// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * 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

   */
  
  /*
   * 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.
   */

  #define pr_fmt(fmt) "TCP: " fmt

  #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/secure_seq.h>

  #include <net/busy_poll.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/inetdevice.h>

  #include <crypto/hash.h>

  #include <linux/scatterlist.h>

  #include <trace/events/tcp.h>

  #ifdef CONFIG_TCP_MD5SIG

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

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

  #endif

  struct inet_hashinfo tcp_hashinfo;

  EXPORT_SYMBOL(tcp_hashinfo);

  static u32 tcp_v4_init_seq(const struct sk_buff *skb)

  {

  	return secure_tcp_seq(ip_hdr(skb)->daddr,
  			      ip_hdr(skb)->saddr,
  			      tcp_hdr(skb)->dest,
  			      tcp_hdr(skb)->source);
  }

  static u32 tcp_v4_init_ts_off(const struct net *net, const struct sk_buff *skb)

  {

  	return secure_tcp_ts_off(net, ip_hdr(skb)->daddr, ip_hdr(skb)->saddr);

  }

  int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
  {

  	const struct inet_timewait_sock *tw = inet_twsk(sktw);

  	const struct tcp_timewait_sock *tcptw = tcp_twsk(sktw);
  	struct tcp_sock *tp = tcp_sk(sk);

  	int reuse = sock_net(sk)->ipv4.sysctl_tcp_tw_reuse;
  
  	if (reuse == 2) {
  		/* Still does not detect *everything* that goes through
  		 * lo, since we require a loopback src or dst address
  		 * or direct binding to 'lo' interface.
  		 */
  		bool loopback = false;
  		if (tw->tw_bound_dev_if == LOOPBACK_IFINDEX)
  			loopback = true;
  #if IS_ENABLED(CONFIG_IPV6)
  		if (tw->tw_family == AF_INET6) {
  			if (ipv6_addr_loopback(&tw->tw_v6_daddr) ||
  			    (ipv6_addr_v4mapped(&tw->tw_v6_daddr) &&
  			     (tw->tw_v6_daddr.s6_addr[12] == 127)) ||
  			    ipv6_addr_loopback(&tw->tw_v6_rcv_saddr) ||
  			    (ipv6_addr_v4mapped(&tw->tw_v6_rcv_saddr) &&
  			     (tw->tw_v6_rcv_saddr.s6_addr[12] == 127)))
  				loopback = true;
  		} else
  #endif
  		{
  			if (ipv4_is_loopback(tw->tw_daddr) ||
  			    ipv4_is_loopback(tw->tw_rcv_saddr))
  				loopback = true;
  		}
  		if (!loopback)
  			reuse = 0;
  	}

  
  	/* 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 || (reuse && time_after32(ktime_get_seconds(),
  					    tcptw->tw_ts_recent_stamp)))) {

  		/* In case of repair and re-using TIME-WAIT sockets we still
  		 * want to be sure that it is safe as above but honor the
  		 * sequence numbers and time stamps set as part of the repair
  		 * process.
  		 *
  		 * Without this check re-using a TIME-WAIT socket with TCP
  		 * repair would accumulate a -1 on the repair assigned
  		 * sequence number. The first time it is reused the sequence
  		 * is -1, the second time -2, etc. This fixes that issue
  		 * without appearing to create any others.
  		 */
  		if (likely(!tp->repair)) {

  			u32 seq = tcptw->tw_snd_nxt + 65535 + 2;
  
  			if (!seq)
  				seq = 1;
  			WRITE_ONCE(tp->write_seq, seq);

  			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);

  static int tcp_v4_pre_connect(struct sock *sk, struct sockaddr *uaddr,
  			      int addr_len)
  {
  	/* This check is replicated from tcp_v4_connect() and intended to
  	 * prevent BPF program called below from accessing bytes that are out
  	 * of the bound specified by user in addr_len.
  	 */
  	if (addr_len < sizeof(struct sockaddr_in))
  		return -EINVAL;
  
  	sock_owned_by_me(sk);
  
  	return BPF_CGROUP_RUN_PROG_INET4_CONNECT(sk, uaddr);
  }

  /* 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;

  	struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;

  
  	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,

  					     lockdep_sock_is_held(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);

  	if (IS_ERR(rt)) {
  		err = PTR_ERR(rt);
  		if (err == -ENETUNREACH)

  			IP_INC_STATS(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;

  	sk_rcv_saddr_set(sk, 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;

  		if (likely(!tp->repair))

  			WRITE_ONCE(tp->write_seq, 0);

  	}

  	inet->inet_dport = usin->sin_port;

  	sk_daddr_set(sk, 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;

  	sk_set_txhash(sk);

  	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);

  	rt = NULL;

  	if (likely(!tp->repair)) {

  		if (!tp->write_seq)

  			WRITE_ONCE(tp->write_seq,
  				   secure_tcp_seq(inet->inet_saddr,
  						  inet->inet_daddr,
  						  inet->inet_sport,
  						  usin->sin_port));

  		tp->tsoffset = secure_tcp_ts_off(sock_net(sk),
  						 inet->inet_saddr,

  						 inet->inet_daddr);

  	}

  	inet->inet_id = prandom_u32();

  	if (tcp_fastopen_defer_connect(sk, &err))
  		return err;
  	if (err)
  		goto failure;

  	err = tcp_connect(sk);

  	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 reacts to ICMP_FRAG_NEEDED mtu indications as defined in RFC1191.
   * It can be called through tcp_release_cb() if socket was owned by user
   * at the time tcp_v4_err() was called to handle ICMP message.

   */

  void tcp_v4_mtu_reduced(struct sock *sk)

  {

  	struct inet_sock *inet = inet_sk(sk);

  	struct dst_entry *dst;
  	u32 mtu;

  	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
  		return;
  	mtu = tcp_sk(sk)->mtu_info;

  	dst = inet_csk_update_pmtu(sk, mtu);
  	if (!dst)

  		return;

  	/* 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 &&

  	    ip_sk_accept_pmtu(sk) &&

  	    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 */
  }

  EXPORT_SYMBOL(tcp_v4_mtu_reduced);

  static void do_redirect(struct sk_buff *skb, struct sock *sk)
  {
  	struct dst_entry *dst = __sk_dst_check(sk, 0);

  	if (dst)

  		dst->ops->redirect(dst, sk, skb);

  }

  
  /* handle ICMP messages on TCP_NEW_SYN_RECV request sockets */

  void tcp_req_err(struct sock *sk, u32 seq, bool abort)

  {
  	struct request_sock *req = inet_reqsk(sk);
  	struct net *net = sock_net(sk);
  
  	/* ICMPs are not backlogged, hence we cannot get
  	 * an established socket here.
  	 */

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

  		__NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS);

  	} else if (abort) {

  		/*
  		 * 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(req->rsk_listener, req);

  		tcp_listendrop(req->rsk_listener);

  	}

  	reqsk_put(req);

  }
  EXPORT_SYMBOL(tcp_req_err);

  /*
   * 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.
   *
   */

  int 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;

  	struct request_sock *fastopen;

  	u32 seq, snd_una;
  	s32 remaining;
  	u32 delta_us;

  	int err;

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

  	sk = __inet_lookup_established(net, &tcp_hashinfo, iph->daddr,
  				       th->dest, iph->saddr, ntohs(th->source),

  				       inet_iif(icmp_skb), 0);

  	if (!sk) {

  		__ICMP_INC_STATS(net, ICMP_MIB_INERRORS);

  		return -ENOENT;

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

  		inet_twsk_put(inet_twsk(sk));

  		return 0;

  	}

  	seq = ntohl(th->seq);

  	if (sk->sk_state == TCP_NEW_SYN_RECV) {
  		tcp_req_err(sk, seq, type == ICMP_PARAMETERPROB ||
  				     type == ICMP_TIME_EXCEEDED ||
  				     (type == ICMP_DEST_UNREACH &&
  				      (code == ICMP_NET_UNREACH ||
  				       code == ICMP_HOST_UNREACH)));
  		return 0;
  	}

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

  	 * We do take care of PMTU discovery (RFC1191) special case :
  	 * we can receive locally generated ICMP messages while socket is held.

  	 */

  	if (sock_owned_by_user(sk)) {
  		if (!(type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED))

  			__NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS);

  	}

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

  	if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) {

  		__NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP);

  		goto out;
  	}

  	icsk = inet_csk(sk);

  	tp = tcp_sk(sk);

  	/* XXX (TFO) - tp->snd_una should be ISN (tcp_create_openreq_child() */

  	fastopen = rcu_dereference(tp->fastopen_rsk);

  	snd_una = fastopen ? tcp_rsk(fastopen)->snt_isn : tp->snd_una;

  	if (sk->sk_state != TCP_LISTEN &&

  	    !between(seq, snd_una, tp->snd_nxt)) {

  		__NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS);

  		goto out;
  	}
  
  	switch (type) {

  	case ICMP_REDIRECT:

  		if (!sock_owned_by_user(sk))
  			do_redirect(icmp_skb, sk);

  		goto out;

  	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) */

  			/* 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)
  				goto out;

  			tp->mtu_info = info;

  			if (!sock_owned_by_user(sk)) {

  				tcp_v4_mtu_reduced(sk);

  			} else {

  				if (!test_and_set_bit(TCP_MTU_REDUCED_DEFERRED, &sk->sk_tsq_flags))

  					sock_hold(sk);
  			}

  			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 || fastopen)

  			break;

  		if (sock_owned_by_user(sk))
  			break;

  		skb = tcp_rtx_queue_head(sk);
  		if (WARN_ON_ONCE(!skb))
  			break;

  		icsk->icsk_backoff--;

  		icsk->icsk_rto = tp->srtt_us ? __tcp_set_rto(tp) :
  					       TCP_TIMEOUT_INIT;
  		icsk->icsk_rto = inet_csk_rto_backoff(icsk, TCP_RTO_MAX);

  		tcp_mstamp_refresh(tp);

  		delta_us = (u32)(tp->tcp_mstamp - tcp_skb_timestamp_us(skb));

  		remaining = icsk->icsk_rto -

  			    usecs_to_jiffies(delta_us);

  		if (remaining > 0) {

  			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) {

  	case TCP_SYN_SENT:

  	case TCP_SYN_RECV:
  		/* Only in fast or simultaneous open. If a fast open socket is
  		 * is already accepted it is treated as a connected one below.
  		 */

  		if (fastopen && !fastopen->sk)

  			break;

  		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);

  	return 0;

  }

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

  {

  	struct tcphdr *th = tcp_hdr(skb);

  	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);

  }

  /* 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);

  /*
   *	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(const 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 = NULL;

  	const __u8 *hash_location = NULL;
  	unsigned char newhash[16];
  	int genhash;
  	struct sock *sk1 = NULL;

  #endif

  	u64 transmit_time = 0;

  	struct sock *ctl_sk;

  	struct net *net;

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

  	/* If sk not NULL, it means we did a successful lookup and incoming
  	 * route had to be correct. prequeue might have dropped our dst.
  	 */
  	if (!sk && 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);

  	net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);

  #ifdef CONFIG_TCP_MD5SIG

  	rcu_read_lock();

  	hash_location = tcp_parse_md5sig_option(th);

  	if (sk && sk_fullsock(sk)) {

  		key = tcp_md5_do_lookup(sk, (union tcp_md5_addr *)
  					&ip_hdr(skb)->saddr, AF_INET);
  	} else if (hash_location) {

  		/*
  		 * active side is lost. Try to find listening socket through
  		 * source port, and then find md5 key through listening socket.
  		 * we are not loose security here:
  		 * Incoming packet is checked with md5 hash with finding key,
  		 * no RST generated if md5 hash doesn't match.
  		 */

  		sk1 = __inet_lookup_listener(net, &tcp_hashinfo, NULL, 0,
  					     ip_hdr(skb)->saddr,

  					     th->source, ip_hdr(skb)->daddr,

  					     ntohs(th->source), inet_iif(skb),
  					     tcp_v4_sdif(skb));

  		/* don't send rst if it can't find key */
  		if (!sk1)

  			goto out;

  		key = tcp_md5_do_lookup(sk1, (union tcp_md5_addr *)
  					&ip_hdr(skb)->saddr, AF_INET);
  		if (!key)

  			goto out;

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

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

  			goto out;

  	}

  	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_transparent(sk)) ? IP_REPLY_ARG_NOSRCCHECK : 0;

  	/* When socket is gone, all binding information is lost.

  	 * routing might fail in this case. No choice here, if we choose to force
  	 * input interface, we will misroute in case of asymmetric route.

  	 */

  	if (sk) {

  		arg.bound_dev_if = sk->sk_bound_dev_if;

  		if (sk_fullsock(sk))
  			trace_tcp_send_reset(sk, skb);

  	}

  	BUILD_BUG_ON(offsetof(struct sock, sk_bound_dev_if) !=
  		     offsetof(struct inet_timewait_sock, tw_bound_dev_if));

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

  	arg.uid = sock_net_uid(net, sk && sk_fullsock(sk) ? sk : NULL);

  	local_bh_disable();

  	ctl_sk = this_cpu_read(*net->ipv4.tcp_sk);

  	if (sk) {

  		ctl_sk->sk_mark = (sk->sk_state == TCP_TIME_WAIT) ?
  				   inet_twsk(sk)->tw_mark : sk->sk_mark;

  		ctl_sk->sk_priority = (sk->sk_state == TCP_TIME_WAIT) ?
  				   inet_twsk(sk)->tw_priority : sk->sk_priority;

  		transmit_time = tcp_transmit_time(sk);

  	}

  	ip_send_unicast_reply(ctl_sk,

  			      skb, &TCP_SKB_CB(skb)->header.h4.opt,

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

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

  	ctl_sk->sk_mark = 0;

  	__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
  	__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);

  	local_bh_enable();

  
  #ifdef CONFIG_TCP_MD5SIG

  out:
  	rcu_read_unlock();

  #endif

  }
  
  /* 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(const struct sock *sk,

  			    struct sk_buff *skb, u32 seq, u32 ack,

  			    u32 win, u32 tsval, u32 tsecr, 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 net *net = sock_net(sk);

  	struct ip_reply_arg arg;

  	struct sock *ctl_sk;

  	u64 transmit_time;

  
  	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 (tsecr) {

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

  		rep.opt[1] = htonl(tsval);
  		rep.opt[2] = htonl(tsecr);

  		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 = (tsecr) ? 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;

  	arg.uid = sock_net_uid(net, sk_fullsock(sk) ? sk : NULL);

  	local_bh_disable();

  	ctl_sk = this_cpu_read(*net->ipv4.tcp_sk);

  	ctl_sk->sk_mark = (sk->sk_state == TCP_TIME_WAIT) ?
  			   inet_twsk(sk)->tw_mark : sk->sk_mark;

  	ctl_sk->sk_priority = (sk->sk_state == TCP_TIME_WAIT) ?
  			   inet_twsk(sk)->tw_priority : sk->sk_priority;

  	transmit_time = tcp_transmit_time(sk);

  	ip_send_unicast_reply(ctl_sk,

  			      skb, &TCP_SKB_CB(skb)->header.h4.opt,

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

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

  	ctl_sk->sk_mark = 0;

  	__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);

  	local_bh_enable();

  }
  
  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(sk, skb,

  			tcptw->tw_snd_nxt, tcptw->tw_rcv_nxt,

  			tcptw->tw_rcv_wnd >> tw->tw_rcv_wscale,

  			tcp_time_stamp_raw() + tcptw->tw_ts_offset,

  			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(const struct sock *sk, struct sk_buff *skb,

  				  struct request_sock *req)

  {

  	/* sk->sk_state == TCP_LISTEN -> for regular TCP_SYN_RECV
  	 * sk->sk_state == TCP_SYN_RECV -> for Fast Open.
  	 */

  	u32 seq = (sk->sk_state == TCP_LISTEN) ? tcp_rsk(req)->snt_isn + 1 :
  					     tcp_sk(sk)->snd_nxt;

  	/* RFC 7323 2.3
  	 * The window field (SEG.WND) of every outgoing segment, with the
  	 * exception of <SYN> segments, MUST be right-shifted by
  	 * Rcv.Wind.Shift bits:
  	 */

  	tcp_v4_send_ack(sk, skb, seq,

  			tcp_rsk(req)->rcv_nxt,
  			req->rsk_rcv_wnd >> inet_rsk(req)->rcv_wscale,

  			tcp_time_stamp_raw() + tcp_rsk(req)->ts_off,

  			req->ts_recent,
  			0,

  			tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->saddr,

  					  AF_INET),

  			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(const struct sock *sk, struct dst_entry *dst,

  			      struct flowi *fl,

  			      struct request_sock *req,

  			      struct tcp_fastopen_cookie *foc,

  			      enum tcp_synack_type synack_type)

  {

  	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, foc, synack_type);

  
  	if (skb) {

  		__tcp_v4_send_check(skb, ireq->ir_loc_addr, ireq->ir_rmt_addr);

  		rcu_read_lock();

  		err = ip_build_and_send_pkt(skb, sk, ireq->ir_loc_addr,
  					    ireq->ir_rmt_addr,

  					    rcu_dereference(ireq->ireq_opt));
  		rcu_read_unlock();

  		err = net_xmit_eval(err);

  	}

  	return err;
  }
  
  /*

   *	IPv4 request_sock destructor.

   */

  static void tcp_v4_reqsk_destructor(struct request_sock *req)

  {

  	kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1));

  }

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

  DEFINE_STATIC_KEY_FALSE(tcp_md5_needed);

  EXPORT_SYMBOL(tcp_md5_needed);

  /* Find the Key structure for an address.  */

  struct tcp_md5sig_key *__tcp_md5_do_lookup(const struct sock *sk,
  					   const union tcp_md5_addr *addr,
  					   int family)

  {

  	const struct tcp_sock *tp = tcp_sk(sk);

  	struct tcp_md5sig_key *key;

  	const struct tcp_md5sig_info *md5sig;

  	__be32 mask;
  	struct tcp_md5sig_key *best_match = NULL;
  	bool match;

  	/* caller either holds rcu_read_lock() or socket lock */
  	md5sig = rcu_dereference_check(tp->md5sig_info,

  				       lockdep_sock_is_held(sk));

  	if (!md5sig)

  		return NULL;

  	hlist_for_each_entry_rcu(key, &md5sig->head, node) {

  		if (key->family != family)
  			continue;

  
  		if (family == AF_INET) {
  			mask = inet_make_mask(key->prefixlen);
  			match = (key->addr.a4.s_addr & mask) ==
  				(addr->a4.s_addr & mask);
  #if IS_ENABLED(CONFIG_IPV6)
  		} else if (family == AF_INET6) {
  			match = ipv6_prefix_equal(&key->addr.a6, &addr->a6,
  						  key->prefixlen);
  #endif
  		} else {
  			match = false;
  		}
  
  		if (match && (!best_match ||
  			      key->prefixlen > best_match->prefixlen))
  			best_match = key;
  	}
  	return best_match;
  }

  EXPORT_SYMBOL(__tcp_md5_do_lookup);

  static struct tcp_md5sig_key *tcp_md5_do_lookup_exact(const struct sock *sk,
  						      const union tcp_md5_addr *addr,
  						      int family, u8 prefixlen)

  {
  	const struct tcp_sock *tp = tcp_sk(sk);
  	struct tcp_md5sig_key *key;
  	unsigned int size = sizeof(struct in_addr);
  	const struct tcp_md5sig_info *md5sig;
  
  	/* caller either holds rcu_read_lock() or socket lock */
  	md5sig = rcu_dereference_check(tp->md5sig_info,
  				       lockdep_sock_is_held(sk));
  	if (!md5sig)
  		return NULL;
  #if IS_ENABLED(CONFIG_IPV6)
  	if (family == AF_INET6)
  		size = sizeof(struct in6_addr);
  #endif
  	hlist_for_each_entry_rcu(key, &md5sig->head, node) {
  		if (key->family != family)
  			continue;
  		if (!memcmp(&key->addr, addr, size) &&
  		    key->prefixlen == prefixlen)

  			return key;

  	}
  	return NULL;
  }

  struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,

  					 const struct sock *addr_sk)

  {

  	const union tcp_md5_addr *addr;

  	addr = (const union tcp_md5_addr *)&addr_sk->sk_daddr;

  	return tcp_md5_do_lookup(sk, addr, AF_INET);

  }

  EXPORT_SYMBOL(tcp_v4_md5_lookup);

  /* This can be called on a newly created socket, from other files */

  int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,

  		   int family, u8 prefixlen, const u8 *newkey, u8 newkeylen,
  		   gfp_t gfp)

  {
  	/* Add Key to the list */

  	struct tcp_md5sig_key *key;

  	struct tcp_sock *tp = tcp_sk(sk);

  	struct tcp_md5sig_info *md5sig;

  	key = tcp_md5_do_lookup_exact(sk, addr, family, prefixlen);

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

  		memcpy(key->key, newkey, newkeylen);

  		key->keylen = newkeylen;

  		return 0;
  	}

  	md5sig = rcu_dereference_protected(tp->md5sig_info,

  					   lockdep_sock_is_held(sk));

  	if (!md5sig) {
  		md5sig = kmalloc(sizeof(*md5sig), gfp);
  		if (!md5sig)

  			return -ENOMEM;

  		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
  		INIT_HLIST_HEAD(&md5sig->head);

  		rcu_assign_pointer(tp->md5sig_info, md5sig);

  	}

  	key = sock_kmalloc(sk, sizeof(*key), gfp);

  	if (!key)
  		return -ENOMEM;

  	if (!tcp_alloc_md5sig_pool()) {

  		sock_kfree_s(sk, key, sizeof(*key));

  		return -ENOMEM;

  	}

  
  	memcpy(key->key, newkey, newkeylen);
  	key->keylen = newkeylen;
  	key->family = family;

  	key->prefixlen = prefixlen;

  	memcpy(&key->addr, addr,
  	       (family == AF_INET6) ? sizeof(struct in6_addr) :
  				      sizeof(struct in_addr));
  	hlist_add_head_rcu(&key->node, &md5sig->head);

  	return 0;
  }

  EXPORT_SYMBOL(tcp_md5_do_add);

  int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr, int family,
  		   u8 prefixlen)

  {

  	struct tcp_md5sig_key *key;

  	key = tcp_md5_do_lookup_exact(sk, addr, family, prefixlen);

  	if (!key)
  		return -ENOENT;
  	hlist_del_rcu(&key->node);

  	atomic_sub(sizeof(*key), &sk->sk_omem_alloc);

  	kfree_rcu(key, rcu);

  	return 0;

  }

  EXPORT_SYMBOL(tcp_md5_do_del);

  static void tcp_clear_md5_list(struct sock *sk)

  {
  	struct tcp_sock *tp = tcp_sk(sk);

  	struct tcp_md5sig_key *key;

  	struct hlist_node *n;

  	struct tcp_md5sig_info *md5sig;

  	md5sig = rcu_dereference_protected(tp->md5sig_info, 1);

  	hlist_for_each_entry_safe(key, n, &md5sig->head, node) {

  		hlist_del_rcu(&key->node);

  		atomic_sub(sizeof(*key), &sk->sk_omem_alloc);

  		kfree_rcu(key, rcu);

  	}
  }

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

  {
  	struct tcp_md5sig cmd;
  	struct sockaddr_in *sin = (struct sockaddr_in *)&cmd.tcpm_addr;

  	u8 prefixlen = 32;

  
  	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 (optname == TCP_MD5SIG_EXT &&
  	    cmd.tcpm_flags & TCP_MD5SIG_FLAG_PREFIX) {
  		prefixlen = cmd.tcpm_prefixlen;
  		if (prefixlen > 32)
  			return -EINVAL;
  	}

  	if (!cmd.tcpm_keylen)

  		return tcp_md5_do_del(sk, (union tcp_md5_addr *)&sin->sin_addr.s_addr,

  				      AF_INET, prefixlen);

  
  	if (cmd.tcpm_keylen > TCP_MD5SIG_MAXKEYLEN)
  		return -EINVAL;

  	return tcp_md5_do_add(sk, (union tcp_md5_addr *)&sin->sin_addr.s_addr,

  			      AF_INET, prefixlen, cmd.tcpm_key, cmd.tcpm_keylen,

  			      GFP_KERNEL);

  }

  static int tcp_v4_md5_hash_headers(struct tcp_md5sig_pool *hp,
  				   __be32 daddr, __be32 saddr,
  				   const struct tcphdr *th, int nbytes)

  {

  	struct tcp4_pseudohdr *bp;

  	struct scatterlist sg;

  	struct tcphdr *_th;

  	bp = hp->scratch;

  	bp->saddr = saddr;
  	bp->daddr = daddr;
  	bp->pad = 0;

  	bp->protocol = IPPROTO_TCP;

  	bp->len = cpu_to_be16(nbytes);

  	_th = (struct tcphdr *)(bp + 1);
  	memcpy(_th, th, sizeof(*th));
  	_th->check = 0;
  
  	sg_init_one(&sg, bp, sizeof(*bp) + sizeof(*th));
  	ahash_request_set_crypt(hp->md5_req, &sg, NULL,
  				sizeof(*bp) + sizeof(*th));

  	return crypto_ahash_update(hp->md5_req);

  }

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

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

  {
  	struct tcp_md5sig_pool *hp;

  	struct ahash_request *req;

  
  	hp = tcp_get_md5sig_pool();
  	if (!hp)
  		goto clear_hash_noput;

  	req = hp->md5_req;

  	if (crypto_ahash_init(req))

  		goto clear_hash;

  	if (tcp_v4_md5_hash_headers(hp, daddr, saddr, th, th->doff << 2))

  		goto clear_hash;
  	if (tcp_md5_hash_key(hp, key))
  		goto clear_hash;

  	ahash_request_set_crypt(req, NULL, md5_hash, 0);
  	if (crypto_ahash_final(req))

  		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, const struct tcp_md5sig_key *key,
  			const struct sock *sk,

  			const struct sk_buff *skb)

  {

  	struct tcp_md5sig_pool *hp;

  	struct ahash_request *req;

  	const struct tcphdr *th = tcp_hdr(skb);

  	__be32 saddr, daddr;

  	if (sk) { /* valid for establish/request sockets */
  		saddr = sk->sk_rcv_saddr;
  		daddr = sk->sk_daddr;

  	} 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;

  	req = hp->md5_req;

  	if (crypto_ahash_init(req))

  		goto clear_hash;

  	if (tcp_v4_md5_hash_headers(hp, daddr, saddr, th, skb->len))

  		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;

  	ahash_request_set_crypt(req, NULL, md5_hash, 0);
  	if (crypto_ahash_final(req))

  		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);

  #endif

  /* Called with rcu_read_lock() */

  static bool tcp_v4_inbound_md5_hash(const struct sock *sk,

  				    const struct sk_buff *skb)

  {

  #ifdef CONFIG_TCP_MD5SIG

  	/*
  	 * 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_md5_do_lookup(sk, (union tcp_md5_addr *)&iph->saddr,
  					  AF_INET);

  	hash_location = tcp_parse_md5sig_option(th);

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

  		return false;

  
  	if (hash_expected && !hash_location) {

  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5NOTFOUND);

  		return true;

  	}
  
  	if (!hash_expected && hash_location) {

  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);

  		return true;

  	}
  
  	/* 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, skb);

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

  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5FAILURE);

  		net_info_ratelimited("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 true;

  	}

  	return false;

  #endif

  	return false;
  }

  static void tcp_v4_init_req(struct request_sock *req,
  			    const struct sock *sk_listener,

  			    struct sk_buff *skb)
  {
  	struct inet_request_sock *ireq = inet_rsk(req);

  	struct net *net = sock_net(sk_listener);