// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * ip_vs_xmit.c: various packet transmitters for IPVS
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *              Julian Anastasov <ja@ssi.bg>
 *
 * 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 pr_fmt(fmt) "IPVS: " fmt

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/tcp.h>                  /* for tcphdr */
#include <net/ip.h>
#include <net/gue.h>
#include <net/gre.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/ip6_checksum.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_obj(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 (READ_ONCE(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, optionally bind route to saddr */
static struct rtable *do_output_route4(struct net *net, __be32 daddr,
                                       int rt_mode, __be32 *ret_saddr)
{
        struct flowi4 fl4;
        struct rtable *rt;

        memset(&fl4, 0, sizeof(fl4));
        fl4.daddr = daddr;
        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)) {
                IP_VS_DBG_RL("ip_route_output error, dest: %pI4\n", &daddr);
                return NULL;
        }
        if (rt_mode & IP_VS_RT_MODE_CONNECT && fl4.saddr) {
                ip_rt_put(rt);
                flowi4_update_output(&fl4, 0, daddr, fl4.saddr);
                rt_mode = 0;
                goto retry;
        }
        if (ret_saddr)
                *ret_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_NON_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(
                        dst_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, true);
}

static inline bool ensure_mtu_is_adequate(struct netns_ipvs *ipvs, 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 = ipvs->net;

                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 && !ip_vs_iph_icmp(ipvsh))
                                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
        {
                /* 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) &&
                             !ip_vs_iph_icmp(ipvsh))) {
                        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;
}

static inline bool decrement_ttl(struct netns_ipvs *ipvs,
                                 int skb_af,
                                 struct sk_buff *skb)
{
        struct net *net = ipvs->net;

#ifdef CONFIG_IP_VS_IPV6
        if (skb_af == AF_INET6) {
                struct dst_entry *dst = skb_dst(skb);

                /* check and decrement ttl */
                if (ipv6_hdr(skb)->hop_limit <= 1) {
                        struct inet6_dev *idev = __in6_dev_get_safely(skb->dev);

                        /* Force OUTPUT device used as source address */
                        skb->dev = dst->dev;
                        icmpv6_send(skb, ICMPV6_TIME_EXCEED,
                                    ICMPV6_EXC_HOPLIMIT, 0);
                        IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);

                        return false;
                }

                /* don't propagate ttl change to cloned packets */
                if (skb_ensure_writable(skb, sizeof(struct ipv6hdr)))
                        return false;

                ipv6_hdr(skb)->hop_limit--;
        } else
#endif
        {
                if (ip_hdr(skb)->ttl <= 1) {
                        /* Tell the sender its packet died... */
                        IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
                        icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
                        return false;
                }

                /* don't propagate ttl change to cloned packets */
                if (skb_ensure_writable(skb, sizeof(struct iphdr)))
                        return false;

                /* Decrease ttl */
                ip_decrease_ttl(ip_hdr(skb));
        }

        return true;
}

/* rt has device that is down */
static bool rt_dev_is_down(const struct net_device *dev)
{
        return dev && !netif_running(dev);
}

/* Get route to destination or remote server */
static int
__ip_vs_get_out_rt(struct netns_ipvs *ipvs, 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 = ipvs->net;
        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 = dst_rtable(dest_dst->dst_cache);
                        if (ret_saddr)
                                *ret_saddr = dest_dst->dst_saddr.ip;
                } 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;
                        }
                        /* It is forbidden to attach dest->dest_dst if
                         * device is going down.
                         */
                        if (!rt_dev_is_down(dst_dev_rcu(&rt->dst)))
                                __ip_vs_dst_set(dest, dest_dst, &rt->dst, 0);
                        else
                                noref = 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,
                                  rcuref_read(&rt->dst.__rcuref));
                        if (ret_saddr)
                                *ret_saddr = dest_dst->dst_saddr.ip;
                        if (!noref)
                                ip_vs_dest_dst_free(dest_dst);
                }
        } else {
                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, ret_saddr);
                if (!rt)
                        goto err_unreach;
        }

        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 (!decrement_ttl(ipvs, skb_af, skb))
                goto err_put;

        if (likely(!(rt_mode & IP_VS_RT_MODE_TUNNEL))) {
                mtu = dst_mtu(&rt->dst);
        } else {
                mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr);
                if (!dest)
                        goto err_put;
                if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                        mtu -= sizeof(struct udphdr) + sizeof(struct guehdr);
                        if ((dest->tun_flags &
                             IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
                            skb->ip_summed == CHECKSUM_PARTIAL)
                                mtu -= GUE_PLEN_REMCSUM + GUE_LEN_PRIV;
                } else if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
                        IP_TUNNEL_DECLARE_FLAGS(tflags) = { };

                        if (dest->tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                                __set_bit(IP_TUNNEL_CSUM_BIT, tflags);
                        mtu -= gre_calc_hlen(tflags);
                }
                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(ipvs, skb_af, rt_mode, ipvsh, skb, mtu))
                goto err_put;

        skb_dst_drop(skb);
        if (noref)
                skb_dst_set_noref(skb, &rt->dst);
        else
                skb_dst_set(skb, &rt->dst);

        return local;

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

err_unreach:
        if (!skb->dev)
                skb->dev = skb_dst(skb)->dev;

        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, int rt_mode)
{
        struct dst_entry *dst;
        struct flowi6 fl6 = {
                .daddr = *daddr,
        };

        if (rt_mode & IP_VS_RT_MODE_KNOWN_NH)
                fl6.flowi6_flags = FLOWI_FLAG_KNOWN_NH;

        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(struct netns_ipvs *ipvs, 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 = ipvs->net;
        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 = dst_rt6_info(dest_dst->dst_cache);
                        if (ret_saddr)
                                *ret_saddr = dest_dst->dst_saddr.in6;
                } 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, rt_mode);
                        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 = dst_rt6_info(dst);
                        cookie = rt6_get_cookie(rt);
                        /* It is forbidden to attach dest->dest_dst if
                         * device is going down.
                         */
                        if (!rt_dev_is_down(dst_dev_rcu(&rt->dst)))
                                __ip_vs_dst_set(dest, dest_dst, &rt->dst, cookie);
                        else
                                noref = 0;
                        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,
                                  rcuref_read(&rt->dst.__rcuref));
                        if (ret_saddr)
                                *ret_saddr = dest_dst->dst_saddr.in6;
                        if (!noref)
                                ip_vs_dest_dst_free(dest_dst);
                }
        } else {
                noref = 0;
                dst = __ip_vs_route_output_v6(net, daddr, ret_saddr, do_xfrm,
                                              rt_mode);
                if (!dst)
                        goto err_unreach;
                rt = dst_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;
        }

        if (!decrement_ttl(ipvs, skb_af, skb))
                goto err_put;

        /* 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 (!dest)
                        goto err_put;
                if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                        mtu -= sizeof(struct udphdr) + sizeof(struct guehdr);
                        if ((dest->tun_flags &
                             IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
                            skb->ip_summed == CHECKSUM_PARTIAL)
                                mtu -= GUE_PLEN_REMCSUM + GUE_LEN_PRIV;
                } else if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
                        IP_TUNNEL_DECLARE_FLAGS(tflags) = { };

                        if (dest->tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                                __set_bit(IP_TUNNEL_CSUM_BIT, tflags);
                        mtu -= gre_calc_hlen(tflags);
                }
                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(ipvs, skb_af, rt_mode, ipvsh, skb, mtu))
                goto err_put;

        skb_dst_drop(skb);
        if (noref)
                skb_dst_set_noref(skb, &rt->dst);
        else
                skb_dst_set(skb, &rt->dst);

        return local;

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

err_unreach:
        /* The ip6_link_failure function requires the dev field to be set
         * in order to get the net (further for the sake of fwmark
         * reflection).
         */
        if (!skb->dev)
                skb->dev = skb_dst(skb)->dev;

        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_ct(skb);
                skb_forward_csum(skb);
                if (skb->dev)
                        skb_clear_tstamp(skb);
        }
        return ret;
}

/* In the event of a remote destination, it's possible that we would have
 * matches against an old socket (particularly a TIME-WAIT socket). This
 * causes havoc down the line (ip_local_out et. al. expect regular sockets
 * and invalid memory accesses will happen) so simply drop the association
 * in this case.
*/
static inline void ip_vs_drop_early_demux_sk(struct sk_buff *skb)
{
        /* If dev is set, the packet came from the LOCAL_IN callback and
         * not from a local TCP socket.
         */
        if (skb->dev)
                skb_orphan(skb);
}

/* 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);

        /* Remove the early_demux association unless it's bound for the
         * exact same port and address on this host after translation.
         */
        if (!local || cp->vport != cp->dport ||
            !ip_vs_addr_equal(cp->af, &cp->vaddr, &cp->daddr))
                ip_vs_drop_early_demux_sk(skb);

        if (!local) {
                skb_forward_csum(skb);
                if (skb->dev)
                        skb_clear_tstamp(skb);
                NF_HOOK(pf, NF_INET_LOCAL_OUT, cp->ipvs->net, NULL, skb,
                        NULL, skb_dst(skb)->dev, dst_output);
        } 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) {
                ip_vs_drop_early_demux_sk(skb);
                skb_forward_csum(skb);
                if (skb->dev)
                        skb_clear_tstamp(skb);
                NF_HOOK(pf, NF_INET_LOCAL_OUT, cp->ipvs->net, NULL, skb,
                        NULL, skb_dst(skb)->dev, dst_output);
        } 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);

        if (__ip_vs_get_out_rt(cp->ipvs, 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);

        return NF_STOLEN;

 tx_error:
        kfree_skb(skb);
        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)
{
        struct ipv6hdr *iph = ipv6_hdr(skb);

        if (__ip_vs_get_out_rt_v6(cp->ipvs, cp->af, skb, NULL,
                                  &iph->daddr, 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);

        return NF_STOLEN;

 tx_error:
        kfree_skb(skb);
        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;

        /* 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->ipvs, 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) {
                        IP_VS_DBG_RL_PKT(10, AF_INET, pp, skb, ipvsh->off,
                                         "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, ipvsh->off,
                                 "ip_vs_nat_xmit(): stopping DNAT to loopback "
                                 "address");
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (skb_ensure_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, ipvsh->off, "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);

        return rc;

  tx_error:
        kfree_skb(skb);
        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;

        /* 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->ipvs, 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 = dst_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) {
                        IP_VS_DBG_RL_PKT(10, AF_INET6, pp, skb, ipvsh->off,
                                         "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(&cp->daddr.in6) & IPV6_ADDR_LOOPBACK) {
                IP_VS_DBG_RL_PKT(1, AF_INET6, pp, skb, ipvsh->off,
                                 "ip_vs_nat_xmit_v6(): "
                                 "stopping DNAT to loopback address");
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (skb_ensure_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, ipvsh->off, "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);

        return rc;

tx_error:
        kfree_skb(skb);
        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;
        __u8 old_dsfield;
#ifdef CONFIG_IP_VS_IPV6
        struct ipv6hdr *old_ipv6h = NULL;
#endif

        ip_vs_drop_early_demux_sk(skb);

        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 =
                                ipv6_payload_len(skb, old_ipv6h) +
                                sizeof(*old_ipv6h);
                old_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);
                old_dsfield = ipv4_get_dsfield(old_iph);
                *ttl = old_iph->ttl;
                if (payload_len)
                        *payload_len = skb_ip_totlen(skb);
        }

        /* Implement full-functionality option for ECN encapsulation */
        *dsfield = INET_ECN_encapsulate(old_dsfield, old_dsfield);

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

static inline int __tun_gso_type_mask(int encaps_af, int orig_af)
{
        switch (encaps_af) {
        case AF_INET:
                return SKB_GSO_IPXIP4;
        case AF_INET6:
                return SKB_GSO_IPXIP6;
        default:
                return 0;
        }
}

static int
ipvs_gue_encap(struct net *net, struct sk_buff *skb,
               struct ip_vs_conn *cp, __u8 *next_protocol)
{
        __be16 dport;
        __be16 sport = udp_flow_src_port(net, skb, 0, 0, false);
        struct udphdr  *udph;   /* Our new UDP header */
        struct guehdr  *gueh;   /* Our new GUE header */
        size_t hdrlen, optlen = 0;
        void *data;
        bool need_priv = false;

        if ((cp->dest->tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
            skb->ip_summed == CHECKSUM_PARTIAL) {
                optlen += GUE_PLEN_REMCSUM + GUE_LEN_PRIV;
                need_priv = true;
        }

        hdrlen = sizeof(struct guehdr) + optlen;

        skb_push(skb, hdrlen);

        gueh = (struct guehdr *)skb->data;

        gueh->control = 0;
        gueh->version = 0;
        gueh->hlen = optlen >> 2;
        gueh->flags = 0;
        gueh->proto_ctype = *next_protocol;

        data = &gueh[1];

        if (need_priv) {
                __be32 *flags = data;
                u16 csum_start = skb_checksum_start_offset(skb);
                __be16 *pd;

                gueh->flags |= GUE_FLAG_PRIV;
                *flags = 0;
                data += GUE_LEN_PRIV;

                if (csum_start < hdrlen)
                        return -EINVAL;

                csum_start -= hdrlen;
                pd = data;
                pd[0] = htons(csum_start);
                pd[1] = htons(csum_start + skb->csum_offset);

                if (!skb_is_gso(skb)) {
                        skb->ip_summed = CHECKSUM_NONE;
                        skb->encapsulation = 0;
                }

                *flags |= GUE_PFLAG_REMCSUM;
                data += GUE_PLEN_REMCSUM;
        }

        skb_push(skb, sizeof(struct udphdr));
        skb_reset_transport_header(skb);

        udph = udp_hdr(skb);

        dport = cp->dest->tun_port;
        udph->dest = dport;
        udph->source = sport;
        udph->len = htons(skb->len);
        udph->check = 0;

        *next_protocol = IPPROTO_UDP;

        return 0;
}

static void
ipvs_gre_encap(struct net *net, struct sk_buff *skb,
               struct ip_vs_conn *cp, __u8 *next_protocol)
{
        __be16 proto = *next_protocol == IPPROTO_IPIP ?
                                htons(ETH_P_IP) : htons(ETH_P_IPV6);
        IP_TUNNEL_DECLARE_FLAGS(tflags) = { };
        size_t hdrlen;

        if (cp->dest->tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                __set_bit(IP_TUNNEL_CSUM_BIT, tflags);

        hdrlen = gre_calc_hlen(tflags);
        gre_build_header(skb, hdrlen, tflags, proto, 0, 0);

        *next_protocol = IPPROTO_GRE;
}

/*
 *   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 netns_ipvs *ipvs = cp->ipvs;
        struct net *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;
        int tun_type, gso_type;
        int tun_flags;

        local = __ip_vs_get_out_rt(ipvs, 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)
                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);

        tun_type = cp->dest->tun_type;
        tun_flags = cp->dest->tun_flags;

        if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                size_t gue_hdrlen, gue_optlen = 0;

                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
                    skb->ip_summed == CHECKSUM_PARTIAL) {
                        gue_optlen += GUE_PLEN_REMCSUM + GUE_LEN_PRIV;
                }
                gue_hdrlen = sizeof(struct guehdr) + gue_optlen;

                max_headroom += sizeof(struct udphdr) + gue_hdrlen;
        } else if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
                IP_TUNNEL_DECLARE_FLAGS(tflags) = { };
                size_t gre_hdrlen;

                if (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                        __set_bit(IP_TUNNEL_CSUM_BIT, tflags);
                gre_hdrlen = gre_calc_hlen(tflags);

                max_headroom += gre_hdrlen;
        }

        /* 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))
                return NF_STOLEN;

        gso_type = __tun_gso_type_mask(AF_INET, cp->af);
        if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM) ||
                    (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM))
                        gso_type |= SKB_GSO_UDP_TUNNEL_CSUM;
                else
                        gso_type |= SKB_GSO_UDP_TUNNEL;
                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
                    skb->ip_summed == CHECKSUM_PARTIAL) {
                        gso_type |= SKB_GSO_TUNNEL_REMCSUM;
                }
        } else if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
                if (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                        gso_type |= SKB_GSO_GRE_CSUM;
                else
                        gso_type |= SKB_GSO_GRE;
        }

        if (iptunnel_handle_offloads(skb, gso_type))
                goto tx_error;

        skb->transport_header = skb->network_header;

        skb_set_inner_ipproto(skb, next_protocol);
        skb_set_inner_mac_header(skb, skb_inner_network_offset(skb));

        if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                bool check = false;

                if (ipvs_gue_encap(net, skb, cp, &next_protocol))
                        goto tx_error;

                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM) ||
                    (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM))
                        check = true;

                udp_set_csum(!check, skb, saddr, cp->daddr.ip, skb->len);
        } else if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE)
                ipvs_gre_encap(net, skb, cp, &next_protocol);

        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(net, skb->sk, skb);
        else if (ret == NF_DROP)
                kfree_skb(skb);

        return NF_STOLEN;

  tx_error:
        kfree_skb(skb);
        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 netns_ipvs *ipvs = cp->ipvs;
        struct net *net = ipvs->net;
        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;
        int tun_type, gso_type;
        int tun_flags;

        local = __ip_vs_get_out_rt_v6(ipvs, 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)
                return ip_vs_send_or_cont(NFPROTO_IPV6, skb, cp, 1);

        rt = dst_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);

        tun_type = cp->dest->tun_type;
        tun_flags = cp->dest->tun_flags;

        if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                size_t gue_hdrlen, gue_optlen = 0;

                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
                    skb->ip_summed == CHECKSUM_PARTIAL) {
                        gue_optlen += GUE_PLEN_REMCSUM + GUE_LEN_PRIV;
                }
                gue_hdrlen = sizeof(struct guehdr) + gue_optlen;

                max_headroom += sizeof(struct udphdr) + gue_hdrlen;
        } else if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
                IP_TUNNEL_DECLARE_FLAGS(tflags) = { };
                size_t gre_hdrlen;

                if (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                        __set_bit(IP_TUNNEL_CSUM_BIT, tflags);
                gre_hdrlen = gre_calc_hlen(tflags);

                max_headroom += gre_hdrlen;
        }

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

        gso_type = __tun_gso_type_mask(AF_INET6, cp->af);
        if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM) ||
                    (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM))
                        gso_type |= SKB_GSO_UDP_TUNNEL_CSUM;
                else
                        gso_type |= SKB_GSO_UDP_TUNNEL;
                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM) &&
                    skb->ip_summed == CHECKSUM_PARTIAL) {
                        gso_type |= SKB_GSO_TUNNEL_REMCSUM;
                }
        } else if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
                if (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM)
                        gso_type |= SKB_GSO_GRE_CSUM;
                else
                        gso_type |= SKB_GSO_GRE;
        }

        if (iptunnel_handle_offloads(skb, gso_type))
                goto tx_error;

        skb->transport_header = skb->network_header;

        skb_set_inner_ipproto(skb, next_protocol);
        skb_set_inner_mac_header(skb, skb_inner_network_offset(skb));

        if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
                bool check = false;

                if (ipvs_gue_encap(net, skb, cp, &next_protocol))
                        goto tx_error;

                if ((tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_CSUM) ||
                    (tun_flags & IP_VS_TUNNEL_ENCAP_FLAG_REMCSUM))
                        check = true;

                udp6_set_csum(!check, skb, &saddr, &cp->daddr.in6, skb->len);
        } else if (tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE)
                ipvs_gre_encap(net, skb, cp, &next_protocol);

        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(net, skb->sk, skb);
        else if (ret == NF_DROP)
                kfree_skb(skb);

        return NF_STOLEN;

tx_error:
        kfree_skb(skb);
        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;

        local = __ip_vs_get_out_rt(cp->ipvs, 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)
                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);

        return NF_STOLEN;

  tx_error:
        kfree_skb(skb);
        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;

        local = __ip_vs_get_out_rt_v6(cp->ipvs, 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_KNOWN_NH);
        if (local < 0)
                goto tx_error;
        if (local)
                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);

        return NF_STOLEN;

tx_error:
        kfree_skb(skb);
        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;

        /* 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);
                return rc;
        }

        /*
         * 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;
        local = __ip_vs_get_out_rt(cp->ipvs, 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) {
                        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_ensure_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;

        return ip_vs_nat_send_or_cont(NFPROTO_IPV4, skb, cp, local);

  tx_error:
        kfree_skb(skb);
        rc = NF_STOLEN;
        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;

        /* 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);
                return rc;
        }

        /*
         * 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;
        local = __ip_vs_get_out_rt_v6(cp->ipvs, cp->af, skb, cp->dest,
                                      &cp->daddr.in6, NULL, ipvsh, 0, rt_mode);
        if (local < 0)
                goto tx_error;
        rt = dst_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) {
                        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(&cp->daddr.in6) & 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_ensure_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;

        return ip_vs_nat_send_or_cont(NFPROTO_IPV6, skb, cp, local);

tx_error:
        kfree_skb(skb);
        rc = NF_STOLEN;
        return rc;
}
#endif