// SPDX-License-Identifier: GPL-2.0

  #include <linux/crypto.h>

  #include <linux/err.h>

  #include <linux/init.h>
  #include <linux/kernel.h>

  #include <linux/list.h>
  #include <linux/tcp.h>
  #include <linux/rcupdate.h>
  #include <linux/rculist.h>
  #include <net/inetpeer.h>
  #include <net/tcp.h>

  void tcp_fastopen_init_key_once(struct net *net)

  {

  	u8 key[TCP_FASTOPEN_KEY_LENGTH];
  	struct tcp_fastopen_context *ctxt;
  
  	rcu_read_lock();
  	ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
  	if (ctxt) {
  		rcu_read_unlock();
  		return;
  	}
  	rcu_read_unlock();

  
  	/* tcp_fastopen_reset_cipher publishes the new context
  	 * atomically, so we allow this race happening here.
  	 *
  	 * All call sites of tcp_fastopen_cookie_gen also check
  	 * for a valid cookie, so this is an acceptable risk.
  	 */

  	get_random_bytes(key, sizeof(key));

  	tcp_fastopen_reset_cipher(net, NULL, key, NULL);

  }

  static void tcp_fastopen_ctx_free(struct rcu_head *head)
  {
  	struct tcp_fastopen_context *ctx =
  	    container_of(head, struct tcp_fastopen_context, rcu);

  	kzfree(ctx);

  }

  void tcp_fastopen_destroy_cipher(struct sock *sk)
  {
  	struct tcp_fastopen_context *ctx;
  
  	ctx = rcu_dereference_protected(
  			inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
  	if (ctx)
  		call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
  }

  void tcp_fastopen_ctx_destroy(struct net *net)
  {
  	struct tcp_fastopen_context *ctxt;
  
  	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
  
  	ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
  				lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
  	rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
  	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
  
  	if (ctxt)
  		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
  }

  int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,

  			      void *primary_key, void *backup_key)

  {

  	struct tcp_fastopen_context *ctx, *octx;

  	struct fastopen_queue *q;

  	int err = 0;

  	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
  	if (!ctx) {
  		err = -ENOMEM;

  		goto out;

  	}

  	ctx->key[0].key[0] = get_unaligned_le64(primary_key);
  	ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);

  	if (backup_key) {

  		ctx->key[1].key[0] = get_unaligned_le64(backup_key);
  		ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);

  		ctx->num = 2;
  	} else {
  		ctx->num = 1;
  	}

  	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);

  	if (sk) {
  		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;

  		octx = rcu_dereference_protected(q->ctx,

  			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));

  		rcu_assign_pointer(q->ctx, ctx);

  	} else {

  		octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
  			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
  		rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);

  	}

  	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);

  
  	if (octx)
  		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);

  out:

  	return err;
  }

  static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
  					     struct sk_buff *syn,

  					     const siphash_key_t *key,

  					     struct tcp_fastopen_cookie *foc)

  {

  	BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));

  	if (req->rsk_ops->family == AF_INET) {
  		const struct iphdr *iph = ip_hdr(syn);

  		foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
  					  sizeof(iph->saddr) +
  					  sizeof(iph->daddr),
  					  key));

  		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
  		return true;
  	}

  #if IS_ENABLED(CONFIG_IPV6)
  	if (req->rsk_ops->family == AF_INET6) {
  		const struct ipv6hdr *ip6h = ipv6_hdr(syn);

  		foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
  					  sizeof(ip6h->saddr) +
  					  sizeof(ip6h->daddr),
  					  key));

  		foc->len = TCP_FASTOPEN_COOKIE_SIZE;

  		return true;

  	}

  #endif
  	return false;

  }

  /* Generate the fastopen cookie by applying SipHash to both the source and
   * destination addresses.

   */

  static void tcp_fastopen_cookie_gen(struct sock *sk,

  				    struct request_sock *req,

  				    struct sk_buff *syn,
  				    struct tcp_fastopen_cookie *foc)
  {

  	struct tcp_fastopen_context *ctx;

  	rcu_read_lock();

  	ctx = tcp_fastopen_get_ctx(sk);

  	if (ctx)

  		__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);

  	rcu_read_unlock();

  }

  /* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
   * queue this additional data / FIN.
   */
  void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
  		return;
  
  	skb = skb_clone(skb, GFP_ATOMIC);
  	if (!skb)
  		return;
  
  	skb_dst_drop(skb);

  	/* segs_in has been initialized to 1 in tcp_create_openreq_child().
  	 * Hence, reset segs_in to 0 before calling tcp_segs_in()
  	 * to avoid double counting.  Also, tcp_segs_in() expects
  	 * skb->len to include the tcp_hdrlen.  Hence, it should
  	 * be called before __skb_pull().
  	 */
  	tp->segs_in = 0;
  	tcp_segs_in(tp, skb);

  	__skb_pull(skb, tcp_hdrlen(skb));

  	sk_forced_mem_schedule(sk, skb->truesize);

  	skb_set_owner_r(skb, sk);

  	TCP_SKB_CB(skb)->seq++;
  	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;

  	tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
  	__skb_queue_tail(&sk->sk_receive_queue, skb);
  	tp->syn_data_acked = 1;
  
  	/* u64_stats_update_begin(&tp->syncp) not needed here,
  	 * as we certainly are not changing upper 32bit value (0)
  	 */
  	tp->bytes_received = skb->len;

  
  	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
  		tcp_fin(sk);

  }

  /* returns 0 - no key match, 1 for primary, 2 for backup */
  static int tcp_fastopen_cookie_gen_check(struct sock *sk,
  					 struct request_sock *req,
  					 struct sk_buff *syn,
  					 struct tcp_fastopen_cookie *orig,
  					 struct tcp_fastopen_cookie *valid_foc)
  {
  	struct tcp_fastopen_cookie search_foc = { .len = -1 };
  	struct tcp_fastopen_cookie *foc = valid_foc;
  	struct tcp_fastopen_context *ctx;
  	int i, ret = 0;
  
  	rcu_read_lock();
  	ctx = tcp_fastopen_get_ctx(sk);
  	if (!ctx)
  		goto out;
  	for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {

  		__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);

  		if (tcp_fastopen_cookie_match(foc, orig)) {
  			ret = i + 1;
  			goto out;
  		}
  		foc = &search_foc;
  	}
  out:
  	rcu_read_unlock();
  	return ret;
  }

  static struct sock *tcp_fastopen_create_child(struct sock *sk,
  					      struct sk_buff *skb,

  					      struct request_sock *req)

  {

  	struct tcp_sock *tp;

  	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;

  	struct sock *child;

  	bool own_req;

  	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
  							 NULL, &own_req);

  	if (!child)

  		return NULL;

  	spin_lock(&queue->fastopenq.lock);
  	queue->fastopenq.qlen++;
  	spin_unlock(&queue->fastopenq.lock);

  
  	/* Initialize the child socket. Have to fix some values to take
  	 * into account the child is a Fast Open socket and is created
  	 * only out of the bits carried in the SYN packet.
  	 */
  	tp = tcp_sk(child);

  	rcu_assign_pointer(tp->fastopen_rsk, req);

  	tcp_rsk(req)->tfo_listener = true;

  
  	/* RFC1323: The window in SYN & SYN/ACK segments is never
  	 * scaled. So correct it appropriately.
  	 */
  	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);

  	tp->max_window = tp->snd_wnd;

  
  	/* Activate the retrans timer so that SYNACK can be retransmitted.

  	 * The request socket is not added to the ehash

  	 * because it's been added to the accept queue directly.
  	 */
  	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
  				  TCP_TIMEOUT_INIT, TCP_RTO_MAX);

  	refcount_set(&req->rsk_refcnt, 2);

  
  	/* Now finish processing the fastopen child socket. */

  	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);

  	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
  
  	tcp_fastopen_add_skb(child, skb);
  
  	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;

  	tp->rcv_wup = tp->rcv_nxt;

  	/* tcp_conn_request() is sending the SYNACK,
  	 * and queues the child into listener accept queue.

  	 */

  	return child;

  }

  
  static bool tcp_fastopen_queue_check(struct sock *sk)
  {
  	struct fastopen_queue *fastopenq;
  
  	/* Make sure the listener has enabled fastopen, and we don't
  	 * exceed the max # of pending TFO requests allowed before trying
  	 * to validating the cookie in order to avoid burning CPU cycles
  	 * unnecessarily.
  	 *
  	 * XXX (TFO) - The implication of checking the max_qlen before
  	 * processing a cookie request is that clients can't differentiate
  	 * between qlen overflow causing Fast Open to be disabled
  	 * temporarily vs a server not supporting Fast Open at all.
  	 */

  	fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
  	if (fastopenq->max_qlen == 0)

  		return false;
  
  	if (fastopenq->qlen >= fastopenq->max_qlen) {
  		struct request_sock *req1;
  		spin_lock(&fastopenq->lock);
  		req1 = fastopenq->rskq_rst_head;

  		if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {

  			__NET_INC_STATS(sock_net(sk),
  					LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);

  			spin_unlock(&fastopenq->lock);

  			return false;
  		}
  		fastopenq->rskq_rst_head = req1->dl_next;
  		fastopenq->qlen--;
  		spin_unlock(&fastopenq->lock);

  		reqsk_put(req1);

  	}
  	return true;
  }

  static bool tcp_fastopen_no_cookie(const struct sock *sk,
  				   const struct dst_entry *dst,
  				   int flag)
  {
  	return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
  	       tcp_sk(sk)->fastopen_no_cookie ||
  	       (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
  }

  /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
   * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
   * cookie request (foc->len == 0).
   */

  struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
  			      struct request_sock *req,

  			      struct tcp_fastopen_cookie *foc,
  			      const struct dst_entry *dst)

  {

  	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;

  	int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
  	struct tcp_fastopen_cookie valid_foc = { .len = -1 };

  	struct sock *child;

  	int ret = 0;

  	if (foc->len == 0) /* Client requests a cookie */

  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);

  	if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&

  	      (syn_data || foc->len >= 0) &&
  	      tcp_fastopen_queue_check(sk))) {
  		foc->len = -1;

  		return NULL;

  	}

  	if (syn_data &&
  	    tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))

  		goto fastopen;

  	if (foc->len == 0) {
  		/* Client requests a cookie. */
  		tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc);
  	} else if (foc->len > 0) {
  		ret = tcp_fastopen_cookie_gen_check(sk, req, skb, foc,
  						    &valid_foc);
  		if (!ret) {
  			NET_INC_STATS(sock_net(sk),
  				      LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
  		} else {
  			/* Cookie is valid. Create a (full) child socket to
  			 * accept the data in SYN before returning a SYN-ACK to
  			 * ack the data. If we fail to create the socket, fall
  			 * back and ack the ISN only but includes the same
  			 * cookie.
  			 *
  			 * Note: Data-less SYN with valid cookie is allowed to
  			 * send data in SYN_RECV state.
  			 */

  fastopen:

  			child = tcp_fastopen_create_child(sk, skb, req);
  			if (child) {
  				if (ret == 2) {
  					valid_foc.exp = foc->exp;
  					*foc = valid_foc;
  					NET_INC_STATS(sock_net(sk),
  						      LINUX_MIB_TCPFASTOPENPASSIVEALTKEY);
  				} else {
  					foc->len = -1;
  				}
  				NET_INC_STATS(sock_net(sk),
  					      LINUX_MIB_TCPFASTOPENPASSIVE);
  				return child;
  			}

  			NET_INC_STATS(sock_net(sk),

  				      LINUX_MIB_TCPFASTOPENPASSIVEFAIL);

  		}

  	}

  	valid_foc.exp = foc->exp;

  	*foc = valid_foc;

  	return NULL;

  }

  
  bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
  			       struct tcp_fastopen_cookie *cookie)
  {

  	const struct dst_entry *dst;

  	tcp_fastopen_cache_get(sk, mss, cookie);

  
  	/* Firewall blackhole issue check */
  	if (tcp_fastopen_active_should_disable(sk)) {
  		cookie->len = -1;
  		return false;
  	}

  	dst = __sk_dst_get(sk);
  
  	if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {

  		cookie->len = -1;
  		return true;
  	}
  	return cookie->len > 0;
  }

  
  /* This function checks if we want to defer sending SYN until the first
   * write().  We defer under the following conditions:
   * 1. fastopen_connect sockopt is set
   * 2. we have a valid cookie
   * Return value: return true if we want to defer until application writes data
   *               return false if we want to send out SYN immediately
   */
  bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
  {
  	struct tcp_fastopen_cookie cookie = { .len = 0 };
  	struct tcp_sock *tp = tcp_sk(sk);
  	u16 mss;
  
  	if (tp->fastopen_connect && !tp->fastopen_req) {
  		if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
  			inet_sk(sk)->defer_connect = 1;
  			return true;
  		}
  
  		/* Alloc fastopen_req in order for FO option to be included
  		 * in SYN
  		 */
  		tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
  					   sk->sk_allocation);
  		if (tp->fastopen_req)
  			tp->fastopen_req->cookie = cookie;
  		else
  			*err = -ENOBUFS;
  	}
  	return false;
  }
  EXPORT_SYMBOL(tcp_fastopen_defer_connect);

  
  /*
   * The following code block is to deal with middle box issues with TFO:
   * Middlebox firewall issues can potentially cause server's data being
   * blackholed after a successful 3WHS using TFO.
   * The proposed solution is to disable active TFO globally under the
   * following circumstances:
   *   1. client side TFO socket receives out of order FIN
   *   2. client side TFO socket receives out of order RST

   *   3. client side TFO socket has timed out three times consecutively during
   *      or after handshake

   * We disable active side TFO globally for 1hr at first. Then if it
   * happens again, we disable it for 2h, then 4h, 8h, ...
   * And we reset the timeout back to 1hr when we see a successful active
   * TFO connection with data exchanges.
   */

  /* Disable active TFO and record current jiffies and
   * tfo_active_disable_times
   */

  void tcp_fastopen_active_disable(struct sock *sk)

  {

  	struct net *net = sock_net(sk);

  	atomic_inc(&net->ipv4.tfo_active_disable_times);
  	net->ipv4.tfo_active_disable_stamp = jiffies;
  	NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);

  }
  
  /* Calculate timeout for tfo active disable
   * Return true if we are still in the active TFO disable period
   * Return false if timeout already expired and we should use active TFO
   */
  bool tcp_fastopen_active_should_disable(struct sock *sk)
  {

  	unsigned int tfo_bh_timeout = sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout;
  	int tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);

  	unsigned long timeout;

  	int multiplier;

  
  	if (!tfo_da_times)
  		return false;
  
  	/* Limit timout to max: 2^6 * initial timeout */
  	multiplier = 1 << min(tfo_da_times - 1, 6);

  	timeout = multiplier * tfo_bh_timeout * HZ;
  	if (time_before(jiffies, sock_net(sk)->ipv4.tfo_active_disable_stamp + timeout))

  		return true;
  
  	/* Mark check bit so we can check for successful active TFO
  	 * condition and reset tfo_active_disable_times
  	 */
  	tcp_sk(sk)->syn_fastopen_ch = 1;
  	return false;
  }
  
  /* Disable active TFO if FIN is the only packet in the ofo queue
   * and no data is received.
   * Also check if we can reset tfo_active_disable_times if data is
   * received successfully on a marked active TFO sockets opened on
   * a non-loopback interface
   */
  void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);

  	struct dst_entry *dst;

  	struct sk_buff *skb;

  
  	if (!tp->syn_fastopen)
  		return;
  
  	if (!tp->data_segs_in) {

  		skb = skb_rb_first(&tp->out_of_order_queue);
  		if (skb && !skb_rb_next(skb)) {

  			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {

  				tcp_fastopen_active_disable(sk);

  				return;
  			}
  		}
  	} else if (tp->syn_fastopen_ch &&

  		   atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {

  		dst = sk_dst_get(sk);
  		if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))

  			atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);

  		dst_release(dst);
  	}
  }

  
  void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
  {
  	u32 timeouts = inet_csk(sk)->icsk_retransmits;
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	/* Broken middle-boxes may black-hole Fast Open connection during or
  	 * even after the handshake. Be extremely conservative and pause
  	 * Fast Open globally after hitting the third consecutive timeout or
  	 * exceeding the configured timeout limit.
  	 */
  	if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
  	    (timeouts == 2 || (timeouts < 2 && expired))) {
  		tcp_fastopen_active_disable(sk);
  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
  	}
  }