/*
   * INET		An implementation of the TCP/IP protocol suite for the LINUX
   *		operating system.  INET is implemented using the  BSD Socket
   *		interface as the means of communication with the user level.
   *
   *		Implementation of the Transmission Control Protocol(TCP).
   *

   *		IPv4 specific functions
   *
   *
   *		code split from:
   *		linux/ipv4/tcp.c
   *		linux/ipv4/tcp_input.c
   *		linux/ipv4/tcp_output.c
   *
   *		See tcp.c for author information
   *
   *	This program is free software; you can redistribute it and/or
   *      modify it under the terms of the GNU General Public License
   *      as published by the Free Software Foundation; either version
   *      2 of the License, or (at your option) any later version.
   */
  
  /*
   * Changes:
   *		David S. Miller	:	New socket lookup architecture.
   *					This code is dedicated to John Dyson.
   *		David S. Miller :	Change semantics of established hash,
   *					half is devoted to TIME_WAIT sockets
   *					and the rest go in the other half.
   *		Andi Kleen :		Add support for syncookies and fixed
   *					some bugs: ip options weren't passed to
   *					the TCP layer, missed a check for an
   *					ACK bit.
   *		Andi Kleen :		Implemented fast path mtu discovery.
   *	     				Fixed many serious bugs in the

   *					request_sock handling and moved

   *					most of it into the af independent code.
   *					Added tail drop and some other bugfixes.

   *					Added new listen semantics.

   *		Mike McLagan	:	Routing by source
   *	Juan Jose Ciarlante:		ip_dynaddr bits
   *		Andi Kleen:		various fixes.
   *	Vitaly E. Lavrov	:	Transparent proxy revived after year
   *					coma.
   *	Andi Kleen		:	Fix new listen.
   *	Andi Kleen		:	Fix accept error reporting.
   *	YOSHIFUJI Hideaki @USAGI and:	Support IPV6_V6ONLY socket option, which
   *	Alexey Kuznetsov		allow both IPv4 and IPv6 sockets to bind
   *					a single port at the same time.
   */

  #include <linux/bottom_half.h>

  #include <linux/types.h>
  #include <linux/fcntl.h>
  #include <linux/module.h>
  #include <linux/random.h>
  #include <linux/cache.h>
  #include <linux/jhash.h>
  #include <linux/init.h>
  #include <linux/times.h>

  #include <linux/slab.h>

  #include <net/net_namespace.h>

  #include <net/icmp.h>

  #include <net/inet_hashtables.h>

  #include <net/tcp.h>

  #include <net/transp_v6.h>

  #include <net/ipv6.h>
  #include <net/inet_common.h>

  #include <net/timewait_sock.h>

  #include <net/xfrm.h>

  #include <net/netdma.h>

  #include <net/secure_seq.h>

  
  #include <linux/inet.h>
  #include <linux/ipv6.h>
  #include <linux/stddef.h>
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>

  #include <linux/crypto.h>
  #include <linux/scatterlist.h>

  int sysctl_tcp_tw_reuse __read_mostly;
  int sysctl_tcp_low_latency __read_mostly;

  EXPORT_SYMBOL(sysctl_tcp_low_latency);

  #ifdef CONFIG_TCP_MD5SIG

  static struct tcp_md5sig_key *tcp_v4_md5_do_lookup(struct sock *sk,
  						   __be32 addr);

  static int tcp_v4_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,

  			       __be32 daddr, __be32 saddr, const struct tcphdr *th);

  #else
  static inline
  struct tcp_md5sig_key *tcp_v4_md5_do_lookup(struct sock *sk, __be32 addr)
  {
  	return NULL;
  }

  #endif

  struct inet_hashinfo tcp_hashinfo;

  EXPORT_SYMBOL(tcp_hashinfo);

  static inline __u32 tcp_v4_init_sequence(const struct sk_buff *skb)

  {

  	return secure_tcp_sequence_number(ip_hdr(skb)->daddr,
  					  ip_hdr(skb)->saddr,

  					  tcp_hdr(skb)->dest,
  					  tcp_hdr(skb)->source);

  }

  int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
  {
  	const struct tcp_timewait_sock *tcptw = tcp_twsk(sktw);
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	/* With PAWS, it is safe from the viewpoint
  	   of data integrity. Even without PAWS it is safe provided sequence
  	   spaces do not overlap i.e. at data rates <= 80Mbit/sec.
  
  	   Actually, the idea is close to VJ's one, only timestamp cache is
  	   held not per host, but per port pair and TW bucket is used as state
  	   holder.
  
  	   If TW bucket has been already destroyed we fall back to VJ's scheme
  	   and use initial timestamp retrieved from peer table.
  	 */
  	if (tcptw->tw_ts_recent_stamp &&
  	    (twp == NULL || (sysctl_tcp_tw_reuse &&

  			     get_seconds() - tcptw->tw_ts_recent_stamp > 1))) {

  		tp->write_seq = tcptw->tw_snd_nxt + 65535 + 2;
  		if (tp->write_seq == 0)
  			tp->write_seq = 1;
  		tp->rx_opt.ts_recent	   = tcptw->tw_ts_recent;
  		tp->rx_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
  		sock_hold(sktw);
  		return 1;
  	}
  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(tcp_twsk_unique);

  /* This will initiate an outgoing connection. */
  int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
  {

  	struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;

  	struct inet_sock *inet = inet_sk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);

  	__be16 orig_sport, orig_dport;

  	__be32 daddr, nexthop;

  	struct flowi4 *fl4;

  	struct rtable *rt;

  	int err;

  	struct ip_options_rcu *inet_opt;

  
  	if (addr_len < sizeof(struct sockaddr_in))
  		return -EINVAL;
  
  	if (usin->sin_family != AF_INET)
  		return -EAFNOSUPPORT;
  
  	nexthop = daddr = usin->sin_addr.s_addr;

  	inet_opt = rcu_dereference_protected(inet->inet_opt,
  					     sock_owned_by_user(sk));
  	if (inet_opt && inet_opt->opt.srr) {

  		if (!daddr)
  			return -EINVAL;

  		nexthop = inet_opt->opt.faddr;

  	}

  	orig_sport = inet->inet_sport;
  	orig_dport = usin->sin_port;

  	fl4 = &inet->cork.fl.u.ip4;
  	rt = ip_route_connect(fl4, nexthop, inet->inet_saddr,

  			      RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
  			      IPPROTO_TCP,
  			      orig_sport, orig_dport, sk, true);
  	if (IS_ERR(rt)) {
  		err = PTR_ERR(rt);
  		if (err == -ENETUNREACH)

  			IP_INC_STATS_BH(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);

  		return err;

  	}

  
  	if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) {
  		ip_rt_put(rt);
  		return -ENETUNREACH;
  	}

  	if (!inet_opt || !inet_opt->opt.srr)

  		daddr = fl4->daddr;

  	if (!inet->inet_saddr)

  		inet->inet_saddr = fl4->saddr;

  	inet->inet_rcv_saddr = inet->inet_saddr;

  	if (tp->rx_opt.ts_recent_stamp && inet->inet_daddr != daddr) {

  		/* Reset inherited state */
  		tp->rx_opt.ts_recent	   = 0;
  		tp->rx_opt.ts_recent_stamp = 0;
  		tp->write_seq		   = 0;
  	}

  	if (tcp_death_row.sysctl_tw_recycle &&

  	    !tp->rx_opt.ts_recent_stamp && fl4->daddr == daddr) {

  		struct inet_peer *peer = rt_get_peer(rt, fl4->daddr);

  		/*
  		 * VJ's idea. We save last timestamp seen from
  		 * the destination in peer table, when entering state
  		 * TIME-WAIT * and initialize rx_opt.ts_recent from it,
  		 * when trying new connection.

  		 */

  		if (peer) {
  			inet_peer_refcheck(peer);
  			if ((u32)get_seconds() - peer->tcp_ts_stamp <= TCP_PAWS_MSL) {
  				tp->rx_opt.ts_recent_stamp = peer->tcp_ts_stamp;
  				tp->rx_opt.ts_recent = peer->tcp_ts;
  			}

  		}
  	}

  	inet->inet_dport = usin->sin_port;
  	inet->inet_daddr = daddr;

  	inet_csk(sk)->icsk_ext_hdr_len = 0;

  	if (inet_opt)
  		inet_csk(sk)->icsk_ext_hdr_len = inet_opt->opt.optlen;

  	tp->rx_opt.mss_clamp = TCP_MSS_DEFAULT;

  
  	/* Socket identity is still unknown (sport may be zero).
  	 * However we set state to SYN-SENT and not releasing socket
  	 * lock select source port, enter ourselves into the hash tables and
  	 * complete initialization after this.
  	 */
  	tcp_set_state(sk, TCP_SYN_SENT);

  	err = inet_hash_connect(&tcp_death_row, sk);

  	if (err)
  		goto failure;

  	rt = ip_route_newports(fl4, rt, orig_sport, orig_dport,

  			       inet->inet_sport, inet->inet_dport, sk);
  	if (IS_ERR(rt)) {
  		err = PTR_ERR(rt);
  		rt = NULL;

  		goto failure;

  	}

  	/* OK, now commit destination to socket.  */

  	sk->sk_gso_type = SKB_GSO_TCPV4;

  	sk_setup_caps(sk, &rt->dst);

  
  	if (!tp->write_seq)

  		tp->write_seq = secure_tcp_sequence_number(inet->inet_saddr,
  							   inet->inet_daddr,
  							   inet->inet_sport,

  							   usin->sin_port);

  	inet->inet_id = tp->write_seq ^ jiffies;

  
  	err = tcp_connect(sk);
  	rt = NULL;
  	if (err)
  		goto failure;
  
  	return 0;
  
  failure:

  	/*
  	 * This unhashes the socket and releases the local port,
  	 * if necessary.
  	 */

  	tcp_set_state(sk, TCP_CLOSE);
  	ip_rt_put(rt);
  	sk->sk_route_caps = 0;

  	inet->inet_dport = 0;

  	return err;
  }

  EXPORT_SYMBOL(tcp_v4_connect);

  /*
   * This routine does path mtu discovery as defined in RFC1191.
   */

  static void do_pmtu_discovery(struct sock *sk, const struct iphdr *iph, u32 mtu)

  {
  	struct dst_entry *dst;
  	struct inet_sock *inet = inet_sk(sk);

  
  	/* We are not interested in TCP_LISTEN and open_requests (SYN-ACKs
  	 * send out by Linux are always <576bytes so they should go through
  	 * unfragmented).
  	 */
  	if (sk->sk_state == TCP_LISTEN)
  		return;
  
  	/* We don't check in the destentry if pmtu discovery is forbidden
  	 * on this route. We just assume that no packet_to_big packets
  	 * are send back when pmtu discovery is not active.

  	 * There is a small race when the user changes this flag in the

  	 * route, but I think that's acceptable.
  	 */
  	if ((dst = __sk_dst_check(sk, 0)) == NULL)
  		return;
  
  	dst->ops->update_pmtu(dst, mtu);
  
  	/* Something is about to be wrong... Remember soft error
  	 * for the case, if this connection will not able to recover.
  	 */
  	if (mtu < dst_mtu(dst) && ip_dont_fragment(sk, dst))
  		sk->sk_err_soft = EMSGSIZE;
  
  	mtu = dst_mtu(dst);
  
  	if (inet->pmtudisc != IP_PMTUDISC_DONT &&

  	    inet_csk(sk)->icsk_pmtu_cookie > mtu) {

  		tcp_sync_mss(sk, mtu);
  
  		/* Resend the TCP packet because it's
  		 * clear that the old packet has been
  		 * dropped. This is the new "fast" path mtu
  		 * discovery.
  		 */
  		tcp_simple_retransmit(sk);
  	} /* else let the usual retransmit timer handle it */
  }
  
  /*
   * This routine is called by the ICMP module when it gets some
   * sort of error condition.  If err < 0 then the socket should
   * be closed and the error returned to the user.  If err > 0
   * it's just the icmp type << 8 | icmp code.  After adjustment
   * header points to the first 8 bytes of the tcp header.  We need
   * to find the appropriate port.
   *
   * The locking strategy used here is very "optimistic". When
   * someone else accesses the socket the ICMP is just dropped
   * and for some paths there is no check at all.
   * A more general error queue to queue errors for later handling
   * is probably better.
   *
   */

  void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)

  {

  	const struct iphdr *iph = (const struct iphdr *)icmp_skb->data;

  	struct tcphdr *th = (struct tcphdr *)(icmp_skb->data + (iph->ihl << 2));

  	struct inet_connection_sock *icsk;

  	struct tcp_sock *tp;
  	struct inet_sock *inet;

  	const int type = icmp_hdr(icmp_skb)->type;
  	const int code = icmp_hdr(icmp_skb)->code;

  	struct sock *sk;

  	struct sk_buff *skb;

  	__u32 seq;

  	__u32 remaining;

  	int err;

  	struct net *net = dev_net(icmp_skb->dev);

  	if (icmp_skb->len < (iph->ihl << 2) + 8) {

  		ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);

  		return;
  	}

  	sk = inet_lookup(net, &tcp_hashinfo, iph->daddr, th->dest,

  			iph->saddr, th->source, inet_iif(icmp_skb));

  	if (!sk) {

  		ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);

  		return;
  	}
  	if (sk->sk_state == TCP_TIME_WAIT) {

  		inet_twsk_put(inet_twsk(sk));

  		return;
  	}
  
  	bh_lock_sock(sk);
  	/* If too many ICMPs get dropped on busy
  	 * servers this needs to be solved differently.
  	 */
  	if (sock_owned_by_user(sk))

  		NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);

  
  	if (sk->sk_state == TCP_CLOSE)
  		goto out;

  	if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) {
  		NET_INC_STATS_BH(net, LINUX_MIB_TCPMINTTLDROP);
  		goto out;
  	}

  	icsk = inet_csk(sk);

  	tp = tcp_sk(sk);
  	seq = ntohl(th->seq);
  	if (sk->sk_state != TCP_LISTEN &&
  	    !between(seq, tp->snd_una, tp->snd_nxt)) {

  		NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);

  		goto out;
  	}
  
  	switch (type) {
  	case ICMP_SOURCE_QUENCH:
  		/* Just silently ignore these. */
  		goto out;
  	case ICMP_PARAMETERPROB:
  		err = EPROTO;
  		break;
  	case ICMP_DEST_UNREACH:
  		if (code > NR_ICMP_UNREACH)
  			goto out;
  
  		if (code == ICMP_FRAG_NEEDED) { /* PMTU discovery (RFC1191) */
  			if (!sock_owned_by_user(sk))
  				do_pmtu_discovery(sk, iph, info);
  			goto out;
  		}
  
  		err = icmp_err_convert[code].errno;

  		/* check if icmp_skb allows revert of backoff
  		 * (see draft-zimmermann-tcp-lcd) */
  		if (code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH)
  			break;
  		if (seq != tp->snd_una  || !icsk->icsk_retransmits ||
  		    !icsk->icsk_backoff)
  			break;

  		if (sock_owned_by_user(sk))
  			break;

  		icsk->icsk_backoff--;

  		inet_csk(sk)->icsk_rto = (tp->srtt ? __tcp_set_rto(tp) :
  			TCP_TIMEOUT_INIT) << icsk->icsk_backoff;

  		tcp_bound_rto(sk);
  
  		skb = tcp_write_queue_head(sk);
  		BUG_ON(!skb);
  
  		remaining = icsk->icsk_rto - min(icsk->icsk_rto,
  				tcp_time_stamp - TCP_SKB_CB(skb)->when);
  
  		if (remaining) {
  			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
  						  remaining, TCP_RTO_MAX);

  		} else {
  			/* RTO revert clocked out retransmission.
  			 * Will retransmit now */
  			tcp_retransmit_timer(sk);
  		}

  		break;
  	case ICMP_TIME_EXCEEDED:
  		err = EHOSTUNREACH;
  		break;
  	default:
  		goto out;
  	}
  
  	switch (sk->sk_state) {

  		struct request_sock *req, **prev;

  	case TCP_LISTEN:
  		if (sock_owned_by_user(sk))
  			goto out;

  		req = inet_csk_search_req(sk, &prev, th->dest,
  					  iph->daddr, iph->saddr);

  		if (!req)
  			goto out;
  
  		/* ICMPs are not backlogged, hence we cannot get
  		   an established socket here.
  		 */

  		WARN_ON(req->sk);

  		if (seq != tcp_rsk(req)->snt_isn) {

  			NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);

  			goto out;
  		}
  
  		/*
  		 * Still in SYN_RECV, just remove it silently.
  		 * There is no good way to pass the error to the newly
  		 * created socket, and POSIX does not want network
  		 * errors returned from accept().
  		 */

  		inet_csk_reqsk_queue_drop(sk, req, prev);

  		goto out;
  
  	case TCP_SYN_SENT:
  	case TCP_SYN_RECV:  /* Cannot happen.
  			       It can f.e. if SYNs crossed.
  			     */
  		if (!sock_owned_by_user(sk)) {

  			sk->sk_err = err;
  
  			sk->sk_error_report(sk);
  
  			tcp_done(sk);
  		} else {
  			sk->sk_err_soft = err;
  		}
  		goto out;
  	}
  
  	/* If we've already connected we will keep trying
  	 * until we time out, or the user gives up.
  	 *
  	 * rfc1122 4.2.3.9 allows to consider as hard errors
  	 * only PROTO_UNREACH and PORT_UNREACH (well, FRAG_FAILED too,
  	 * but it is obsoleted by pmtu discovery).
  	 *
  	 * Note, that in modern internet, where routing is unreliable
  	 * and in each dark corner broken firewalls sit, sending random
  	 * errors ordered by their masters even this two messages finally lose
  	 * their original sense (even Linux sends invalid PORT_UNREACHs)
  	 *
  	 * Now we are in compliance with RFCs.
  	 *							--ANK (980905)
  	 */
  
  	inet = inet_sk(sk);
  	if (!sock_owned_by_user(sk) && inet->recverr) {
  		sk->sk_err = err;
  		sk->sk_error_report(sk);
  	} else	{ /* Only an error on timeout */
  		sk->sk_err_soft = err;
  	}
  
  out:
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }

  static void __tcp_v4_send_check(struct sk_buff *skb,
  				__be32 saddr, __be32 daddr)

  {

  	struct tcphdr *th = tcp_hdr(skb);

  	if (skb->ip_summed == CHECKSUM_PARTIAL) {

  		th->check = ~tcp_v4_check(skb->len, saddr, daddr, 0);

  		skb->csum_start = skb_transport_header(skb) - skb->head;

  		skb->csum_offset = offsetof(struct tcphdr, check);

  	} else {

  		th->check = tcp_v4_check(skb->len, saddr, daddr,

  					 csum_partial(th,

  						      th->doff << 2,
  						      skb->csum));
  	}
  }

  /* This routine computes an IPv4 TCP checksum. */

  void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb)

  {

  	const struct inet_sock *inet = inet_sk(sk);

  
  	__tcp_v4_send_check(skb, inet->inet_saddr, inet->inet_daddr);
  }

  EXPORT_SYMBOL(tcp_v4_send_check);

  int tcp_v4_gso_send_check(struct sk_buff *skb)
  {

  	const struct iphdr *iph;

  	struct tcphdr *th;
  
  	if (!pskb_may_pull(skb, sizeof(*th)))
  		return -EINVAL;

  	iph = ip_hdr(skb);

  	th = tcp_hdr(skb);

  
  	th->check = 0;

  	skb->ip_summed = CHECKSUM_PARTIAL;

  	__tcp_v4_send_check(skb, iph->saddr, iph->daddr);

  	return 0;
  }

  /*
   *	This routine will send an RST to the other tcp.
   *
   *	Someone asks: why I NEVER use socket parameters (TOS, TTL etc.)
   *		      for reset.
   *	Answer: if a packet caused RST, it is not for a socket
   *		existing in our system, if it is matched to a socket,
   *		it is just duplicate segment or bug in other side's TCP.
   *		So that we build reply only basing on parameters
   *		arrived with segment.
   *	Exception: precedence violation. We do not implement it in any case.
   */

  static void tcp_v4_send_reset(struct sock *sk, struct sk_buff *skb)

  {

  	const struct tcphdr *th = tcp_hdr(skb);

  	struct {
  		struct tcphdr th;
  #ifdef CONFIG_TCP_MD5SIG

  		__be32 opt[(TCPOLEN_MD5SIG_ALIGNED >> 2)];

  #endif
  	} rep;

  	struct ip_reply_arg arg;

  #ifdef CONFIG_TCP_MD5SIG
  	struct tcp_md5sig_key *key;
  #endif

  	struct net *net;

  
  	/* Never send a reset in response to a reset. */
  	if (th->rst)
  		return;

  	if (skb_rtable(skb)->rt_type != RTN_LOCAL)

  		return;
  
  	/* Swap the send and the receive. */

  	memset(&rep, 0, sizeof(rep));
  	rep.th.dest   = th->source;
  	rep.th.source = th->dest;
  	rep.th.doff   = sizeof(struct tcphdr) / 4;
  	rep.th.rst    = 1;

  
  	if (th->ack) {

  		rep.th.seq = th->ack_seq;

  	} else {

  		rep.th.ack = 1;
  		rep.th.ack_seq = htonl(ntohl(th->seq) + th->syn + th->fin +
  				       skb->len - (th->doff << 2));

  	}

  	memset(&arg, 0, sizeof(arg));

  	arg.iov[0].iov_base = (unsigned char *)&rep;
  	arg.iov[0].iov_len  = sizeof(rep.th);
  
  #ifdef CONFIG_TCP_MD5SIG

  	key = sk ? tcp_v4_md5_do_lookup(sk, ip_hdr(skb)->daddr) : NULL;

  	if (key) {
  		rep.opt[0] = htonl((TCPOPT_NOP << 24) |
  				   (TCPOPT_NOP << 16) |
  				   (TCPOPT_MD5SIG << 8) |
  				   TCPOLEN_MD5SIG);
  		/* Update length and the length the header thinks exists */
  		arg.iov[0].iov_len += TCPOLEN_MD5SIG_ALIGNED;
  		rep.th.doff = arg.iov[0].iov_len / 4;

  		tcp_v4_md5_hash_hdr((__u8 *) &rep.opt[1],

  				     key, ip_hdr(skb)->saddr,
  				     ip_hdr(skb)->daddr, &rep.th);

  	}
  #endif

  	arg.csum = csum_tcpudp_nofold(ip_hdr(skb)->daddr,
  				      ip_hdr(skb)->saddr, /* XXX */

  				      arg.iov[0].iov_len, IPPROTO_TCP, 0);

  	arg.csumoffset = offsetof(struct tcphdr, check) / 2;

  	arg.flags = (sk && inet_sk(sk)->transparent) ? IP_REPLY_ARG_NOSRCCHECK : 0;

  	net = dev_net(skb_dst(skb)->dev);

  	arg.tos = ip_hdr(skb)->tos;

  	ip_send_reply(net->ipv4.tcp_sock, skb, ip_hdr(skb)->saddr,

  		      &arg, arg.iov[0].iov_len);

  	TCP_INC_STATS_BH(net, TCP_MIB_OUTSEGS);
  	TCP_INC_STATS_BH(net, TCP_MIB_OUTRSTS);

  }
  
  /* The code following below sending ACKs in SYN-RECV and TIME-WAIT states
     outside socket context is ugly, certainly. What can I do?
   */

  static void tcp_v4_send_ack(struct sk_buff *skb, u32 seq, u32 ack,
  			    u32 win, u32 ts, int oif,

  			    struct tcp_md5sig_key *key,

  			    int reply_flags, u8 tos)

  {

  	const struct tcphdr *th = tcp_hdr(skb);

  	struct {
  		struct tcphdr th;

  		__be32 opt[(TCPOLEN_TSTAMP_ALIGNED >> 2)

  #ifdef CONFIG_TCP_MD5SIG

  			   + (TCPOLEN_MD5SIG_ALIGNED >> 2)

  #endif
  			];

  	} rep;
  	struct ip_reply_arg arg;

  	struct net *net = dev_net(skb_dst(skb)->dev);

  
  	memset(&rep.th, 0, sizeof(struct tcphdr));

  	memset(&arg, 0, sizeof(arg));

  
  	arg.iov[0].iov_base = (unsigned char *)&rep;
  	arg.iov[0].iov_len  = sizeof(rep.th);
  	if (ts) {

  		rep.opt[0] = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
  				   (TCPOPT_TIMESTAMP << 8) |
  				   TCPOLEN_TIMESTAMP);
  		rep.opt[1] = htonl(tcp_time_stamp);
  		rep.opt[2] = htonl(ts);

  		arg.iov[0].iov_len += TCPOLEN_TSTAMP_ALIGNED;

  	}
  
  	/* Swap the send and the receive. */
  	rep.th.dest    = th->source;
  	rep.th.source  = th->dest;
  	rep.th.doff    = arg.iov[0].iov_len / 4;
  	rep.th.seq     = htonl(seq);
  	rep.th.ack_seq = htonl(ack);
  	rep.th.ack     = 1;
  	rep.th.window  = htons(win);

  #ifdef CONFIG_TCP_MD5SIG

  	if (key) {
  		int offset = (ts) ? 3 : 0;
  
  		rep.opt[offset++] = htonl((TCPOPT_NOP << 24) |
  					  (TCPOPT_NOP << 16) |
  					  (TCPOPT_MD5SIG << 8) |
  					  TCPOLEN_MD5SIG);
  		arg.iov[0].iov_len += TCPOLEN_MD5SIG_ALIGNED;
  		rep.th.doff = arg.iov[0].iov_len/4;

  		tcp_v4_md5_hash_hdr((__u8 *) &rep.opt[offset],

  				    key, ip_hdr(skb)->saddr,
  				    ip_hdr(skb)->daddr, &rep.th);

  	}
  #endif

  	arg.flags = reply_flags;

  	arg.csum = csum_tcpudp_nofold(ip_hdr(skb)->daddr,
  				      ip_hdr(skb)->saddr, /* XXX */

  				      arg.iov[0].iov_len, IPPROTO_TCP, 0);
  	arg.csumoffset = offsetof(struct tcphdr, check) / 2;

  	if (oif)
  		arg.bound_dev_if = oif;

  	arg.tos = tos;

  	ip_send_reply(net->ipv4.tcp_sock, skb, ip_hdr(skb)->saddr,

  		      &arg, arg.iov[0].iov_len);

  	TCP_INC_STATS_BH(net, TCP_MIB_OUTSEGS);

  }
  
  static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
  {

  	struct inet_timewait_sock *tw = inet_twsk(sk);

  	struct tcp_timewait_sock *tcptw = tcp_twsk(sk);

  	tcp_v4_send_ack(skb, tcptw->tw_snd_nxt, tcptw->tw_rcv_nxt,

  			tcptw->tw_rcv_wnd >> tw->tw_rcv_wscale,

  			tcptw->tw_ts_recent,
  			tw->tw_bound_dev_if,

  			tcp_twsk_md5_key(tcptw),

  			tw->tw_transparent ? IP_REPLY_ARG_NOSRCCHECK : 0,
  			tw->tw_tos

  			);

  	inet_twsk_put(tw);

  }

  static void tcp_v4_reqsk_send_ack(struct sock *sk, struct sk_buff *skb,

  				  struct request_sock *req)

  {

  	tcp_v4_send_ack(skb, tcp_rsk(req)->snt_isn + 1,

  			tcp_rsk(req)->rcv_isn + 1, req->rcv_wnd,

  			req->ts_recent,
  			0,

  			tcp_v4_md5_do_lookup(sk, ip_hdr(skb)->daddr),

  			inet_rsk(req)->no_srccheck ? IP_REPLY_ARG_NOSRCCHECK : 0,
  			ip_hdr(skb)->tos);

  }

  /*

   *	Send a SYN-ACK after having received a SYN.

   *	This still operates on a request_sock only, not on a big

   *	socket.
   */

  static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
  			      struct request_sock *req,
  			      struct request_values *rvp)

  {

  	const struct inet_request_sock *ireq = inet_rsk(req);

  	struct flowi4 fl4;

  	int err = -1;
  	struct sk_buff * skb;
  
  	/* First, grab a route. */

  	if (!dst && (dst = inet_csk_route_req(sk, &fl4, req)) == NULL)

  		return -1;

  	skb = tcp_make_synack(sk, dst, req, rvp);

  
  	if (skb) {

  		__tcp_v4_send_check(skb, ireq->loc_addr, ireq->rmt_addr);

  		err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
  					    ireq->rmt_addr,
  					    ireq->opt);

  		err = net_xmit_eval(err);

  	}

  	dst_release(dst);
  	return err;
  }

  static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req,

  			      struct request_values *rvp)

  {

  	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
  	return tcp_v4_send_synack(sk, NULL, req, rvp);

  }

  /*

   *	IPv4 request_sock destructor.

   */

  static void tcp_v4_reqsk_destructor(struct request_sock *req)

  {

  	kfree(inet_rsk(req)->opt);

  }

  /*
   * Return 1 if a syncookie should be sent
   */
  int tcp_syn_flood_action(struct sock *sk,
  			 const struct sk_buff *skb,
  			 const char *proto)

  {

  	const char *msg = "Dropping request";
  	int want_cookie = 0;
  	struct listen_sock *lopt;

  #ifdef CONFIG_SYN_COOKIES

  	if (sysctl_tcp_syncookies) {

  		msg = "Sending cookies";

  		want_cookie = 1;
  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
  	} else

  #endif

  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
  
  	lopt = inet_csk(sk)->icsk_accept_queue.listen_opt;
  	if (!lopt->synflood_warned) {
  		lopt->synflood_warned = 1;
  		pr_info("%s: Possible SYN flooding on port %d. %s. "
  			" Check SNMP counters.
  ",
  			proto, ntohs(tcp_hdr(skb)->dest), msg);
  	}
  	return want_cookie;

  }

  EXPORT_SYMBOL(tcp_syn_flood_action);

  
  /*

   * Save and compile IPv4 options into the request_sock if needed.

   */

  static struct ip_options_rcu *tcp_v4_save_options(struct sock *sk,
  						  struct sk_buff *skb)

  {

  	const struct ip_options *opt = &(IPCB(skb)->opt);
  	struct ip_options_rcu *dopt = NULL;

  
  	if (opt && opt->optlen) {

  		int opt_size = sizeof(*dopt) + opt->optlen;

  		dopt = kmalloc(opt_size, GFP_ATOMIC);
  		if (dopt) {

  			if (ip_options_echo(&dopt->opt, skb)) {

  				kfree(dopt);
  				dopt = NULL;
  			}
  		}
  	}
  	return dopt;
  }

  #ifdef CONFIG_TCP_MD5SIG
  /*
   * RFC2385 MD5 checksumming requires a mapping of
   * IP address->MD5 Key.
   * We need to maintain these in the sk structure.
   */
  
  /* Find the Key structure for an address.  */

  static struct tcp_md5sig_key *
  			tcp_v4_md5_do_lookup(struct sock *sk, __be32 addr)

  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	int i;
  
  	if (!tp->md5sig_info || !tp->md5sig_info->entries4)
  		return NULL;
  	for (i = 0; i < tp->md5sig_info->entries4; i++) {
  		if (tp->md5sig_info->keys4[i].addr == addr)

  			return &tp->md5sig_info->keys4[i].base;

  	}
  	return NULL;
  }
  
  struct tcp_md5sig_key *tcp_v4_md5_lookup(struct sock *sk,
  					 struct sock *addr_sk)
  {

  	return tcp_v4_md5_do_lookup(sk, inet_sk(addr_sk)->inet_daddr);

  }

  EXPORT_SYMBOL(tcp_v4_md5_lookup);

  static struct tcp_md5sig_key *tcp_v4_reqsk_md5_lookup(struct sock *sk,
  						      struct request_sock *req)

  {
  	return tcp_v4_md5_do_lookup(sk, inet_rsk(req)->rmt_addr);
  }
  
  /* This can be called on a newly created socket, from other files */
  int tcp_v4_md5_do_add(struct sock *sk, __be32 addr,
  		      u8 *newkey, u8 newkeylen)
  {
  	/* Add Key to the list */

  	struct tcp_md5sig_key *key;

  	struct tcp_sock *tp = tcp_sk(sk);
  	struct tcp4_md5sig_key *keys;

  	key = tcp_v4_md5_do_lookup(sk, addr);

  	if (key) {
  		/* Pre-existing entry - just update that one. */

  		kfree(key->key);
  		key->key = newkey;
  		key->keylen = newkeylen;

  	} else {

  		struct tcp_md5sig_info *md5sig;

  		if (!tp->md5sig_info) {

  			tp->md5sig_info = kzalloc(sizeof(*tp->md5sig_info),
  						  GFP_ATOMIC);

  			if (!tp->md5sig_info) {
  				kfree(newkey);
  				return -ENOMEM;
  			}

  			sk_nocaps_add(sk, NETIF_F_GSO_MASK);

  		}

  
  		md5sig = tp->md5sig_info;
  		if (md5sig->entries4 == 0 &&
  		    tcp_alloc_md5sig_pool(sk) == NULL) {

  			kfree(newkey);
  			return -ENOMEM;
  		}

  
  		if (md5sig->alloced4 == md5sig->entries4) {
  			keys = kmalloc((sizeof(*keys) *

  					(md5sig->entries4 + 1)), GFP_ATOMIC);

  			if (!keys) {
  				kfree(newkey);

  				if (md5sig->entries4 == 0)
  					tcp_free_md5sig_pool();

  				return -ENOMEM;
  			}

  			if (md5sig->entries4)
  				memcpy(keys, md5sig->keys4,
  				       sizeof(*keys) * md5sig->entries4);

  
  			/* Free old key list, and reference new one */

  			kfree(md5sig->keys4);

  			md5sig->keys4 = keys;
  			md5sig->alloced4++;

  		}

  		md5sig->entries4++;

  		md5sig->keys4[md5sig->entries4 - 1].addr        = addr;
  		md5sig->keys4[md5sig->entries4 - 1].base.key    = newkey;
  		md5sig->keys4[md5sig->entries4 - 1].base.keylen = newkeylen;

  	}
  	return 0;
  }

  EXPORT_SYMBOL(tcp_v4_md5_do_add);
  
  static int tcp_v4_md5_add_func(struct sock *sk, struct sock *addr_sk,
  			       u8 *newkey, u8 newkeylen)
  {

  	return tcp_v4_md5_do_add(sk, inet_sk(addr_sk)->inet_daddr,

  				 newkey, newkeylen);
  }
  
  int tcp_v4_md5_do_del(struct sock *sk, __be32 addr)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	int i;
  
  	for (i = 0; i < tp->md5sig_info->entries4; i++) {
  		if (tp->md5sig_info->keys4[i].addr == addr) {
  			/* Free the key */

  			kfree(tp->md5sig_info->keys4[i].base.key);

  			tp->md5sig_info->entries4--;
  
  			if (tp->md5sig_info->entries4 == 0) {
  				kfree(tp->md5sig_info->keys4);
  				tp->md5sig_info->keys4 = NULL;

  				tp->md5sig_info->alloced4 = 0;

  				tcp_free_md5sig_pool();

  			} else if (tp->md5sig_info->entries4 != i) {

  				/* Need to do some manipulation */

  				memmove(&tp->md5sig_info->keys4[i],
  					&tp->md5sig_info->keys4[i+1],
  					(tp->md5sig_info->entries4 - i) *
  					 sizeof(struct tcp4_md5sig_key));

  			}

  			return 0;
  		}
  	}
  	return -ENOENT;
  }

  EXPORT_SYMBOL(tcp_v4_md5_do_del);

  static void tcp_v4_clear_md5_list(struct sock *sk)

  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	/* Free each key, then the set of key keys,
  	 * the crypto element, and then decrement our
  	 * hold on the last resort crypto.
  	 */
  	if (tp->md5sig_info->entries4) {
  		int i;
  		for (i = 0; i < tp->md5sig_info->entries4; i++)

  			kfree(tp->md5sig_info->keys4[i].base.key);

  		tp->md5sig_info->entries4 = 0;
  		tcp_free_md5sig_pool();
  	}
  	if (tp->md5sig_info->keys4) {
  		kfree(tp->md5sig_info->keys4);
  		tp->md5sig_info->keys4 = NULL;
  		tp->md5sig_info->alloced4  = 0;
  	}
  }

  static int tcp_v4_parse_md5_keys(struct sock *sk, char __user *optval,
  				 int optlen)

  {
  	struct tcp_md5sig cmd;
  	struct sockaddr_in *sin = (struct sockaddr_in *)&cmd.tcpm_addr;
  	u8 *newkey;
  
  	if (optlen < sizeof(cmd))
  		return -EINVAL;

  	if (copy_from_user(&cmd, optval, sizeof(cmd)))

  		return -EFAULT;
  
  	if (sin->sin_family != AF_INET)
  		return -EINVAL;
  
  	if (!cmd.tcpm_key || !cmd.tcpm_keylen) {
  		if (!tcp_sk(sk)->md5sig_info)
  			return -ENOENT;
  		return tcp_v4_md5_do_del(sk, sin->sin_addr.s_addr);
  	}
  
  	if (cmd.tcpm_keylen > TCP_MD5SIG_MAXKEYLEN)
  		return -EINVAL;
  
  	if (!tcp_sk(sk)->md5sig_info) {
  		struct tcp_sock *tp = tcp_sk(sk);

  		struct tcp_md5sig_info *p;

  		p = kzalloc(sizeof(*p), sk->sk_allocation);

  		if (!p)
  			return -EINVAL;
  
  		tp->md5sig_info = p;

  		sk_nocaps_add(sk, NETIF_F_GSO_MASK);

  	}

  	newkey = kmemdup(cmd.tcpm_key, cmd.tcpm_keylen, sk->sk_allocation);

  	if (!newkey)
  		return -ENOMEM;

  	return tcp_v4_md5_do_add(sk, sin->sin_addr.s_addr,
  				 newkey, cmd.tcpm_keylen);
  }

  static int tcp_v4_md5_hash_pseudoheader(struct tcp_md5sig_pool *hp,
  					__be32 daddr, __be32 saddr, int nbytes)

  {

  	struct tcp4_pseudohdr *bp;

  	struct scatterlist sg;

  
  	bp = &hp->md5_blk.ip4;

  
  	/*

  	 * 1. the TCP pseudo-header (in the order: source IP address,

  	 * destination IP address, zero-padded protocol number, and
  	 * segment length)
  	 */
  	bp->saddr = saddr;
  	bp->daddr = daddr;
  	bp->pad = 0;

  	bp->protocol = IPPROTO_TCP;

  	bp->len = cpu_to_be16(nbytes);

  	sg_init_one(&sg, bp, sizeof(*bp));
  	return crypto_hash_update(&hp->md5_desc, &sg, sizeof(*bp));
  }
  
  static int tcp_v4_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,

  			       __be32 daddr, __be32 saddr, const struct tcphdr *th)

  {
  	struct tcp_md5sig_pool *hp;
  	struct hash_desc *desc;
  
  	hp = tcp_get_md5sig_pool();
  	if (!hp)
  		goto clear_hash_noput;
  	desc = &hp->md5_desc;
  
  	if (crypto_hash_init(desc))
  		goto clear_hash;
  	if (tcp_v4_md5_hash_pseudoheader(hp, daddr, saddr, th->doff << 2))
  		goto clear_hash;
  	if (tcp_md5_hash_header(hp, th))
  		goto clear_hash;
  	if (tcp_md5_hash_key(hp, key))
  		goto clear_hash;
  	if (crypto_hash_final(desc, md5_hash))

  		goto clear_hash;

  	tcp_put_md5sig_pool();

  	return 0;

  clear_hash:
  	tcp_put_md5sig_pool();
  clear_hash_noput:
  	memset(md5_hash, 0, 16);

  	return 1;

  }

  int tcp_v4_md5_hash_skb(char *md5_hash, struct tcp_md5sig_key *key,

  			const struct sock *sk, const struct request_sock *req,
  			const struct sk_buff *skb)

  {

  	struct tcp_md5sig_pool *hp;
  	struct hash_desc *desc;

  	const struct tcphdr *th = tcp_hdr(skb);

  	__be32 saddr, daddr;
  
  	if (sk) {

  		saddr = inet_sk(sk)->inet_saddr;
  		daddr = inet_sk(sk)->inet_daddr;

  	} else if (req) {
  		saddr = inet_rsk(req)->loc_addr;
  		daddr = inet_rsk(req)->rmt_addr;

  	} else {

  		const struct iphdr *iph = ip_hdr(skb);
  		saddr = iph->saddr;
  		daddr = iph->daddr;

  	}

  
  	hp = tcp_get_md5sig_pool();
  	if (!hp)
  		goto clear_hash_noput;
  	desc = &hp->md5_desc;
  
  	if (crypto_hash_init(desc))
  		goto clear_hash;
  
  	if (tcp_v4_md5_hash_pseudoheader(hp, daddr, saddr, skb->len))
  		goto clear_hash;
  	if (tcp_md5_hash_header(hp, th))
  		goto clear_hash;
  	if (tcp_md5_hash_skb_data(hp, skb, th->doff << 2))
  		goto clear_hash;
  	if (tcp_md5_hash_key(hp, key))
  		goto clear_hash;
  	if (crypto_hash_final(desc, md5_hash))
  		goto clear_hash;
  
  	tcp_put_md5sig_pool();
  	return 0;
  
  clear_hash:
  	tcp_put_md5sig_pool();
  clear_hash_noput:
  	memset(md5_hash, 0, 16);
  	return 1;

  }

  EXPORT_SYMBOL(tcp_v4_md5_hash_skb);

  static int tcp_v4_inbound_md5_hash(struct sock *sk, const struct sk_buff *skb)

  {
  	/*
  	 * This gets called for each TCP segment that arrives
  	 * so we want to be efficient.
  	 * We have 3 drop cases:
  	 * o No MD5 hash and one expected.
  	 * o MD5 hash and we're not expecting one.
  	 * o MD5 hash and its wrong.
  	 */

  	const __u8 *hash_location = NULL;

  	struct tcp_md5sig_key *hash_expected;

  	const struct iphdr *iph = ip_hdr(skb);

  	const struct tcphdr *th = tcp_hdr(skb);

  	int genhash;

  	unsigned char newhash[16];
  
  	hash_expected = tcp_v4_md5_do_lookup(sk, iph->saddr);

  	hash_location = tcp_parse_md5sig_option(th);

  	/* We've parsed the options - do we have a hash? */
  	if (!hash_expected && !hash_location)
  		return 0;
  
  	if (hash_expected && !hash_location) {

  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);

  		return 1;
  	}
  
  	if (!hash_expected && hash_location) {

  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);

  		return 1;
  	}
  
  	/* Okay, so this is hash_expected and hash_location -
  	 * so we need to calculate the checksum.
  	 */

  	genhash = tcp_v4_md5_hash_skb(newhash,
  				      hash_expected,
  				      NULL, NULL, skb);

  
  	if (genhash || memcmp(hash_location, newhash, 16) != 0) {
  		if (net_ratelimit()) {

  			printk(KERN_INFO "MD5 Hash failed for (%pI4, %d)->(%pI4, %d)%s
  ",
  			       &iph->saddr, ntohs(th->source),
  			       &iph->daddr, ntohs(th->dest),

  			       genhash ? " tcp_v4_calc_md5_hash failed" : "");

  		}
  		return 1;
  	}
  	return 0;
  }
  
  #endif

  struct request_sock_ops tcp_request_sock_ops __read_mostly = {

  	.family		=	PF_INET,

  	.obj_size	=	sizeof(struct tcp_request_sock),

  	.rtx_syn_ack	=	tcp_v4_rtx_synack,

  	.send_ack	=	tcp_v4_reqsk_send_ack,
  	.destructor	=	tcp_v4_reqsk_destructor,

  	.send_reset	=	tcp_v4_send_reset,

  	.syn_ack_timeout = 	tcp_syn_ack_timeout,

  };

  #ifdef CONFIG_TCP_MD5SIG

  static const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {

  	.md5_lookup	=	tcp_v4_reqsk_md5_lookup,

  	.calc_md5_hash	=	tcp_v4_md5_hash_skb,

  };

  #endif

  int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
  {

  	struct tcp_extend_values tmp_ext;

  	struct tcp_options_received tmp_opt;

  	const u8 *hash_location;

  	struct request_sock *req;

  	struct inet_request_sock *ireq;

  	struct tcp_sock *tp = tcp_sk(sk);

  	struct dst_entry *dst = NULL;

  	__be32 saddr = ip_hdr(skb)->saddr;
  	__be32 daddr = ip_hdr(skb)->daddr;

  	__u32 isn = TCP_SKB_CB(skb)->when;

  	int want_cookie = 0;

  
  	/* Never answer to SYNs send to broadcast or multicast */

  	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))

  		goto drop;
  
  	/* TW buckets are converted to open requests without
  	 * limitations, they conserve resources and peer is
  	 * evidently real one.
  	 */

  	if (inet_csk_reqsk_queue_is_full(sk) && !isn) {

  		want_cookie = tcp_syn_flood_action(sk, skb, "TCP");
  		if (!want_cookie)
  			goto drop;

  	}
  
  	/* Accept backlog is full. If we have already queued enough
  	 * of warm entries in syn queue, drop request. It is better than
  	 * clogging syn queue with openreqs with exponentially increasing
  	 * timeout.
  	 */

  	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)

  		goto drop;

  	req = inet_reqsk_alloc(&tcp_request_sock_ops);

  	if (!req)
  		goto drop;

  #ifdef CONFIG_TCP_MD5SIG
  	tcp_rsk(req)->af_specific = &tcp_request_sock_ipv4_ops;
  #endif

  	tcp_clear_options(&tmp_opt);

  	tmp_opt.mss_clamp = TCP_MSS_DEFAULT;

  	tmp_opt.user_mss  = tp->rx_opt.user_mss;

  	tcp_parse_options(skb, &tmp_opt, &hash_location, 0);

  
  	if (tmp_opt.cookie_plus > 0 &&
  	    tmp_opt.saw_tstamp &&
  	    !tp->rx_opt.cookie_out_never &&
  	    (sysctl_tcp_cookie_size > 0 ||
  	     (tp->cookie_values != NULL &&
  	      tp->cookie_values->cookie_desired > 0))) {
  		u8 *c;
  		u32 *mess = &tmp_ext.cookie_bakery[COOKIE_DIGEST_WORDS];
  		int l = tmp_opt.cookie_plus - TCPOLEN_COOKIE_BASE;
  
  		if (tcp_cookie_generator(&tmp_ext.cookie_bakery[0]) != 0)
  			goto drop_and_release;
  
  		/* Secret recipe starts with IP addresses */

  		*mess++ ^= (__force u32)daddr;
  		*mess++ ^= (__force u32)saddr;

  		/* plus variable length Initiator Cookie */
  		c = (u8 *)mess;
  		while (l-- > 0)
  			*c++ ^= *hash_location++;

  		want_cookie = 0;	/* not our kind of cookie */

  		tmp_ext.cookie_out_never = 0; /* false */
  		tmp_ext.cookie_plus = tmp_opt.cookie_plus;
  	} else if (!tp->rx_opt.cookie_in_always) {
  		/* redundant indications, but ensure initialization. */
  		tmp_ext.cookie_out_never = 1; /* true */
  		tmp_ext.cookie_plus = 0;
  	} else {
  		goto drop_and_release;
  	}
  	tmp_ext.cookie_in_always = tp->rx_opt.cookie_in_always;

  	if (want_cookie && !tmp_opt.saw_tstamp)

  		tcp_clear_options(&tmp_opt);

  	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;

  	tcp_openreq_init(req, &tmp_opt, skb);

  	ireq = inet_rsk(req);
  	ireq->loc_addr = daddr;
  	ireq->rmt_addr = saddr;
  	ireq->no_srccheck = inet_sk(sk)->transparent;
  	ireq->opt = tcp_v4_save_options(sk, skb);

  	if (security_inet_conn_request(sk, skb, req))

  		goto drop_and_free;

  	if (!want_cookie || tmp_opt.tstamp_ok)

  		TCP_ECN_create_request(req, tcp_hdr(skb));

  
  	if (want_cookie) {

  		isn = cookie_v4_init_sequence(sk, skb, &req->mss);

  		req->cookie_ts = tmp_opt.tstamp_ok;

  	} else if (!isn) {
  		struct inet_peer *peer = NULL;

  		struct flowi4 fl4;

  
  		/* VJ's idea. We save last timestamp seen
  		 * from the destination in peer table, when entering
  		 * state TIME-WAIT, and check against it before
  		 * accepting new connection request.
  		 *
  		 * If "isn" is not zero, this request hit alive
  		 * timewait bucket, so that all the necessary checks
  		 * are made in the function processing timewait state.
  		 */
  		if (tmp_opt.saw_tstamp &&

  		    tcp_death_row.sysctl_tw_recycle &&

  		    (dst = inet_csk_route_req(sk, &fl4, req)) != NULL &&

  		    fl4.daddr == saddr &&
  		    (peer = rt_get_peer((struct rtable *)dst, fl4.daddr)) != NULL) {

  			inet_peer_refcheck(peer);

  			if ((u32)get_seconds() - peer->tcp_ts_stamp < TCP_PAWS_MSL &&

  			    (s32)(peer->tcp_ts - req->ts_recent) >
  							TCP_PAWS_WINDOW) {

  				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);

  				goto drop_and_release;

  			}
  		}
  		/* Kill the following clause, if you dislike this way. */
  		else if (!sysctl_tcp_syncookies &&

  			 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <

  			  (sysctl_max_syn_backlog >> 2)) &&
  			 (!peer || !peer->tcp_ts_stamp) &&
  			 (!dst || !dst_metric(dst, RTAX_RTT))) {
  			/* Without syncookies last quarter of
  			 * backlog is filled with destinations,
  			 * proven to be alive.
  			 * It means that we continue to communicate
  			 * to destinations, already remembered
  			 * to the moment of synflood.
  			 */

  			LIMIT_NETDEBUG(KERN_DEBUG "TCP: drop open request from %pI4/%u
  ",
  				       &saddr, ntohs(tcp_hdr(skb)->source));

  			goto drop_and_release;

  		}

  		isn = tcp_v4_init_sequence(skb);

  	}

  	tcp_rsk(req)->snt_isn = isn;

  	tcp_rsk(req)->snt_synack = tcp_time_stamp;

  	if (tcp_v4_send_synack(sk, dst, req,
  			       (struct request_values *)&tmp_ext) ||

  	    want_cookie)

  		goto drop_and_free;

  	inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);

  	return 0;

  drop_and_release:
  	dst_release(dst);

  drop_and_free:

  	reqsk_free(req);

  drop:

  	return 0;
  }

  EXPORT_SYMBOL(tcp_v4_conn_request);

  
  
  /*
   * The three way handshake has completed - we got a valid synack -
   * now create the new socket.
   */
  struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,

  				  struct request_sock *req,

  				  struct dst_entry *dst)
  {

  	struct inet_request_sock *ireq;

  	struct inet_sock *newinet;
  	struct tcp_sock *newtp;
  	struct sock *newsk;

  #ifdef CONFIG_TCP_MD5SIG
  	struct tcp_md5sig_key *key;
  #endif

  	struct ip_options_rcu *inet_opt;

  
  	if (sk_acceptq_is_full(sk))
  		goto exit_overflow;

  	newsk = tcp_create_openreq_child(sk, req, skb);
  	if (!newsk)

  		goto exit_nonewsk;

  	newsk->sk_gso_type = SKB_GSO_TCPV4;

  
  	newtp		      = tcp_sk(newsk);
  	newinet		      = inet_sk(newsk);

  	ireq		      = inet_rsk(req);

  	newinet->inet_daddr   = ireq->rmt_addr;
  	newinet->inet_rcv_saddr = ireq->loc_addr;
  	newinet->inet_saddr	      = ireq->loc_addr;

  	inet_opt	      = ireq->opt;
  	rcu_assign_pointer(newinet->inet_opt, inet_opt);

  	ireq->opt	      = NULL;

  	newinet->mc_index     = inet_iif(skb);

  	newinet->mc_ttl	      = ip_hdr(skb)->ttl;

  	inet_csk(newsk)->icsk_ext_hdr_len = 0;

  	if (inet_opt)
  		inet_csk(newsk)->icsk_ext_hdr_len = inet_opt->opt.optlen;

  	newinet->inet_id = newtp->write_seq ^ jiffies;

  	if (!dst && (dst = inet_csk_route_child_sock(sk, newsk, req)) == NULL)
  		goto put_and_exit;
  
  	sk_setup_caps(newsk, dst);

  	tcp_mtup_init(newsk);

  	tcp_sync_mss(newsk, dst_mtu(dst));

  	newtp->advmss = dst_metric_advmss(dst);

  	if (tcp_sk(sk)->rx_opt.user_mss &&
  	    tcp_sk(sk)->rx_opt.user_mss < newtp->advmss)
  		newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;

  	tcp_initialize_rcv_mss(newsk);

  	if (tcp_rsk(req)->snt_synack)
  		tcp_valid_rtt_meas(newsk,
  		    tcp_time_stamp - tcp_rsk(req)->snt_synack);
  	newtp->total_retrans = req->retrans;

  #ifdef CONFIG_TCP_MD5SIG
  	/* Copy over the MD5 key from the original socket */

  	key = tcp_v4_md5_do_lookup(sk, newinet->inet_daddr);
  	if (key != NULL) {

  		/*
  		 * We're using one, so create a matching key
  		 * on the newsk structure. If we fail to get
  		 * memory, then we end up not copying the key
  		 * across. Shucks.
  		 */

  		char *newkey = kmemdup(key->key, key->keylen, GFP_ATOMIC);
  		if (newkey != NULL)

  			tcp_v4_md5_do_add(newsk, newinet->inet_daddr,

  					  newkey, key->keylen);

  		sk_nocaps_add(newsk, NETIF_F_GSO_MASK);

  	}
  #endif

  	if (__inet_inherit_port(sk, newsk) < 0)
  		goto put_and_exit;

  	__inet_hash_nolisten(newsk, NULL);

  
  	return newsk;
  
  exit_overflow:

  	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);

  exit_nonewsk:
  	dst_release(dst);

  exit:

  	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);

  	return NULL;

  put_and_exit:

  	tcp_clear_xmit_timers(newsk);

  	bh_unlock_sock(newsk);

  	sock_put(newsk);
  	goto exit;

  }

  EXPORT_SYMBOL(tcp_v4_syn_recv_sock);

  
  static struct sock *tcp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
  {

  	struct tcphdr *th = tcp_hdr(skb);

  	const struct iphdr *iph = ip_hdr(skb);

  	struct sock *nsk;

  	struct request_sock **prev;

  	/* Find possible connection requests. */

  	struct request_sock *req = inet_csk_search_req(sk, &prev, th->source,
  						       iph->saddr, iph->daddr);

  	if (req)
  		return tcp_check_req(sk, skb, req, prev);

  	nsk = inet_lookup_established(sock_net(sk), &tcp_hashinfo, iph->saddr,

  			th->source, iph->daddr, th->dest, inet_iif(skb));

  
  	if (nsk) {
  		if (nsk->sk_state != TCP_TIME_WAIT) {
  			bh_lock_sock(nsk);
  			return nsk;
  		}

  		inet_twsk_put(inet_twsk(nsk));

  		return NULL;
  	}
  
  #ifdef CONFIG_SYN_COOKIES

  	if (!th->syn)

  		sk = cookie_v4_check(sk, skb, &(IPCB(skb)->opt));
  #endif
  	return sk;
  }

  static __sum16 tcp_v4_checksum_init(struct sk_buff *skb)

  {

  	const struct iphdr *iph = ip_hdr(skb);

  	if (skb->ip_summed == CHECKSUM_COMPLETE) {

  		if (!tcp_v4_check(skb->len, iph->saddr,
  				  iph->daddr, skb->csum)) {

  			skb->ip_summed = CHECKSUM_UNNECESSARY;

  			return 0;

  		}

  	}

  	skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,

  				       skb->len, IPPROTO_TCP, 0);

  	if (skb->len <= 76) {

  		return __skb_checksum_complete(skb);

  	}
  	return 0;
  }
  
  
  /* The socket must have it's spinlock held when we get
   * here.
   *
   * We have a potential double-lock case here, so even when
   * doing backlog processing we use the BH locking scheme.
   * This is because we cannot sleep with the original spinlock
   * held.
   */
  int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
  {

  	struct sock *rsk;
  #ifdef CONFIG_TCP_MD5SIG
  	/*
  	 * We really want to reject the packet as early as possible
  	 * if:
  	 *  o We're expecting an MD5'd packet and this is no MD5 tcp option
  	 *  o There is an MD5 option and we're not expecting one
  	 */

  	if (tcp_v4_inbound_md5_hash(sk, skb))

  		goto discard;
  #endif

  	if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */

  		sock_rps_save_rxhash(sk, skb);

  		if (tcp_rcv_established(sk, skb, tcp_hdr(skb), skb->len)) {

  			rsk = sk;

  			goto reset;

  		}

  		return 0;
  	}

  	if (skb->len < tcp_hdrlen(skb) || tcp_checksum_complete(skb))

  		goto csum_err;
  
  	if (sk->sk_state == TCP_LISTEN) {
  		struct sock *nsk = tcp_v4_hnd_req(sk, skb);
  		if (!nsk)
  			goto discard;
  
  		if (nsk != sk) {

  			sock_rps_save_rxhash(nsk, skb);

  			if (tcp_child_process(sk, nsk, skb)) {
  				rsk = nsk;

  				goto reset;

  			}

  			return 0;
  		}

  	} else

  		sock_rps_save_rxhash(sk, skb);