/*
 * ip_vs_xmit.c: various packet transmitters for IPVS
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *              Julian Anastasov <ja@ssi.bg>
 *
 *              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:
 *
 * Description of forwarding methods:
 * - all transmitters are called from LOCAL_IN (remote clients) and
 * LOCAL_OUT (local clients) but for ICMP can be called from FORWARD
 * - not all connections have destination server, for example,
 * connections in backup server when fwmark is used
 * - bypass connections use daddr from packet
 * - we can use dst without ref while sending in RCU section, we use
 * ref when returning NF_ACCEPT for NAT-ed packet via loopback
 * LOCAL_OUT rules:
 * - skb->dev is NULL, skb->protocol is not set (both are set in POST_ROUTING)
 * - skb->pkt_type is not set yet
 * - the only place where we can see skb->sk != NULL
 */

#define KMSG_COMPONENT "IPVS"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/tcp.h>                  /* for tcphdr */
#include <net/ip.h>
#include <net/tcp.h>                    /* for csum_tcpudp_magic */
#include <net/udp.h>
#include <net/icmp.h>                   /* for icmp_send */
#include <net/route.h>                  /* for ip_route_output */
#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/ip_tunnels.h>
#include <net/addrconf.h>
#include <linux/icmpv6.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>

#include <net/ip_vs.h>

enum {
        IP_VS_RT_MODE_LOCAL     = 1, /* Allow local dest */
        IP_VS_RT_MODE_NON_LOCAL = 2, /* Allow non-local dest */
        IP_VS_RT_MODE_RDR       = 4, /* Allow redirect from remote daddr to
                                      * local
                                      */
        IP_VS_RT_MODE_CONNECT   = 8, /* Always bind route to saddr */
        IP_VS_RT_MODE_KNOWN_NH  = 16,/* Route via remote addr */
        IP_VS_RT_MODE_TUNNEL    = 32,/* Tunnel mode */
};

static inline struct ip_vs_dest_dst *ip_vs_dest_dst_alloc(void)
{
        return kmalloc(sizeof(struct ip_vs_dest_dst), GFP_ATOMIC);
}

static inline void ip_vs_dest_dst_free(struct ip_vs_dest_dst *dest_dst)
{
        kfree(dest_dst);
}

/*
 *      Destination cache to speed up outgoing route lookup
 */
static inline void
__ip_vs_dst_set(struct ip_vs_dest *dest, struct ip_vs_dest_dst *dest_dst,
                struct dst_entry *dst, u32 dst_cookie)
{
        struct ip_vs_dest_dst *old;

        old = rcu_dereference_protected(dest->dest_dst,
                                        lockdep_is_held(&dest->dst_lock));

        if (dest_dst) {
                dest_dst->dst_cache = dst;
                dest_dst->dst_cookie = dst_cookie;
        }
        rcu_assign_pointer(dest->dest_dst, dest_dst);

        if (old)
                call_rcu(&old->rcu_head, ip_vs_dest_dst_rcu_free);
}

static inline struct ip_vs_dest_dst *
__ip_vs_dst_check(struct ip_vs_dest *dest)
{
        struct ip_vs_dest_dst *dest_dst = rcu_dereference(dest->dest_dst);
        struct dst_entry *dst;

        if (!dest_dst)
                return NULL;
        dst = dest_dst->dst_cache;
        if (dst->obsolete &&
            dst->ops->check(dst, dest_dst->dst_cookie) == NULL)
                return NULL;
        return dest_dst;
}

static inline bool
__mtu_check_toobig_v6(const struct sk_buff *skb, u32 mtu)
{
        if (IP6CB(skb)->frag_max_size) {
                /* frag_max_size tell us that, this packet have been
                 * defragmented by netfilter IPv6 conntrack module.
                 */
                if (IP6CB(skb)->frag_max_size > mtu)
                        return true; /* largest fragment violate MTU */
        }
        else if (skb->len > mtu && !skb_is_gso(skb)) {
                return true; /* Packet size violate MTU size */
        }
        return false;
}

/* Get route to daddr, update *saddr, optionally bind route to saddr */
static struct rtable *do_output_route4(struct net *net, __be32 daddr,
                                       int rt_mode, __be32 *saddr)
{
        struct flowi4 fl4;
        struct rtable *rt;
        int loop = 0;

        memset(&fl4, 0, sizeof(fl4));
        fl4.daddr = daddr;
        fl4.saddr = (rt_mode & IP_VS_RT_MODE_CONNECT) ? *saddr : 0;
        fl4.flowi4_flags = (rt_mode & IP_VS_RT_MODE_KNOWN_NH) ?
                           FLOWI_FLAG_KNOWN_NH : 0;

retry:
        rt = ip_route_output_key(net, &fl4);
        if (IS_ERR(rt)) {
                /* Invalid saddr ? */
                if (PTR_ERR(rt) == -EINVAL && *saddr &&
                    rt_mode & IP_VS_RT_MODE_CONNECT && !loop) {
                        *saddr = 0;
                        flowi4_update_output(&fl4, 0, 0, daddr, 0);
                        goto retry;
                }
                IP_VS_DBG_RL("ip_route_output error, dest: %pI4\n", &daddr);
                return NULL;
        } else if (!*saddr && rt_mode & IP_VS_RT_MODE_CONNECT && fl4.saddr) {
                ip_rt_put(rt);
                *saddr = fl4.saddr;
                flowi4_update_output(&fl4, 0, 0, daddr, fl4.saddr);
                loop++;
                goto retry;
        }
        *saddr = fl4.saddr;
        return rt;
}

#ifdef CONFIG_IP_VS_IPV6
static inline int __ip_vs_is_local_route6(struct rt6_info *rt)
{
        return rt->dst.dev && rt->dst.dev->flags & IFF_LOOPBACK;
}
#endif

static inline bool crosses_local_route_boundary(int skb_af, struct sk_buff *skb,
                                                int rt_mode,
                                                bool new_rt_is_local)
{
        bool rt_mode_allow_local = !!(rt_mode & IP_VS_RT_MODE_LOCAL);
        bool rt_mode_allow_non_local = !!(rt_mode & IP_VS_RT_MODE_LOCAL);
        bool rt_mode_allow_redirect = !!(rt_mode & IP_VS_RT_MODE_RDR);
        bool source_is_loopback;
        bool old_rt_is_local;

#ifdef CONFIG_IP_VS_IPV6
        if (skb_af == AF_INET6) {
                int addr_type = ipv6_addr_type(&ipv6_hdr(skb)->saddr);

                source_is_loopback =
                        (!skb->dev || skb->dev->flags & IFF_LOOPBACK) &&
                        (addr_type & IPV6_ADDR_LOOPBACK);
                old_rt_is_local = __ip_vs_is_local_route6(
                        (struct rt6_info *)skb_dst(skb));
        } else
#endif
        {
                source_is_loopback = ipv4_is_loopback(ip_hdr(skb)->saddr);
                old_rt_is_local = skb_rtable(skb)->rt_flags & RTCF_LOCAL;
        }

        if (unlikely(new_rt_is_local)) {
                if (!rt_mode_allow_local)
                        return true;
                if (!rt_mode_allow_redirect && !old_rt_is_local)
                        return true;
        } else {
                if (!rt_mode_allow_non_local)
                        return true;
                if (source_is_loopback)
                        return true;
        }
        return false;
}

static inline void maybe_update_pmtu(int skb_af, struct sk_buff *skb, int mtu)
{
        struct sock *sk = skb->sk;
        struct rtable *ort = skb_rtable(skb);

        if (!skb->dev && sk && sk_fullsock(sk))
                ort->dst.ops->update_pmtu(&ort->dst, sk, NULL, mtu);
}

static inline bool ensure_mtu_is_adequate(int skb_af, int rt_mode,
                                          struct ip_vs_iphdr *ipvsh,
                                          struct sk_buff *skb, int mtu)
{
#ifdef CONFIG_IP_VS_IPV6
        if (skb_af == AF_INET6) {
                struct net *net = dev_net(skb_dst(skb)->dev);

                if (unlikely(__mtu_check_toobig_v6(skb, mtu))) {
                        if (!skb->dev)
                                skb->dev = net->loopback_dev;
                        /* only send ICMP too big on first fragment */
                        if (!ipvsh->fragoffs)
                                icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
                        IP_VS_DBG(1, "frag needed for %pI6c\n",
                                  &ipv6_hdr(skb)->saddr);
                        return false;
                }
        } else
#endif
        {
                struct netns_ipvs *ipvs = net_ipvs(skb_net(skb));

                /* If we're going to tunnel the packet and pmtu discovery
                 * is disabled, we'll just fragment it anyway
                 */
                if ((rt_mode & IP_VS_RT_MODE_TUNNEL) && !sysctl_pmtu_disc(ipvs))
                        return true;

                if (unlikely(ip_hdr(skb)->frag_off & htons(IP_DF) &&
                             skb->len > mtu && !skb_is_gso(skb))) {
                        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
                                  htonl(mtu));
                        IP_VS_DBG(1, "frag needed for %pI4\n",
                                  &ip_hdr(skb)->saddr);
                        return false;
                }
        }

        return true;
}

/* Get route to destination or remote server */
static int
__ip_vs_get_out_rt(int skb_af, struct sk_buff *skb, struct ip_vs_dest *dest,
                   __be32 daddr, int rt_mode, __be32 *ret_saddr,
                   struct ip_vs_iphdr *ipvsh)
{
        struct net *net = dev_net(skb_dst(skb)->dev);
        struct ip_vs_dest_dst *dest_dst;
        struct rtable *rt;                      /* Route to the other host */
        int mtu;
        int local, noref = 1;

        if (dest) {
                dest_dst = __ip_vs_dst_check(dest);
                if (likely(dest_dst))
                        rt = (struct rtable *) dest_dst->dst_cache;
                else {
                        dest_dst = ip_vs_dest_dst_alloc();
                        spin_lock_bh(&dest->dst_lock);
                        if (!dest_dst) {
                                __ip_vs_dst_set(dest, NULL, NULL, 0);
                                spin_unlock_bh(&dest->dst_lock);
                                goto err_unreach;
                        }
                        rt = do_output_route4(net, dest->addr.ip, rt_mode,
                                              &dest_dst->dst_saddr.ip);
                        if (!rt) {
                                __ip_vs_dst_set(dest, NULL, NULL, 0);
                                spin_unlock_bh(&dest->dst_lock);
                                ip_vs_dest_dst_free(dest_dst);
                                goto err_unreach;
                        }
                        __ip_vs_dst_set(dest, dest_dst, &rt->dst, 0);
                        spin_unlock_bh(&dest->dst_lock);
                        IP_VS_DBG(10, "new dst %pI4, src %pI4, refcnt=%d\n",
                                  &dest->addr.ip, &dest_dst->dst_saddr.ip,
                                  atomic_read(&rt->dst.__refcnt));
                }
                if (ret_saddr)
                        *ret_saddr = dest_dst->dst_saddr.ip;
        } else {
                __be32 saddr = htonl(INADDR_ANY);

                noref = 0;

                /* For such unconfigured boxes avoid many route lookups
                 * for performance reasons because we do not remember saddr
                 */
                rt_mode &= ~IP_VS_RT_MODE_CONNECT;
                rt = do_output_route4(net, daddr, rt_mode, &saddr);
                if (!rt)
                        goto err_unreach;
                if (ret_saddr)
                        *ret_saddr = saddr;
        }

        local = (rt->rt_flags & RTCF_LOCAL) ? 1 : 0;
        if (unlikely(crosses_local_route_boundary(skb_af, skb, rt_mode,
                                                  local))) {
                IP_VS_DBG_RL("We are crossing local and non-local addresses"
                             " daddr=%pI4\n", &daddr);
                goto err_put;
        }

        if (unlikely(local)) {
                /* skb to local stack, preserve old route */
                if (!noref)
                        ip_rt_put(rt);
                return local;
        }

        if (likely(!(rt_mode & IP_VS_RT_MODE_TUNNEL))) {
                mtu = dst_mtu(&rt->dst);
        } else {
                mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr);
                if (mtu < 68) {
                        IP_VS_DBG_RL("%s(): mtu less than 68\n", __func__);
                        goto err_put;
                }
                maybe_update_pmtu(skb_af, skb, mtu);
        }

        if (!ensure_mtu_is_adequate(skb_af, rt_mode, ipvsh, skb, mtu))
                goto err_put;

        skb_dst_drop(skb);
        if (noref) {
                if (!local)
                        skb_dst_set_noref(skb, &rt->dst);
                else
                        skb_dst_set(skb, dst_clone(&rt->dst));
        } else
                skb_dst_set(skb, &rt->dst);

        return local;

err_put:
        if (!noref)
                ip_rt_put(rt);
        return -1;

err_unreach:
        dst_link_failure(skb);
        return -1;
}

#ifdef CONFIG_IP_VS_IPV6
static struct dst_entry *
__ip_vs_route_output_v6(struct net *net, struct in6_addr *daddr,
                        struct in6_addr *ret_saddr, int do_xfrm)
{
        struct dst_entry *dst;
        struct flowi6 fl6 = {
                .daddr = *daddr,
        };

        dst = ip6_route_output(net, NULL, &fl6);
        if (dst->error)
                goto out_err;
        if (!ret_saddr)
                return dst;
        if (ipv6_addr_any(&fl6.saddr) &&
            ipv6_dev_get_saddr(net, ip6_dst_idev(dst)->dev,
                               &fl6.daddr, 0, &fl6.saddr) < 0)
                goto out_err;
        if (do_xfrm) {
                dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
                if (IS_ERR(dst)) {
                        dst = NULL;
                        goto out_err;
                }
        }
        *ret_saddr = fl6.saddr;
        return dst;

out_err:
        dst_release(dst);
        IP_VS_DBG_RL("ip6_route_output error, dest: %pI6\n", daddr);
        return NULL;
}

/*
 * Get route to destination or remote server
 */
static int
__ip_vs_get_out_rt_v6(int skb_af, struct sk_buff *skb, struct ip_vs_dest *dest,
                      struct in6_addr *daddr, struct in6_addr *ret_saddr,
                      struct ip_vs_iphdr *ipvsh, int do_xfrm, int rt_mode)
{
        struct net *net = dev_net(skb_dst(skb)->dev);
        struct ip_vs_dest_dst *dest_dst;
        struct rt6_info *rt;                    /* Route to the other host */
        struct dst_entry *dst;
        int mtu;
        int local, noref = 1;

        if (dest) {
                dest_dst = __ip_vs_dst_check(dest);
                if (likely(dest_dst))
                        rt = (struct rt6_info *) dest_dst->dst_cache;
                else {
                        u32 cookie;

                        dest_dst = ip_vs_dest_dst_alloc();
                        spin_lock_bh(&dest->dst_lock);
                        if (!dest_dst) {
                                __ip_vs_dst_set(dest, NULL, NULL, 0);
                                spin_unlock_bh(&dest->dst_lock);
                                goto err_unreach;
                        }
                        dst = __ip_vs_route_output_v6(net, &dest->addr.in6,
                                                      &dest_dst->dst_saddr.in6,
                                                      do_xfrm);
                        if (!dst) {
                                __ip_vs_dst_set(dest, NULL, NULL, 0);
                                spin_unlock_bh(&dest->dst_lock);
                                ip_vs_dest_dst_free(dest_dst);
                                goto err_unreach;
                        }
                        rt = (struct rt6_info *) dst;
                        cookie = rt->rt6i_node ? rt->rt6i_node->fn_sernum : 0;
                        __ip_vs_dst_set(dest, dest_dst, &rt->dst, cookie);
                        spin_unlock_bh(&dest->dst_lock);
                        IP_VS_DBG(10, "new dst %pI6, src %pI6, refcnt=%d\n",
                                  &dest->addr.in6, &dest_dst->dst_saddr.in6,
                                  atomic_read(&rt->dst.__refcnt));
                }
                if (ret_saddr)
                        *ret_saddr = dest_dst->dst_saddr.in6;
        } else {
                noref = 0;
                dst = __ip_vs_route_output_v6(net, daddr, ret_saddr, do_xfrm);
                if (!dst)
                        goto err_unreach;
                rt = (struct rt6_info *) dst;
        }

        local = __ip_vs_is_local_route6(rt);

        if (unlikely(crosses_local_route_boundary(skb_af, skb, rt_mode,
                                                  local))) {
                IP_VS_DBG_RL("We are crossing local and non-local addresses"
                             " daddr=%pI6\n", daddr);
                goto err_put;
        }

        if (unlikely(local)) {
                /* skb to local stack, preserve old route */
                if (!noref)
                        dst_release(&rt->dst);
                return local;
        }

        /* MTU checking */
        if (likely(!(rt_mode & IP_VS_RT_MODE_TUNNEL)))
                mtu = dst_mtu(&rt->dst);
        else {
                mtu = dst_mtu(&rt->dst) - sizeof(struct ipv6hdr);
                if (mtu < IPV6_MIN_MTU) {
                        IP_VS_DBG_RL("%s(): mtu less than %d\n", __func__,
                                     IPV6_MIN_MTU);
                        goto err_put;
                }
                maybe_update_pmtu(skb_af, skb, mtu);
        }

        if (!ensure_mtu_is_adequate(skb_af, rt_mode, ipvsh, skb, mtu))
                goto err_put;

        skb_dst_drop(skb);
        if (noref) {
                if (!local)
                        skb_dst_set_noref(skb, &rt->dst);
                else
                        skb_dst_set(skb, dst_clone(&rt->dst));
        } else
                skb_dst_set(skb, &rt->dst);

        return local;

err_put:
        if (!noref)
                dst_release(&rt->dst);
        return -1;

err_unreach:
        dst_link_failure(skb);
        return -1;
}
#endif


/* return NF_ACCEPT to allow forwarding or other NF_xxx on error */
static inline int ip_vs_tunnel_xmit_prepare(struct sk_buff *skb,
                                            struct ip_vs_conn *cp)
{
        int ret = NF_ACCEPT;

        skb->ipvs_property = 1;
        if (unlikely(cp->flags & IP_VS_CONN_F_NFCT))
                ret = ip_vs_confirm_conntrack(skb);
        if (ret == NF_ACCEPT) {
                nf_reset(skb);
                skb_forward_csum(skb);
        }
        return ret;
}

/* return NF_STOLEN (sent) or NF_ACCEPT if local=1 (not sent) */
static inline int ip_vs_nat_send_or_cont(int pf, struct sk_buff *skb,
                                         struct ip_vs_conn *cp, int local)
{
        int ret = NF_STOLEN;

        skb->ipvs_property = 1;
        if (likely(!(cp->flags & IP_VS_CONN_F_NFCT)))
                ip_vs_notrack(skb);
        else
                ip_vs_update_conntrack(skb, cp, 1);
        if (!local) {
                skb_forward_csum(skb);
                NF_HOOK(pf, NF_INET_LOCAL_OUT, NULL, skb,
                        NULL, skb_dst(skb)->dev, dst_output_sk);
        } else
                ret = NF_ACCEPT;
        return ret;
}

/* return NF_STOLEN (sent) or NF_ACCEPT if local=1 (not sent) */
static inline int ip_vs_send_or_cont(int pf, struct sk_buff *skb,
                                     struct ip_vs_conn *cp, int local)
{
        int ret = NF_STOLEN;

        skb->ipvs_property = 1;
        if (likely(!(cp->flags & IP_VS_CONN_F_NFCT)))
                ip_vs_notrack(skb);
        if (!local) {
                skb_forward_csum(skb);
                NF_HOOK(pf, NF_INET_LOCAL_OUT, NULL, skb,
                        NULL, skb_dst(skb)->dev, dst_output_sk);
        } else
                ret = NF_ACCEPT;
        return ret;
}


/*
 *      NULL transmitter (do nothing except return NF_ACCEPT)
 */
int
ip_vs_null_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        /* we do not touch skb and do not need pskb ptr */
        return ip_vs_send_or_cont(NFPROTO_IPV4, skb, cp, 1);
}


/*
 *      Bypass transmitter
 *      Let packets bypass the destination when the destination is not
 *      available, it may be only used in transparent cache cluster.
 */
int
ip_vs_bypass_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                  struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        struct iphdr  *iph = ip_hdr(skb);

        EnterFunction(10);

        rcu_read_lock();
        if (__ip_vs_get_out_rt(cp->af, skb, NULL, iph->daddr,
                               IP_VS_RT_MODE_NON_LOCAL, NULL, ipvsh) < 0)
                goto tx_error;

        ip_send_check(iph);

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        ip_vs_send_or_cont(NFPROTO_IPV4, skb, cp, 0);
        rcu_read_unlock();

        LeaveFunction(10);
        return NF_STOLEN;

 tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}

#ifdef CONFIG_IP_VS_IPV6
int
ip_vs_bypass_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
                     struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        EnterFunction(10);

        rcu_read_lock();
        if (__ip_vs_get_out_rt_v6(cp->af, skb, NULL, &ipvsh->daddr.in6, NULL,
                                  ipvsh, 0, IP_VS_RT_MODE_NON_LOCAL) < 0)
                goto tx_error;

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        ip_vs_send_or_cont(NFPROTO_IPV6, skb, cp, 0);
        rcu_read_unlock();

        LeaveFunction(10);
        return NF_STOLEN;

 tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}
#endif

/*
 *      NAT transmitter (only for outside-to-inside nat forwarding)
 *      Not used for related ICMP
 */
int
ip_vs_nat_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
               struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        struct rtable *rt;              /* Route to the other host */
        int local, rc, was_input;

        EnterFunction(10);

        rcu_read_lock();
        /* check if it is a connection of no-client-port */
        if (unlikely(cp->flags & IP_VS_CONN_F_NO_CPORT)) {
                __be16 _pt, *p;

                p = skb_header_pointer(skb, ipvsh->len, sizeof(_pt), &_pt);
                if (p == NULL)
                        goto tx_error;
                ip_vs_conn_fill_cport(cp, *p);
                IP_VS_DBG(10, "filled cport=%d\n", ntohs(*p));
        }

        was_input = rt_is_input_route(skb_rtable(skb));
        local = __ip_vs_get_out_rt(cp->af, skb, cp->dest, cp->daddr.ip,
                                   IP_VS_RT_MODE_LOCAL |
                                   IP_VS_RT_MODE_NON_LOCAL |
                                   IP_VS_RT_MODE_RDR, NULL, ipvsh);
        if (local < 0)
                goto tx_error;
        rt = skb_rtable(skb);
        /*
         * Avoid duplicate tuple in reply direction for NAT traffic
         * to local address when connection is sync-ed
         */
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        if (cp->flags & IP_VS_CONN_F_SYNC && local) {
                enum ip_conntrack_info ctinfo;
                struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

                if (ct && !nf_ct_is_untracked(ct)) {
                        IP_VS_DBG_RL_PKT(10, AF_INET, pp, skb, 0,
                                         "ip_vs_nat_xmit(): "
                                         "stopping DNAT to local address");
                        goto tx_error;
                }
        }
#endif

        /* From world but DNAT to loopback address? */
        if (local && ipv4_is_loopback(cp->daddr.ip) && was_input) {
                IP_VS_DBG_RL_PKT(1, AF_INET, pp, skb, 0, "ip_vs_nat_xmit(): "
                                 "stopping DNAT to loopback address");
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (!skb_make_writable(skb, sizeof(struct iphdr)))
                goto tx_error;

        if (skb_cow(skb, rt->dst.dev->hard_header_len))
                goto tx_error;

        /* mangle the packet */
        if (pp->dnat_handler && !pp->dnat_handler(skb, pp, cp, ipvsh))
                goto tx_error;
        ip_hdr(skb)->daddr = cp->daddr.ip;
        ip_send_check(ip_hdr(skb));

        IP_VS_DBG_PKT(10, AF_INET, pp, skb, 0, "After DNAT");

        /* FIXME: when application helper enlarges the packet and the length
           is larger than the MTU of outgoing device, there will be still
           MTU problem. */

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        rc = ip_vs_nat_send_or_cont(NFPROTO_IPV4, skb, cp, local);
        rcu_read_unlock();

        LeaveFunction(10);
        return rc;

  tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}

#ifdef CONFIG_IP_VS_IPV6
int
ip_vs_nat_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
                  struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        struct rt6_info *rt;            /* Route to the other host */
        int local, rc;

        EnterFunction(10);

        rcu_read_lock();
        /* check if it is a connection of no-client-port */
        if (unlikely(cp->flags & IP_VS_CONN_F_NO_CPORT && !ipvsh->fragoffs)) {
                __be16 _pt, *p;
                p = skb_header_pointer(skb, ipvsh->len, sizeof(_pt), &_pt);
                if (p == NULL)
                        goto tx_error;
                ip_vs_conn_fill_cport(cp, *p);
                IP_VS_DBG(10, "filled cport=%d\n", ntohs(*p));
        }

        local = __ip_vs_get_out_rt_v6(cp->af, skb, cp->dest, &cp->daddr.in6,
                                      NULL, ipvsh, 0,
                                      IP_VS_RT_MODE_LOCAL |
                                      IP_VS_RT_MODE_NON_LOCAL |
                                      IP_VS_RT_MODE_RDR);
        if (local < 0)
                goto tx_error;
        rt = (struct rt6_info *) skb_dst(skb);
        /*
         * Avoid duplicate tuple in reply direction for NAT traffic
         * to local address when connection is sync-ed
         */
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        if (cp->flags & IP_VS_CONN_F_SYNC && local) {
                enum ip_conntrack_info ctinfo;
                struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

                if (ct && !nf_ct_is_untracked(ct)) {
                        IP_VS_DBG_RL_PKT(10, AF_INET6, pp, skb, 0,
                                         "ip_vs_nat_xmit_v6(): "
                                         "stopping DNAT to local address");
                        goto tx_error;
                }
        }
#endif

        /* From world but DNAT to loopback address? */
        if (local && skb->dev && !(skb->dev->flags & IFF_LOOPBACK) &&
            ipv6_addr_type(&rt->rt6i_dst.addr) & IPV6_ADDR_LOOPBACK) {
                IP_VS_DBG_RL_PKT(1, AF_INET6, pp, skb, 0,
                                 "ip_vs_nat_xmit_v6(): "
                                 "stopping DNAT to loopback address");
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (!skb_make_writable(skb, sizeof(struct ipv6hdr)))
                goto tx_error;

        if (skb_cow(skb, rt->dst.dev->hard_header_len))
                goto tx_error;

        /* mangle the packet */
        if (pp->dnat_handler && !pp->dnat_handler(skb, pp, cp, ipvsh))
                goto tx_error;
        ipv6_hdr(skb)->daddr = cp->daddr.in6;

        IP_VS_DBG_PKT(10, AF_INET6, pp, skb, 0, "After DNAT");

        /* FIXME: when application helper enlarges the packet and the length
           is larger than the MTU of outgoing device, there will be still
           MTU problem. */

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        rc = ip_vs_nat_send_or_cont(NFPROTO_IPV6, skb, cp, local);
        rcu_read_unlock();

        LeaveFunction(10);
        return rc;

tx_error:
        LeaveFunction(10);
        kfree_skb(skb);
        rcu_read_unlock();
        return NF_STOLEN;
}
#endif

/* When forwarding a packet, we must ensure that we've got enough headroom
 * for the encapsulation packet in the skb.  This also gives us an
 * opportunity to figure out what the payload_len, dsfield, ttl, and df
 * values should be, so that we won't need to look at the old ip header
 * again
 */
static struct sk_buff *
ip_vs_prepare_tunneled_skb(struct sk_buff *skb, int skb_af,
                           unsigned int max_headroom, __u8 *next_protocol,
                           __u32 *payload_len, __u8 *dsfield, __u8 *ttl,
                           __be16 *df)
{
        struct sk_buff *new_skb = NULL;
        struct iphdr *old_iph = NULL;
#ifdef CONFIG_IP_VS_IPV6
        struct ipv6hdr *old_ipv6h = NULL;
#endif

        if (skb_headroom(skb) < max_headroom || skb_cloned(skb)) {
                new_skb = skb_realloc_headroom(skb, max_headroom);
                if (!new_skb)
                        goto error;
                if (skb->sk)
                        skb_set_owner_w(new_skb, skb->sk);
                consume_skb(skb);
                skb = new_skb;
        }

#ifdef CONFIG_IP_VS_IPV6
        if (skb_af == AF_INET6) {
                old_ipv6h = ipv6_hdr(skb);
                *next_protocol = IPPROTO_IPV6;
                if (payload_len)
                        *payload_len =
                                ntohs(old_ipv6h->payload_len) +
                                sizeof(*old_ipv6h);
                *dsfield = ipv6_get_dsfield(old_ipv6h);
                *ttl = old_ipv6h->hop_limit;
                if (df)
                        *df = 0;
        } else
#endif
        {
                old_iph = ip_hdr(skb);
                /* Copy DF, reset fragment offset and MF */
                if (df)
                        *df = (old_iph->frag_off & htons(IP_DF));
                *next_protocol = IPPROTO_IPIP;

                /* fix old IP header checksum */
                ip_send_check(old_iph);
                *dsfield = ipv4_get_dsfield(old_iph);
                *ttl = old_iph->ttl;
                if (payload_len)
                        *payload_len = ntohs(old_iph->tot_len);
        }

        return skb;
error:
        kfree_skb(skb);
        return ERR_PTR(-ENOMEM);
}

static inline int __tun_gso_type_mask(int encaps_af, int orig_af)
{
        if (encaps_af == AF_INET) {
                if (orig_af == AF_INET)
                        return SKB_GSO_IPIP;

                return SKB_GSO_SIT;
        }

        /* GSO: we need to provide proper SKB_GSO_ value for IPv6:
         * SKB_GSO_SIT/IPV6
         */
        return 0;
}

/*
 *   IP Tunneling transmitter
 *
 *   This function encapsulates the packet in a new IP packet, its
 *   destination will be set to cp->daddr. Most code of this function
 *   is taken from ipip.c.
 *
 *   It is used in VS/TUN cluster. The load balancer selects a real
 *   server from a cluster based on a scheduling algorithm,
 *   encapsulates the request packet and forwards it to the selected
 *   server. For example, all real servers are configured with
 *   "ifconfig tunl0 <Virtual IP Address> up". When the server receives
 *   the encapsulated packet, it will decapsulate the packet, processe
 *   the request and return the response packets directly to the client
 *   without passing the load balancer. This can greatly increase the
 *   scalability of virtual server.
 *
 *   Used for ANY protocol
 */
int
ip_vs_tunnel_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                  struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        struct net *net = skb_net(skb);
        struct netns_ipvs *ipvs = net_ipvs(net);
        struct rtable *rt;                      /* Route to the other host */
        __be32 saddr;                           /* Source for tunnel */
        struct net_device *tdev;                /* Device to other host */
        __u8 next_protocol = 0;
        __u8 dsfield = 0;
        __u8 ttl = 0;
        __be16 df = 0;
        __be16 *dfp = NULL;
        struct iphdr  *iph;                     /* Our new IP header */
        unsigned int max_headroom;              /* The extra header space needed */
        int ret, local;

        EnterFunction(10);

        rcu_read_lock();
        local = __ip_vs_get_out_rt(cp->af, skb, cp->dest, cp->daddr.ip,
                                   IP_VS_RT_MODE_LOCAL |
                                   IP_VS_RT_MODE_NON_LOCAL |
                                   IP_VS_RT_MODE_CONNECT |
                                   IP_VS_RT_MODE_TUNNEL, &saddr, ipvsh);
        if (local < 0)
                goto tx_error;
        if (local) {
                rcu_read_unlock();
                return ip_vs_send_or_cont(NFPROTO_IPV4, skb, cp, 1);
        }

        rt = skb_rtable(skb);
        tdev = rt->dst.dev;

        /*
         * Okay, now see if we can stuff it in the buffer as-is.
         */
        max_headroom = LL_RESERVED_SPACE(tdev) + sizeof(struct iphdr);

        /* We only care about the df field if sysctl_pmtu_disc(ipvs) is set */
        dfp = sysctl_pmtu_disc(ipvs) ? &df : NULL;
        skb = ip_vs_prepare_tunneled_skb(skb, cp->af, max_headroom,
                                         &next_protocol, NULL, &dsfield,
                                         &ttl, dfp);
        if (IS_ERR(skb))
                goto tx_error;

        skb = iptunnel_handle_offloads(
                skb, false, __tun_gso_type_mask(AF_INET, cp->af));
        if (IS_ERR(skb))
                goto tx_error;

        skb->transport_header = skb->network_header;

        skb_push(skb, sizeof(struct iphdr));
        skb_reset_network_header(skb);
        memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));

        /*
         *      Push down and install the IPIP header.
         */
        iph                     =       ip_hdr(skb);
        iph->version            =       4;
        iph->ihl                =       sizeof(struct iphdr)>>2;
        iph->frag_off           =       df;
        iph->protocol           =       next_protocol;
        iph->tos                =       dsfield;
        iph->daddr              =       cp->daddr.ip;
        iph->saddr              =       saddr;
        iph->ttl                =       ttl;
        ip_select_ident(net, skb, NULL);

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        ret = ip_vs_tunnel_xmit_prepare(skb, cp);

        if (ret == NF_ACCEPT)
                ip_local_out(skb);
        else if (ret == NF_DROP)
                kfree_skb(skb);
        rcu_read_unlock();

        LeaveFunction(10);

        return NF_STOLEN;

  tx_error:
        if (!IS_ERR(skb))
                kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}

#ifdef CONFIG_IP_VS_IPV6
int
ip_vs_tunnel_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
                     struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        struct rt6_info *rt;            /* Route to the other host */
        struct in6_addr saddr;          /* Source for tunnel */
        struct net_device *tdev;        /* Device to other host */
        __u8 next_protocol = 0;
        __u32 payload_len = 0;
        __u8 dsfield = 0;
        __u8 ttl = 0;
        struct ipv6hdr  *iph;           /* Our new IP header */
        unsigned int max_headroom;      /* The extra header space needed */
        int ret, local;

        EnterFunction(10);

        rcu_read_lock();
        local = __ip_vs_get_out_rt_v6(cp->af, skb, cp->dest, &cp->daddr.in6,
                                      &saddr, ipvsh, 1,
                                      IP_VS_RT_MODE_LOCAL |
                                      IP_VS_RT_MODE_NON_LOCAL |
                                      IP_VS_RT_MODE_TUNNEL);
        if (local < 0)
                goto tx_error;
        if (local) {
                rcu_read_unlock();
                return ip_vs_send_or_cont(NFPROTO_IPV6, skb, cp, 1);
        }

        rt = (struct rt6_info *) skb_dst(skb);
        tdev = rt->dst.dev;

        /*
         * Okay, now see if we can stuff it in the buffer as-is.
         */
        max_headroom = LL_RESERVED_SPACE(tdev) + sizeof(struct ipv6hdr);

        skb = ip_vs_prepare_tunneled_skb(skb, cp->af, max_headroom,
                                         &next_protocol, &payload_len,
                                         &dsfield, &ttl, NULL);
        if (IS_ERR(skb))
                goto tx_error;

        skb = iptunnel_handle_offloads(
                skb, false, __tun_gso_type_mask(AF_INET6, cp->af));
        if (IS_ERR(skb))
                goto tx_error;

        skb->transport_header = skb->network_header;

        skb_push(skb, sizeof(struct ipv6hdr));
        skb_reset_network_header(skb);
        memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));

        /*
         *      Push down and install the IPIP header.
         */
        iph                     =       ipv6_hdr(skb);
        iph->version            =       6;
        iph->nexthdr            =       next_protocol;
        iph->payload_len        =       htons(payload_len);
        memset(&iph->flow_lbl, 0, sizeof(iph->flow_lbl));
        ipv6_change_dsfield(iph, 0, dsfield);
        iph->daddr = cp->daddr.in6;
        iph->saddr = saddr;
        iph->hop_limit          =       ttl;

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        ret = ip_vs_tunnel_xmit_prepare(skb, cp);
        if (ret == NF_ACCEPT)
                ip6_local_out(skb);
        else if (ret == NF_DROP)
                kfree_skb(skb);
        rcu_read_unlock();

        LeaveFunction(10);

        return NF_STOLEN;

tx_error:
        if (!IS_ERR(skb))
                kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}
#endif


/*
 *      Direct Routing transmitter
 *      Used for ANY protocol
 */
int
ip_vs_dr_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
              struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        int local;

        EnterFunction(10);

        rcu_read_lock();
        local = __ip_vs_get_out_rt(cp->af, skb, cp->dest, cp->daddr.ip,
                                   IP_VS_RT_MODE_LOCAL |
                                   IP_VS_RT_MODE_NON_LOCAL |
                                   IP_VS_RT_MODE_KNOWN_NH, NULL, ipvsh);
        if (local < 0)
                goto tx_error;
        if (local) {
                rcu_read_unlock();
                return ip_vs_send_or_cont(NFPROTO_IPV4, skb, cp, 1);
        }

        ip_send_check(ip_hdr(skb));

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        ip_vs_send_or_cont(NFPROTO_IPV4, skb, cp, 0);
        rcu_read_unlock();

        LeaveFunction(10);
        return NF_STOLEN;

  tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}

#ifdef CONFIG_IP_VS_IPV6
int
ip_vs_dr_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
                 struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
{
        int local;

        EnterFunction(10);

        rcu_read_lock();
        local = __ip_vs_get_out_rt_v6(cp->af, skb, cp->dest, &cp->daddr.in6,
                                      NULL, ipvsh, 0,
                                      IP_VS_RT_MODE_LOCAL |
                                      IP_VS_RT_MODE_NON_LOCAL);
        if (local < 0)
                goto tx_error;
        if (local) {
                rcu_read_unlock();
                return ip_vs_send_or_cont(NFPROTO_IPV6, skb, cp, 1);
        }

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        ip_vs_send_or_cont(NFPROTO_IPV6, skb, cp, 0);
        rcu_read_unlock();

        LeaveFunction(10);
        return NF_STOLEN;

tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        LeaveFunction(10);
        return NF_STOLEN;
}
#endif


/*
 *      ICMP packet transmitter
 *      called by the ip_vs_in_icmp
 */
int
ip_vs_icmp_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                struct ip_vs_protocol *pp, int offset, unsigned int hooknum,
                struct ip_vs_iphdr *iph)
{
        struct rtable   *rt;    /* Route to the other host */
        int rc;
        int local;
        int rt_mode, was_input;

        EnterFunction(10);

        /* The ICMP packet for VS/TUN, VS/DR and LOCALNODE will be
           forwarded directly here, because there is no need to
           translate address/port back */
        if (IP_VS_FWD_METHOD(cp) != IP_VS_CONN_F_MASQ) {
                if (cp->packet_xmit)
                        rc = cp->packet_xmit(skb, cp, pp, iph);
                else
                        rc = NF_ACCEPT;
                /* do not touch skb anymore */
                atomic_inc(&cp->in_pkts);
                goto out;
        }

        /*
         * mangle and send the packet here (only for VS/NAT)
         */
        was_input = rt_is_input_route(skb_rtable(skb));

        /* LOCALNODE from FORWARD hook is not supported */
        rt_mode = (hooknum != NF_INET_FORWARD) ?
                  IP_VS_RT_MODE_LOCAL | IP_VS_RT_MODE_NON_LOCAL |
                  IP_VS_RT_MODE_RDR : IP_VS_RT_MODE_NON_LOCAL;
        rcu_read_lock();
        local = __ip_vs_get_out_rt(cp->af, skb, cp->dest, cp->daddr.ip, rt_mode,
                                   NULL, iph);
        if (local < 0)
                goto tx_error;
        rt = skb_rtable(skb);

        /*
         * Avoid duplicate tuple in reply direction for NAT traffic
         * to local address when connection is sync-ed
         */
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        if (cp->flags & IP_VS_CONN_F_SYNC && local) {
                enum ip_conntrack_info ctinfo;
                struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

                if (ct && !nf_ct_is_untracked(ct)) {
                        IP_VS_DBG(10, "%s(): "
                                  "stopping DNAT to local address %pI4\n",
                                  __func__, &cp->daddr.ip);
                        goto tx_error;
                }
        }
#endif

        /* From world but DNAT to loopback address? */
        if (local && ipv4_is_loopback(cp->daddr.ip) && was_input) {
                IP_VS_DBG(1, "%s(): "
                          "stopping DNAT to loopback %pI4\n",
                          __func__, &cp->daddr.ip);
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (!skb_make_writable(skb, offset))
                goto tx_error;

        if (skb_cow(skb, rt->dst.dev->hard_header_len))
                goto tx_error;

        ip_vs_nat_icmp(skb, pp, cp, 0);

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        rc = ip_vs_nat_send_or_cont(NFPROTO_IPV4, skb, cp, local);
        rcu_read_unlock();
        goto out;

  tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        rc = NF_STOLEN;
  out:
        LeaveFunction(10);
        return rc;
}

#ifdef CONFIG_IP_VS_IPV6
int
ip_vs_icmp_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
                struct ip_vs_protocol *pp, int offset, unsigned int hooknum,
                struct ip_vs_iphdr *ipvsh)
{
        struct rt6_info *rt;    /* Route to the other host */
        int rc;
        int local;
        int rt_mode;

        EnterFunction(10);

        /* The ICMP packet for VS/TUN, VS/DR and LOCALNODE will be
           forwarded directly here, because there is no need to
           translate address/port back */
        if (IP_VS_FWD_METHOD(cp) != IP_VS_CONN_F_MASQ) {
                if (cp->packet_xmit)
                        rc = cp->packet_xmit(skb, cp, pp, ipvsh);
                else
                        rc = NF_ACCEPT;
                /* do not touch skb anymore */
                atomic_inc(&cp->in_pkts);
                goto out;
        }

        /*
         * mangle and send the packet here (only for VS/NAT)
         */

        /* LOCALNODE from FORWARD hook is not supported */
        rt_mode = (hooknum != NF_INET_FORWARD) ?
                  IP_VS_RT_MODE_LOCAL | IP_VS_RT_MODE_NON_LOCAL |
                  IP_VS_RT_MODE_RDR : IP_VS_RT_MODE_NON_LOCAL;
        rcu_read_lock();
        local = __ip_vs_get_out_rt_v6(cp->af, skb, cp->dest, &cp->daddr.in6,
                                      NULL, ipvsh, 0, rt_mode);
        if (local < 0)
                goto tx_error;
        rt = (struct rt6_info *) skb_dst(skb);
        /*
         * Avoid duplicate tuple in reply direction for NAT traffic
         * to local address when connection is sync-ed
         */
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        if (cp->flags & IP_VS_CONN_F_SYNC && local) {
                enum ip_conntrack_info ctinfo;
                struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

                if (ct && !nf_ct_is_untracked(ct)) {
                        IP_VS_DBG(10, "%s(): "
                                  "stopping DNAT to local address %pI6\n",
                                  __func__, &cp->daddr.in6);
                        goto tx_error;
                }
        }
#endif

        /* From world but DNAT to loopback address? */
        if (local && skb->dev && !(skb->dev->flags & IFF_LOOPBACK) &&
            ipv6_addr_type(&rt->rt6i_dst.addr) & IPV6_ADDR_LOOPBACK) {
                IP_VS_DBG(1, "%s(): "
                          "stopping DNAT to loopback %pI6\n",
                          __func__, &cp->daddr.in6);
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (!skb_make_writable(skb, offset))
                goto tx_error;

        if (skb_cow(skb, rt->dst.dev->hard_header_len))
                goto tx_error;

        ip_vs_nat_icmp_v6(skb, pp, cp, 0);

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->ignore_df = 1;

        rc = ip_vs_nat_send_or_cont(NFPROTO_IPV6, skb, cp, local);
        rcu_read_unlock();
        goto out;

tx_error:
        kfree_skb(skb);
        rcu_read_unlock();
        rc = NF_STOLEN;
out:
        LeaveFunction(10);
        return rc;
}
#endif