// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      IPv6 output functions
 *      Linux INET6 implementation
 *
 *      Authors:
 *      Pedro Roque             <roque@di.fc.ul.pt>
 *
 *      Based on linux/net/ipv4/ip_output.c
 *
 *      Changes:
 *      A.N.Kuznetsov   :       airthmetics in fragmentation.
 *                              extension headers are implemented.
 *                              route changes now work.
 *                              ip6_forward does not confuse sniffers.
 *                              etc.
 *
 *      H. von Brand    :       Added missing #include <linux/string.h>
 *      Imran Patel     :       frag id should be in NBO
 *      Kazunori MIYAZAWA @USAGI
 *                      :       add ip6_append_data and related functions
 *                              for datagram xmit
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/if_arp.h>
#include <linux/in6.h>
#include <linux/tcp.h>
#include <linux/route.h>
#include <linux/module.h>
#include <linux/slab.h>

#include <linux/bpf-cgroup.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv6.h>

#include <net/sock.h>
#include <net/snmp.h>

#include <net/ipv6.h>
#include <net/ndisc.h>
#include <net/protocol.h>
#include <net/ip6_route.h>
#include <net/addrconf.h>
#include <net/rawv6.h>
#include <net/icmp.h>
#include <net/xfrm.h>
#include <net/checksum.h>
#include <linux/mroute6.h>
#include <net/l3mdev.h>
#include <net/lwtunnel.h>
#include <net/ip_tunnels.h>

static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct dst_entry *dst = skb_dst(skb);
        struct net_device *dev = dst->dev;
        unsigned int hh_len = LL_RESERVED_SPACE(dev);
        int delta = hh_len - skb_headroom(skb);
        const struct in6_addr *nexthop;
        struct neighbour *neigh;
        int ret;

        /* Be paranoid, rather than too clever. */
        if (unlikely(delta > 0) && dev->header_ops) {
                /* pskb_expand_head() might crash, if skb is shared */
                if (skb_shared(skb)) {
                        struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);

                        if (likely(nskb)) {
                                if (skb->sk)
                                        skb_set_owner_w(nskb, skb->sk);
                                consume_skb(skb);
                        } else {
                                kfree_skb(skb);
                        }
                        skb = nskb;
                }
                if (skb &&
                    pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
                        kfree_skb(skb);
                        skb = NULL;
                }
                if (!skb) {
                        IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTDISCARDS);
                        return -ENOMEM;
                }
        }

        if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr)) {
                struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));

                if (!(dev->flags & IFF_LOOPBACK) && sk_mc_loop(sk) &&
                    ((mroute6_is_socket(net, skb) &&
                     !(IP6CB(skb)->flags & IP6SKB_FORWARDED)) ||
                     ipv6_chk_mcast_addr(dev, &ipv6_hdr(skb)->daddr,
                                         &ipv6_hdr(skb)->saddr))) {
                        struct sk_buff *newskb = skb_clone(skb, GFP_ATOMIC);

                        /* Do not check for IFF_ALLMULTI; multicast routing
                           is not supported in any case.
                         */
                        if (newskb)
                                NF_HOOK(NFPROTO_IPV6, NF_INET_POST_ROUTING,
                                        net, sk, newskb, NULL, newskb->dev,
                                        dev_loopback_xmit);

                        if (ipv6_hdr(skb)->hop_limit == 0) {
                                IP6_INC_STATS(net, idev,
                                              IPSTATS_MIB_OUTDISCARDS);
                                kfree_skb(skb);
                                return 0;
                        }
                }

                IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_OUTMCAST, skb->len);

                if (IPV6_ADDR_MC_SCOPE(&ipv6_hdr(skb)->daddr) <=
                    IPV6_ADDR_SCOPE_NODELOCAL &&
                    !(dev->flags & IFF_LOOPBACK)) {
                        kfree_skb(skb);
                        return 0;
                }
        }

        if (lwtunnel_xmit_redirect(dst->lwtstate)) {
                int res = lwtunnel_xmit(skb);

                if (res < 0 || res == LWTUNNEL_XMIT_DONE)
                        return res;
        }

        rcu_read_lock_bh();
        nexthop = rt6_nexthop((struct rt6_info *)dst, &ipv6_hdr(skb)->daddr);
        neigh = __ipv6_neigh_lookup_noref(dst->dev, nexthop);
        if (unlikely(!neigh))
                neigh = __neigh_create(&nd_tbl, nexthop, dst->dev, false);
        if (!IS_ERR(neigh)) {
                sock_confirm_neigh(skb, neigh);
                ret = neigh_output(neigh, skb, false);
                rcu_read_unlock_bh();
                return ret;
        }
        rcu_read_unlock_bh();

        IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
        kfree_skb(skb);
        return -EINVAL;
}

static int
ip6_finish_output_gso_slowpath_drop(struct net *net, struct sock *sk,
                                    struct sk_buff *skb, unsigned int mtu)
{
        struct sk_buff *segs, *nskb;
        netdev_features_t features;
        int ret = 0;

        /* Please see corresponding comment in ip_finish_output_gso
         * describing the cases where GSO segment length exceeds the
         * egress MTU.
         */
        features = netif_skb_features(skb);
        segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
        if (IS_ERR_OR_NULL(segs)) {
                kfree_skb(skb);
                return -ENOMEM;
        }

        consume_skb(skb);

        skb_list_walk_safe(segs, segs, nskb) {
                int err;

                skb_mark_not_on_list(segs);
                err = ip6_fragment(net, sk, segs, ip6_finish_output2);
                if (err && ret == 0)
                        ret = err;
        }

        return ret;
}

static int __ip6_finish_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        unsigned int mtu;

#if defined(CONFIG_NETFILTER) && defined(CONFIG_XFRM)
        /* Policy lookup after SNAT yielded a new policy */
        if (skb_dst(skb)->xfrm) {
                IPCB(skb)->flags |= IPSKB_REROUTED;
                return dst_output(net, sk, skb);
        }
#endif

        mtu = ip6_skb_dst_mtu(skb);
        if (skb_is_gso(skb) && !skb_gso_validate_network_len(skb, mtu))
                return ip6_finish_output_gso_slowpath_drop(net, sk, skb, mtu);

        if ((skb->len > mtu && !skb_is_gso(skb)) ||
            dst_allfrag(skb_dst(skb)) ||
            (IP6CB(skb)->frag_max_size && skb->len > IP6CB(skb)->frag_max_size))
                return ip6_fragment(net, sk, skb, ip6_finish_output2);
        else
                return ip6_finish_output2(net, sk, skb);
}

static int ip6_finish_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        int ret;

        ret = BPF_CGROUP_RUN_PROG_INET_EGRESS(sk, skb);
        switch (ret) {
        case NET_XMIT_SUCCESS:
                return __ip6_finish_output(net, sk, skb);
        case NET_XMIT_CN:
                return __ip6_finish_output(net, sk, skb) ? : ret;
        default:
                kfree_skb(skb);
                return ret;
        }
}

int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct net_device *dev = skb_dst(skb)->dev, *indev = skb->dev;
        struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));

        skb->protocol = htons(ETH_P_IPV6);
        skb->dev = dev;

        if (unlikely(idev->cnf.disable_ipv6)) {
                IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
                kfree_skb(skb);
                return 0;
        }

        return NF_HOOK_COND(NFPROTO_IPV6, NF_INET_POST_ROUTING,
                            net, sk, skb, indev, dev,
                            ip6_finish_output,
                            !(IP6CB(skb)->flags & IP6SKB_REROUTED));
}
EXPORT_SYMBOL(ip6_output);

bool ip6_autoflowlabel(struct net *net, const struct ipv6_pinfo *np)
{
        if (!np->autoflowlabel_set)
                return ip6_default_np_autolabel(net);
        else
                return np->autoflowlabel;
}

/*
 * xmit an sk_buff (used by TCP, SCTP and DCCP)
 * Note : socket lock is not held for SYNACK packets, but might be modified
 * by calls to skb_set_owner_w() and ipv6_local_error(),
 * which are using proper atomic operations or spinlocks.
 */
int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
             __u32 mark, struct ipv6_txoptions *opt, int tclass, u32 priority)
{
        struct net *net = sock_net(sk);
        const struct ipv6_pinfo *np = inet6_sk(sk);
        struct in6_addr *first_hop = &fl6->daddr;
        struct dst_entry *dst = skb_dst(skb);
        unsigned int head_room;
        struct ipv6hdr *hdr;
        u8  proto = fl6->flowi6_proto;
        int seg_len = skb->len;
        int hlimit = -1;
        u32 mtu;

        head_room = sizeof(struct ipv6hdr) + LL_RESERVED_SPACE(dst->dev);
        if (opt)
                head_room += opt->opt_nflen + opt->opt_flen;

        if (unlikely(skb_headroom(skb) < head_room)) {
                struct sk_buff *skb2 = skb_realloc_headroom(skb, head_room);
                if (!skb2) {
                        IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
                                      IPSTATS_MIB_OUTDISCARDS);
                        kfree_skb(skb);
                        return -ENOBUFS;
                }
                if (skb->sk)
                        skb_set_owner_w(skb2, skb->sk);
                consume_skb(skb);
                skb = skb2;
        }

        if (opt) {
                seg_len += opt->opt_nflen + opt->opt_flen;

                if (opt->opt_flen)
                        ipv6_push_frag_opts(skb, opt, &proto);

                if (opt->opt_nflen)
                        ipv6_push_nfrag_opts(skb, opt, &proto, &first_hop,
                                             &fl6->saddr);
        }

        skb_push(skb, sizeof(struct ipv6hdr));
        skb_reset_network_header(skb);
        hdr = ipv6_hdr(skb);

        /*
         *      Fill in the IPv6 header
         */
        if (np)
                hlimit = np->hop_limit;
        if (hlimit < 0)
                hlimit = ip6_dst_hoplimit(dst);

        ip6_flow_hdr(hdr, tclass, ip6_make_flowlabel(net, skb, fl6->flowlabel,
                                ip6_autoflowlabel(net, np), fl6));

        hdr->payload_len = htons(seg_len);
        hdr->nexthdr = proto;
        hdr->hop_limit = hlimit;

        hdr->saddr = fl6->saddr;
        hdr->daddr = *first_hop;

        skb->protocol = htons(ETH_P_IPV6);
        skb->priority = priority;
        skb->mark = mark;

        mtu = dst_mtu(dst);
        if ((skb->len <= mtu) || skb->ignore_df || skb_is_gso(skb)) {
                IP6_UPD_PO_STATS(net, ip6_dst_idev(skb_dst(skb)),
                              IPSTATS_MIB_OUT, skb->len);

                /* if egress device is enslaved to an L3 master device pass the
                 * skb to its handler for processing
                 */
                skb = l3mdev_ip6_out((struct sock *)sk, skb);
                if (unlikely(!skb))
                        return 0;

                /* hooks should never assume socket lock is held.
                 * we promote our socket to non const
                 */
                return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
                               net, (struct sock *)sk, skb, NULL, dst->dev,
                               dst_output);
        }

        skb->dev = dst->dev;
        /* ipv6_local_error() does not require socket lock,
         * we promote our socket to non const
         */
        ipv6_local_error((struct sock *)sk, EMSGSIZE, fl6, mtu);

        IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_FRAGFAILS);
        kfree_skb(skb);
        return -EMSGSIZE;
}
EXPORT_SYMBOL(ip6_xmit);

static int ip6_call_ra_chain(struct sk_buff *skb, int sel)
{
        struct ip6_ra_chain *ra;
        struct sock *last = NULL;

        read_lock(&ip6_ra_lock);
        for (ra = ip6_ra_chain; ra; ra = ra->next) {
                struct sock *sk = ra->sk;
                if (sk && ra->sel == sel &&
                    (!sk->sk_bound_dev_if ||
                     sk->sk_bound_dev_if == skb->dev->ifindex)) {
                        struct ipv6_pinfo *np = inet6_sk(sk);

                        if (np && np->rtalert_isolate &&
                            !net_eq(sock_net(sk), dev_net(skb->dev))) {
                                continue;
                        }
                        if (last) {
                                struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
                                if (skb2)
                                        rawv6_rcv(last, skb2);
                        }
                        last = sk;
                }
        }

        if (last) {
                rawv6_rcv(last, skb);
                read_unlock(&ip6_ra_lock);
                return 1;
        }
        read_unlock(&ip6_ra_lock);
        return 0;
}

static int ip6_forward_proxy_check(struct sk_buff *skb)
{
        struct ipv6hdr *hdr = ipv6_hdr(skb);
        u8 nexthdr = hdr->nexthdr;
        __be16 frag_off;
        int offset;

        if (ipv6_ext_hdr(nexthdr)) {
                offset = ipv6_skip_exthdr(skb, sizeof(*hdr), &nexthdr, &frag_off);
                if (offset < 0)
                        return 0;
        } else
                offset = sizeof(struct ipv6hdr);

        if (nexthdr == IPPROTO_ICMPV6) {
                struct icmp6hdr *icmp6;

                if (!pskb_may_pull(skb, (skb_network_header(skb) +
                                         offset + 1 - skb->data)))
                        return 0;

                icmp6 = (struct icmp6hdr *)(skb_network_header(skb) + offset);

                switch (icmp6->icmp6_type) {
                case NDISC_ROUTER_SOLICITATION:
                case NDISC_ROUTER_ADVERTISEMENT:
                case NDISC_NEIGHBOUR_SOLICITATION:
                case NDISC_NEIGHBOUR_ADVERTISEMENT:
                case NDISC_REDIRECT:
                        /* For reaction involving unicast neighbor discovery
                         * message destined to the proxied address, pass it to
                         * input function.
                         */
                        return 1;
                default:
                        break;
                }
        }

        /*
         * The proxying router can't forward traffic sent to a link-local
         * address, so signal the sender and discard the packet. This
         * behavior is clarified by the MIPv6 specification.
         */
        if (ipv6_addr_type(&hdr->daddr) & IPV6_ADDR_LINKLOCAL) {
                dst_link_failure(skb);
                return -1;
        }

        return 0;
}

static inline int ip6_forward_finish(struct net *net, struct sock *sk,
                                     struct sk_buff *skb)
{
        struct dst_entry *dst = skb_dst(skb);

        __IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTFORWDATAGRAMS);
        __IP6_ADD_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTOCTETS, skb->len);

#ifdef CONFIG_NET_SWITCHDEV
        if (skb->offload_l3_fwd_mark) {
                consume_skb(skb);
                return 0;
        }
#endif

        skb->tstamp = 0;
        return dst_output(net, sk, skb);
}

static bool ip6_pkt_too_big(const struct sk_buff *skb, unsigned int mtu)
{
        if (skb->len <= mtu)
                return false;

        /* ipv6 conntrack defrag sets max_frag_size + ignore_df */
        if (IP6CB(skb)->frag_max_size && IP6CB(skb)->frag_max_size > mtu)
                return true;

        if (skb->ignore_df)
                return false;

        if (skb_is_gso(skb) && skb_gso_validate_network_len(skb, mtu))
                return false;

        return true;
}

int ip6_forward(struct sk_buff *skb)
{
        struct inet6_dev *idev = __in6_dev_get_safely(skb->dev);
        struct dst_entry *dst = skb_dst(skb);
        struct ipv6hdr *hdr = ipv6_hdr(skb);
        struct inet6_skb_parm *opt = IP6CB(skb);
        struct net *net = dev_net(dst->dev);
        u32 mtu;

        if (net->ipv6.devconf_all->forwarding == 0)
                goto error;

        if (skb->pkt_type != PACKET_HOST)
                goto drop;

        if (unlikely(skb->sk))
                goto drop;

        if (skb_warn_if_lro(skb))
                goto drop;

        if (!net->ipv6.devconf_all->disable_policy &&
            !idev->cnf.disable_policy &&
            !xfrm6_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
                __IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
                goto drop;
        }

        skb_forward_csum(skb);

        /*
         *      We DO NOT make any processing on
         *      RA packets, pushing them to user level AS IS
         *      without ane WARRANTY that application will be able
         *      to interpret them. The reason is that we
         *      cannot make anything clever here.
         *
         *      We are not end-node, so that if packet contains
         *      AH/ESP, we cannot make anything.
         *      Defragmentation also would be mistake, RA packets
         *      cannot be fragmented, because there is no warranty
         *      that different fragments will go along one path. --ANK
         */
        if (unlikely(opt->flags & IP6SKB_ROUTERALERT)) {
                if (ip6_call_ra_chain(skb, ntohs(opt->ra)))
                        return 0;
        }

        /*
         *      check and decrement ttl
         */
        if (hdr->hop_limit <= 1) {
                icmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT, 0);
                __IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);

                kfree_skb(skb);
                return -ETIMEDOUT;
        }

        /* XXX: idev->cnf.proxy_ndp? */
        if (net->ipv6.devconf_all->proxy_ndp &&
            pneigh_lookup(&nd_tbl, net, &hdr->daddr, skb->dev, 0)) {
                int proxied = ip6_forward_proxy_check(skb);
                if (proxied > 0) {
                        hdr->hop_limit--;
                        return ip6_input(skb);
                } else if (proxied < 0) {
                        __IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
                        goto drop;
                }
        }

        if (!xfrm6_route_forward(skb)) {
                __IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
                goto drop;
        }
        dst = skb_dst(skb);

        /* IPv6 specs say nothing about it, but it is clear that we cannot
           send redirects to source routed frames.
           We don't send redirects to frames decapsulated from IPsec.
         */
        if (IP6CB(skb)->iif == dst->dev->ifindex &&
            opt->srcrt == 0 && !skb_sec_path(skb)) {
                struct in6_addr *target = NULL;
                struct inet_peer *peer;
                struct rt6_info *rt;

                /*
                 *      incoming and outgoing devices are the same
                 *      send a redirect.
                 */

                rt = (struct rt6_info *) dst;
                if (rt->rt6i_flags & RTF_GATEWAY)
                        target = &rt->rt6i_gateway;
                else
                        target = &hdr->daddr;

                peer = inet_getpeer_v6(net->ipv6.peers, &hdr->daddr, 1);

                /* Limit redirects both by destination (here)
                   and by source (inside ndisc_send_redirect)
                 */
                if (inet_peer_xrlim_allow(peer, 1*HZ))
                        ndisc_send_redirect(skb, target);
                if (peer)
                        inet_putpeer(peer);
        } else {
                int addrtype = ipv6_addr_type(&hdr->saddr);

                /* This check is security critical. */
                if (addrtype == IPV6_ADDR_ANY ||
                    addrtype & (IPV6_ADDR_MULTICAST | IPV6_ADDR_LOOPBACK))
                        goto error;
                if (addrtype & IPV6_ADDR_LINKLOCAL) {
                        icmpv6_send(skb, ICMPV6_DEST_UNREACH,
                                    ICMPV6_NOT_NEIGHBOUR, 0);
                        goto error;
                }
        }

        mtu = ip6_dst_mtu_forward(dst);
        if (mtu < IPV6_MIN_MTU)
                mtu = IPV6_MIN_MTU;

        if (ip6_pkt_too_big(skb, mtu)) {
                /* Again, force OUTPUT device used as source address */
                skb->dev = dst->dev;
                icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
                __IP6_INC_STATS(net, idev, IPSTATS_MIB_INTOOBIGERRORS);
                __IP6_INC_STATS(net, ip6_dst_idev(dst),
                                IPSTATS_MIB_FRAGFAILS);
                kfree_skb(skb);
                return -EMSGSIZE;
        }

        if (skb_cow(skb, dst->dev->hard_header_len)) {
                __IP6_INC_STATS(net, ip6_dst_idev(dst),
                                IPSTATS_MIB_OUTDISCARDS);
                goto drop;
        }

        hdr = ipv6_hdr(skb);

        /* Mangling hops number delayed to point after skb COW */

        hdr->hop_limit--;

        return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD,
                       net, NULL, skb, skb->dev, dst->dev,
                       ip6_forward_finish);

error:
        __IP6_INC_STATS(net, idev, IPSTATS_MIB_INADDRERRORS);
drop:
        kfree_skb(skb);
        return -EINVAL;
}

static void ip6_copy_metadata(struct sk_buff *to, struct sk_buff *from)
{
        to->pkt_type = from->pkt_type;
        to->priority = from->priority;
        to->protocol = from->protocol;
        skb_dst_drop(to);
        skb_dst_set(to, dst_clone(skb_dst(from)));
        to->dev = from->dev;
        to->mark = from->mark;

        skb_copy_hash(to, from);

#ifdef CONFIG_NET_SCHED
        to->tc_index = from->tc_index;
#endif
        nf_copy(to, from);
        skb_ext_copy(to, from);
        skb_copy_secmark(to, from);
}

int ip6_fraglist_init(struct sk_buff *skb, unsigned int hlen, u8 *prevhdr,
                      u8 nexthdr, __be32 frag_id,
                      struct ip6_fraglist_iter *iter)
{
        unsigned int first_len;
        struct frag_hdr *fh;

        /* BUILD HEADER */
        *prevhdr = NEXTHDR_FRAGMENT;
        iter->tmp_hdr = kmemdup(skb_network_header(skb), hlen, GFP_ATOMIC);
        if (!iter->tmp_hdr)
                return -ENOMEM;

        iter->frag = skb_shinfo(skb)->frag_list;
        skb_frag_list_init(skb);

        iter->offset = 0;
        iter->hlen = hlen;
        iter->frag_id = frag_id;
        iter->nexthdr = nexthdr;

        __skb_pull(skb, hlen);
        fh = __skb_push(skb, sizeof(struct frag_hdr));
        __skb_push(skb, hlen);
        skb_reset_network_header(skb);
        memcpy(skb_network_header(skb), iter->tmp_hdr, hlen);

        fh->nexthdr = nexthdr;
        fh->reserved = 0;
        fh->frag_off = htons(IP6_MF);
        fh->identification = frag_id;

        first_len = skb_pagelen(skb);
        skb->data_len = first_len - skb_headlen(skb);
        skb->len = first_len;
        ipv6_hdr(skb)->payload_len = htons(first_len - sizeof(struct ipv6hdr));

        return 0;
}
EXPORT_SYMBOL(ip6_fraglist_init);

void ip6_fraglist_prepare(struct sk_buff *skb,
                          struct ip6_fraglist_iter *iter)
{
        struct sk_buff *frag = iter->frag;
        unsigned int hlen = iter->hlen;
        struct frag_hdr *fh;

        frag->ip_summed = CHECKSUM_NONE;
        skb_reset_transport_header(frag);
        fh = __skb_push(frag, sizeof(struct frag_hdr));
        __skb_push(frag, hlen);
        skb_reset_network_header(frag);
        memcpy(skb_network_header(frag), iter->tmp_hdr, hlen);
        iter->offset += skb->len - hlen - sizeof(struct frag_hdr);
        fh->nexthdr = iter->nexthdr;
        fh->reserved = 0;
        fh->frag_off = htons(iter->offset);
        if (frag->next)
                fh->frag_off |= htons(IP6_MF);
        fh->identification = iter->frag_id;
        ipv6_hdr(frag)->payload_len = htons(frag->len - sizeof(struct ipv6hdr));
        ip6_copy_metadata(frag, skb);
}
EXPORT_SYMBOL(ip6_fraglist_prepare);

void ip6_frag_init(struct sk_buff *skb, unsigned int hlen, unsigned int mtu,
                   unsigned short needed_tailroom, int hdr_room, u8 *prevhdr,
                   u8 nexthdr, __be32 frag_id, struct ip6_frag_state *state)
{
        state->prevhdr = prevhdr;
        state->nexthdr = nexthdr;
        state->frag_id = frag_id;

        state->hlen = hlen;
        state->mtu = mtu;

        state->left = skb->len - hlen;  /* Space per frame */
        state->ptr = hlen;              /* Where to start from */

        state->hroom = hdr_room;
        state->troom = needed_tailroom;

        state->offset = 0;
}
EXPORT_SYMBOL(ip6_frag_init);

struct sk_buff *ip6_frag_next(struct sk_buff *skb, struct ip6_frag_state *state)
{
        u8 *prevhdr = state->prevhdr, *fragnexthdr_offset;
        struct sk_buff *frag;
        struct frag_hdr *fh;
        unsigned int len;

        len = state->left;
        /* IF: it doesn't fit, use 'mtu' - the data space left */
        if (len > state->mtu)
                len = state->mtu;
        /* IF: we are not sending up to and including the packet end
           then align the next start on an eight byte boundary */
        if (len < state->left)
                len &= ~7;

        /* Allocate buffer */
        frag = alloc_skb(len + state->hlen + sizeof(struct frag_hdr) +
                         state->hroom + state->troom, GFP_ATOMIC);
        if (!frag)
                return ERR_PTR(-ENOMEM);

        /*
         *      Set up data on packet
         */

        ip6_copy_metadata(frag, skb);
        skb_reserve(frag, state->hroom);
        skb_put(frag, len + state->hlen + sizeof(struct frag_hdr));
        skb_reset_network_header(frag);
        fh = (struct frag_hdr *)(skb_network_header(frag) + state->hlen);
        frag->transport_header = (frag->network_header + state->hlen +
                                  sizeof(struct frag_hdr));

        /*
         *      Charge the memory for the fragment to any owner
         *      it might possess
         */
        if (skb->sk)
                skb_set_owner_w(frag, skb->sk);

        /*
         *      Copy the packet header into the new buffer.
         */
        skb_copy_from_linear_data(skb, skb_network_header(frag), state->hlen);

        fragnexthdr_offset = skb_network_header(frag);
        fragnexthdr_offset += prevhdr - skb_network_header(skb);
        *fragnexthdr_offset = NEXTHDR_FRAGMENT;

        /*
         *      Build fragment header.
         */
        fh->nexthdr = state->nexthdr;
        fh->reserved = 0;
        fh->identification = state->frag_id;

        /*
         *      Copy a block of the IP datagram.
         */
        BUG_ON(skb_copy_bits(skb, state->ptr, skb_transport_header(frag),
                             len));
        state->left -= len;

        fh->frag_off = htons(state->offset);
        if (state->left > 0)
                fh->frag_off |= htons(IP6_MF);
        ipv6_hdr(frag)->payload_len = htons(frag->len - sizeof(struct ipv6hdr));

        state->ptr += len;
        state->offset += len;

        return frag;
}
EXPORT_SYMBOL(ip6_frag_next);

int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
                 int (*output)(struct net *, struct sock *, struct sk_buff *))
{
        struct sk_buff *frag;
        struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);
        struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
                                inet6_sk(skb->sk) : NULL;
        struct ip6_frag_state state;
        unsigned int mtu, hlen, nexthdr_offset;
        ktime_t tstamp = skb->tstamp;
        int hroom, err = 0;
        __be32 frag_id;
        u8 *prevhdr, nexthdr = 0;

        err = ip6_find_1stfragopt(skb, &prevhdr);
        if (err < 0)
                goto fail;
        hlen = err;
        nexthdr = *prevhdr;
        nexthdr_offset = prevhdr - skb_network_header(skb);

        mtu = ip6_skb_dst_mtu(skb);

        /* We must not fragment if the socket is set to force MTU discovery
         * or if the skb it not generated by a local socket.
         */
        if (unlikely(!skb->ignore_df && skb->len > mtu))
                goto fail_toobig;

        if (IP6CB(skb)->frag_max_size) {
                if (IP6CB(skb)->frag_max_size > mtu)
                        goto fail_toobig;

                /* don't send fragments larger than what we received */
                mtu = IP6CB(skb)->frag_max_size;
                if (mtu < IPV6_MIN_MTU)
                        mtu = IPV6_MIN_MTU;
        }

        if (np && np->frag_size < mtu) {
                if (np->frag_size)
                        mtu = np->frag_size;
        }
        if (mtu < hlen + sizeof(struct frag_hdr) + 8)
                goto fail_toobig;
        mtu -= hlen + sizeof(struct frag_hdr);

        frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
                                    &ipv6_hdr(skb)->saddr);

        if (skb->ip_summed == CHECKSUM_PARTIAL &&
            (err = skb_checksum_help(skb)))
                goto fail;

        prevhdr = skb_network_header(skb) + nexthdr_offset;
        hroom = LL_RESERVED_SPACE(rt->dst.dev);
        if (skb_has_frag_list(skb)) {
                unsigned int first_len = skb_pagelen(skb);
                struct ip6_fraglist_iter iter;
                struct sk_buff *frag2;

                if (first_len - hlen > mtu ||
                    ((first_len - hlen) & 7) ||
                    skb_cloned(skb) ||
                    skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
                        goto slow_path;

                skb_walk_frags(skb, frag) {
                        /* Correct geometry. */
                        if (frag->len > mtu ||
                            ((frag->len & 7) && frag->next) ||
                            skb_headroom(frag) < (hlen + hroom + sizeof(struct frag_hdr)))
                                goto slow_path_clean;

                        /* Partially cloned skb? */
                        if (skb_shared(frag))
                                goto slow_path_clean;

                        BUG_ON(frag->sk);
                        if (skb->sk) {
                                frag->sk = skb->sk;
                                frag->destructor = sock_wfree;
                        }
                        skb->truesize -= frag->truesize;
                }

                err = ip6_fraglist_init(skb, hlen, prevhdr, nexthdr, frag_id,
                                        &iter);
                if (err < 0)
                        goto fail;

                for (;;) {
                        /* Prepare header of the next frame,
                         * before previous one went down. */
                        if (iter.frag)
                                ip6_fraglist_prepare(skb, &iter);

                        skb->tstamp = tstamp;
                        err = output(net, sk, skb);
                        if (!err)
                                IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
                                              IPSTATS_MIB_FRAGCREATES);

                        if (err || !iter.frag)
                                break;

                        skb = ip6_fraglist_next(&iter);
                }

                kfree(iter.tmp_hdr);

                if (err == 0) {
                        IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
                                      IPSTATS_MIB_FRAGOKS);
                        return 0;
                }

                kfree_skb_list(iter.frag);

                IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
                              IPSTATS_MIB_FRAGFAILS);
                return err;

slow_path_clean:
                skb_walk_frags(skb, frag2) {
                        if (frag2 == frag)
                                break;
                        frag2->sk = NULL;
                        frag2->destructor = NULL;
                        skb->truesize += frag2->truesize;
                }
        }

slow_path:
        /*
         *      Fragment the datagram.
         */

        ip6_frag_init(skb, hlen, mtu, rt->dst.dev->needed_tailroom,
                      LL_RESERVED_SPACE(rt->dst.dev), prevhdr, nexthdr, frag_id,
                      &state);

        /*
         *      Keep copying data until we run out.
         */

        while (state.left > 0) {
                frag = ip6_frag_next(skb, &state);
                if (IS_ERR(frag)) {
                        err = PTR_ERR(frag);
                        goto fail;
                }

                /*
                 *      Put this fragment into the sending queue.
                 */
                frag->tstamp = tstamp;
                err = output(net, sk, frag);
                if (err)
                        goto fail;

                IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
                              IPSTATS_MIB_FRAGCREATES);
        }
        IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
                      IPSTATS_MIB_FRAGOKS);
        consume_skb(skb);
        return err;

fail_toobig:
        if (skb->sk && dst_allfrag(skb_dst(skb)))
                sk_nocaps_add(skb->sk, NETIF_F_GSO_MASK);

        icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
        err = -EMSGSIZE;

fail:
        IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
                      IPSTATS_MIB_FRAGFAILS);
        kfree_skb(skb);
        return err;
}

static inline int ip6_rt_check(const struct rt6key *rt_key,
                               const struct in6_addr *fl_addr,
                               const struct in6_addr *addr_cache)
{
        return (rt_key->plen != 128 || !ipv6_addr_equal(fl_addr, &rt_key->addr)) &&
                (!addr_cache || !ipv6_addr_equal(fl_addr, addr_cache));
}

static struct dst_entry *ip6_sk_dst_check(struct sock *sk,
                                          struct dst_entry *dst,
                                          const struct flowi6 *fl6)
{
        struct ipv6_pinfo *np = inet6_sk(sk);
        struct rt6_info *rt;

        if (!dst)
                goto out;

        if (dst->ops->family != AF_INET6) {
                dst_release(dst);
                return NULL;
        }

        rt = (struct rt6_info *)dst;
        /* Yes, checking route validity in not connected
         * case is not very simple. Take into account,
         * that we do not support routing by source, TOS,
         * and MSG_DONTROUTE            --ANK (980726)
         *
         * 1. ip6_rt_check(): If route was host route,
         *    check that cached destination is current.
         *    If it is network route, we still may
         *    check its validity using saved pointer
         *    to the last used address: daddr_cache.
         *    We do not want to save whole address now,
         *    (because main consumer of this service
         *    is tcp, which has not this problem),
         *    so that the last trick works only on connected
         *    sockets.
         * 2. oif also should be the same.
         */
        if (ip6_rt_check(&rt->rt6i_dst, &fl6->daddr, np->daddr_cache) ||
#ifdef CONFIG_IPV6_SUBTREES
            ip6_rt_check(&rt->rt6i_src, &fl6->saddr, np->saddr_cache) ||
#endif
           (!(fl6->flowi6_flags & FLOWI_FLAG_SKIP_NH_OIF) &&
              (fl6->flowi6_oif && fl6->flowi6_oif != dst->dev->ifindex))) {
                dst_release(dst);
                dst = NULL;
        }

out:
        return dst;
}

static int ip6_dst_lookup_tail(struct net *net, const struct sock *sk,
                               struct dst_entry **dst, struct flowi6 *fl6)
{
#ifdef CONFIG_IPV6_OPTIMISTIC_DAD
        struct neighbour *n;
        struct rt6_info *rt;
#endif
        int err;
        int flags = 0;

        /* The correct way to handle this would be to do
         * ip6_route_get_saddr, and then ip6_route_output; however,
         * the route-specific preferred source forces the
         * ip6_route_output call _before_ ip6_route_get_saddr.
         *
         * In source specific routing (no src=any default route),
         * ip6_route_output will fail given src=any saddr, though, so
         * that's why we try it again later.
         */
        if (ipv6_addr_any(&fl6->saddr)) {
                struct fib6_info *from;
                struct rt6_info *rt;

                *dst = ip6_route_output(net, sk, fl6);
                rt = (*dst)->error ? NULL : (struct rt6_info *)*dst;

                rcu_read_lock();
                from = rt ? rcu_dereference(rt->from) : NULL;
                err = ip6_route_get_saddr(net, from, &fl6->daddr,
                                          sk ? inet6_sk(sk)->srcprefs : 0,
                                          &fl6->saddr);
                rcu_read_unlock();

                if (err)
                        goto out_err_release;

                /* If we had an erroneous initial result, pretend it
                 * never existed and let the SA-enabled version take
                 * over.
                 */
                if ((*dst)->error) {
                        dst_release(*dst);
                        *dst = NULL;
                }

                if (fl6->flowi6_oif)
                        flags |= RT6_LOOKUP_F_IFACE;
        }

        if (!*dst)
                *dst = ip6_route_output_flags(net, sk, fl6, flags);

        err = (*dst)->error;
        if (err)
                goto out_err_release;

#ifdef CONFIG_IPV6_OPTIMISTIC_DAD
        /*
         * Here if the dst entry we've looked up
         * has a neighbour entry that is in the INCOMPLETE
         * state and the src address from the flow is
         * marked as OPTIMISTIC, we release the found
         * dst entry and replace it instead with the
         * dst entry of the nexthop router
         */
        rt = (struct rt6_info *) *dst;
        rcu_read_lock_bh();
        n = __ipv6_neigh_lookup_noref(rt->dst.dev,
                                      rt6_nexthop(rt, &fl6->daddr));
        err = n && !(n->nud_state & NUD_VALID) ? -EINVAL : 0;
        rcu_read_unlock_bh();

        if (err) {
                struct inet6_ifaddr *ifp;
                struct flowi6 fl_gw6;
                int redirect;

                ifp = ipv6_get_ifaddr(net, &fl6->saddr,
                                      (*dst)->dev, 1);

                redirect = (ifp && ifp->flags & IFA_F_OPTIMISTIC);
                if (ifp)
                        in6_ifa_put(ifp);

                if (redirect) {
                        /*
                         * We need to get the dst entry for the
                         * default router instead
                         */
                        dst_release(*dst);
                        memcpy(&fl_gw6, fl6, sizeof(struct flowi6));
                        memset(&fl_gw6.daddr, 0, sizeof(struct in6_addr));
                        *dst = ip6_route_output(net, sk, &fl_gw6);
                        err = (*dst)->error;
                        if (err)
                                goto out_err_release;
                }
        }
#endif
        if (ipv6_addr_v4mapped(&fl6->saddr) &&
            !(ipv6_addr_v4mapped(&fl6->daddr) || ipv6_addr_any(&fl6->daddr))) {
                err = -EAFNOSUPPORT;
                goto out_err_release;
        }

        return 0;

out_err_release:
        dst_release(*dst);
        *dst = NULL;

        if (err == -ENETUNREACH)
                IP6_INC_STATS(net, NULL, IPSTATS_MIB_OUTNOROUTES);
        return err;
}

/**
 *      ip6_dst_lookup - perform route lookup on flow
 *      @net: Network namespace to perform lookup in
 *      @sk: socket which provides route info
 *      @dst: pointer to dst_entry * for result
 *      @fl6: flow to lookup
 *
 *      This function performs a route lookup on the given flow.
 *
 *      It returns zero on success, or a standard errno code on error.
 */
int ip6_dst_lookup(struct net *net, struct sock *sk, struct dst_entry **dst,
                   struct flowi6 *fl6)
{
        *dst = NULL;
        return ip6_dst_lookup_tail(net, sk, dst, fl6);
}
EXPORT_SYMBOL_GPL(ip6_dst_lookup);

/**
 *      ip6_dst_lookup_flow - perform route lookup on flow with ipsec
 *      @net: Network namespace to perform lookup in
 *      @sk: socket which provides route info
 *      @fl6: flow to lookup
 *      @final_dst: final destination address for ipsec lookup
 *
 *      This function performs a route lookup on the given flow.
 *
 *      It returns a valid dst pointer on success, or a pointer encoded
 *      error code.
 */
struct dst_entry *ip6_dst_lookup_flow(struct net *net, const struct sock *sk, struct flowi6 *fl6,
                                      const struct in6_addr *final_dst)
{
        struct dst_entry *dst = NULL;
        int err;

        err = ip6_dst_lookup_tail(net, sk, &dst, fl6);
        if (err)
                return ERR_PTR(err);
        if (final_dst)
                fl6->daddr = *final_dst;

        return xfrm_lookup_route(net, dst, flowi6_to_flowi(fl6), sk, 0);
}
EXPORT_SYMBOL_GPL(ip6_dst_lookup_flow);

/**
 *      ip6_sk_dst_lookup_flow - perform socket cached route lookup on flow
 *      @sk: socket which provides the dst cache and route info
 *      @fl6: flow to lookup
 *      @final_dst: final destination address for ipsec lookup
 *      @connected: whether @sk is connected or not
 *
 *      This function performs a route lookup on the given flow with the
 *      possibility of using the cached route in the socket if it is valid.
 *      It will take the socket dst lock when operating on the dst cache.
 *      As a result, this function can only be used in process context.
 *
 *      In addition, for a connected socket, cache the dst in the socket
 *      if the current cache is not valid.
 *
 *      It returns a valid dst pointer on success, or a pointer encoded
 *      error code.
 */
struct dst_entry *ip6_sk_dst_lookup_flow(struct sock *sk, struct flowi6 *fl6,
                                         const struct in6_addr *final_dst,
                                         bool connected)
{
        struct dst_entry *dst = sk_dst_check(sk, inet6_sk(sk)->dst_cookie);

        dst = ip6_sk_dst_check(sk, dst, fl6);
        if (dst)
                return dst;

        dst = ip6_dst_lookup_flow(sock_net(sk), sk, fl6, final_dst);
        if (connected && !IS_ERR(dst))
                ip6_sk_dst_store_flow(sk, dst_clone(dst), fl6);

        return dst;
}
EXPORT_SYMBOL_GPL(ip6_sk_dst_lookup_flow);

/**
 *      ip6_dst_lookup_tunnel - perform route lookup on tunnel
 *      @skb: Packet for which lookup is done
 *      @dev: Tunnel device
 *      @net: Network namespace of tunnel device
 *      @sock: Socket which provides route info
 *      @saddr: Memory to store the src ip address
 *      @info: Tunnel information
 *      @protocol: IP protocol
 *      @use_cache: Flag to enable cache usage
 *      This function performs a route lookup on a tunnel
 *
 *      It returns a valid dst pointer and stores src address to be used in
 *      tunnel in param saddr on success, else a pointer encoded error code.
 */

struct dst_entry *ip6_dst_lookup_tunnel(struct sk_buff *skb,
                                        struct net_device *dev,
                                        struct net *net,
                                        struct socket *sock,
                                        struct in6_addr *saddr,
                                        const struct ip_tunnel_info *info,
                                        u8 protocol,
                                        bool use_cache)
{
        struct dst_entry *dst = NULL;
#ifdef CONFIG_DST_CACHE
        struct dst_cache *dst_cache;
#endif
        struct flowi6 fl6;
        __u8 prio;

#ifdef CONFIG_DST_CACHE
        dst_cache = (struct dst_cache *)&info->dst_cache;
        if (use_cache) {
                dst = dst_cache_get_ip6(dst_cache, saddr);
                if (dst)
                        return dst;
        }
#endif
        memset(&fl6, 0, sizeof(fl6));
        fl6.flowi6_mark = skb->mark;
        fl6.flowi6_proto = protocol;
        fl6.daddr = info->key.u.ipv6.dst;
        fl6.saddr = info->key.u.ipv6.src;
        prio = info->key.tos;
        fl6.flowlabel = ip6_make_flowinfo(RT_TOS(prio),
                                          info->key.label);

        dst = ipv6_stub->ipv6_dst_lookup_flow(net, sock->sk, &fl6,
                                              NULL);
        if (IS_ERR(dst)) {
                netdev_dbg(dev, "no route to %pI6\n", &fl6.daddr);
                return ERR_PTR(-ENETUNREACH);
        }
        if (dst->dev == dev) { /* is this necessary? */
                netdev_dbg(dev, "circular route to %pI6\n", &fl6.daddr);
                dst_release(dst);
                return ERR_PTR(-ELOOP);
        }
#ifdef CONFIG_DST_CACHE
        if (use_cache)
                dst_cache_set_ip6(dst_cache, dst, &fl6.saddr);
#endif
        *saddr = fl6.saddr;
        return dst;
}
EXPORT_SYMBOL_GPL(ip6_dst_lookup_tunnel);

static inline struct ipv6_opt_hdr *ip6_opt_dup(struct ipv6_opt_hdr *src,
                                               gfp_t gfp)
{
        return src ? kmemdup(src, (src->hdrlen + 1) * 8, gfp) : NULL;
}

static inline struct ipv6_rt_hdr *ip6_rthdr_dup(struct ipv6_rt_hdr *src,
                                                gfp_t gfp)
{
        return src ? kmemdup(src, (src->hdrlen + 1) * 8, gfp) : NULL;
}

static void ip6_append_data_mtu(unsigned int *mtu,
                                int *maxfraglen,
                                unsigned int fragheaderlen,
                                struct sk_buff *skb,
                                struct rt6_info *rt,
                                unsigned int orig_mtu)
{
        if (!(rt->dst.flags & DST_XFRM_TUNNEL)) {
                if (!skb) {
                        /* first fragment, reserve header_len */
                        *mtu = orig_mtu - rt->dst.header_len;

                } else {
                        /*
                         * this fragment is not first, the headers
                         * space is regarded as data space.
                         */
                        *mtu = orig_mtu;
                }
                *maxfraglen = ((*mtu - fragheaderlen) & ~7)
                              + fragheaderlen - sizeof(struct frag_hdr);
        }
}

static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
                          struct inet6_cork *v6_cork, struct ipcm6_cookie *ipc6,
                          struct rt6_info *rt, struct flowi6 *fl6)
{
        struct ipv6_pinfo *np = inet6_sk(sk);
        unsigned int mtu;
        struct ipv6_txoptions *opt = ipc6->opt;

        /*
         * setup for corking
         */
        if (opt) {
                if (WARN_ON(v6_cork->opt))
                        return -EINVAL;

                v6_cork->opt = kzalloc(sizeof(*opt), sk->sk_allocation);
                if (unlikely(!v6_cork->opt))
                        return -ENOBUFS;

                v6_cork->opt->tot_len = sizeof(*opt);
                v6_cork->opt->opt_flen = opt->opt_flen;
                v6_cork->opt->opt_nflen = opt->opt_nflen;

                v6_cork->opt->dst0opt = ip6_opt_dup(opt->dst0opt,
                                                    sk->sk_allocation);
                if (opt->dst0opt && !v6_cork->opt->dst0opt)
                        return -ENOBUFS;

                v6_cork->opt->dst1opt = ip6_opt_dup(opt->dst1opt,
                                                    sk->sk_allocation);
                if (opt->dst1opt && !v6_cork->opt->dst1opt)
                        return -ENOBUFS;

                v6_cork->opt->hopopt = ip6_opt_dup(opt->hopopt,
                                                   sk->sk_allocation);
                if (opt->hopopt && !v6_cork->opt->hopopt)
                        return -ENOBUFS;

                v6_cork->opt->srcrt = ip6_rthdr_dup(opt->srcrt,
                                                    sk->sk_allocation);
                if (opt->srcrt && !v6_cork->opt->srcrt)
                        return -ENOBUFS;

                /* need source address above miyazawa*/
        }
        dst_hold(&rt->dst);
        cork->base.dst = &rt->dst;
        cork->fl.u.ip6 = *fl6;
        v6_cork->hop_limit = ipc6->hlimit;
        v6_cork->tclass = ipc6->tclass;
        if (rt->dst.flags & DST_XFRM_TUNNEL)
                mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
                      READ_ONCE(rt->dst.dev->mtu) : dst_mtu(&rt->dst);
        else
                mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
                        READ_ONCE(rt->dst.dev->mtu) : dst_mtu(xfrm_dst_path(&rt->dst));
        if (np->frag_size < mtu) {
                if (np->frag_size)
                        mtu = np->frag_size;
        }
        if (mtu < IPV6_MIN_MTU)
                return -EINVAL;
        cork->base.fragsize = mtu;
        cork->base.gso_size = ipc6->gso_size;
        cork->base.tx_flags = 0;
        cork->base.mark = ipc6->sockc.mark;
        sock_tx_timestamp(sk, ipc6->sockc.tsflags, &cork->base.tx_flags);

        if (dst_allfrag(xfrm_dst_path(&rt->dst)))
                cork->base.flags |= IPCORK_ALLFRAG;
        cork->base.length = 0;

        cork->base.transmit_time = ipc6->sockc.transmit_time;

        return 0;
}

static int __ip6_append_data(struct sock *sk,
                             struct flowi6 *fl6,
                             struct sk_buff_head *queue,
                             struct inet_cork *cork,
                             struct inet6_cork *v6_cork,
                             struct page_frag *pfrag,
                             int getfrag(void *from, char *to, int offset,
                                         int len, int odd, struct sk_buff *skb),
                             void *from, int length, int transhdrlen,
                             unsigned int flags, struct ipcm6_cookie *ipc6)
{
        struct sk_buff *skb, *skb_prev = NULL;
        unsigned int maxfraglen, fragheaderlen, mtu, orig_mtu, pmtu;
        struct ubuf_info *uarg = NULL;
        int exthdrlen = 0;
        int dst_exthdrlen = 0;
        int hh_len;
        int copy;
        int err;
        int offset = 0;
        u32 tskey = 0;
        struct rt6_info *rt = (struct rt6_info *)cork->dst;
        struct ipv6_txoptions *opt = v6_cork->opt;
        int csummode = CHECKSUM_NONE;
        unsigned int maxnonfragsize, headersize;
        unsigned int wmem_alloc_delta = 0;
        bool paged, extra_uref = false;

        skb = skb_peek_tail(queue);
        if (!skb) {
                exthdrlen = opt ? opt->opt_flen : 0;
                dst_exthdrlen = rt->dst.header_len - rt->rt6i_nfheader_len;
        }

        paged = !!cork->gso_size;
        mtu = cork->gso_size ? IP6_MAX_MTU : cork->fragsize;
        orig_mtu = mtu;

        if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
            sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
                tskey = sk->sk_tskey++;

        hh_len = LL_RESERVED_SPACE(rt->dst.dev);

        fragheaderlen = sizeof(struct ipv6hdr) + rt->rt6i_nfheader_len +
                        (opt ? opt->opt_nflen : 0);
        maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen -
                     sizeof(struct frag_hdr);

        headersize = sizeof(struct ipv6hdr) +
                     (opt ? opt->opt_flen + opt->opt_nflen : 0) +
                     (dst_allfrag(&rt->dst) ?
                      sizeof(struct frag_hdr) : 0) +
                     rt->rt6i_nfheader_len;

        /* as per RFC 7112 section 5, the entire IPv6 Header Chain must fit
         * the first fragment
         */
        if (headersize + transhdrlen > mtu)
                goto emsgsize;

        if (cork->length + length > mtu - headersize && ipc6->dontfrag &&
            (sk->sk_protocol == IPPROTO_UDP ||
             sk->sk_protocol == IPPROTO_RAW)) {
                ipv6_local_rxpmtu(sk, fl6, mtu - headersize +
                                sizeof(struct ipv6hdr));
                goto emsgsize;
        }

        if (ip6_sk_ignore_df(sk))
                maxnonfragsize = sizeof(struct ipv6hdr) + IPV6_MAXPLEN;
        else
                maxnonfragsize = mtu;

        if (cork->length + length > maxnonfragsize - headersize) {
emsgsize:
                pmtu = max_t(int, mtu - headersize + sizeof(struct ipv6hdr), 0);
                ipv6_local_error(sk, EMSGSIZE, fl6, pmtu);
                return -EMSGSIZE;
        }

        /* CHECKSUM_PARTIAL only with no extension headers and when
         * we are not going to fragment
         */
        if (transhdrlen && sk->sk_protocol == IPPROTO_UDP &&
            headersize == sizeof(struct ipv6hdr) &&
            length <= mtu - headersize &&
            (!(flags & MSG_MORE) || cork->gso_size) &&
            rt->dst.dev->features & (NETIF_F_IPV6_CSUM | NETIF_F_HW_CSUM))
                csummode = CHECKSUM_PARTIAL;

        if (flags & MSG_ZEROCOPY && length && sock_flag(sk, SOCK_ZEROCOPY)) {
                uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb));
                if (!uarg)
                        return -ENOBUFS;
                extra_uref = !skb_zcopy(skb);   /* only ref on new uarg */
                if (rt->dst.dev->features & NETIF_F_SG &&
                    csummode == CHECKSUM_PARTIAL) {
                        paged = true;
                } else {
                        uarg->zerocopy = 0;
                        skb_zcopy_set(skb, uarg, &extra_uref);
                }
        }

        /*
         * Let's try using as much space as possible.
         * Use MTU if total length of the message fits into the MTU.
         * Otherwise, we need to reserve fragment header and
         * fragment alignment (= 8-15 octects, in total).
         *
         * Note that we may need to "move" the data from the tail
         * of the buffer to the new fragment when we split
         * the message.
         *
         * FIXME: It may be fragmented into multiple chunks
         *        at once if non-fragmentable extension headers
         *        are too large.
         * --yoshfuji
         */

        cork->length += length;
        if (!skb)
                goto alloc_new_skb;

        while (length > 0) {
                /* Check if the remaining data fits into current packet. */
                copy = (cork->length <= mtu && !(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - skb->len;
                if (copy < length)
                        copy = maxfraglen - skb->len;

                if (copy <= 0) {
                        char *data;
                        unsigned int datalen;
                        unsigned int fraglen;
                        unsigned int fraggap;
                        unsigned int alloclen, alloc_extra;
                        unsigned int pagedlen;
alloc_new_skb:
                        /* There's no room in the current skb */
                        if (skb)
                                fraggap = skb->len - maxfraglen;
                        else
                                fraggap = 0;
                        /* update mtu and maxfraglen if necessary */
                        if (!skb || !skb_prev)
                                ip6_append_data_mtu(&mtu, &maxfraglen,
                                                    fragheaderlen, skb, rt,
                                                    orig_mtu);

                        skb_prev = skb;

                        /*
                         * If remaining data exceeds the mtu,
                         * we know we need more fragment(s).
                         */
                        datalen = length + fraggap;

                        if (datalen > (cork->length <= mtu && !(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - fragheaderlen)
                                datalen = maxfraglen - fragheaderlen - rt->dst.trailer_len;
                        fraglen = datalen + fragheaderlen;
                        pagedlen = 0;

                        alloc_extra = hh_len;
                        alloc_extra += dst_exthdrlen;
                        alloc_extra += rt->dst.trailer_len;

                        /* We just reserve space for fragment header.
                         * Note: this may be overallocation if the message
                         * (without MSG_MORE) fits into the MTU.
                         */
                        alloc_extra += sizeof(struct frag_hdr);

                        if ((flags & MSG_MORE) &&
                            !(rt->dst.dev->features&NETIF_F_SG))
                                alloclen = mtu;
                        else if (!paged &&
                                 (fraglen + alloc_extra < SKB_MAX_ALLOC ||
                                  !(rt->dst.dev->features & NETIF_F_SG)))
                                alloclen = fraglen;
                        else {
                                alloclen = min_t(int, fraglen, MAX_HEADER);
                                pagedlen = fraglen - alloclen;
                        }
                        alloclen += alloc_extra;

                        if (datalen != length + fraggap) {
                                /*
                                 * this is not the last fragment, the trailer
                                 * space is regarded as data space.
                                 */
                                datalen += rt->dst.trailer_len;
                        }

                        fraglen = datalen + fragheaderlen;

                        copy = datalen - transhdrlen - fraggap - pagedlen;
                        if (copy < 0) {
                                err = -EINVAL;
                                goto error;
                        }
                        if (transhdrlen) {
                                skb = sock_alloc_send_skb(sk, alloclen,
                                                (flags & MSG_DONTWAIT), &err);
                        } else {
                                skb = NULL;
                                if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=
                                    2 * sk->sk_sndbuf)
                                        skb = alloc_skb(alloclen,
                                                        sk->sk_allocation);
                                if (unlikely(!skb))
                                        err = -ENOBUFS;
                        }
                        if (!skb)
                                goto error;
                        /*
                         *      Fill in the control structures
                         */
                        skb->protocol = htons(ETH_P_IPV6);
                        skb->ip_summed = csummode;
                        skb->csum = 0;
                        /* reserve for fragmentation and ipsec header */
                        skb_reserve(skb, hh_len + sizeof(struct frag_hdr) +
                                    dst_exthdrlen);

                        /*
                         *      Find where to start putting bytes
                         */
                        data = skb_put(skb, fraglen - pagedlen);
                        skb_set_network_header(skb, exthdrlen);
                        data += fragheaderlen;
                        skb->transport_header = (skb->network_header +
                                                 fragheaderlen);
                        if (fraggap) {
                                skb->csum = skb_copy_and_csum_bits(
                                        skb_prev, maxfraglen,
                                        data + transhdrlen, fraggap);
                                skb_prev->csum = csum_sub(skb_prev->csum,
                                                          skb->csum);
                                data += fraggap;
                                pskb_trim_unique(skb_prev, maxfraglen);
                        }
                        if (copy > 0 &&
                            getfrag(from, data + transhdrlen, offset,
                                    copy, fraggap, skb) < 0) {
                                err = -EFAULT;
                                kfree_skb(skb);
                                goto error;
                        }

                        offset += copy;
                        length -= copy + transhdrlen;
                        transhdrlen = 0;
                        exthdrlen = 0;
                        dst_exthdrlen = 0;

                        /* Only the initial fragment is time stamped */
                        skb_shinfo(skb)->tx_flags = cork->tx_flags;
                        cork->tx_flags = 0;
                        skb_shinfo(skb)->tskey = tskey;
                        tskey = 0;
                        skb_zcopy_set(skb, uarg, &extra_uref);

                        if ((flags & MSG_CONFIRM) && !skb_prev)
                                skb_set_dst_pending_confirm(skb, 1);

                        /*
                         * Put the packet on the pending queue
                         */
                        if (!skb->destructor) {
                                skb->destructor = sock_wfree;
                                skb->sk = sk;
                                wmem_alloc_delta += skb->truesize;
                        }
                        __skb_queue_tail(queue, skb);
                        continue;
                }

                if (copy > length)
                        copy = length;

                if (!(rt->dst.dev->features&NETIF_F_SG) &&
                    skb_tailroom(skb) >= copy) {
                        unsigned int off;

                        off = skb->len;
                        if (getfrag(from, skb_put(skb, copy),
                                                offset, copy, off, skb) < 0) {
                                __skb_trim(skb, off);
                                err = -EFAULT;
                                goto error;
                        }
                } else if (!uarg || !uarg->zerocopy) {
                        int i = skb_shinfo(skb)->nr_frags;

                        err = -ENOMEM;
                        if (!sk_page_frag_refill(sk, pfrag))
                                goto error;

                        if (!skb_can_coalesce(skb, i, pfrag->page,
                                              pfrag->offset)) {
                                err = -EMSGSIZE;
                                if (i == MAX_SKB_FRAGS)
                                        goto error;

                                __skb_fill_page_desc(skb, i, pfrag->page,
                                                     pfrag->offset, 0);
                                skb_shinfo(skb)->nr_frags = ++i;
                                get_page(pfrag->page);
                        }
                        copy = min_t(int, copy, pfrag->size - pfrag->offset);
                        if (getfrag(from,
                                    page_address(pfrag->page) + pfrag->offset,
                                    offset, copy, skb->len, skb) < 0)
                                goto error_efault;

                        pfrag->offset += copy;
                        skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
                        skb->len += copy;
                        skb->data_len += copy;
                        skb->truesize += copy;
                        wmem_alloc_delta += copy;
                } else {
                        err = skb_zerocopy_iter_dgram(skb, from, copy);
                        if (err < 0)
                                goto error;
                }
                offset += copy;
                length -= copy;
        }

        if (wmem_alloc_delta)
                refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
        return 0;

error_efault:
        err = -EFAULT;
error:
        net_zcopy_put_abort(uarg, extra_uref);
        cork->length -= length;
        IP6_INC_STATS(sock_net(sk), rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
        refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
        return err;
}

int ip6_append_data(struct sock *sk,
                    int getfrag(void *from, char *to, int offset, int len,
                                int odd, struct sk_buff *skb),
                    void *from, int length, int transhdrlen,
                    struct ipcm6_cookie *ipc6, struct flowi6 *fl6,
                    struct rt6_info *rt, unsigned int flags)
{
        struct inet_sock *inet = inet_sk(sk);
        struct ipv6_pinfo *np = inet6_sk(sk);
        int exthdrlen;
        int err;

        if (flags&MSG_PROBE)
                return 0;
        if (skb_queue_empty(&sk->sk_write_queue)) {
                /*
                 * setup for corking
                 */
                err = ip6_setup_cork(sk, &inet->cork, &np->cork,
                                     ipc6, rt, fl6);
                if (err)
                        return err;

                exthdrlen = (ipc6->opt ? ipc6->opt->opt_flen : 0);
                length += exthdrlen;
                transhdrlen += exthdrlen;
        } else {
                fl6 = &inet->cork.fl.u.ip6;
                transhdrlen = 0;
        }

        return __ip6_append_data(sk, fl6, &sk->sk_write_queue, &inet->cork.base,
                                 &np->cork, sk_page_frag(sk), getfrag,
                                 from, length, transhdrlen, flags, ipc6);
}
EXPORT_SYMBOL_GPL(ip6_append_data);

static void ip6_cork_release(struct inet_cork_full *cork,
                             struct inet6_cork *v6_cork)
{
        if (v6_cork->opt) {
                kfree(v6_cork->opt->dst0opt);
                kfree(v6_cork->opt->dst1opt);
                kfree(v6_cork->opt->hopopt);
                kfree(v6_cork->opt->srcrt);
                kfree(v6_cork->opt);
                v6_cork->opt = NULL;
        }

        if (cork->base.dst) {
                dst_release(cork->base.dst);
                cork->base.dst = NULL;
                cork->base.flags &= ~IPCORK_ALLFRAG;
        }
        memset(&cork->fl, 0, sizeof(cork->fl));
}

struct sk_buff *__ip6_make_skb(struct sock *sk,
                               struct sk_buff_head *queue,
                               struct inet_cork_full *cork,
                               struct inet6_cork *v6_cork)
{
        struct sk_buff *skb, *tmp_skb;
        struct sk_buff **tail_skb;
        struct in6_addr final_dst_buf, *final_dst = &final_dst_buf;
        struct ipv6_pinfo *np = inet6_sk(sk);
        struct net *net = sock_net(sk);
        struct ipv6hdr *hdr;
        struct ipv6_txoptions *opt = v6_cork->opt;
        struct rt6_info *rt = (struct rt6_info *)cork->base.dst;
        struct flowi6 *fl6 = &cork->fl.u.ip6;
        unsigned char proto = fl6->flowi6_proto;

        skb = __skb_dequeue(queue);
        if (!skb)
                goto out;
        tail_skb = &(skb_shinfo(skb)->frag_list);

        /* move skb->data to ip header from ext header */
        if (skb->data < skb_network_header(skb))
                __skb_pull(skb, skb_network_offset(skb));
        while ((tmp_skb = __skb_dequeue(queue)) != NULL) {
                __skb_pull(tmp_skb, skb_network_header_len(skb));
                *tail_skb = tmp_skb;
                tail_skb = &(tmp_skb->next);
                skb->len += tmp_skb->len;
                skb->data_len += tmp_skb->len;
                skb->truesize += tmp_skb->truesize;
                tmp_skb->destructor = NULL;
                tmp_skb->sk = NULL;
        }

        /* Allow local fragmentation. */
        skb->ignore_df = ip6_sk_ignore_df(sk);

        *final_dst = fl6->daddr;
        __skb_pull(skb, skb_network_header_len(skb));
        if (opt && opt->opt_flen)
                ipv6_push_frag_opts(skb, opt, &proto);
        if (opt && opt->opt_nflen)
                ipv6_push_nfrag_opts(skb, opt, &proto, &final_dst, &fl6->saddr);

        skb_push(skb, sizeof(struct ipv6hdr));
        skb_reset_network_header(skb);
        hdr = ipv6_hdr(skb);

        ip6_flow_hdr(hdr, v6_cork->tclass,
                     ip6_make_flowlabel(net, skb, fl6->flowlabel,
                                        ip6_autoflowlabel(net, np), fl6));
        hdr->hop_limit = v6_cork->hop_limit;
        hdr->nexthdr = proto;
        hdr->saddr = fl6->saddr;
        hdr->daddr = *final_dst;

        skb->priority = sk->sk_priority;
        skb->mark = cork->base.mark;

        skb->tstamp = cork->base.transmit_time;

        skb_dst_set(skb, dst_clone(&rt->dst));
        IP6_UPD_PO_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUT, skb->len);
        if (proto == IPPROTO_ICMPV6) {
                struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));

                ICMP6MSGOUT_INC_STATS(net, idev, icmp6_hdr(skb)->icmp6_type);
                ICMP6_INC_STATS(net, idev, ICMP6_MIB_OUTMSGS);
        }

        ip6_cork_release(cork, v6_cork);
out:
        return skb;
}

int ip6_send_skb(struct sk_buff *skb)
{
        struct net *net = sock_net(skb->sk);
        struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);
        int err;

        err = ip6_local_out(net, skb->sk, skb);
        if (err) {
                if (err > 0)
                        err = net_xmit_errno(err);
                if (err)
                        IP6_INC_STATS(net, rt->rt6i_idev,
                                      IPSTATS_MIB_OUTDISCARDS);
        }

        return err;
}

int ip6_push_pending_frames(struct sock *sk)
{
        struct sk_buff *skb;

        skb = ip6_finish_skb(sk);
        if (!skb)
                return 0;

        return ip6_send_skb(skb);
}
EXPORT_SYMBOL_GPL(ip6_push_pending_frames);

static void __ip6_flush_pending_frames(struct sock *sk,
                                       struct sk_buff_head *queue,
                                       struct inet_cork_full *cork,
                                       struct inet6_cork *v6_cork)
{
        struct sk_buff *skb;

        while ((skb = __skb_dequeue_tail(queue)) != NULL) {
                if (skb_dst(skb))
                        IP6_INC_STATS(sock_net(sk), ip6_dst_idev(skb_dst(skb)),
                                      IPSTATS_MIB_OUTDISCARDS);
                kfree_skb(skb);
        }

        ip6_cork_release(cork, v6_cork);
}

void ip6_flush_pending_frames(struct sock *sk)
{
        __ip6_flush_pending_frames(sk, &sk->sk_write_queue,
                                   &inet_sk(sk)->cork, &inet6_sk(sk)->cork);
}
EXPORT_SYMBOL_GPL(ip6_flush_pending_frames);

struct sk_buff *ip6_make_skb(struct sock *sk,
                             int getfrag(void *from, char *to, int offset,
                                         int len, int odd, struct sk_buff *skb),
                             void *from, int length, int transhdrlen,
                             struct ipcm6_cookie *ipc6, struct flowi6 *fl6,
                             struct rt6_info *rt, unsigned int flags,
                             struct inet_cork_full *cork)
{
        struct inet6_cork v6_cork;
        struct sk_buff_head queue;
        int exthdrlen = (ipc6->opt ? ipc6->opt->opt_flen : 0);
        int err;

        if (flags & MSG_PROBE)
                return NULL;

        __skb_queue_head_init(&queue);

        cork->base.flags = 0;
        cork->base.addr = 0;
        cork->base.opt = NULL;
        cork->base.dst = NULL;
        v6_cork.opt = NULL;
        err = ip6_setup_cork(sk, cork, &v6_cork, ipc6, rt, fl6);
        if (err) {
                ip6_cork_release(cork, &v6_cork);
                return ERR_PTR(err);
        }
        if (ipc6->dontfrag < 0)
                ipc6->dontfrag = inet6_sk(sk)->dontfrag;

        err = __ip6_append_data(sk, fl6, &queue, &cork->base, &v6_cork,
                                &current->task_frag, getfrag, from,
                                length + exthdrlen, transhdrlen + exthdrlen,
                                flags, ipc6);
        if (err) {
                __ip6_flush_pending_frames(sk, &queue, cork, &v6_cork);
                return ERR_PTR(err);
        }

        return __ip6_make_skb(sk, &queue, cork, &v6_cork);
}