptcp.h | 10 +++++++++
>  net/mptcp/subflow.c | 53 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 64 insertions(+)
> 
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 3bdec31ce8f4..1f706157b551 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -118,6 +118,7 @@ struct tcp_request_sock {
>  	struct inet_request_sock 	req;
>  	const struct tcp_request_sock_ops *af_specific;
>  	u64				snt_synack; /* first SYNACK sent time */
> +	u8				syncookie:1;

As this field will only be used in init_req, would it make sense to rather
pass want_cookie from tcp_conn_request as an argument to the callback?


Christoph

>  	bool				tfo_listener;
>  	bool				is_mptcp;
>  #if IS_ENABLED(CONFIG_MPTCP)
> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> index 985344512f31..653acfe58d04 100644
> --- a/include/net/mptcp.h
> +++ b/include/net/mptcp.h
> @@ -131,6 +131,9 @@ static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
>  }
>  
>  void mptcp_seq_show(struct seq_file *seq);
> +int mptcp_subflow_init_cookie_req(struct request_sock *req,
> +				  const struct sock *sk_listener,
> +				  struct sk_buff *skb);
>  #else
>  
>  static inline void mptcp_init(void)
> @@ -204,6 +207,13 @@ static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
>  
>  static inline void mptcp_space(const struct sock *ssk, int *s, int *fs) { }
>  static inline void mptcp_seq_show(struct seq_file *seq) { }
> +
> +static inline int mptcp_subflow_init_cookie_req(struct request_sock *req,
> +						const struct sock *sk_listener,
> +						struct sk_buff *skb)
> +{
> +	return 0; /* TCP fallback */
> +}
>  #endif /* CONFIG_MPTCP */
>  
>  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index cc9eaec14037..943fa650f1e9 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -154,6 +154,20 @@ static void subflow_init_req(struct request_sock *req,
>  			get_random_bytes(&subflow_req->local_key, sizeof(subflow_req->local_key));
>  		} while (subflow_req->local_key == 0);
>  
> +		if (unlikely(tcp_rsk(req)->syncookie)) {
> +			mptcp_crypto_key_sha(subflow_req->local_key,
> +					     &subflow_req->token,
> +					     &subflow_req->idsn);
> +			if (mptcp_token_get_sock(subflow_req->token)) {
> +				if (retries-- > 0)
> +					goto again;
> +			} else {
> +				subflow_req->mp_capable = 1;
> +			}
> +			subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
> +			return;
> +		}
> +
>  		err = mptcp_token_new_request(req);
>  		if (err == 0)
>  			subflow_req->mp_capable = 1;
> @@ -174,6 +188,45 @@ static void subflow_init_req(struct request_sock *req,
>  	}
>  }
>  
> +int mptcp_subflow_init_cookie_req(struct request_sock *req,
> +				  const struct sock *sk_listener,
> +				  struct sk_buff *skb)
> +{
> +	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
> +	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
> +	struct mptcp_options_received mp_opt;
> +	int ret;
> +
> +	ret = __subflow_init_req(req, sk_listener);
> +	if (ret)
> +		return ret;
> +
> +	mptcp_get_options(skb, &mp_opt);
> +	ret = __subflow_check_options(&mp_opt, req);
> +	if (ret)
> +		return ret;
> +
> +	if (mp_opt.mp_capable && listener->request_mptcp) {
> +		int err;
> +
> +		if (mp_opt.sndr_key == 0)
> +			return -EINVAL;
> +
> +		subflow_req->local_key = mp_opt.rcvr_key;
> +		err = mptcp_token_new_request(req);
> +		if (err)
> +			return err;
> +
> +		subflow_req->mp_capable = 1;
> +		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
> +	}
> +	/* JOIN cannot be handled via cookies due to need
> +	 * to store the remote peer nonce value.
> +	 */
> +
> +	return 0;
> +}
> +
>  static void subflow_v4_init_req(struct request_sock *req,
>  				const struct sock *sk_listener,
>  				struct sk_buff *skb)
> -- 
> 2.26.2
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