Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1501 insertions, 0 deletions

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
new file mode 100644
index 0000000000..762817d6c8
--- /dev/null
+++ b/net/ipv4/inet_connection_sock.c
@@ -0,0 +1,1501 @@
+// 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.
+ *
+ *		Support for INET connection oriented protocols.
+ *
+ * Authors:	See the TCP sources
+ */
+
+#include <linux/module.h>
+#include <linux/jhash.h>
+
+#include <net/inet_connection_sock.h>
+#include <net/inet_hashtables.h>
+#include <net/inet_timewait_sock.h>
+#include <net/ip.h>
+#include <net/route.h>
+#include <net/tcp_states.h>
+#include <net/xfrm.h>
+#include <net/tcp.h>
+#include <net/sock_reuseport.h>
+#include <net/addrconf.h>
+
+#if IS_ENABLED(CONFIG_IPV6)
+/* match_sk*_wildcard == true:  IPV6_ADDR_ANY equals to any IPv6 addresses
+ *				if IPv6 only, and any IPv4 addresses
+ *				if not IPv6 only
+ * match_sk*_wildcard == false: addresses must be exactly the same, i.e.
+ *				IPV6_ADDR_ANY only equals to IPV6_ADDR_ANY,
+ *				and 0.0.0.0 equals to 0.0.0.0 only
+ */
+static bool ipv6_rcv_saddr_equal(const struct in6_addr *sk1_rcv_saddr6,
+				 const struct in6_addr *sk2_rcv_saddr6,
+				 __be32 sk1_rcv_saddr, __be32 sk2_rcv_saddr,
+				 bool sk1_ipv6only, bool sk2_ipv6only,
+				 bool match_sk1_wildcard,
+				 bool match_sk2_wildcard)
+{
+	int addr_type = ipv6_addr_type(sk1_rcv_saddr6);
+	int addr_type2 = sk2_rcv_saddr6 ? ipv6_addr_type(sk2_rcv_saddr6) : IPV6_ADDR_MAPPED;
+
+	/* if both are mapped, treat as IPv4 */
+	if (addr_type == IPV6_ADDR_MAPPED && addr_type2 == IPV6_ADDR_MAPPED) {
+		if (!sk2_ipv6only) {
+			if (sk1_rcv_saddr == sk2_rcv_saddr)
+				return true;
+			return (match_sk1_wildcard && !sk1_rcv_saddr) ||
+				(match_sk2_wildcard && !sk2_rcv_saddr);
+		}
+		return false;
+	}
+
+	if (addr_type == IPV6_ADDR_ANY && addr_type2 == IPV6_ADDR_ANY)
+		return true;
+
+	if (addr_type2 == IPV6_ADDR_ANY && match_sk2_wildcard &&
+	    !(sk2_ipv6only && addr_type == IPV6_ADDR_MAPPED))
+		return true;
+
+	if (addr_type == IPV6_ADDR_ANY && match_sk1_wildcard &&
+	    !(sk1_ipv6only && addr_type2 == IPV6_ADDR_MAPPED))
+		return true;
+
+	if (sk2_rcv_saddr6 &&
+	    ipv6_addr_equal(sk1_rcv_saddr6, sk2_rcv_saddr6))
+		return true;
+
+	return false;
+}
+#endif
+
+/* match_sk*_wildcard == true:  0.0.0.0 equals to any IPv4 addresses
+ * match_sk*_wildcard == false: addresses must be exactly the same, i.e.
+ *				0.0.0.0 only equals to 0.0.0.0
+ */
+static bool ipv4_rcv_saddr_equal(__be32 sk1_rcv_saddr, __be32 sk2_rcv_saddr,
+				 bool sk2_ipv6only, bool match_sk1_wildcard,
+				 bool match_sk2_wildcard)
+{
+	if (!sk2_ipv6only) {
+		if (sk1_rcv_saddr == sk2_rcv_saddr)
+			return true;
+		return (match_sk1_wildcard && !sk1_rcv_saddr) ||
+			(match_sk2_wildcard && !sk2_rcv_saddr);
+	}
+	return false;
+}
+
+bool inet_rcv_saddr_equal(const struct sock *sk, const struct sock *sk2,
+			  bool match_wildcard)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return ipv6_rcv_saddr_equal(&sk->sk_v6_rcv_saddr,
+					    inet6_rcv_saddr(sk2),
+					    sk->sk_rcv_saddr,
+					    sk2->sk_rcv_saddr,
+					    ipv6_only_sock(sk),
+					    ipv6_only_sock(sk2),
+					    match_wildcard,
+					    match_wildcard);
+#endif
+	return ipv4_rcv_saddr_equal(sk->sk_rcv_saddr, sk2->sk_rcv_saddr,
+				    ipv6_only_sock(sk2), match_wildcard,
+				    match_wildcard);
+}
+EXPORT_SYMBOL(inet_rcv_saddr_equal);
+
+bool inet_rcv_saddr_any(const struct sock *sk)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return ipv6_addr_any(&sk->sk_v6_rcv_saddr);
+#endif
+	return !sk->sk_rcv_saddr;
+}
+
+void inet_get_local_port_range(const struct net *net, int *low, int *high)
+{
+	unsigned int seq;
+
+	do {
+		seq = read_seqbegin(&net->ipv4.ip_local_ports.lock);
+
+		*low = net->ipv4.ip_local_ports.range[0];
+		*high = net->ipv4.ip_local_ports.range[1];
+	} while (read_seqretry(&net->ipv4.ip_local_ports.lock, seq));
+}
+EXPORT_SYMBOL(inet_get_local_port_range);
+
+void inet_sk_get_local_port_range(const struct sock *sk, int *low, int *high)
+{
+	const struct inet_sock *inet = inet_sk(sk);
+	const struct net *net = sock_net(sk);
+	int lo, hi, sk_lo, sk_hi;
+
+	inet_get_local_port_range(net, &lo, &hi);
+
+	sk_lo = inet->local_port_range.lo;
+	sk_hi = inet->local_port_range.hi;
+
+	if (unlikely(lo <= sk_lo && sk_lo <= hi))
+		lo = sk_lo;
+	if (unlikely(lo <= sk_hi && sk_hi <= hi))
+		hi = sk_hi;
+
+	*low = lo;
+	*high = hi;
+}
+EXPORT_SYMBOL(inet_sk_get_local_port_range);
+
+static bool inet_use_bhash2_on_bind(const struct sock *sk)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sk->sk_family == AF_INET6) {
+		int addr_type = ipv6_addr_type(&sk->sk_v6_rcv_saddr);
+
+		return addr_type != IPV6_ADDR_ANY &&
+			addr_type != IPV6_ADDR_MAPPED;
+	}
+#endif
+	return sk->sk_rcv_saddr != htonl(INADDR_ANY);
+}
+
+static bool inet_bind_conflict(const struct sock *sk, struct sock *sk2,
+			       kuid_t sk_uid, bool relax,
+			       bool reuseport_cb_ok, bool reuseport_ok)
+{
+	int bound_dev_if2;
+
+	if (sk == sk2)
+		return false;
+
+	bound_dev_if2 = READ_ONCE(sk2->sk_bound_dev_if);
+
+	if (!sk->sk_bound_dev_if || !bound_dev_if2 ||
+	    sk->sk_bound_dev_if == bound_dev_if2) {
+		if (sk->sk_reuse && sk2->sk_reuse &&
+		    sk2->sk_state != TCP_LISTEN) {
+			if (!relax || (!reuseport_ok && sk->sk_reuseport &&
+				       sk2->sk_reuseport && reuseport_cb_ok &&
+				       (sk2->sk_state == TCP_TIME_WAIT ||
+					uid_eq(sk_uid, sock_i_uid(sk2)))))
+				return true;
+		} else if (!reuseport_ok || !sk->sk_reuseport ||
+			   !sk2->sk_reuseport || !reuseport_cb_ok ||
+			   (sk2->sk_state != TCP_TIME_WAIT &&
+			    !uid_eq(sk_uid, sock_i_uid(sk2)))) {
+			return true;
+		}
+	}
+	return false;
+}
+
+static bool __inet_bhash2_conflict(const struct sock *sk, struct sock *sk2,
+				   kuid_t sk_uid, bool relax,
+				   bool reuseport_cb_ok, bool reuseport_ok)
+{
+	if (sk->sk_family == AF_INET && ipv6_only_sock(sk2))
+		return false;
+
+	return inet_bind_conflict(sk, sk2, sk_uid, relax,
+				  reuseport_cb_ok, reuseport_ok);
+}
+
+static bool inet_bhash2_conflict(const struct sock *sk,
+				 const struct inet_bind2_bucket *tb2,
+				 kuid_t sk_uid,
+				 bool relax, bool reuseport_cb_ok,
+				 bool reuseport_ok)
+{
+	struct inet_timewait_sock *tw2;
+	struct sock *sk2;
+
+	sk_for_each_bound_bhash2(sk2, &tb2->owners) {
+		if (__inet_bhash2_conflict(sk, sk2, sk_uid, relax,
+					   reuseport_cb_ok, reuseport_ok))
+			return true;
+	}
+
+	twsk_for_each_bound_bhash2(tw2, &tb2->deathrow) {
+		sk2 = (struct sock *)tw2;
+
+		if (__inet_bhash2_conflict(sk, sk2, sk_uid, relax,
+					   reuseport_cb_ok, reuseport_ok))
+			return true;
+	}
+
+	return false;
+}
+
+/* This should be called only when the tb and tb2 hashbuckets' locks are held */
+static int inet_csk_bind_conflict(const struct sock *sk,
+				  const struct inet_bind_bucket *tb,
+				  const struct inet_bind2_bucket *tb2, /* may be null */
+				  bool relax, bool reuseport_ok)
+{
+	bool reuseport_cb_ok;
+	struct sock_reuseport *reuseport_cb;
+	kuid_t uid = sock_i_uid((struct sock *)sk);
+
+	rcu_read_lock();
+	reuseport_cb = rcu_dereference(sk->sk_reuseport_cb);
+	/* paired with WRITE_ONCE() in __reuseport_(add|detach)_closed_sock */
+	reuseport_cb_ok = !reuseport_cb || READ_ONCE(reuseport_cb->num_closed_socks);
+	rcu_read_unlock();
+
+	/*
+	 * Unlike other sk lookup places we do not check
+	 * for sk_net here, since _all_ the socks listed
+	 * in tb->owners and tb2->owners list belong
+	 * to the same net - the one this bucket belongs to.
+	 */
+
+	if (!inet_use_bhash2_on_bind(sk)) {
+		struct sock *sk2;
+
+		sk_for_each_bound(sk2, &tb->owners)
+			if (inet_bind_conflict(sk, sk2, uid, relax,
+					       reuseport_cb_ok, reuseport_ok) &&
+			    inet_rcv_saddr_equal(sk, sk2, true))
+				return true;
+
+		return false;
+	}
+
+	/* Conflicts with an existing IPV6_ADDR_ANY (if ipv6) or INADDR_ANY (if
+	 * ipv4) should have been checked already. We need to do these two
+	 * checks separately because their spinlocks have to be acquired/released
+	 * independently of each other, to prevent possible deadlocks
+	 */
+	return tb2 && inet_bhash2_conflict(sk, tb2, uid, relax, reuseport_cb_ok,
+					   reuseport_ok);
+}
+
+/* Determine if there is a bind conflict with an existing IPV6_ADDR_ANY (if ipv6) or
+ * INADDR_ANY (if ipv4) socket.
+ *
+ * Caller must hold bhash hashbucket lock with local bh disabled, to protect
+ * against concurrent binds on the port for addr any
+ */
+static bool inet_bhash2_addr_any_conflict(const struct sock *sk, int port, int l3mdev,
+					  bool relax, bool reuseport_ok)
+{
+	kuid_t uid = sock_i_uid((struct sock *)sk);
+	const struct net *net = sock_net(sk);
+	struct sock_reuseport *reuseport_cb;
+	struct inet_bind_hashbucket *head2;
+	struct inet_bind2_bucket *tb2;
+	bool reuseport_cb_ok;
+
+	rcu_read_lock();
+	reuseport_cb = rcu_dereference(sk->sk_reuseport_cb);
+	/* paired with WRITE_ONCE() in __reuseport_(add|detach)_closed_sock */
+	reuseport_cb_ok = !reuseport_cb || READ_ONCE(reuseport_cb->num_closed_socks);
+	rcu_read_unlock();
+
+	head2 = inet_bhash2_addr_any_hashbucket(sk, net, port);
+
+	spin_lock(&head2->lock);
+
+	inet_bind_bucket_for_each(tb2, &head2->chain)
+		if (inet_bind2_bucket_match_addr_any(tb2, net, port, l3mdev, sk))
+			break;
+
+	if (tb2 && inet_bhash2_conflict(sk, tb2, uid, relax, reuseport_cb_ok,
+					reuseport_ok)) {
+		spin_unlock(&head2->lock);
+		return true;
+	}
+
+	spin_unlock(&head2->lock);
+	return false;
+}
+
+/*
+ * Find an open port number for the socket.  Returns with the
+ * inet_bind_hashbucket locks held if successful.
+ */
+static struct inet_bind_hashbucket *
+inet_csk_find_open_port(const struct sock *sk, struct inet_bind_bucket **tb_ret,
+			struct inet_bind2_bucket **tb2_ret,
+			struct inet_bind_hashbucket **head2_ret, int *port_ret)
+{
+	struct inet_hashinfo *hinfo = tcp_or_dccp_get_hashinfo(sk);
+	int i, low, high, attempt_half, port, l3mdev;
+	struct inet_bind_hashbucket *head, *head2;
+	struct net *net = sock_net(sk);
+	struct inet_bind2_bucket *tb2;
+	struct inet_bind_bucket *tb;
+	u32 remaining, offset;
+	bool relax = false;
+
+	l3mdev = inet_sk_bound_l3mdev(sk);
+ports_exhausted:
+	attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0;
+other_half_scan:
+	inet_sk_get_local_port_range(sk, &low, &high);
+	high++; /* [32768, 60999] -> [32768, 61000[ */
+	if (high - low < 4)
+		attempt_half = 0;
+	if (attempt_half) {
+		int half = low + (((high - low) >> 2) << 1);
+
+		if (attempt_half == 1)
+			high = half;
+		else
+			low = half;
+	}
+	remaining = high - low;
+	if (likely(remaining > 1))
+		remaining &= ~1U;
+
+	offset = get_random_u32_below(remaining);
+	/* __inet_hash_connect() favors ports having @low parity
+	 * We do the opposite to not pollute connect() users.
+	 */
+	offset |= 1U;
+
+other_parity_scan:
+	port = low + offset;
+	for (i = 0; i < remaining; i += 2, port += 2) {
+		if (unlikely(port >= high))
+			port -= remaining;
+		if (inet_is_local_reserved_port(net, port))
+			continue;
+		head = &hinfo->bhash[inet_bhashfn(net, port,
+						  hinfo->bhash_size)];
+		spin_lock_bh(&head->lock);
+		if (inet_use_bhash2_on_bind(sk)) {
+			if (inet_bhash2_addr_any_conflict(sk, port, l3mdev, relax, false))
+				goto next_port;
+		}
+
+		head2 = inet_bhashfn_portaddr(hinfo, sk, net, port);
+		spin_lock(&head2->lock);
+		tb2 = inet_bind2_bucket_find(head2, net, port, l3mdev, sk);
+		inet_bind_bucket_for_each(tb, &head->chain)
+			if (inet_bind_bucket_match(tb, net, port, l3mdev)) {
+				if (!inet_csk_bind_conflict(sk, tb, tb2,
+							    relax, false))
+					goto success;
+				spin_unlock(&head2->lock);
+				goto next_port;
+			}
+		tb = NULL;
+		goto success;
+next_port:
+		spin_unlock_bh(&head->lock);
+		cond_resched();
+	}
+
+	offset--;
+	if (!(offset & 1))
+		goto other_parity_scan;
+
+	if (attempt_half == 1) {
+		/* OK we now try the upper half of the range */
+		attempt_half = 2;
+		goto other_half_scan;
+	}
+
+	if (READ_ONCE(net->ipv4.sysctl_ip_autobind_reuse) && !relax) {
+		/* We still have a chance to connect to different destinations */
+		relax = true;
+		goto ports_exhausted;
+	}
+	return NULL;
+success:
+	*port_ret = port;
+	*tb_ret = tb;
+	*tb2_ret = tb2;
+	*head2_ret = head2;
+	return head;
+}
+
+static inline int sk_reuseport_match(struct inet_bind_bucket *tb,
+				     struct sock *sk)
+{
+	kuid_t uid = sock_i_uid(sk);
+
+	if (tb->fastreuseport <= 0)
+		return 0;
+	if (!sk->sk_reuseport)
+		return 0;
+	if (rcu_access_pointer(sk->sk_reuseport_cb))
+		return 0;
+	if (!uid_eq(tb->fastuid, uid))
+		return 0;
+	/* We only need to check the rcv_saddr if this tb was once marked
+	 * without fastreuseport and then was reset, as we can only know that
+	 * the fast_*rcv_saddr doesn't have any conflicts with the socks on the
+	 * owners list.
+	 */
+	if (tb->fastreuseport == FASTREUSEPORT_ANY)
+		return 1;
+#if IS_ENABLED(CONFIG_IPV6)
+	if (tb->fast_sk_family == AF_INET6)
+		return ipv6_rcv_saddr_equal(&tb->fast_v6_rcv_saddr,
+					    inet6_rcv_saddr(sk),
+					    tb->fast_rcv_saddr,
+					    sk->sk_rcv_saddr,
+					    tb->fast_ipv6_only,
+					    ipv6_only_sock(sk), true, false);
+#endif
+	return ipv4_rcv_saddr_equal(tb->fast_rcv_saddr, sk->sk_rcv_saddr,
+				    ipv6_only_sock(sk), true, false);
+}
+
+void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
+			       struct sock *sk)
+{
+	kuid_t uid = sock_i_uid(sk);
+	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
+
+	if (hlist_empty(&tb->owners)) {
+		tb->fastreuse = reuse;
+		if (sk->sk_reuseport) {
+			tb->fastreuseport = FASTREUSEPORT_ANY;
+			tb->fastuid = uid;
+			tb->fast_rcv_saddr = sk->sk_rcv_saddr;
+			tb->fast_ipv6_only = ipv6_only_sock(sk);
+			tb->fast_sk_family = sk->sk_family;
+#if IS_ENABLED(CONFIG_IPV6)
+			tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
+#endif
+		} else {
+			tb->fastreuseport = 0;
+		}
+	} else {
+		if (!reuse)
+			tb->fastreuse = 0;
+		if (sk->sk_reuseport) {
+			/* We didn't match or we don't have fastreuseport set on
+			 * the tb, but we have sk_reuseport set on this socket
+			 * and we know that there are no bind conflicts with
+			 * this socket in this tb, so reset our tb's reuseport
+			 * settings so that any subsequent sockets that match
+			 * our current socket will be put on the fast path.
+			 *
+			 * If we reset we need to set FASTREUSEPORT_STRICT so we
+			 * do extra checking for all subsequent sk_reuseport
+			 * socks.
+			 */
+			if (!sk_reuseport_match(tb, sk)) {
+				tb->fastreuseport = FASTREUSEPORT_STRICT;
+				tb->fastuid = uid;
+				tb->fast_rcv_saddr = sk->sk_rcv_saddr;
+				tb->fast_ipv6_only = ipv6_only_sock(sk);
+				tb->fast_sk_family = sk->sk_family;
+#if IS_ENABLED(CONFIG_IPV6)
+				tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
+#endif
+			}
+		} else {
+			tb->fastreuseport = 0;
+		}
+	}
+}
+
+/* Obtain a reference to a local port for the given sock,
+ * if snum is zero it means select any available local port.
+ * We try to allocate an odd port (and leave even ports for connect())
+ */
+int inet_csk_get_port(struct sock *sk, unsigned short snum)
+{
+	struct inet_hashinfo *hinfo = tcp_or_dccp_get_hashinfo(sk);
+	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
+	bool found_port = false, check_bind_conflict = true;
+	bool bhash_created = false, bhash2_created = false;
+	int ret = -EADDRINUSE, port = snum, l3mdev;
+	struct inet_bind_hashbucket *head, *head2;
+	struct inet_bind2_bucket *tb2 = NULL;
+	struct inet_bind_bucket *tb = NULL;
+	bool head2_lock_acquired = false;
+	struct net *net = sock_net(sk);
+
+	l3mdev = inet_sk_bound_l3mdev(sk);
+
+	if (!port) {
+		head = inet_csk_find_open_port(sk, &tb, &tb2, &head2, &port);
+		if (!head)
+			return ret;
+
+		head2_lock_acquired = true;
+
+		if (tb && tb2)
+			goto success;
+		found_port = true;
+	} else {
+		head = &hinfo->bhash[inet_bhashfn(net, port,
+						  hinfo->bhash_size)];
+		spin_lock_bh(&head->lock);
+		inet_bind_bucket_for_each(tb, &head->chain)
+			if (inet_bind_bucket_match(tb, net, port, l3mdev))
+				break;
+	}
+
+	if (!tb) {
+		tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep, net,
+					     head, port, l3mdev);
+		if (!tb)
+			goto fail_unlock;
+		bhash_created = true;
+	}
+
+	if (!found_port) {
+		if (!hlist_empty(&tb->owners)) {
+			if (sk->sk_reuse == SK_FORCE_REUSE ||
+			    (tb->fastreuse > 0 && reuse) ||
+			    sk_reuseport_match(tb, sk))
+				check_bind_conflict = false;
+		}
+
+		if (check_bind_conflict && inet_use_bhash2_on_bind(sk)) {
+			if (inet_bhash2_addr_any_conflict(sk, port, l3mdev, true, true))
+				goto fail_unlock;
+		}
+
+		head2 = inet_bhashfn_portaddr(hinfo, sk, net, port);
+		spin_lock(&head2->lock);
+		head2_lock_acquired = true;
+		tb2 = inet_bind2_bucket_find(head2, net, port, l3mdev, sk);
+	}
+
+	if (!tb2) {
+		tb2 = inet_bind2_bucket_create(hinfo->bind2_bucket_cachep,
+					       net, head2, port, l3mdev, sk);
+		if (!tb2)
+			goto fail_unlock;
+		bhash2_created = true;
+	}
+
+	if (!found_port && check_bind_conflict) {
+		if (inet_csk_bind_conflict(sk, tb, tb2, true, true))
+			goto fail_unlock;
+	}
+
+success:
+	inet_csk_update_fastreuse(tb, sk);
+
+	if (!inet_csk(sk)->icsk_bind_hash)
+		inet_bind_hash(sk, tb, tb2, port);
+	WARN_ON(inet_csk(sk)->icsk_bind_hash != tb);
+	WARN_ON(inet_csk(sk)->icsk_bind2_hash != tb2);
+	ret = 0;
+
+fail_unlock:
+	if (ret) {
+		if (bhash_created)
+			inet_bind_bucket_destroy(hinfo->bind_bucket_cachep, tb);
+		if (bhash2_created)
+			inet_bind2_bucket_destroy(hinfo->bind2_bucket_cachep,
+						  tb2);
+	}
+	if (head2_lock_acquired)
+		spin_unlock(&head2->lock);
+	spin_unlock_bh(&head->lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(inet_csk_get_port);
+
+/*
+ * Wait for an incoming connection, avoid race conditions. This must be called
+ * with the socket locked.
+ */
+static int inet_csk_wait_for_connect(struct sock *sk, long timeo)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	DEFINE_WAIT(wait);
+	int err;
+
+	/*
+	 * True wake-one mechanism for incoming connections: only
+	 * one process gets woken up, not the 'whole herd'.
+	 * Since we do not 'race & poll' for established sockets
+	 * anymore, the common case will execute the loop only once.
+	 *
+	 * Subtle issue: "add_wait_queue_exclusive()" will be added
+	 * after any current non-exclusive waiters, and we know that
+	 * it will always _stay_ after any new non-exclusive waiters
+	 * because all non-exclusive waiters are added at the
+	 * beginning of the wait-queue. As such, it's ok to "drop"
+	 * our exclusiveness temporarily when we get woken up without
+	 * having to remove and re-insert us on the wait queue.
+	 */
+	for (;;) {
+		prepare_to_wait_exclusive(sk_sleep(sk), &wait,
+					  TASK_INTERRUPTIBLE);
+		release_sock(sk);
+		if (reqsk_queue_empty(&icsk->icsk_accept_queue))
+			timeo = schedule_timeout(timeo);
+		sched_annotate_sleep();
+		lock_sock(sk);
+		err = 0;
+		if (!reqsk_queue_empty(&icsk->icsk_accept_queue))
+			break;
+		err = -EINVAL;
+		if (sk->sk_state != TCP_LISTEN)
+			break;
+		err = sock_intr_errno(timeo);
+		if (signal_pending(current))
+			break;
+		err = -EAGAIN;
+		if (!timeo)
+			break;
+	}
+	finish_wait(sk_sleep(sk), &wait);
+	return err;
+}
+
+/*
+ * This will accept the next outstanding connection.
+ */
+struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct request_sock_queue *queue = &icsk->icsk_accept_queue;
+	struct request_sock *req;
+	struct sock *newsk;
+	int error;
+
+	lock_sock(sk);
+
+	/* We need to make sure that this socket is listening,
+	 * and that it has something pending.
+	 */
+	error = -EINVAL;
+	if (sk->sk_state != TCP_LISTEN)
+		goto out_err;
+
+	/* Find already established connection */
+	if (reqsk_queue_empty(queue)) {
+		long timeo = sock_rcvtimeo(sk, flags & O_NONBLOCK);
+
+		/* If this is a non blocking socket don't sleep */
+		error = -EAGAIN;
+		if (!timeo)
+			goto out_err;
+
+		error = inet_csk_wait_for_connect(sk, timeo);
+		if (error)
+			goto out_err;
+	}
+	req = reqsk_queue_remove(queue, sk);
+	newsk = req->sk;
+
+	if (sk->sk_protocol == IPPROTO_TCP &&
+	    tcp_rsk(req)->tfo_listener) {
+		spin_lock_bh(&queue->fastopenq.lock);
+		if (tcp_rsk(req)->tfo_listener) {
+			/* We are still waiting for the final ACK from 3WHS
+			 * so can't free req now. Instead, we set req->sk to
+			 * NULL to signify that the child socket is taken
+			 * so reqsk_fastopen_remove() will free the req
+			 * when 3WHS finishes (or is aborted).
+			 */
+			req->sk = NULL;
+			req = NULL;
+		}
+		spin_unlock_bh(&queue->fastopenq.lock);
+	}
+
+out:
+	release_sock(sk);
+	if (newsk && mem_cgroup_sockets_enabled) {
+		int amt = 0;
+
+		/* atomically get the memory usage, set and charge the
+		 * newsk->sk_memcg.
+		 */
+		lock_sock(newsk);
+
+		mem_cgroup_sk_alloc(newsk);
+		if (newsk->sk_memcg) {
+			/* The socket has not been accepted yet, no need
+			 * to look at newsk->sk_wmem_queued.
+			 */
+			amt = sk_mem_pages(newsk->sk_forward_alloc +
+					   atomic_read(&newsk->sk_rmem_alloc));
+		}
+
+		if (amt)
+			mem_cgroup_charge_skmem(newsk->sk_memcg, amt,
+						GFP_KERNEL | __GFP_NOFAIL);
+
+		release_sock(newsk);
+	}
+	if (req)
+		reqsk_put(req);
+
+	if (newsk)
+		inet_init_csk_locks(newsk);
+
+	return newsk;
+out_err:
+	newsk = NULL;
+	req = NULL;
+	*err = error;
+	goto out;
+}
+EXPORT_SYMBOL(inet_csk_accept);
+
+/*
+ * Using different timers for retransmit, delayed acks and probes
+ * We may wish use just one timer maintaining a list of expire jiffies
+ * to optimize.
+ */
+void inet_csk_init_xmit_timers(struct sock *sk,
+			       void (*retransmit_handler)(struct timer_list *t),
+			       void (*delack_handler)(struct timer_list *t),
+			       void (*keepalive_handler)(struct timer_list *t))
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	timer_setup(&icsk->icsk_retransmit_timer, retransmit_handler, 0);
+	timer_setup(&icsk->icsk_delack_timer, delack_handler, 0);
+	timer_setup(&sk->sk_timer, keepalive_handler, 0);
+	icsk->icsk_pending = icsk->icsk_ack.pending = 0;
+}
+EXPORT_SYMBOL(inet_csk_init_xmit_timers);
+
+void inet_csk_clear_xmit_timers(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	icsk->icsk_pending = icsk->icsk_ack.pending = 0;
+
+	sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
+	sk_stop_timer(sk, &icsk->icsk_delack_timer);
+	sk_stop_timer(sk, &sk->sk_timer);
+}
+EXPORT_SYMBOL(inet_csk_clear_xmit_timers);
+
+void inet_csk_delete_keepalive_timer(struct sock *sk)
+{
+	sk_stop_timer(sk, &sk->sk_timer);
+}
+EXPORT_SYMBOL(inet_csk_delete_keepalive_timer);
+
+void inet_csk_reset_keepalive_timer(struct sock *sk, unsigned long len)
+{
+	sk_reset_timer(sk, &sk->sk_timer, jiffies + len);
+}
+EXPORT_SYMBOL(inet_csk_reset_keepalive_timer);
+
+struct dst_entry *inet_csk_route_req(const struct sock *sk,
+				     struct flowi4 *fl4,
+				     const struct request_sock *req)
+{
+	const struct inet_request_sock *ireq = inet_rsk(req);
+	struct net *net = read_pnet(&ireq->ireq_net);
+	struct ip_options_rcu *opt;
+	struct rtable *rt;
+
+	rcu_read_lock();
+	opt = rcu_dereference(ireq->ireq_opt);
+
+	flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
+			   ip_sock_rt_tos(sk), ip_sock_rt_scope(sk),
+			   sk->sk_protocol, inet_sk_flowi_flags(sk),
+			   (opt && opt->opt.srr) ? opt->opt.faddr : ireq->ir_rmt_addr,
+			   ireq->ir_loc_addr, ireq->ir_rmt_port,
+			   htons(ireq->ir_num), sk->sk_uid);
+	security_req_classify_flow(req, flowi4_to_flowi_common(fl4));
+	rt = ip_route_output_flow(net, fl4, sk);
+	if (IS_ERR(rt))
+		goto no_route;
+	if (opt && opt->opt.is_strictroute && rt->rt_uses_gateway)
+		goto route_err;
+	rcu_read_unlock();
+	return &rt->dst;
+
+route_err:
+	ip_rt_put(rt);
+no_route:
+	rcu_read_unlock();
+	__IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(inet_csk_route_req);
+
+struct dst_entry *inet_csk_route_child_sock(const struct sock *sk,
+					    struct sock *newsk,
+					    const struct request_sock *req)
+{
+	const struct inet_request_sock *ireq = inet_rsk(req);
+	struct net *net = read_pnet(&ireq->ireq_net);
+	struct inet_sock *newinet = inet_sk(newsk);
+	struct ip_options_rcu *opt;
+	struct flowi4 *fl4;
+	struct rtable *rt;
+
+	opt = rcu_dereference(ireq->ireq_opt);
+	fl4 = &newinet->cork.fl.u.ip4;
+
+	flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
+			   ip_sock_rt_tos(sk), ip_sock_rt_scope(sk),
+			   sk->sk_protocol, inet_sk_flowi_flags(sk),
+			   (opt && opt->opt.srr) ? opt->opt.faddr : ireq->ir_rmt_addr,
+			   ireq->ir_loc_addr, ireq->ir_rmt_port,
+			   htons(ireq->ir_num), sk->sk_uid);
+	security_req_classify_flow(req, flowi4_to_flowi_common(fl4));
+	rt = ip_route_output_flow(net, fl4, sk);
+	if (IS_ERR(rt))
+		goto no_route;
+	if (opt && opt->opt.is_strictroute && rt->rt_uses_gateway)
+		goto route_err;
+	return &rt->dst;
+
+route_err:
+	ip_rt_put(rt);
+no_route:
+	__IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(inet_csk_route_child_sock);
+
+/* Decide when to expire the request and when to resend SYN-ACK */
+static void syn_ack_recalc(struct request_sock *req,
+			   const int max_syn_ack_retries,
+			   const u8 rskq_defer_accept,
+			   int *expire, int *resend)
+{
+	if (!rskq_defer_accept) {
+		*expire = req->num_timeout >= max_syn_ack_retries;
+		*resend = 1;
+		return;
+	}
+	*expire = req->num_timeout >= max_syn_ack_retries &&
+		  (!inet_rsk(req)->acked || req->num_timeout >= rskq_defer_accept);
+	/* Do not resend while waiting for data after ACK,
+	 * start to resend on end of deferring period to give
+	 * last chance for data or ACK to create established socket.
+	 */
+	*resend = !inet_rsk(req)->acked ||
+		  req->num_timeout >= rskq_defer_accept - 1;
+}
+
+int inet_rtx_syn_ack(const struct sock *parent, struct request_sock *req)
+{
+	int err = req->rsk_ops->rtx_syn_ack(parent, req);
+
+	if (!err)
+		req->num_retrans++;
+	return err;
+}
+EXPORT_SYMBOL(inet_rtx_syn_ack);
+
+static struct request_sock *inet_reqsk_clone(struct request_sock *req,
+					     struct sock *sk)
+{
+	struct sock *req_sk, *nreq_sk;
+	struct request_sock *nreq;
+
+	nreq = kmem_cache_alloc(req->rsk_ops->slab, GFP_ATOMIC | __GFP_NOWARN);
+	if (!nreq) {
+		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
+
+		/* paired with refcount_inc_not_zero() in reuseport_migrate_sock() */
+		sock_put(sk);
+		return NULL;
+	}
+
+	req_sk = req_to_sk(req);
+	nreq_sk = req_to_sk(nreq);
+
+	memcpy(nreq_sk, req_sk,
+	       offsetof(struct sock, sk_dontcopy_begin));
+	memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
+	       req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end));
+
+	sk_node_init(&nreq_sk->sk_node);
+	nreq_sk->sk_tx_queue_mapping = req_sk->sk_tx_queue_mapping;
+#ifdef CONFIG_SOCK_RX_QUEUE_MAPPING
+	nreq_sk->sk_rx_queue_mapping = req_sk->sk_rx_queue_mapping;
+#endif
+	nreq_sk->sk_incoming_cpu = req_sk->sk_incoming_cpu;
+
+	nreq->rsk_listener = sk;
+
+	/* We need not acquire fastopenq->lock
+	 * because the child socket is locked in inet_csk_listen_stop().
+	 */
+	if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(nreq)->tfo_listener)
+		rcu_assign_pointer(tcp_sk(nreq->sk)->fastopen_rsk, nreq);
+
+	return nreq;
+}
+
+static void reqsk_queue_migrated(struct request_sock_queue *queue,
+				 const struct request_sock *req)
+{
+	if (req->num_timeout == 0)
+		atomic_inc(&queue->young);
+	atomic_inc(&queue->qlen);
+}
+
+static void reqsk_migrate_reset(struct request_sock *req)
+{
+	req->saved_syn = NULL;
+#if IS_ENABLED(CONFIG_IPV6)
+	inet_rsk(req)->ipv6_opt = NULL;
+	inet_rsk(req)->pktopts = NULL;
+#else
+	inet_rsk(req)->ireq_opt = NULL;
+#endif
+}
+
+/* return true if req was found in the ehash table */
+static bool reqsk_queue_unlink(struct request_sock *req)
+{
+	struct sock *sk = req_to_sk(req);
+	bool found = false;
+
+	if (sk_hashed(sk)) {
+		struct inet_hashinfo *hashinfo = tcp_or_dccp_get_hashinfo(sk);
+		spinlock_t *lock = inet_ehash_lockp(hashinfo, req->rsk_hash);
+
+		spin_lock(lock);
+		found = __sk_nulls_del_node_init_rcu(sk);
+		spin_unlock(lock);
+	}
+	if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer))
+		reqsk_put(req);
+	return found;
+}
+
+bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req)
+{
+	bool unlinked = reqsk_queue_unlink(req);
+
+	if (unlinked) {
+		reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
+		reqsk_put(req);
+	}
+	return unlinked;
+}
+EXPORT_SYMBOL(inet_csk_reqsk_queue_drop);
+
+void inet_csk_reqsk_queue_drop_and_put(struct sock *sk, struct request_sock *req)
+{
+	inet_csk_reqsk_queue_drop(sk, req);
+	reqsk_put(req);
+}
+EXPORT_SYMBOL(inet_csk_reqsk_queue_drop_and_put);
+
+static void reqsk_timer_handler(struct timer_list *t)
+{
+	struct request_sock *req = from_timer(req, t, rsk_timer);
+	struct request_sock *nreq = NULL, *oreq = req;
+	struct sock *sk_listener = req->rsk_listener;
+	struct inet_connection_sock *icsk;
+	struct request_sock_queue *queue;
+	struct net *net;
+	int max_syn_ack_retries, qlen, expire = 0, resend = 0;
+
+	if (inet_sk_state_load(sk_listener) != TCP_LISTEN) {
+		struct sock *nsk;
+
+		nsk = reuseport_migrate_sock(sk_listener, req_to_sk(req), NULL);
+		if (!nsk)
+			goto drop;
+
+		nreq = inet_reqsk_clone(req, nsk);
+		if (!nreq)
+			goto drop;
+
+		/* The new timer for the cloned req can decrease the 2
+		 * by calling inet_csk_reqsk_queue_drop_and_put(), so
+		 * hold another count to prevent use-after-free and
+		 * call reqsk_put() just before return.
+		 */
+		refcount_set(&nreq->rsk_refcnt, 2 + 1);
+		timer_setup(&nreq->rsk_timer, reqsk_timer_handler, TIMER_PINNED);
+		reqsk_queue_migrated(&inet_csk(nsk)->icsk_accept_queue, req);
+
+		req = nreq;
+		sk_listener = nsk;
+	}
+
+	icsk = inet_csk(sk_listener);
+	net = sock_net(sk_listener);
+	max_syn_ack_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
+		READ_ONCE(net->ipv4.sysctl_tcp_synack_retries);
+	/* Normally all the openreqs are young and become mature
+	 * (i.e. converted to established socket) for first timeout.
+	 * If synack was not acknowledged for 1 second, it means
+	 * one of the following things: synack was lost, ack was lost,
+	 * rtt is high or nobody planned to ack (i.e. synflood).
+	 * When server is a bit loaded, queue is populated with old
+	 * open requests, reducing effective size of queue.
+	 * When server is well loaded, queue size reduces to zero
+	 * after several minutes of work. It is not synflood,
+	 * it is normal operation. The solution is pruning
+	 * too old entries overriding normal timeout, when
+	 * situation becomes dangerous.
+	 *
+	 * Essentially, we reserve half of room for young
+	 * embrions; and abort old ones without pity, if old
+	 * ones are about to clog our table.
+	 */
+	queue = &icsk->icsk_accept_queue;
+	qlen = reqsk_queue_len(queue);
+	if ((qlen << 1) > max(8U, READ_ONCE(sk_listener->sk_max_ack_backlog))) {
+		int young = reqsk_queue_len_young(queue) << 1;
+
+		while (max_syn_ack_retries > 2) {
+			if (qlen < young)
+				break;
+			max_syn_ack_retries--;
+			young <<= 1;
+		}
+	}
+	syn_ack_recalc(req, max_syn_ack_retries, READ_ONCE(queue->rskq_defer_accept),
+		       &expire, &resend);
+	req->rsk_ops->syn_ack_timeout(req);
+	if (!expire &&
+	    (!resend ||
+	     !inet_rtx_syn_ack(sk_listener, req) ||
+	     inet_rsk(req)->acked)) {
+		if (req->num_timeout++ == 0)
+			atomic_dec(&queue->young);
+		mod_timer(&req->rsk_timer, jiffies + reqsk_timeout(req, TCP_RTO_MAX));
+
+		if (!nreq)
+			return;
+
+		if (!inet_ehash_insert(req_to_sk(nreq), req_to_sk(oreq), NULL)) {
+			/* delete timer */
+			inet_csk_reqsk_queue_drop(sk_listener, nreq);
+			goto no_ownership;
+		}
+
+		__NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQSUCCESS);
+		reqsk_migrate_reset(oreq);
+		reqsk_queue_removed(&inet_csk(oreq->rsk_listener)->icsk_accept_queue, oreq);
+		reqsk_put(oreq);
+
+		reqsk_put(nreq);
+		return;
+	}
+
+	/* Even if we can clone the req, we may need not retransmit any more
+	 * SYN+ACKs (nreq->num_timeout > max_syn_ack_retries, etc), or another
+	 * CPU may win the "own_req" race so that inet_ehash_insert() fails.
+	 */
+	if (nreq) {
+		__NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQFAILURE);
+no_ownership:
+		reqsk_migrate_reset(nreq);
+		reqsk_queue_removed(queue, nreq);
+		__reqsk_free(nreq);
+	}
+
+drop:
+	inet_csk_reqsk_queue_drop_and_put(oreq->rsk_listener, oreq);
+}
+
+static void reqsk_queue_hash_req(struct request_sock *req,
+				 unsigned long timeout)
+{
+	timer_setup(&req->rsk_timer, reqsk_timer_handler, TIMER_PINNED);
+	mod_timer(&req->rsk_timer, jiffies + timeout);
+
+	inet_ehash_insert(req_to_sk(req), NULL, NULL);
+	/* before letting lookups find us, make sure all req fields
+	 * are committed to memory and refcnt initialized.
+	 */
+	smp_wmb();
+	refcount_set(&req->rsk_refcnt, 2 + 1);
+}
+
+void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
+				   unsigned long timeout)
+{
+	reqsk_queue_hash_req(req, timeout);
+	inet_csk_reqsk_queue_added(sk);
+}
+EXPORT_SYMBOL_GPL(inet_csk_reqsk_queue_hash_add);
+
+static void inet_clone_ulp(const struct request_sock *req, struct sock *newsk,
+			   const gfp_t priority)
+{
+	struct inet_connection_sock *icsk = inet_csk(newsk);
+
+	if (!icsk->icsk_ulp_ops)
+		return;
+
+	icsk->icsk_ulp_ops->clone(req, newsk, priority);
+}
+
+/**
+ *	inet_csk_clone_lock - clone an inet socket, and lock its clone
+ *	@sk: the socket to clone
+ *	@req: request_sock
+ *	@priority: for allocation (%GFP_KERNEL, %GFP_ATOMIC, etc)
+ *
+ *	Caller must unlock socket even in error path (bh_unlock_sock(newsk))
+ */
+struct sock *inet_csk_clone_lock(const struct sock *sk,
+				 const struct request_sock *req,
+				 const gfp_t priority)
+{
+	struct sock *newsk = sk_clone_lock(sk, priority);
+
+	if (newsk) {
+		struct inet_connection_sock *newicsk = inet_csk(newsk);
+
+		inet_sk_set_state(newsk, TCP_SYN_RECV);
+		newicsk->icsk_bind_hash = NULL;
+		newicsk->icsk_bind2_hash = NULL;
+
+		inet_sk(newsk)->inet_dport = inet_rsk(req)->ir_rmt_port;
+		inet_sk(newsk)->inet_num = inet_rsk(req)->ir_num;
+		inet_sk(newsk)->inet_sport = htons(inet_rsk(req)->ir_num);
+
+		/* listeners have SOCK_RCU_FREE, not the children */
+		sock_reset_flag(newsk, SOCK_RCU_FREE);
+
+		inet_sk(newsk)->mc_list = NULL;
+
+		newsk->sk_mark = inet_rsk(req)->ir_mark;
+		atomic64_set(&newsk->sk_cookie,
+			     atomic64_read(&inet_rsk(req)->ir_cookie));
+
+		newicsk->icsk_retransmits = 0;
+		newicsk->icsk_backoff	  = 0;
+		newicsk->icsk_probes_out  = 0;
+		newicsk->icsk_probes_tstamp = 0;
+
+		/* Deinitialize accept_queue to trap illegal accesses. */
+		memset(&newicsk->icsk_accept_queue, 0, sizeof(newicsk->icsk_accept_queue));
+
+		inet_clone_ulp(req, newsk, priority);
+
+		security_inet_csk_clone(newsk, req);
+	}
+	return newsk;
+}
+EXPORT_SYMBOL_GPL(inet_csk_clone_lock);
+
+/*
+ * At this point, there should be no process reference to this
+ * socket, and thus no user references at all.  Therefore we
+ * can assume the socket waitqueue is inactive and nobody will
+ * try to jump onto it.
+ */
+void inet_csk_destroy_sock(struct sock *sk)
+{
+	WARN_ON(sk->sk_state != TCP_CLOSE);
+	WARN_ON(!sock_flag(sk, SOCK_DEAD));
+
+	/* It cannot be in hash table! */
+	WARN_ON(!sk_unhashed(sk));
+
+	/* If it has not 0 inet_sk(sk)->inet_num, it must be bound */
+	WARN_ON(inet_sk(sk)->inet_num && !inet_csk(sk)->icsk_bind_hash);
+
+	sk->sk_prot->destroy(sk);
+
+	sk_stream_kill_queues(sk);
+
+	xfrm_sk_free_policy(sk);
+
+	this_cpu_dec(*sk->sk_prot->orphan_count);
+
+	sock_put(sk);
+}
+EXPORT_SYMBOL(inet_csk_destroy_sock);
+
+/* This function allows to force a closure of a socket after the call to
+ * tcp/dccp_create_openreq_child().
+ */
+void inet_csk_prepare_forced_close(struct sock *sk)
+	__releases(&sk->sk_lock.slock)
+{
+	/* sk_clone_lock locked the socket and set refcnt to 2 */
+	bh_unlock_sock(sk);
+	sock_put(sk);
+	inet_csk_prepare_for_destroy_sock(sk);
+	inet_sk(sk)->inet_num = 0;
+}
+EXPORT_SYMBOL(inet_csk_prepare_forced_close);
+
+static int inet_ulp_can_listen(const struct sock *sk)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+
+	if (icsk->icsk_ulp_ops && !icsk->icsk_ulp_ops->clone)
+		return -EINVAL;
+
+	return 0;
+}
+
+int inet_csk_listen_start(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct inet_sock *inet = inet_sk(sk);
+	int err;
+
+	err = inet_ulp_can_listen(sk);
+	if (unlikely(err))
+		return err;
+
+	reqsk_queue_alloc(&icsk->icsk_accept_queue);
+
+	sk->sk_ack_backlog = 0;
+	inet_csk_delack_init(sk);
+
+	/* There is race window here: we announce ourselves listening,
+	 * but this transition is still not validated by get_port().
+	 * It is OK, because this socket enters to hash table only
+	 * after validation is complete.
+	 */
+	inet_sk_state_store(sk, TCP_LISTEN);
+	err = sk->sk_prot->get_port(sk, inet->inet_num);
+	if (!err) {
+		inet->inet_sport = htons(inet->inet_num);
+
+		sk_dst_reset(sk);
+		err = sk->sk_prot->hash(sk);
+
+		if (likely(!err))
+			return 0;
+	}
+
+	inet_sk_set_state(sk, TCP_CLOSE);
+	return err;
+}
+EXPORT_SYMBOL_GPL(inet_csk_listen_start);
+
+static void inet_child_forget(struct sock *sk, struct request_sock *req,
+			      struct sock *child)
+{
+	sk->sk_prot->disconnect(child, O_NONBLOCK);
+
+	sock_orphan(child);
+
+	this_cpu_inc(*sk->sk_prot->orphan_count);
+
+	if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(req)->tfo_listener) {
+		BUG_ON(rcu_access_pointer(tcp_sk(child)->fastopen_rsk) != req);
+		BUG_ON(sk != req->rsk_listener);
+
+		/* Paranoid, to prevent race condition if
+		 * an inbound pkt destined for child is
+		 * blocked by sock lock in tcp_v4_rcv().
+		 * Also to satisfy an assertion in
+		 * tcp_v4_destroy_sock().
+		 */
+		RCU_INIT_POINTER(tcp_sk(child)->fastopen_rsk, NULL);
+	}
+	inet_csk_destroy_sock(child);
+}
+
+struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
+				      struct request_sock *req,
+				      struct sock *child)
+{
+	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
+
+	spin_lock(&queue->rskq_lock);
+	if (unlikely(sk->sk_state != TCP_LISTEN)) {
+		inet_child_forget(sk, req, child);
+		child = NULL;
+	} else {
+		req->sk = child;
+		req->dl_next = NULL;
+		if (queue->rskq_accept_head == NULL)
+			WRITE_ONCE(queue->rskq_accept_head, req);
+		else
+			queue->rskq_accept_tail->dl_next = req;
+		queue->rskq_accept_tail = req;
+		sk_acceptq_added(sk);
+	}
+	spin_unlock(&queue->rskq_lock);
+	return child;
+}
+EXPORT_SYMBOL(inet_csk_reqsk_queue_add);
+
+struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,
+					 struct request_sock *req, bool own_req)
+{
+	if (own_req) {
+		inet_csk_reqsk_queue_drop(req->rsk_listener, req);
+		reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req);
+
+		if (sk != req->rsk_listener) {
+			/* another listening sk has been selected,
+			 * migrate the req to it.
+			 */
+			struct request_sock *nreq;
+
+			/* hold a refcnt for the nreq->rsk_listener
+			 * which is assigned in inet_reqsk_clone()
+			 */
+			sock_hold(sk);
+			nreq = inet_reqsk_clone(req, sk);
+			if (!nreq) {
+				inet_child_forget(sk, req, child);
+				goto child_put;
+			}
+
+			refcount_set(&nreq->rsk_refcnt, 1);
+			if (inet_csk_reqsk_queue_add(sk, nreq, child)) {
+				__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQSUCCESS);
+				reqsk_migrate_reset(req);
+				reqsk_put(req);
+				return child;
+			}
+
+			__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
+			reqsk_migrate_reset(nreq);
+			__reqsk_free(nreq);
+		} else if (inet_csk_reqsk_queue_add(sk, req, child)) {
+			return child;
+		}
+	}
+	/* Too bad, another child took ownership of the request, undo. */
+child_put:
+	bh_unlock_sock(child);
+	sock_put(child);
+	return NULL;
+}
+EXPORT_SYMBOL(inet_csk_complete_hashdance);
+
+/*
+ *	This routine closes sockets which have been at least partially
+ *	opened, but not yet accepted.
+ */
+void inet_csk_listen_stop(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct request_sock_queue *queue = &icsk->icsk_accept_queue;
+	struct request_sock *next, *req;
+
+	/* Following specs, it would be better either to send FIN
+	 * (and enter FIN-WAIT-1, it is normal close)
+	 * or to send active reset (abort).
+	 * Certainly, it is pretty dangerous while synflood, but it is
+	 * bad justification for our negligence 8)
+	 * To be honest, we are not able to make either
+	 * of the variants now.			--ANK
+	 */
+	while ((req = reqsk_queue_remove(queue, sk)) != NULL) {
+		struct sock *child = req->sk, *nsk;
+		struct request_sock *nreq;
+
+		local_bh_disable();
+		bh_lock_sock(child);
+		WARN_ON(sock_owned_by_user(child));
+		sock_hold(child);
+
+		nsk = reuseport_migrate_sock(sk, child, NULL);
+		if (nsk) {
+			nreq = inet_reqsk_clone(req, nsk);
+			if (nreq) {
+				refcount_set(&nreq->rsk_refcnt, 1);
+
+				if (inet_csk_reqsk_queue_add(nsk, nreq, child)) {
+					__NET_INC_STATS(sock_net(nsk),
+							LINUX_MIB_TCPMIGRATEREQSUCCESS);
+					reqsk_migrate_reset(req);
+				} else {
+					__NET_INC_STATS(sock_net(nsk),
+							LINUX_MIB_TCPMIGRATEREQFAILURE);
+					reqsk_migrate_reset(nreq);
+					__reqsk_free(nreq);
+				}
+
+				/* inet_csk_reqsk_queue_add() has already
+				 * called inet_child_forget() on failure case.
+				 */
+				goto skip_child_forget;
+			}
+		}
+
+		inet_child_forget(sk, req, child);
+skip_child_forget:
+		reqsk_put(req);
+		bh_unlock_sock(child);
+		local_bh_enable();
+		sock_put(child);
+
+		cond_resched();
+	}
+	if (queue->fastopenq.rskq_rst_head) {
+		/* Free all the reqs queued in rskq_rst_head. */
+		spin_lock_bh(&queue->fastopenq.lock);
+		req = queue->fastopenq.rskq_rst_head;
+		queue->fastopenq.rskq_rst_head = NULL;
+		spin_unlock_bh(&queue->fastopenq.lock);
+		while (req != NULL) {
+			next = req->dl_next;
+			reqsk_put(req);
+			req = next;
+		}
+	}
+	WARN_ON_ONCE(sk->sk_ack_backlog);
+}
+EXPORT_SYMBOL_GPL(inet_csk_listen_stop);
+
+void inet_csk_addr2sockaddr(struct sock *sk, struct sockaddr *uaddr)
+{
+	struct sockaddr_in *sin = (struct sockaddr_in *)uaddr;
+	const struct inet_sock *inet = inet_sk(sk);
+
+	sin->sin_family		= AF_INET;
+	sin->sin_addr.s_addr	= inet->inet_daddr;
+	sin->sin_port		= inet->inet_dport;
+}
+EXPORT_SYMBOL_GPL(inet_csk_addr2sockaddr);
+
+static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *fl)
+{
+	const struct inet_sock *inet = inet_sk(sk);
+	const struct ip_options_rcu *inet_opt;
+	__be32 daddr = inet->inet_daddr;
+	struct flowi4 *fl4;
+	struct rtable *rt;
+
+	rcu_read_lock();
+	inet_opt = rcu_dereference(inet->inet_opt);
+	if (inet_opt && inet_opt->opt.srr)
+		daddr = inet_opt->opt.faddr;
+	fl4 = &fl->u.ip4;
+	rt = ip_route_output_ports(sock_net(sk), fl4, sk, daddr,
+				   inet->inet_saddr, inet->inet_dport,
+				   inet->inet_sport, sk->sk_protocol,
+				   RT_CONN_FLAGS(sk), sk->sk_bound_dev_if);
+	if (IS_ERR(rt))
+		rt = NULL;
+	if (rt)
+		sk_setup_caps(sk, &rt->dst);
+	rcu_read_unlock();
+
+	return &rt->dst;
+}
+
+struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu)
+{
+	struct dst_entry *dst = __sk_dst_check(sk, 0);
+	struct inet_sock *inet = inet_sk(sk);
+
+	if (!dst) {
+		dst = inet_csk_rebuild_route(sk, &inet->cork.fl);
+		if (!dst)
+			goto out;
+	}
+	dst->ops->update_pmtu(dst, sk, NULL, mtu, true);
+
+	dst = __sk_dst_check(sk, 0);
+	if (!dst)
+		dst = inet_csk_rebuild_route(sk, &inet->cork.fl);
+out:
+	return dst;
+}
+EXPORT_SYMBOL_GPL(inet_csk_update_pmtu);