// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              ROUTE - implementation of the IP router.
 *
 * Authors:     Ross Biro
 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
 *              Linus Torvalds, <Linus.Torvalds@helsinki.fi>
 *              Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *
 * Fixes:
 *              Alan Cox        :       Verify area fixes.
 *              Alan Cox        :       cli() protects routing changes
 *              Rui Oliveira    :       ICMP routing table updates
 *              (rco@di.uminho.pt)      Routing table insertion and update
 *              Linus Torvalds  :       Rewrote bits to be sensible
 *              Alan Cox        :       Added BSD route gw semantics
 *              Alan Cox        :       Super /proc >4K
 *              Alan Cox        :       MTU in route table
 *              Alan Cox        :       MSS actually. Also added the window
 *                                      clamper.
 *              Sam Lantinga    :       Fixed route matching in rt_del()
 *              Alan Cox        :       Routing cache support.
 *              Alan Cox        :       Removed compatibility cruft.
 *              Alan Cox        :       RTF_REJECT support.
 *              Alan Cox        :       TCP irtt support.
 *              Jonathan Naylor :       Added Metric support.
 *      Miquel van Smoorenburg  :       BSD API fixes.
 *      Miquel van Smoorenburg  :       Metrics.
 *              Alan Cox        :       Use __u32 properly
 *              Alan Cox        :       Aligned routing errors more closely with BSD
 *                                      our system is still very different.
 *              Alan Cox        :       Faster /proc handling
 *      Alexey Kuznetsov        :       Massive rework to support tree based routing,
 *                                      routing caches and better behaviour.
 *
 *              Olaf Erb        :       irtt wasn't being copied right.
 *              Bjorn Ekwall    :       Kerneld route support.
 *              Alan Cox        :       Multicast fixed (I hope)
 *              Pavel Krauz     :       Limited broadcast fixed
 *              Mike McLagan    :       Routing by source
 *      Alexey Kuznetsov        :       End of old history. Split to fib.c and
 *                                      route.c and rewritten from scratch.
 *              Andi Kleen      :       Load-limit warning messages.
 *      Vitaly E. Lavrov        :       Transparent proxy revived after year coma.
 *      Vitaly E. Lavrov        :       Race condition in ip_route_input_slow.
 *      Tobias Ringstrom        :       Uninitialized res.type in ip_route_output_slow.
 *      Vladimir V. Ivanov      :       IP rule info (flowid) is really useful.
 *              Marc Boucher    :       routing by fwmark
 *      Robert Olsson           :       Added rt_cache statistics
 *      Arnaldo C. Melo         :       Convert proc stuff to seq_file
 *      Eric Dumazet            :       hashed spinlocks and rt_check_expire() fixes.
 *      Ilia Sotnikov           :       Ignore TOS on PMTUD and Redirect
 *      Ilia Sotnikov           :       Removed TOS from hash calculations
 */

#define pr_fmt(fmt) "IPv4: " fmt

#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/memblock.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/errno.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/proc_fs.h>
#include <linux/init.h>
#include <linux/skbuff.h>
#include <linux/inetdevice.h>
#include <linux/igmp.h>
#include <linux/pkt_sched.h>
#include <linux/mroute.h>
#include <linux/netfilter_ipv4.h>
#include <linux/random.h>
#include <linux/rcupdate.h>
#include <linux/times.h>
#include <linux/slab.h>
#include <linux/jhash.h>
#include <net/dst.h>
#include <net/dst_metadata.h>
#include <net/net_namespace.h>
#include <net/protocol.h>
#include <net/ip.h>
#include <net/route.h>
#include <net/inetpeer.h>
#include <net/sock.h>
#include <net/ip_fib.h>
#include <net/nexthop.h>
#include <net/arp.h>
#include <net/tcp.h>
#include <net/icmp.h>
#include <net/xfrm.h>
#include <net/lwtunnel.h>
#include <net/netevent.h>
#include <net/rtnetlink.h>
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
#endif
#include <net/secure_seq.h>
#include <net/ip_tunnels.h>
#include <net/l3mdev.h>

#include "fib_lookup.h"

#define RT_FL_TOS(oldflp4) \
        ((oldflp4)->flowi4_tos & (IPTOS_RT_MASK | RTO_ONLINK))

#define RT_GC_TIMEOUT (300*HZ)

static int ip_rt_max_size;
static int ip_rt_redirect_number __read_mostly  = 9;
static int ip_rt_redirect_load __read_mostly    = HZ / 50;
static int ip_rt_redirect_silence __read_mostly = ((HZ / 50) << (9 + 1));
static int ip_rt_error_cost __read_mostly       = HZ;
static int ip_rt_error_burst __read_mostly      = 5 * HZ;
static int ip_rt_mtu_expires __read_mostly      = 10 * 60 * HZ;
static u32 ip_rt_min_pmtu __read_mostly         = 512 + 20 + 20;
static int ip_rt_min_advmss __read_mostly       = 256;

static int ip_rt_gc_timeout __read_mostly       = RT_GC_TIMEOUT;

/*
 *      Interface to generic destination cache.
 */

INDIRECT_CALLABLE_SCOPE
struct dst_entry        *ipv4_dst_check(struct dst_entry *dst, u32 cookie);
static unsigned int      ipv4_default_advmss(const struct dst_entry *dst);
INDIRECT_CALLABLE_SCOPE
unsigned int            ipv4_mtu(const struct dst_entry *dst);
static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst);
static void              ipv4_link_failure(struct sk_buff *skb);
static void              ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
                                           struct sk_buff *skb, u32 mtu,
                                           bool confirm_neigh);
static void              ip_do_redirect(struct dst_entry *dst, struct sock *sk,
                                        struct sk_buff *skb);
static void             ipv4_dst_destroy(struct dst_entry *dst);

static u32 *ipv4_cow_metrics(struct dst_entry *dst, unsigned long old)
{
        WARN_ON(1);
        return NULL;
}

static struct neighbour *ipv4_neigh_lookup(const struct dst_entry *dst,
                                           struct sk_buff *skb,
                                           const void *daddr);
static void ipv4_confirm_neigh(const struct dst_entry *dst, const void *daddr);

static struct dst_ops ipv4_dst_ops = {
        .family =               AF_INET,
        .check =                ipv4_dst_check,
        .default_advmss =       ipv4_default_advmss,
        .mtu =                  ipv4_mtu,
        .cow_metrics =          ipv4_cow_metrics,
        .destroy =              ipv4_dst_destroy,
        .negative_advice =      ipv4_negative_advice,
        .link_failure =         ipv4_link_failure,
        .update_pmtu =          ip_rt_update_pmtu,
        .redirect =             ip_do_redirect,
        .local_out =            __ip_local_out,
        .neigh_lookup =         ipv4_neigh_lookup,
        .confirm_neigh =        ipv4_confirm_neigh,
};

#define ECN_OR_COST(class)      TC_PRIO_##class

const __u8 ip_tos2prio[16] = {
        TC_PRIO_BESTEFFORT,
        ECN_OR_COST(BESTEFFORT),
        TC_PRIO_BESTEFFORT,
        ECN_OR_COST(BESTEFFORT),
        TC_PRIO_BULK,
        ECN_OR_COST(BULK),
        TC_PRIO_BULK,
        ECN_OR_COST(BULK),
        TC_PRIO_INTERACTIVE,
        ECN_OR_COST(INTERACTIVE),
        TC_PRIO_INTERACTIVE,
        ECN_OR_COST(INTERACTIVE),
        TC_PRIO_INTERACTIVE_BULK,
        ECN_OR_COST(INTERACTIVE_BULK),
        TC_PRIO_INTERACTIVE_BULK,
        ECN_OR_COST(INTERACTIVE_BULK)
};
EXPORT_SYMBOL(ip_tos2prio);

static DEFINE_PER_CPU(struct rt_cache_stat, rt_cache_stat);
#define RT_CACHE_STAT_INC(field) raw_cpu_inc(rt_cache_stat.field)

#ifdef CONFIG_PROC_FS
static void *rt_cache_seq_start(struct seq_file *seq, loff_t *pos)
{
        if (*pos)
                return NULL;
        return SEQ_START_TOKEN;
}

static void *rt_cache_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        ++*pos;
        return NULL;
}

static void rt_cache_seq_stop(struct seq_file *seq, void *v)
{
}

static int rt_cache_seq_show(struct seq_file *seq, void *v)
{
        if (v == SEQ_START_TOKEN)
                seq_printf(seq, "%-127s\n",
                           "Iface\tDestination\tGateway \tFlags\t\tRefCnt\tUse\t"
                           "Metric\tSource\t\tMTU\tWindow\tIRTT\tTOS\tHHRef\t"
                           "HHUptod\tSpecDst");
        return 0;
}

static const struct seq_operations rt_cache_seq_ops = {
        .start  = rt_cache_seq_start,
        .next   = rt_cache_seq_next,
        .stop   = rt_cache_seq_stop,
        .show   = rt_cache_seq_show,
};

static void *rt_cpu_seq_start(struct seq_file *seq, loff_t *pos)
{
        int cpu;

        if (*pos == 0)
                return SEQ_START_TOKEN;

        for (cpu = *pos-1; cpu < nr_cpu_ids; ++cpu) {
                if (!cpu_possible(cpu))
                        continue;
                *pos = cpu+1;
                return &per_cpu(rt_cache_stat, cpu);
        }
        return NULL;
}

static void *rt_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        int cpu;

        for (cpu = *pos; cpu < nr_cpu_ids; ++cpu) {
                if (!cpu_possible(cpu))
                        continue;
                *pos = cpu+1;
                return &per_cpu(rt_cache_stat, cpu);
        }
        (*pos)++;
        return NULL;

}

static void rt_cpu_seq_stop(struct seq_file *seq, void *v)
{

}

static int rt_cpu_seq_show(struct seq_file *seq, void *v)
{
        struct rt_cache_stat *st = v;

        if (v == SEQ_START_TOKEN) {
                seq_printf(seq, "entries  in_hit in_slow_tot in_slow_mc in_no_route in_brd in_martian_dst in_martian_src  out_hit out_slow_tot out_slow_mc  gc_total gc_ignored gc_goal_miss gc_dst_overflow in_hlist_search out_hlist_search\n");
                return 0;
        }

        seq_printf(seq,"%08x  %08x %08x %08x %08x %08x %08x %08x "
                   " %08x %08x %08x %08x %08x %08x %08x %08x %08x \n",
                   dst_entries_get_slow(&ipv4_dst_ops),
                   0, /* st->in_hit */
                   st->in_slow_tot,
                   st->in_slow_mc,
                   st->in_no_route,
                   st->in_brd,
                   st->in_martian_dst,
                   st->in_martian_src,

                   0, /* st->out_hit */
                   st->out_slow_tot,
                   st->out_slow_mc,

                   0, /* st->gc_total */
                   0, /* st->gc_ignored */
                   0, /* st->gc_goal_miss */
                   0, /* st->gc_dst_overflow */
                   0, /* st->in_hlist_search */
                   0  /* st->out_hlist_search */
                );
        return 0;
}

static const struct seq_operations rt_cpu_seq_ops = {
        .start  = rt_cpu_seq_start,
        .next   = rt_cpu_seq_next,
        .stop   = rt_cpu_seq_stop,
        .show   = rt_cpu_seq_show,
};

#ifdef CONFIG_IP_ROUTE_CLASSID
static int rt_acct_proc_show(struct seq_file *m, void *v)
{
        struct ip_rt_acct *dst, *src;
        unsigned int i, j;

        dst = kcalloc(256, sizeof(struct ip_rt_acct), GFP_KERNEL);
        if (!dst)
                return -ENOMEM;

        for_each_possible_cpu(i) {
                src = (struct ip_rt_acct *)per_cpu_ptr(ip_rt_acct, i);
                for (j = 0; j < 256; j++) {
                        dst[j].o_bytes   += src[j].o_bytes;
                        dst[j].o_packets += src[j].o_packets;
                        dst[j].i_bytes   += src[j].i_bytes;
                        dst[j].i_packets += src[j].i_packets;
                }
        }

        seq_write(m, dst, 256 * sizeof(struct ip_rt_acct));
        kfree(dst);
        return 0;
}
#endif

static int __net_init ip_rt_do_proc_init(struct net *net)
{
        struct proc_dir_entry *pde;

        pde = proc_create_seq("rt_cache", 0444, net->proc_net,
                              &rt_cache_seq_ops);
        if (!pde)
                goto err1;

        pde = proc_create_seq("rt_cache", 0444, net->proc_net_stat,
                              &rt_cpu_seq_ops);
        if (!pde)
                goto err2;

#ifdef CONFIG_IP_ROUTE_CLASSID
        pde = proc_create_single("rt_acct", 0, net->proc_net,
                        rt_acct_proc_show);
        if (!pde)
                goto err3;
#endif
        return 0;

#ifdef CONFIG_IP_ROUTE_CLASSID
err3:
        remove_proc_entry("rt_cache", net->proc_net_stat);
#endif
err2:
        remove_proc_entry("rt_cache", net->proc_net);
err1:
        return -ENOMEM;
}

static void __net_exit ip_rt_do_proc_exit(struct net *net)
{
        remove_proc_entry("rt_cache", net->proc_net_stat);
        remove_proc_entry("rt_cache", net->proc_net);
#ifdef CONFIG_IP_ROUTE_CLASSID
        remove_proc_entry("rt_acct", net->proc_net);
#endif
}

static struct pernet_operations ip_rt_proc_ops __net_initdata =  {
        .init = ip_rt_do_proc_init,
        .exit = ip_rt_do_proc_exit,
};

static int __init ip_rt_proc_init(void)
{
        return register_pernet_subsys(&ip_rt_proc_ops);
}

#else
static inline int ip_rt_proc_init(void)
{
        return 0;
}
#endif /* CONFIG_PROC_FS */

static inline bool rt_is_expired(const struct rtable *rth)
{
        return rth->rt_genid != rt_genid_ipv4(dev_net(rth->dst.dev));
}

void rt_cache_flush(struct net *net)
{
        rt_genid_bump_ipv4(net);
}

static struct neighbour *ipv4_neigh_lookup(const struct dst_entry *dst,
                                           struct sk_buff *skb,
                                           const void *daddr)
{
        const struct rtable *rt = container_of(dst, struct rtable, dst);
        struct net_device *dev = dst->dev;
        struct neighbour *n;

        rcu_read_lock_bh();

        if (likely(rt->rt_gw_family == AF_INET)) {
                n = ip_neigh_gw4(dev, rt->rt_gw4);
        } else if (rt->rt_gw_family == AF_INET6) {
                n = ip_neigh_gw6(dev, &rt->rt_gw6);
        } else {
                __be32 pkey;

                pkey = skb ? ip_hdr(skb)->daddr : *((__be32 *) daddr);
                n = ip_neigh_gw4(dev, pkey);
        }

        if (!IS_ERR(n) && !refcount_inc_not_zero(&n->refcnt))
                n = NULL;

        rcu_read_unlock_bh();

        return n;
}

static void ipv4_confirm_neigh(const struct dst_entry *dst, const void *daddr)
{
        const struct rtable *rt = container_of(dst, struct rtable, dst);
        struct net_device *dev = dst->dev;
        const __be32 *pkey = daddr;

        if (rt->rt_gw_family == AF_INET) {
                pkey = (const __be32 *)&rt->rt_gw4;
        } else if (rt->rt_gw_family == AF_INET6) {
                return __ipv6_confirm_neigh_stub(dev, &rt->rt_gw6);
        } else if (!daddr ||
                 (rt->rt_flags &
                  (RTCF_MULTICAST | RTCF_BROADCAST | RTCF_LOCAL))) {
                return;
        }
        __ipv4_confirm_neigh(dev, *(__force u32 *)pkey);
}

/* Hash tables of size 2048..262144 depending on RAM size.
 * Each bucket uses 8 bytes.
 */
static u32 ip_idents_mask __read_mostly;
static atomic_t *ip_idents __read_mostly;
static u32 *ip_tstamps __read_mostly;

/* In order to protect privacy, we add a perturbation to identifiers
 * if one generator is seldom used. This makes hard for an attacker
 * to infer how many packets were sent between two points in time.
 */
u32 ip_idents_reserve(u32 hash, int segs)
{
        u32 bucket, old, now = (u32)jiffies;
        atomic_t *p_id;
        u32 *p_tstamp;
        u32 delta = 0;

        bucket = hash & ip_idents_mask;
        p_tstamp = ip_tstamps + bucket;
        p_id = ip_idents + bucket;
        old = READ_ONCE(*p_tstamp);

        if (old != now && cmpxchg(p_tstamp, old, now) == old)
                delta = prandom_u32_max(now - old);

        /* If UBSAN reports an error there, please make sure your compiler
         * supports -fno-strict-overflow before reporting it that was a bug
         * in UBSAN, and it has been fixed in GCC-8.
         */
        return atomic_add_return(segs + delta, p_id) - segs;
}
EXPORT_SYMBOL(ip_idents_reserve);

void __ip_select_ident(struct net *net, struct iphdr *iph, int segs)
{
        u32 hash, id;

        /* Note the following code is not safe, but this is okay. */
        if (unlikely(siphash_key_is_zero(&net->ipv4.ip_id_key)))
                get_random_bytes(&net->ipv4.ip_id_key,
                                 sizeof(net->ipv4.ip_id_key));

        hash = siphash_3u32((__force u32)iph->daddr,
                            (__force u32)iph->saddr,
                            iph->protocol,
                            &net->ipv4.ip_id_key);
        id = ip_idents_reserve(hash, segs);
        iph->id = htons(id);
}
EXPORT_SYMBOL(__ip_select_ident);

static void __build_flow_key(const struct net *net, struct flowi4 *fl4,
                             const struct sock *sk,
                             const struct iphdr *iph,
                             int oif, u8 tos,
                             u8 prot, u32 mark, int flow_flags)
{
        if (sk) {
                const struct inet_sock *inet = inet_sk(sk);

                oif = sk->sk_bound_dev_if;
                mark = sk->sk_mark;
                tos = RT_CONN_FLAGS(sk);
                prot = inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol;
        }
        flowi4_init_output(fl4, oif, mark, tos,
                           RT_SCOPE_UNIVERSE, prot,
                           flow_flags,
                           iph->daddr, iph->saddr, 0, 0,
                           sock_net_uid(net, sk));
}

static void build_skb_flow_key(struct flowi4 *fl4, const struct sk_buff *skb,
                               const struct sock *sk)
{
        const struct net *net = dev_net(skb->dev);
        const struct iphdr *iph = ip_hdr(skb);
        int oif = skb->dev->ifindex;
        u8 tos = RT_TOS(iph->tos);
        u8 prot = iph->protocol;
        u32 mark = skb->mark;

        __build_flow_key(net, fl4, sk, iph, oif, tos, prot, mark, 0);
}

static void build_sk_flow_key(struct flowi4 *fl4, const struct sock *sk)
{
        const struct inet_sock *inet = inet_sk(sk);
        const struct ip_options_rcu *inet_opt;
        __be32 daddr = inet->inet_daddr;

        rcu_read_lock();
        inet_opt = rcu_dereference(inet->inet_opt);
        if (inet_opt && inet_opt->opt.srr)
                daddr = inet_opt->opt.faddr;
        flowi4_init_output(fl4, sk->sk_bound_dev_if, sk->sk_mark,
                           RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
                           inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol,
                           inet_sk_flowi_flags(sk),
                           daddr, inet->inet_saddr, 0, 0, sk->sk_uid);
        rcu_read_unlock();
}

static void ip_rt_build_flow_key(struct flowi4 *fl4, const struct sock *sk,
                                 const struct sk_buff *skb)
{
        if (skb)
                build_skb_flow_key(fl4, skb, sk);
        else
                build_sk_flow_key(fl4, sk);
}

static DEFINE_SPINLOCK(fnhe_lock);

static void fnhe_flush_routes(struct fib_nh_exception *fnhe)
{
        struct rtable *rt;

        rt = rcu_dereference(fnhe->fnhe_rth_input);
        if (rt) {
                RCU_INIT_POINTER(fnhe->fnhe_rth_input, NULL);
                dst_dev_put(&rt->dst);
                dst_release(&rt->dst);
        }
        rt = rcu_dereference(fnhe->fnhe_rth_output);
        if (rt) {
                RCU_INIT_POINTER(fnhe->fnhe_rth_output, NULL);
                dst_dev_put(&rt->dst);
                dst_release(&rt->dst);
        }
}

static struct fib_nh_exception *fnhe_oldest(struct fnhe_hash_bucket *hash)
{
        struct fib_nh_exception *fnhe, *oldest;

        oldest = rcu_dereference(hash->chain);
        for (fnhe = rcu_dereference(oldest->fnhe_next); fnhe;
             fnhe = rcu_dereference(fnhe->fnhe_next)) {
                if (time_before(fnhe->fnhe_stamp, oldest->fnhe_stamp))
                        oldest = fnhe;
        }
        fnhe_flush_routes(oldest);
        return oldest;
}

static u32 fnhe_hashfun(__be32 daddr)
{
        static siphash_key_t fnhe_hash_key __read_mostly;
        u64 hval;

        net_get_random_once(&fnhe_hash_key, sizeof(fnhe_hash_key));
        hval = siphash_1u32((__force u32)daddr, &fnhe_hash_key);
        return hash_64(hval, FNHE_HASH_SHIFT);
}

static void fill_route_from_fnhe(struct rtable *rt, struct fib_nh_exception *fnhe)
{
        rt->rt_pmtu = fnhe->fnhe_pmtu;
        rt->rt_mtu_locked = fnhe->fnhe_mtu_locked;
        rt->dst.expires = fnhe->fnhe_expires;

        if (fnhe->fnhe_gw) {
                rt->rt_flags |= RTCF_REDIRECTED;
                rt->rt_uses_gateway = 1;
                rt->rt_gw_family = AF_INET;
                rt->rt_gw4 = fnhe->fnhe_gw;
        }
}

static void update_or_create_fnhe(struct fib_nh_common *nhc, __be32 daddr,
                                  __be32 gw, u32 pmtu, bool lock,
                                  unsigned long expires)
{
        struct fnhe_hash_bucket *hash;
        struct fib_nh_exception *fnhe;
        struct rtable *rt;
        u32 genid, hval;
        unsigned int i;
        int depth;

        genid = fnhe_genid(dev_net(nhc->nhc_dev));
        hval = fnhe_hashfun(daddr);

        spin_lock_bh(&fnhe_lock);

        hash = rcu_dereference(nhc->nhc_exceptions);
        if (!hash) {
                hash = kcalloc(FNHE_HASH_SIZE, sizeof(*hash), GFP_ATOMIC);
                if (!hash)
                        goto out_unlock;
                rcu_assign_pointer(nhc->nhc_exceptions, hash);
        }

        hash += hval;

        depth = 0;
        for (fnhe = rcu_dereference(hash->chain); fnhe;
             fnhe = rcu_dereference(fnhe->fnhe_next)) {
                if (fnhe->fnhe_daddr == daddr)
                        break;
                depth++;
        }

        if (fnhe) {
                if (fnhe->fnhe_genid != genid)
                        fnhe->fnhe_genid = genid;
                if (gw)
                        fnhe->fnhe_gw = gw;
                if (pmtu) {
                        fnhe->fnhe_pmtu = pmtu;
                        fnhe->fnhe_mtu_locked = lock;
                }
                fnhe->fnhe_expires = max(1UL, expires);
                /* Update all cached dsts too */
                rt = rcu_dereference(fnhe->fnhe_rth_input);
                if (rt)
                        fill_route_from_fnhe(rt, fnhe);
                rt = rcu_dereference(fnhe->fnhe_rth_output);
                if (rt)
                        fill_route_from_fnhe(rt, fnhe);
        } else {
                if (depth > FNHE_RECLAIM_DEPTH)
                        fnhe = fnhe_oldest(hash);
                else {
                        fnhe = kzalloc(sizeof(*fnhe), GFP_ATOMIC);
                        if (!fnhe)
                                goto out_unlock;

                        fnhe->fnhe_next = hash->chain;
                        rcu_assign_pointer(hash->chain, fnhe);
                }
                fnhe->fnhe_genid = genid;
                fnhe->fnhe_daddr = daddr;
                fnhe->fnhe_gw = gw;
                fnhe->fnhe_pmtu = pmtu;
                fnhe->fnhe_mtu_locked = lock;
                fnhe->fnhe_expires = max(1UL, expires);

                /* Exception created; mark the cached routes for the nexthop
                 * stale, so anyone caching it rechecks if this exception
                 * applies to them.
                 */
                rt = rcu_dereference(nhc->nhc_rth_input);
                if (rt)
                        rt->dst.obsolete = DST_OBSOLETE_KILL;

                for_each_possible_cpu(i) {
                        struct rtable __rcu **prt;

                        prt = per_cpu_ptr(nhc->nhc_pcpu_rth_output, i);
                        rt = rcu_dereference(*prt);
                        if (rt)
                                rt->dst.obsolete = DST_OBSOLETE_KILL;
                }
        }

        fnhe->fnhe_stamp = jiffies;

out_unlock:
        spin_unlock_bh(&fnhe_lock);
}

static void __ip_do_redirect(struct rtable *rt, struct sk_buff *skb, struct flowi4 *fl4,
                             bool kill_route)
{
        __be32 new_gw = icmp_hdr(skb)->un.gateway;
        __be32 old_gw = ip_hdr(skb)->saddr;
        struct net_device *dev = skb->dev;
        struct in_device *in_dev;
        struct fib_result res;
        struct neighbour *n;
        struct net *net;

        switch (icmp_hdr(skb)->code & 7) {
        case ICMP_REDIR_NET:
        case ICMP_REDIR_NETTOS:
        case ICMP_REDIR_HOST:
        case ICMP_REDIR_HOSTTOS:
                break;

        default:
                return;
        }

        if (rt->rt_gw_family != AF_INET || rt->rt_gw4 != old_gw)
                return;

        in_dev = __in_dev_get_rcu(dev);
        if (!in_dev)
                return;

        net = dev_net(dev);
        if (new_gw == old_gw || !IN_DEV_RX_REDIRECTS(in_dev) ||
            ipv4_is_multicast(new_gw) || ipv4_is_lbcast(new_gw) ||
            ipv4_is_zeronet(new_gw))
                goto reject_redirect;

        if (!IN_DEV_SHARED_MEDIA(in_dev)) {
                if (!inet_addr_onlink(in_dev, new_gw, old_gw))
                        goto reject_redirect;
                if (IN_DEV_SEC_REDIRECTS(in_dev) && ip_fib_check_default(new_gw, dev))
                        goto reject_redirect;
        } else {
                if (inet_addr_type(net, new_gw) != RTN_UNICAST)
                        goto reject_redirect;
        }

        n = __ipv4_neigh_lookup(rt->dst.dev, new_gw);
        if (!n)
                n = neigh_create(&arp_tbl, &new_gw, rt->dst.dev);
        if (!IS_ERR(n)) {
                if (!(n->nud_state & NUD_VALID)) {
                        neigh_event_send(n, NULL);
                } else {
                        if (fib_lookup(net, fl4, &res, 0) == 0) {
                                struct fib_nh_common *nhc;

                                fib_select_path(net, &res, fl4, skb);
                                nhc = FIB_RES_NHC(res);
                                update_or_create_fnhe(nhc, fl4->daddr, new_gw,
                                                0, false,
                                                jiffies + ip_rt_gc_timeout);
                        }
                        if (kill_route)
                                rt->dst.obsolete = DST_OBSOLETE_KILL;
                        call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, n);
                }
                neigh_release(n);
        }
        return;

reject_redirect:
#ifdef CONFIG_IP_ROUTE_VERBOSE
        if (IN_DEV_LOG_MARTIANS(in_dev)) {
                const struct iphdr *iph = (const struct iphdr *) skb->data;
                __be32 daddr = iph->daddr;
                __be32 saddr = iph->saddr;

                net_info_ratelimited("Redirect from %pI4 on %s about %pI4 ignored\n"
                                     "  Advised path = %pI4 -> %pI4\n",
                                     &old_gw, dev->name, &new_gw,
                                     &saddr, &daddr);
        }
#endif
        ;
}

static void ip_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_buff *skb)
{
        struct rtable *rt;
        struct flowi4 fl4;
        const struct iphdr *iph = (const struct iphdr *) skb->data;
        struct net *net = dev_net(skb->dev);
        int oif = skb->dev->ifindex;
        u8 tos = RT_TOS(iph->tos);
        u8 prot = iph->protocol;
        u32 mark = skb->mark;

        rt = (struct rtable *) dst;

        __build_flow_key(net, &fl4, sk, iph, oif, tos, prot, mark, 0);
        __ip_do_redirect(rt, skb, &fl4, true);
}

static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
{
        struct rtable *rt = (struct rtable *)dst;
        struct dst_entry *ret = dst;

        if (rt) {
                if (dst->obsolete > 0) {
                        ip_rt_put(rt);
                        ret = NULL;
                } else if ((rt->rt_flags & RTCF_REDIRECTED) ||
                           rt->dst.expires) {
                        ip_rt_put(rt);
                        ret = NULL;
                }
        }
        return ret;
}

/*
 * Algorithm:
 *      1. The first ip_rt_redirect_number redirects are sent
 *         with exponential backoff, then we stop sending them at all,
 *         assuming that the host ignores our redirects.
 *      2. If we did not see packets requiring redirects
 *         during ip_rt_redirect_silence, we assume that the host
 *         forgot redirected route and start to send redirects again.
 *
 * This algorithm is much cheaper and more intelligent than dumb load limiting
 * in icmp.c.
 *
 * NOTE. Do not forget to inhibit load limiting for redirects (redundant)
 * and "frag. need" (breaks PMTU discovery) in icmp.c.
 */

void ip_rt_send_redirect(struct sk_buff *skb)
{
        struct rtable *rt = skb_rtable(skb);
        struct in_device *in_dev;
        struct inet_peer *peer;
        struct net *net;
        int log_martians;
        int vif;

        rcu_read_lock();
        in_dev = __in_dev_get_rcu(rt->dst.dev);
        if (!in_dev || !IN_DEV_TX_REDIRECTS(in_dev)) {
                rcu_read_unlock();
                return;
        }
        log_martians = IN_DEV_LOG_MARTIANS(in_dev);
        vif = l3mdev_master_ifindex_rcu(rt->dst.dev);
        rcu_read_unlock();

        net = dev_net(rt->dst.dev);
        peer = inet_getpeer_v4(net->ipv4.peers, ip_hdr(skb)->saddr, vif, 1);
        if (!peer) {
                icmp_send(skb, ICMP_REDIRECT, ICMP_REDIR_HOST,
                          rt_nexthop(rt, ip_hdr(skb)->daddr));
                return;
        }

        /* No redirected packets during ip_rt_redirect_silence;
         * reset the algorithm.
         */
        if (time_after(jiffies, peer->rate_last + ip_rt_redirect_silence)) {
                peer->rate_tokens = 0;
                peer->n_redirects = 0;
        }

        /* Too many ignored redirects; do not send anything
         * set dst.rate_last to the last seen redirected packet.
         */
        if (peer->n_redirects >= ip_rt_redirect_number) {
                peer->rate_last = jiffies;
                goto out_put_peer;
        }

        /* Check for load limit; set rate_last to the latest sent
         * redirect.
         */
        if (peer->n_redirects == 0 ||
            time_after(jiffies,
                       (peer->rate_last +
                        (ip_rt_redirect_load << peer->n_redirects)))) {
                __be32 gw = rt_nexthop(rt, ip_hdr(skb)->daddr);

                icmp_send(skb, ICMP_REDIRECT, ICMP_REDIR_HOST, gw);
                peer->rate_last = jiffies;
                ++peer->n_redirects;
#ifdef CONFIG_IP_ROUTE_VERBOSE
                if (log_martians &&
                    peer->n_redirects == ip_rt_redirect_number)
                        net_warn_ratelimited("host %pI4/if%d ignores redirects for %pI4 to %pI4\n",
                                             &ip_hdr(skb)->saddr, inet_iif(skb),
                                             &ip_hdr(skb)->daddr, &gw);
#endif
        }
out_put_peer:
        inet_putpeer(peer);
}

static int ip_error(struct sk_buff *skb)
{
        struct rtable *rt = skb_rtable(skb);
        struct net_device *dev = skb->dev;
        struct in_device *in_dev;
        struct inet_peer *peer;
        unsigned long now;
        struct net *net;
        bool send;
        int code;

        if (netif_is_l3_master(skb->dev)) {
                dev = __dev_get_by_index(dev_net(skb->dev), IPCB(skb)->iif);
                if (!dev)
                        goto out;
        }

        in_dev = __in_dev_get_rcu(dev);

        /* IP on this device is disabled. */
        if (!in_dev)
                goto out;

        net = dev_net(rt->dst.dev);
        if (!IN_DEV_FORWARD(in_dev)) {
                switch (rt->dst.error) {
                case EHOSTUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INADDRERRORS);
                        break;

                case ENETUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INNOROUTES);
                        break;
                }
                goto out;
        }

        switch (rt->dst.error) {
        case EINVAL:
        default:
                goto out;
        case EHOSTUNREACH:
                code = ICMP_HOST_UNREACH;
                break;
        case ENETUNREACH:
                code = ICMP_NET_UNREACH;
                __IP_INC_STATS(net, IPSTATS_MIB_INNOROUTES);
                break;
        case EACCES:
                code = ICMP_PKT_FILTERED;
                break;
        }

        peer = inet_getpeer_v4(net->ipv4.peers, ip_hdr(skb)->saddr,
                               l3mdev_master_ifindex(skb->dev), 1);

        send = true;
        if (peer) {
                now = jiffies;
                peer->rate_tokens += now - peer->rate_last;
                if (peer->rate_tokens > ip_rt_error_burst)
                        peer->rate_tokens = ip_rt_error_burst;
                peer->rate_last = now;
                if (peer->rate_tokens >= ip_rt_error_cost)
                        peer->rate_tokens -= ip_rt_error_cost;
                else
                        send = false;
                inet_putpeer(peer);
        }
        if (send)
                icmp_send(skb, ICMP_DEST_UNREACH, code, 0);

out:    kfree_skb(skb);
        return 0;
}

static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
{

        struct dst_entry *dst = &rt->dst;
        struct net *net = dev_net(dst->dev);
        struct fib_result res;
        bool lock = false;
        u32 old_mtu;

        if (ip_mtu_locked(dst))
                return;

        old_mtu = ipv4_mtu(dst);
        if (old_mtu < mtu)
                return;

        if (mtu < ip_rt_min_pmtu) {
                lock = true;
                mtu = min(old_mtu, ip_rt_min_pmtu);
        }

        if (rt->rt_pmtu == mtu && !lock &&
            time_before(jiffies, dst->expires - ip_rt_mtu_expires / 2))
                return;

        rcu_read_lock();
        if (fib_lookup(net, fl4, &res, 0) == 0) {
                struct fib_nh_common *nhc;

                fib_select_path(net, &res, fl4, NULL);
                nhc = FIB_RES_NHC(res);
                update_or_create_fnhe(nhc, fl4->daddr, 0, mtu, lock,
                                      jiffies + ip_rt_mtu_expires);
        }
        rcu_read_unlock();
}

static void ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
                              struct sk_buff *skb, u32 mtu,
                              bool confirm_neigh)
{
        struct rtable *rt = (struct rtable *) dst;
        struct flowi4 fl4;

        ip_rt_build_flow_key(&fl4, sk, skb);

        /* Don't make lookup fail for bridged encapsulations */
        if (skb && netif_is_any_bridge_port(skb->dev))
                fl4.flowi4_oif = 0;

        __ip_rt_update_pmtu(rt, &fl4, mtu);
}

void ipv4_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
                      int oif, u8 protocol)
{
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct flowi4 fl4;
        struct rtable *rt;
        u32 mark = IP4_REPLY_MARK(net, skb->mark);

        __build_flow_key(net, &fl4, NULL, iph, oif,
                         RT_TOS(iph->tos), protocol, mark, 0);
        rt = __ip_route_output_key(net, &fl4);
        if (!IS_ERR(rt)) {
                __ip_rt_update_pmtu(rt, &fl4, mtu);
                ip_rt_put(rt);
        }
}
EXPORT_SYMBOL_GPL(ipv4_update_pmtu);

static void __ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
{
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct flowi4 fl4;
        struct rtable *rt;

        __build_flow_key(sock_net(sk), &fl4, sk, iph, 0, 0, 0, 0, 0);

        if (!fl4.flowi4_mark)
                fl4.flowi4_mark = IP4_REPLY_MARK(sock_net(sk), skb->mark);

        rt = __ip_route_output_key(sock_net(sk), &fl4);
        if (!IS_ERR(rt)) {
                __ip_rt_update_pmtu(rt, &fl4, mtu);
                ip_rt_put(rt);
        }
}

void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
{
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct flowi4 fl4;
        struct rtable *rt;
        struct dst_entry *odst = NULL;
        bool new = false;
        struct net *net = sock_net(sk);

        bh_lock_sock(sk);

        if (!ip_sk_accept_pmtu(sk))
                goto out;

        odst = sk_dst_get(sk);

        if (sock_owned_by_user(sk) || !odst) {
                __ipv4_sk_update_pmtu(skb, sk, mtu);
                goto out;
        }

        __build_flow_key(net, &fl4, sk, iph, 0, 0, 0, 0, 0);

        rt = (struct rtable *)odst;
        if (odst->obsolete && !odst->ops->check(odst, 0)) {
                rt = ip_route_output_flow(sock_net(sk), &fl4, sk);
                if (IS_ERR(rt))
                        goto out;

                new = true;
        }

        __ip_rt_update_pmtu((struct rtable *)xfrm_dst_path(&rt->dst), &fl4, mtu);

        if (!dst_check(&rt->dst, 0)) {
                if (new)
                        dst_release(&rt->dst);

                rt = ip_route_output_flow(sock_net(sk), &fl4, sk);
                if (IS_ERR(rt))
                        goto out;

                new = true;
        }

        if (new)
                sk_dst_set(sk, &rt->dst);

out:
        bh_unlock_sock(sk);
        dst_release(odst);
}
EXPORT_SYMBOL_GPL(ipv4_sk_update_pmtu);

void ipv4_redirect(struct sk_buff *skb, struct net *net,
                   int oif, u8 protocol)
{
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct flowi4 fl4;
        struct rtable *rt;

        __build_flow_key(net, &fl4, NULL, iph, oif,
                         RT_TOS(iph->tos), protocol, 0, 0);
        rt = __ip_route_output_key(net, &fl4);
        if (!IS_ERR(rt)) {
                __ip_do_redirect(rt, skb, &fl4, false);
                ip_rt_put(rt);
        }
}
EXPORT_SYMBOL_GPL(ipv4_redirect);

void ipv4_sk_redirect(struct sk_buff *skb, struct sock *sk)
{
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct flowi4 fl4;
        struct rtable *rt;
        struct net *net = sock_net(sk);

        __build_flow_key(net, &fl4, sk, iph, 0, 0, 0, 0, 0);
        rt = __ip_route_output_key(net, &fl4);
        if (!IS_ERR(rt)) {
                __ip_do_redirect(rt, skb, &fl4, false);
                ip_rt_put(rt);
        }
}
EXPORT_SYMBOL_GPL(ipv4_sk_redirect);

INDIRECT_CALLABLE_SCOPE struct dst_entry *ipv4_dst_check(struct dst_entry *dst,
                                                         u32 cookie)
{
        struct rtable *rt = (struct rtable *) dst;

        /* All IPV4 dsts are created with ->obsolete set to the value
         * DST_OBSOLETE_FORCE_CHK which forces validation calls down
         * into this function always.
         *
         * When a PMTU/redirect information update invalidates a route,
         * this is indicated by setting obsolete to DST_OBSOLETE_KILL or
         * DST_OBSOLETE_DEAD.
         */
        if (dst->obsolete != DST_OBSOLETE_FORCE_CHK || rt_is_expired(rt))
                return NULL;
        return dst;
}
EXPORT_INDIRECT_CALLABLE(ipv4_dst_check);

static void ipv4_send_dest_unreach(struct sk_buff *skb)
{
        struct ip_options opt;
        int res;

        /* Recompile ip options since IPCB may not be valid anymore.
         * Also check we have a reasonable ipv4 header.
         */
        if (!pskb_network_may_pull(skb, sizeof(struct iphdr)) ||
            ip_hdr(skb)->version != 4 || ip_hdr(skb)->ihl < 5)
                return;

        memset(&opt, 0, sizeof(opt));
        if (ip_hdr(skb)->ihl > 5) {
                if (!pskb_network_may_pull(skb, ip_hdr(skb)->ihl * 4))
                        return;
                opt.optlen = ip_hdr(skb)->ihl * 4 - sizeof(struct iphdr);

                rcu_read_lock();
                res = __ip_options_compile(dev_net(skb->dev), &opt, skb, NULL);
                rcu_read_unlock();

                if (res)
                        return;
        }
        __icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0, &opt);
}

static void ipv4_link_failure(struct sk_buff *skb)
{
        struct rtable *rt;

        ipv4_send_dest_unreach(skb);

        rt = skb_rtable(skb);
        if (rt)
                dst_set_expires(&rt->dst, 0);
}

static int ip_rt_bug(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        pr_debug("%s: %pI4 -> %pI4, %s\n",
                 __func__, &ip_hdr(skb)->saddr, &ip_hdr(skb)->daddr,
                 skb->dev ? skb->dev->name : "?");
        kfree_skb(skb);
        WARN_ON(1);
        return 0;
}

/*
 * We do not cache source address of outgoing interface,
 * because it is used only by IP RR, TS and SRR options,
 * so that it out of fast path.
 *
 * BTW remember: "addr" is allowed to be not aligned
 * in IP options!
 */

void ip_rt_get_source(u8 *addr, struct sk_buff *skb, struct rtable *rt)
{
        __be32 src;

        if (rt_is_output_route(rt))
                src = ip_hdr(skb)->saddr;
        else {
                struct fib_result res;
                struct iphdr *iph = ip_hdr(skb);
                struct flowi4 fl4 = {
                        .daddr = iph->daddr,
                        .saddr = iph->saddr,
                        .flowi4_tos = RT_TOS(iph->tos),
                        .flowi4_oif = rt->dst.dev->ifindex,
                        .flowi4_iif = skb->dev->ifindex,
                        .flowi4_mark = skb->mark,
                };

                rcu_read_lock();
                if (fib_lookup(dev_net(rt->dst.dev), &fl4, &res, 0) == 0)
                        src = fib_result_prefsrc(dev_net(rt->dst.dev), &res);
                else
                        src = inet_select_addr(rt->dst.dev,
                                               rt_nexthop(rt, iph->daddr),
                                               RT_SCOPE_UNIVERSE);
                rcu_read_unlock();
        }
        memcpy(addr, &src, 4);
}

#ifdef CONFIG_IP_ROUTE_CLASSID
static void set_class_tag(struct rtable *rt, u32 tag)
{
        if (!(rt->dst.tclassid & 0xFFFF))
                rt->dst.tclassid |= tag & 0xFFFF;
        if (!(rt->dst.tclassid & 0xFFFF0000))
                rt->dst.tclassid |= tag & 0xFFFF0000;
}
#endif

static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
{
        unsigned int header_size = sizeof(struct tcphdr) + sizeof(struct iphdr);
        unsigned int advmss = max_t(unsigned int, ipv4_mtu(dst) - header_size,
                                    ip_rt_min_advmss);

        return min(advmss, IPV4_MAX_PMTU - header_size);
}

INDIRECT_CALLABLE_SCOPE unsigned int ipv4_mtu(const struct dst_entry *dst)
{
        const struct rtable *rt = (const struct rtable *)dst;
        unsigned int mtu = rt->rt_pmtu;

        if (!mtu || time_after_eq(jiffies, rt->dst.expires))
                mtu = dst_metric_raw(dst, RTAX_MTU);

        if (mtu)
                goto out;

        mtu = READ_ONCE(dst->dev->mtu);

        if (unlikely(ip_mtu_locked(dst))) {
                if (rt->rt_uses_gateway && mtu > 576)
                        mtu = 576;
        }

out:
        mtu = min_t(unsigned int, mtu, IP_MAX_MTU);

        return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
}
EXPORT_INDIRECT_CALLABLE(ipv4_mtu);

static void ip_del_fnhe(struct fib_nh_common *nhc, __be32 daddr)
{
        struct fnhe_hash_bucket *hash;
        struct fib_nh_exception *fnhe, __rcu **fnhe_p;
        u32 hval = fnhe_hashfun(daddr);

        spin_lock_bh(&fnhe_lock);

        hash = rcu_dereference_protected(nhc->nhc_exceptions,
                                         lockdep_is_held(&fnhe_lock));
        hash += hval;

        fnhe_p = &hash->chain;
        fnhe = rcu_dereference_protected(*fnhe_p, lockdep_is_held(&fnhe_lock));
        while (fnhe) {
                if (fnhe->fnhe_daddr == daddr) {
                        rcu_assign_pointer(*fnhe_p, rcu_dereference_protected(
                                fnhe->fnhe_next, lockdep_is_held(&fnhe_lock)));
                        /* set fnhe_daddr to 0 to ensure it won't bind with
                         * new dsts in rt_bind_exception().
                         */
                        fnhe->fnhe_daddr = 0;
                        fnhe_flush_routes(fnhe);
                        kfree_rcu(fnhe, rcu);
                        break;
                }
                fnhe_p = &fnhe->fnhe_next;
                fnhe = rcu_dereference_protected(fnhe->fnhe_next,
                                                 lockdep_is_held(&fnhe_lock));
        }

        spin_unlock_bh(&fnhe_lock);
}

static struct fib_nh_exception *find_exception(struct fib_nh_common *nhc,
                                               __be32 daddr)
{
        struct fnhe_hash_bucket *hash = rcu_dereference(nhc->nhc_exceptions);
        struct fib_nh_exception *fnhe;
        u32 hval;

        if (!hash)
                return NULL;

        hval = fnhe_hashfun(daddr);

        for (fnhe = rcu_dereference(hash[hval].chain); fnhe;
             fnhe = rcu_dereference(fnhe->fnhe_next)) {
                if (fnhe->fnhe_daddr == daddr) {
                        if (fnhe->fnhe_expires &&
                            time_after(jiffies, fnhe->fnhe_expires)) {
                                ip_del_fnhe(nhc, daddr);
                                break;
                        }
                        return fnhe;
                }
        }
        return NULL;
}

/* MTU selection:
 * 1. mtu on route is locked - use it
 * 2. mtu from nexthop exception
 * 3. mtu from egress device
 */

u32 ip_mtu_from_fib_result(struct fib_result *res, __be32 daddr)
{
        struct fib_nh_common *nhc = res->nhc;
        struct net_device *dev = nhc->nhc_dev;
        struct fib_info *fi = res->fi;
        u32 mtu = 0;

        if (dev_net(dev)->ipv4.sysctl_ip_fwd_use_pmtu ||
            fi->fib_metrics->metrics[RTAX_LOCK - 1] & (1 << RTAX_MTU))
                mtu = fi->fib_mtu;

        if (likely(!mtu)) {
                struct fib_nh_exception *fnhe;

                fnhe = find_exception(nhc, daddr);
                if (fnhe && !time_after_eq(jiffies, fnhe->fnhe_expires))
                        mtu = fnhe->fnhe_pmtu;
        }

        if (likely(!mtu))
                mtu = min(READ_ONCE(dev->mtu), IP_MAX_MTU);

        return mtu - lwtunnel_headroom(nhc->nhc_lwtstate, mtu);
}

static bool rt_bind_exception(struct rtable *rt, struct fib_nh_exception *fnhe,
                              __be32 daddr, const bool do_cache)
{
        bool ret = false;

        spin_lock_bh(&fnhe_lock);

        if (daddr == fnhe->fnhe_daddr) {
                struct rtable __rcu **porig;
                struct rtable *orig;
                int genid = fnhe_genid(dev_net(rt->dst.dev));

                if (rt_is_input_route(rt))
                        porig = &fnhe->fnhe_rth_input;
                else
                        porig = &fnhe->fnhe_rth_output;
                orig = rcu_dereference(*porig);

                if (fnhe->fnhe_genid != genid) {
                        fnhe->fnhe_genid = genid;
                        fnhe->fnhe_gw = 0;
                        fnhe->fnhe_pmtu = 0;
                        fnhe->fnhe_expires = 0;
                        fnhe->fnhe_mtu_locked = false;
                        fnhe_flush_routes(fnhe);
                        orig = NULL;
                }
                fill_route_from_fnhe(rt, fnhe);
                if (!rt->rt_gw4) {
                        rt->rt_gw4 = daddr;
                        rt->rt_gw_family = AF_INET;
                }

                if (do_cache) {
                        dst_hold(&rt->dst);
                        rcu_assign_pointer(*porig, rt);
                        if (orig) {
                                dst_dev_put(&orig->dst);
                                dst_release(&orig->dst);
                        }
                        ret = true;
                }

                fnhe->fnhe_stamp = jiffies;
        }
        spin_unlock_bh(&fnhe_lock);

        return ret;
}

static bool rt_cache_route(struct fib_nh_common *nhc, struct rtable *rt)
{
        struct rtable *orig, *prev, **p;
        bool ret = true;

        if (rt_is_input_route(rt)) {
                p = (struct rtable **)&nhc->nhc_rth_input;
        } else {
                p = (struct rtable **)raw_cpu_ptr(nhc->nhc_pcpu_rth_output);
        }
        orig = *p;

        /* hold dst before doing cmpxchg() to avoid race condition
         * on this dst
         */
        dst_hold(&rt->dst);
        prev = cmpxchg(p, orig, rt);
        if (prev == orig) {
                if (orig) {
                        rt_add_uncached_list(orig);
                        dst_release(&orig->dst);
                }
        } else {
                dst_release(&rt->dst);
                ret = false;
        }

        return ret;
}

struct uncached_list {
        spinlock_t              lock;
        struct list_head        head;
};

static DEFINE_PER_CPU_ALIGNED(struct uncached_list, rt_uncached_list);

void rt_add_uncached_list(struct rtable *rt)
{
        struct uncached_list *ul = raw_cpu_ptr(&rt_uncached_list);

        rt->rt_uncached_list = ul;

        spin_lock_bh(&ul->lock);
        list_add_tail(&rt->rt_uncached, &ul->head);
        spin_unlock_bh(&ul->lock);
}

void rt_del_uncached_list(struct rtable *rt)
{
        if (!list_empty(&rt->rt_uncached)) {
                struct uncached_list *ul = rt->rt_uncached_list;

                spin_lock_bh(&ul->lock);
                list_del(&rt->rt_uncached);
                spin_unlock_bh(&ul->lock);
        }
}

static void ipv4_dst_destroy(struct dst_entry *dst)
{
        struct rtable *rt = (struct rtable *)dst;

        ip_dst_metrics_put(dst);
        rt_del_uncached_list(rt);
}

void rt_flush_dev(struct net_device *dev)
{
        struct rtable *rt;
        int cpu;

        for_each_possible_cpu(cpu) {
                struct uncached_list *ul = &per_cpu(rt_uncached_list, cpu);

                spin_lock_bh(&ul->lock);
                list_for_each_entry(rt, &ul->head, rt_uncached) {
                        if (rt->dst.dev != dev)
                                continue;
                        rt->dst.dev = blackhole_netdev;
                        dev_hold(rt->dst.dev);
                        dev_put(dev);
                }
                spin_unlock_bh(&ul->lock);
        }
}

static bool rt_cache_valid(const struct rtable *rt)
{
        return  rt &&
                rt->dst.obsolete == DST_OBSOLETE_FORCE_CHK &&
                !rt_is_expired(rt);
}

static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
                           const struct fib_result *res,
                           struct fib_nh_exception *fnhe,
                           struct fib_info *fi, u16 type, u32 itag,
                           const bool do_cache)
{
        bool cached = false;

        if (fi) {
                struct fib_nh_common *nhc = FIB_RES_NHC(*res);

                if (nhc->nhc_gw_family && nhc->nhc_scope == RT_SCOPE_LINK) {
                        rt->rt_uses_gateway = 1;
                        rt->rt_gw_family = nhc->nhc_gw_family;
                        /* only INET and INET6 are supported */
                        if (likely(nhc->nhc_gw_family == AF_INET))
                                rt->rt_gw4 = nhc->nhc_gw.ipv4;
                        else
                                rt->rt_gw6 = nhc->nhc_gw.ipv6;
                }

                ip_dst_init_metrics(&rt->dst, fi->fib_metrics);

#ifdef CONFIG_IP_ROUTE_CLASSID
                if (nhc->nhc_family == AF_INET) {
                        struct fib_nh *nh;

                        nh = container_of(nhc, struct fib_nh, nh_common);
                        rt->dst.tclassid = nh->nh_tclassid;
                }
#endif
                rt->dst.lwtstate = lwtstate_get(nhc->nhc_lwtstate);
                if (unlikely(fnhe))
                        cached = rt_bind_exception(rt, fnhe, daddr, do_cache);
                else if (do_cache)
                        cached = rt_cache_route(nhc, rt);
                if (unlikely(!cached)) {
                        /* Routes we intend to cache in nexthop exception or
                         * FIB nexthop have the DST_NOCACHE bit clear.
                         * However, if we are unsuccessful at storing this
                         * route into the cache we really need to set it.
                         */
                        if (!rt->rt_gw4) {
                                rt->rt_gw_family = AF_INET;
                                rt->rt_gw4 = daddr;
                        }
                        rt_add_uncached_list(rt);
                }
        } else
                rt_add_uncached_list(rt);

#ifdef CONFIG_IP_ROUTE_CLASSID
#ifdef CONFIG_IP_MULTIPLE_TABLES
        set_class_tag(rt, res->tclassid);
#endif
        set_class_tag(rt, itag);
#endif
}

struct rtable *rt_dst_alloc(struct net_device *dev,
                            unsigned int flags, u16 type,
                            bool nopolicy, bool noxfrm)
{
        struct rtable *rt;

        rt = dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
                       (nopolicy ? DST_NOPOLICY : 0) |
                       (noxfrm ? DST_NOXFRM : 0));

        if (rt) {
                rt->rt_genid = rt_genid_ipv4(dev_net(dev));
                rt->rt_flags = flags;
                rt->rt_type = type;
                rt->rt_is_input = 0;
                rt->rt_iif = 0;
                rt->rt_pmtu = 0;
                rt->rt_mtu_locked = 0;
                rt->rt_uses_gateway = 0;
                rt->rt_gw_family = 0;
                rt->rt_gw4 = 0;
                INIT_LIST_HEAD(&rt->rt_uncached);

                rt->dst.output = ip_output;
                if (flags & RTCF_LOCAL)
                        rt->dst.input = ip_local_deliver;
        }

        return rt;
}
EXPORT_SYMBOL(rt_dst_alloc);

struct rtable *rt_dst_clone(struct net_device *dev, struct rtable *rt)
{
        struct rtable *new_rt;

        new_rt = dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
                           rt->dst.flags);

        if (new_rt) {
                new_rt->rt_genid = rt_genid_ipv4(dev_net(dev));
                new_rt->rt_flags = rt->rt_flags;
                new_rt->rt_type = rt->rt_type;
                new_rt->rt_is_input = rt->rt_is_input;
                new_rt->rt_iif = rt->rt_iif;
                new_rt->rt_pmtu = rt->rt_pmtu;
                new_rt->rt_mtu_locked = rt->rt_mtu_locked;
                new_rt->rt_gw_family = rt->rt_gw_family;
                if (rt->rt_gw_family == AF_INET)
                        new_rt->rt_gw4 = rt->rt_gw4;
                else if (rt->rt_gw_family == AF_INET6)
                        new_rt->rt_gw6 = rt->rt_gw6;
                INIT_LIST_HEAD(&new_rt->rt_uncached);

                new_rt->dst.input = rt->dst.input;
                new_rt->dst.output = rt->dst.output;
                new_rt->dst.error = rt->dst.error;
                new_rt->dst.lastuse = jiffies;
                new_rt->dst.lwtstate = lwtstate_get(rt->dst.lwtstate);
        }
        return new_rt;
}
EXPORT_SYMBOL(rt_dst_clone);

/* called in rcu_read_lock() section */
int ip_mc_validate_source(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                          u8 tos, struct net_device *dev,
                          struct in_device *in_dev, u32 *itag)
{
        int err;

        /* Primary sanity checks. */
        if (!in_dev)
                return -EINVAL;

        if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr) ||
            skb->protocol != htons(ETH_P_IP))
                return -EINVAL;

        if (ipv4_is_loopback(saddr) && !IN_DEV_ROUTE_LOCALNET(in_dev))
                return -EINVAL;

        if (ipv4_is_zeronet(saddr)) {
                if (!ipv4_is_local_multicast(daddr) &&
                    ip_hdr(skb)->protocol != IPPROTO_IGMP)
                        return -EINVAL;
        } else {
                err = fib_validate_source(skb, saddr, 0, tos, 0, dev,
                                          in_dev, itag);
                if (err < 0)
                        return err;
        }
        return 0;
}

/* called in rcu_read_lock() section */
static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                             u8 tos, struct net_device *dev, int our)
{
        struct in_device *in_dev = __in_dev_get_rcu(dev);
        unsigned int flags = RTCF_MULTICAST;
        struct rtable *rth;
        u32 itag = 0;
        int err;

        err = ip_mc_validate_source(skb, daddr, saddr, tos, dev, in_dev, &itag);
        if (err)
                return err;

        if (our)
                flags |= RTCF_LOCAL;

        rth = rt_dst_alloc(dev_net(dev)->loopback_dev, flags, RTN_MULTICAST,
                           IN_DEV_ORCONF(in_dev, NOPOLICY), false);
        if (!rth)
                return -ENOBUFS;

#ifdef CONFIG_IP_ROUTE_CLASSID
        rth->dst.tclassid = itag;
#endif
        rth->dst.output = ip_rt_bug;
        rth->rt_is_input= 1;

#ifdef CONFIG_IP_MROUTE
        if (!ipv4_is_local_multicast(daddr) && IN_DEV_MFORWARD(in_dev))
                rth->dst.input = ip_mr_input;
#endif
        RT_CACHE_STAT_INC(in_slow_mc);

        skb_dst_set(skb, &rth->dst);
        return 0;
}


static void ip_handle_martian_source(struct net_device *dev,
                                     struct in_device *in_dev,
                                     struct sk_buff *skb,
                                     __be32 daddr,
                                     __be32 saddr)
{
        RT_CACHE_STAT_INC(in_martian_src);
#ifdef CONFIG_IP_ROUTE_VERBOSE
        if (IN_DEV_LOG_MARTIANS(in_dev) && net_ratelimit()) {
                /*
                 *      RFC1812 recommendation, if source is martian,
                 *      the only hint is MAC header.
                 */
                pr_warn("martian source %pI4 from %pI4, on dev %s\n",
                        &daddr, &saddr, dev->name);
                if (dev->hard_header_len && skb_mac_header_was_set(skb)) {
                        print_hex_dump(KERN_WARNING, "ll header: ",
                                       DUMP_PREFIX_OFFSET, 16, 1,
                                       skb_mac_header(skb),
                                       dev->hard_header_len, false);
                }
        }
#endif
}

/* called in rcu_read_lock() section */
static int __mkroute_input(struct sk_buff *skb,
                           const struct fib_result *res,
                           struct in_device *in_dev,
                           __be32 daddr, __be32 saddr, u32 tos)
{
        struct fib_nh_common *nhc = FIB_RES_NHC(*res);
        struct net_device *dev = nhc->nhc_dev;
        struct fib_nh_exception *fnhe;
        struct rtable *rth;
        int err;
        struct in_device *out_dev;
        bool do_cache;
        u32 itag = 0;

        /* get a working reference to the output device */
        out_dev = __in_dev_get_rcu(dev);
        if (!out_dev) {
                net_crit_ratelimited("Bug in ip_route_input_slow(). Please report.\n");
                return -EINVAL;
        }

        err = fib_validate_source(skb, saddr, daddr, tos, FIB_RES_OIF(*res),
                                  in_dev->dev, in_dev, &itag);
        if (err < 0) {
                ip_handle_martian_source(in_dev->dev, in_dev, skb, daddr,
                                         saddr);

                goto cleanup;
        }

        do_cache = res->fi && !itag;
        if (out_dev == in_dev && err && IN_DEV_TX_REDIRECTS(out_dev) &&
            skb->protocol == htons(ETH_P_IP)) {
                __be32 gw;

                gw = nhc->nhc_gw_family == AF_INET ? nhc->nhc_gw.ipv4 : 0;
                if (IN_DEV_SHARED_MEDIA(out_dev) ||
                    inet_addr_onlink(out_dev, saddr, gw))
                        IPCB(skb)->flags |= IPSKB_DOREDIRECT;
        }

        if (skb->protocol != htons(ETH_P_IP)) {
                /* Not IP (i.e. ARP). Do not create route, if it is
                 * invalid for proxy arp. DNAT routes are always valid.
                 *
                 * Proxy arp feature have been extended to allow, ARP
                 * replies back to the same interface, to support
                 * Private VLAN switch technologies. See arp.c.
                 */
                if (out_dev == in_dev &&
                    IN_DEV_PROXY_ARP_PVLAN(in_dev) == 0) {
                        err = -EINVAL;
                        goto cleanup;
                }
        }

        fnhe = find_exception(nhc, daddr);
        if (do_cache) {
                if (fnhe)
                        rth = rcu_dereference(fnhe->fnhe_rth_input);
                else
                        rth = rcu_dereference(nhc->nhc_rth_input);
                if (rt_cache_valid(rth)) {
                        skb_dst_set_noref(skb, &rth->dst);
                        goto out;
                }
        }

        rth = rt_dst_alloc(out_dev->dev, 0, res->type,
                           IN_DEV_ORCONF(in_dev, NOPOLICY),
                           IN_DEV_ORCONF(out_dev, NOXFRM));
        if (!rth) {
                err = -ENOBUFS;
                goto cleanup;
        }

        rth->rt_is_input = 1;
        RT_CACHE_STAT_INC(in_slow_tot);

        rth->dst.input = ip_forward;

        rt_set_nexthop(rth, daddr, res, fnhe, res->fi, res->type, itag,
                       do_cache);
        lwtunnel_set_redirect(&rth->dst);
        skb_dst_set(skb, &rth->dst);
out:
        err = 0;
 cleanup:
        return err;
}

#ifdef CONFIG_IP_ROUTE_MULTIPATH
/* To make ICMP packets follow the right flow, the multipath hash is
 * calculated from the inner IP addresses.
 */
static void ip_multipath_l3_keys(const struct sk_buff *skb,
                                 struct flow_keys *hash_keys)
{
        const struct iphdr *outer_iph = ip_hdr(skb);
        const struct iphdr *key_iph = outer_iph;
        const struct iphdr *inner_iph;
        const struct icmphdr *icmph;
        struct iphdr _inner_iph;
        struct icmphdr _icmph;

        if (likely(outer_iph->protocol != IPPROTO_ICMP))
                goto out;

        if (unlikely((outer_iph->frag_off & htons(IP_OFFSET)) != 0))
                goto out;

        icmph = skb_header_pointer(skb, outer_iph->ihl * 4, sizeof(_icmph),
                                   &_icmph);
        if (!icmph)
                goto out;

        if (!icmp_is_err(icmph->type))
                goto out;

        inner_iph = skb_header_pointer(skb,
                                       outer_iph->ihl * 4 + sizeof(_icmph),
                                       sizeof(_inner_iph), &_inner_iph);
        if (!inner_iph)
                goto out;

        key_iph = inner_iph;
out:
        hash_keys->addrs.v4addrs.src = key_iph->saddr;
        hash_keys->addrs.v4addrs.dst = key_iph->daddr;
}

static u32 fib_multipath_custom_hash_outer(const struct net *net,
                                           const struct sk_buff *skb,
                                           bool *p_has_inner)
{
        u32 hash_fields = net->ipv4.sysctl_fib_multipath_hash_fields;
        struct flow_keys keys, hash_keys;

        if (!(hash_fields & FIB_MULTIPATH_HASH_FIELD_OUTER_MASK))
                return 0;

        memset(&hash_keys, 0, sizeof(hash_keys));
        skb_flow_dissect_flow_keys(skb, &keys, FLOW_DISSECTOR_F_STOP_AT_ENCAP);

        hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_SRC_IP)
                hash_keys.addrs.v4addrs.src = keys.addrs.v4addrs.src;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_DST_IP)
                hash_keys.addrs.v4addrs.dst = keys.addrs.v4addrs.dst;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_IP_PROTO)
                hash_keys.basic.ip_proto = keys.basic.ip_proto;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_SRC_PORT)
                hash_keys.ports.src = keys.ports.src;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_DST_PORT)
                hash_keys.ports.dst = keys.ports.dst;

        *p_has_inner = !!(keys.control.flags & FLOW_DIS_ENCAPSULATION);
        return flow_hash_from_keys(&hash_keys);
}

static u32 fib_multipath_custom_hash_inner(const struct net *net,
                                           const struct sk_buff *skb,
                                           bool has_inner)
{
        u32 hash_fields = net->ipv4.sysctl_fib_multipath_hash_fields;
        struct flow_keys keys, hash_keys;

        /* We assume the packet carries an encapsulation, but if none was
         * encountered during dissection of the outer flow, then there is no
         * point in calling the flow dissector again.
         */
        if (!has_inner)
                return 0;

        if (!(hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_MASK))
                return 0;

        memset(&hash_keys, 0, sizeof(hash_keys));
        skb_flow_dissect_flow_keys(skb, &keys, 0);

        if (!(keys.control.flags & FLOW_DIS_ENCAPSULATION))
                return 0;

        if (keys.control.addr_type == FLOW_DISSECTOR_KEY_IPV4_ADDRS) {
                hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_SRC_IP)
                        hash_keys.addrs.v4addrs.src = keys.addrs.v4addrs.src;
                if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_DST_IP)
                        hash_keys.addrs.v4addrs.dst = keys.addrs.v4addrs.dst;
        } else if (keys.control.addr_type == FLOW_DISSECTOR_KEY_IPV6_ADDRS) {
                hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
                if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_SRC_IP)
                        hash_keys.addrs.v6addrs.src = keys.addrs.v6addrs.src;
                if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_DST_IP)
                        hash_keys.addrs.v6addrs.dst = keys.addrs.v6addrs.dst;
                if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_FLOWLABEL)
                        hash_keys.tags.flow_label = keys.tags.flow_label;
        }

        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_IP_PROTO)
                hash_keys.basic.ip_proto = keys.basic.ip_proto;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_SRC_PORT)
                hash_keys.ports.src = keys.ports.src;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_DST_PORT)
                hash_keys.ports.dst = keys.ports.dst;

        return flow_hash_from_keys(&hash_keys);
}

static u32 fib_multipath_custom_hash_skb(const struct net *net,
                                         const struct sk_buff *skb)
{
        u32 mhash, mhash_inner;
        bool has_inner = true;

        mhash = fib_multipath_custom_hash_outer(net, skb, &has_inner);
        mhash_inner = fib_multipath_custom_hash_inner(net, skb, has_inner);

        return jhash_2words(mhash, mhash_inner, 0);
}

static u32 fib_multipath_custom_hash_fl4(const struct net *net,

                                         const struct flowi4 *fl4)
{
        u32 hash_fields = net->ipv4.sysctl_fib_multipath_hash_fields;
        struct flow_keys hash_keys;

        if (!(hash_fields & FIB_MULTIPATH_HASH_FIELD_OUTER_MASK))
                return 0;

        memset(&hash_keys, 0, sizeof(hash_keys));
        hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_SRC_IP)
                hash_keys.addrs.v4addrs.src = fl4->saddr;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_DST_IP)
                hash_keys.addrs.v4addrs.dst = fl4->daddr;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_IP_PROTO)
                hash_keys.basic.ip_proto = fl4->flowi4_proto;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_SRC_PORT)
                hash_keys.ports.src = fl4->fl4_sport;
        if (hash_fields & FIB_MULTIPATH_HASH_FIELD_DST_PORT)
                hash_keys.ports.dst = fl4->fl4_dport;

        return flow_hash_from_keys(&hash_keys);
}

/* if skb is set it will be used and fl4 can be NULL */
int fib_multipath_hash(const struct net *net, const struct flowi4 *fl4,
                       const struct sk_buff *skb, struct flow_keys *flkeys)
{
        u32 multipath_hash = fl4 ? fl4->flowi4_multipath_hash : 0;
        struct flow_keys hash_keys;
        u32 mhash = 0;

        switch (net->ipv4.sysctl_fib_multipath_hash_policy) {
        case 0:
                memset(&hash_keys, 0, sizeof(hash_keys));
                hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                if (skb) {
                        ip_multipath_l3_keys(skb, &hash_keys);
                } else {
                        hash_keys.addrs.v4addrs.src = fl4->saddr;
                        hash_keys.addrs.v4addrs.dst = fl4->daddr;
                }
                mhash = flow_hash_from_keys(&hash_keys);
                break;
        case 1:
                /* skb is currently provided only when forwarding */
                if (skb) {
                        unsigned int flag = FLOW_DISSECTOR_F_STOP_AT_ENCAP;
                        struct flow_keys keys;

                        /* short-circuit if we already have L4 hash present */
                        if (skb->l4_hash)
                                return skb_get_hash_raw(skb) >> 1;

                        memset(&hash_keys, 0, sizeof(hash_keys));

                        if (!flkeys) {
                                skb_flow_dissect_flow_keys(skb, &keys, flag);
                                flkeys = &keys;
                        }

                        hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                        hash_keys.addrs.v4addrs.src = flkeys->addrs.v4addrs.src;
                        hash_keys.addrs.v4addrs.dst = flkeys->addrs.v4addrs.dst;
                        hash_keys.ports.src = flkeys->ports.src;
                        hash_keys.ports.dst = flkeys->ports.dst;
                        hash_keys.basic.ip_proto = flkeys->basic.ip_proto;
                } else {
                        memset(&hash_keys, 0, sizeof(hash_keys));
                        hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                        hash_keys.addrs.v4addrs.src = fl4->saddr;
                        hash_keys.addrs.v4addrs.dst = fl4->daddr;
                        hash_keys.ports.src = fl4->fl4_sport;
                        hash_keys.ports.dst = fl4->fl4_dport;
                        hash_keys.basic.ip_proto = fl4->flowi4_proto;
                }
                mhash = flow_hash_from_keys(&hash_keys);
                break;
        case 2:
                memset(&hash_keys, 0, sizeof(hash_keys));
                /* skb is currently provided only when forwarding */
                if (skb) {
                        struct flow_keys keys;

                        skb_flow_dissect_flow_keys(skb, &keys, 0);
                        /* Inner can be v4 or v6 */
                        if (keys.control.addr_type == FLOW_DISSECTOR_KEY_IPV4_ADDRS) {
                                hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                                hash_keys.addrs.v4addrs.src = keys.addrs.v4addrs.src;
                                hash_keys.addrs.v4addrs.dst = keys.addrs.v4addrs.dst;
                        } else if (keys.control.addr_type == FLOW_DISSECTOR_KEY_IPV6_ADDRS) {
                                hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
                                hash_keys.addrs.v6addrs.src = keys.addrs.v6addrs.src;
                                hash_keys.addrs.v6addrs.dst = keys.addrs.v6addrs.dst;
                                hash_keys.tags.flow_label = keys.tags.flow_label;
                                hash_keys.basic.ip_proto = keys.basic.ip_proto;
                        } else {
                                /* Same as case 0 */
                                hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                                ip_multipath_l3_keys(skb, &hash_keys);
                        }
                } else {
                        /* Same as case 0 */
                        hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
                        hash_keys.addrs.v4addrs.src = fl4->saddr;
                        hash_keys.addrs.v4addrs.dst = fl4->daddr;
                }
                mhash = flow_hash_from_keys(&hash_keys);
                break;
        case 3:
                if (skb)
                        mhash = fib_multipath_custom_hash_skb(net, skb);
                else
                        mhash = fib_multipath_custom_hash_fl4(net, fl4);
                break;
        }

        if (multipath_hash)
                mhash = jhash_2words(mhash, multipath_hash, 0);

        return mhash >> 1;
}
#endif /* CONFIG_IP_ROUTE_MULTIPATH */

static int ip_mkroute_input(struct sk_buff *skb,
                            struct fib_result *res,
                            struct in_device *in_dev,
                            __be32 daddr, __be32 saddr, u32 tos,
                            struct flow_keys *hkeys)
{
#ifdef CONFIG_IP_ROUTE_MULTIPATH
        if (res->fi && fib_info_num_path(res->fi) > 1) {
                int h = fib_multipath_hash(res->fi->fib_net, NULL, skb, hkeys);

                fib_select_multipath(res, h);
        }
#endif

        /* create a routing cache entry */
        return __mkroute_input(skb, res, in_dev, daddr, saddr, tos);
}

/* Implements all the saddr-related checks as ip_route_input_slow(),
 * assuming daddr is valid and the destination is not a local broadcast one.
 * Uses the provided hint instead of performing a route lookup.
 */
int ip_route_use_hint(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                      u8 tos, struct net_device *dev,
                      const struct sk_buff *hint)
{
        struct in_device *in_dev = __in_dev_get_rcu(dev);
        struct rtable *rt = skb_rtable(hint);
        struct net *net = dev_net(dev);
        int err = -EINVAL;
        u32 tag = 0;

        if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr))
                goto martian_source;

        if (ipv4_is_zeronet(saddr))
                goto martian_source;

        if (ipv4_is_loopback(saddr) && !IN_DEV_NET_ROUTE_LOCALNET(in_dev, net))
                goto martian_source;

        if (rt->rt_type != RTN_LOCAL)
                goto skip_validate_source;

        tos &= IPTOS_RT_MASK;
        err = fib_validate_source(skb, saddr, daddr, tos, 0, dev, in_dev, &tag);
        if (err < 0)
                goto martian_source;

skip_validate_source:
        skb_dst_copy(skb, hint);
        return 0;

martian_source:
        ip_handle_martian_source(dev, in_dev, skb, daddr, saddr);
        return err;
}

/* get device for dst_alloc with local routes */
static struct net_device *ip_rt_get_dev(struct net *net,
                                        const struct fib_result *res)
{
        struct fib_nh_common *nhc = res->fi ? res->nhc : NULL;
        struct net_device *dev = NULL;

        if (nhc)
                dev = l3mdev_master_dev_rcu(nhc->nhc_dev);

        return dev ? : net->loopback_dev;
}

/*
 *      NOTE. We drop all the packets that has local source
 *      addresses, because every properly looped back packet
 *      must have correct destination already attached by output routine.
 *      Changes in the enforced policies must be applied also to
 *      ip_route_use_hint().
 *
 *      Such approach solves two big problems:
 *      1. Not simplex devices are handled properly.
 *      2. IP spoofing attempts are filtered with 100% of guarantee.
 *      called with rcu_read_lock()
 */

static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                               u8 tos, struct net_device *dev,
                               struct fib_result *res)
{
        struct in_device *in_dev = __in_dev_get_rcu(dev);
        struct flow_keys *flkeys = NULL, _flkeys;
        struct net    *net = dev_net(dev);
        struct ip_tunnel_info *tun_info;
        int             err = -EINVAL;
        unsigned int    flags = 0;
        u32             itag = 0;
        struct rtable   *rth;
        struct flowi4   fl4;
        bool do_cache = true;

        /* IP on this device is disabled. */

        if (!in_dev)
                goto out;

        /* Check for the most weird martians, which can be not detected
         * by fib_lookup.
         */

        tun_info = skb_tunnel_info(skb);
        if (tun_info && !(tun_info->mode & IP_TUNNEL_INFO_TX))
                fl4.flowi4_tun_key.tun_id = tun_info->key.tun_id;
        else
                fl4.flowi4_tun_key.tun_id = 0;
        skb_dst_drop(skb);

        if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr))
                goto martian_source;

        res->fi = NULL;
        res->table = NULL;
        if (ipv4_is_lbcast(daddr) || (saddr == 0 && daddr == 0))
                goto brd_input;

        /* Accept zero addresses only to limited broadcast;
         * I even do not know to fix it or not. Waiting for complains :-)
         */
        if (ipv4_is_zeronet(saddr))
                goto martian_source;

        if (ipv4_is_zeronet(daddr))
                goto martian_destination;

        /* Following code try to avoid calling IN_DEV_NET_ROUTE_LOCALNET(),
         * and call it once if daddr or/and saddr are loopback addresses
         */
        if (ipv4_is_loopback(daddr)) {
                if (!IN_DEV_NET_ROUTE_LOCALNET(in_dev, net))
                        goto martian_destination;
        } else if (ipv4_is_loopback(saddr)) {
                if (!IN_DEV_NET_ROUTE_LOCALNET(in_dev, net))
                        goto martian_source;
        }

        /*
         *      Now we are ready to route packet.
         */
        fl4.flowi4_oif = 0;
        fl4.flowi4_iif = dev->ifindex;
        fl4.flowi4_mark = skb->mark;
        fl4.flowi4_tos = tos;
        fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
        fl4.flowi4_flags = 0;
        fl4.daddr = daddr;
        fl4.saddr = saddr;
        fl4.flowi4_uid = sock_net_uid(net, NULL);
        fl4.flowi4_multipath_hash = 0;

        if (fib4_rules_early_flow_dissect(net, skb, &fl4, &_flkeys)) {
                flkeys = &_flkeys;
        } else {
                fl4.flowi4_proto = 0;
                fl4.fl4_sport = 0;
                fl4.fl4_dport = 0;
        }

        err = fib_lookup(net, &fl4, res, 0);
        if (err != 0) {
                if (!IN_DEV_FORWARD(in_dev))
                        err = -EHOSTUNREACH;
                goto no_route;
        }

        if (res->type == RTN_BROADCAST) {
                if (IN_DEV_BFORWARD(in_dev))
                        goto make_route;
                /* not do cache if bc_forwarding is enabled */
                if (IPV4_DEVCONF_ALL(net, BC_FORWARDING))
                        do_cache = false;
                goto brd_input;
        }

        if (res->type == RTN_LOCAL) {
                err = fib_validate_source(skb, saddr, daddr, tos,
                                          0, dev, in_dev, &itag);
                if (err < 0)
                        goto martian_source;
                goto local_input;
        }

        if (!IN_DEV_FORWARD(in_dev)) {
                err = -EHOSTUNREACH;
                goto no_route;
        }
        if (res->type != RTN_UNICAST)
                goto martian_destination;

make_route:
        err = ip_mkroute_input(skb, res, in_dev, daddr, saddr, tos, flkeys);
out:    return err;

brd_input:
        if (skb->protocol != htons(ETH_P_IP))
                goto e_inval;

        if (!ipv4_is_zeronet(saddr)) {
                err = fib_validate_source(skb, saddr, 0, tos, 0, dev,
                                          in_dev, &itag);
                if (err < 0)
                        goto martian_source;
        }
        flags |= RTCF_BROADCAST;
        res->type = RTN_BROADCAST;
        RT_CACHE_STAT_INC(in_brd);

local_input:
        do_cache &= res->fi && !itag;
        if (do_cache) {
                struct fib_nh_common *nhc = FIB_RES_NHC(*res);

                rth = rcu_dereference(nhc->nhc_rth_input);
                if (rt_cache_valid(rth)) {
                        skb_dst_set_noref(skb, &rth->dst);
                        err = 0;
                        goto out;
                }
        }

        rth = rt_dst_alloc(ip_rt_get_dev(net, res),
                           flags | RTCF_LOCAL, res->type,
                           IN_DEV_ORCONF(in_dev, NOPOLICY), false);
        if (!rth)
                goto e_nobufs;

        rth->dst.output= ip_rt_bug;
#ifdef CONFIG_IP_ROUTE_CLASSID
        rth->dst.tclassid = itag;
#endif
        rth->rt_is_input = 1;

        RT_CACHE_STAT_INC(in_slow_tot);
        if (res->type == RTN_UNREACHABLE) {
                rth->dst.input= ip_error;
                rth->dst.error= -err;
                rth->rt_flags   &= ~RTCF_LOCAL;
        }

        if (do_cache) {
                struct fib_nh_common *nhc = FIB_RES_NHC(*res);

                rth->dst.lwtstate = lwtstate_get(nhc->nhc_lwtstate);
                if (lwtunnel_input_redirect(rth->dst.lwtstate)) {
                        WARN_ON(rth->dst.input == lwtunnel_input);
                        rth->dst.lwtstate->orig_input = rth->dst.input;
                        rth->dst.input = lwtunnel_input;
                }

                if (unlikely(!rt_cache_route(nhc, rth)))
                        rt_add_uncached_list(rth);
        }
        skb_dst_set(skb, &rth->dst);
        err = 0;
        goto out;

no_route:
        RT_CACHE_STAT_INC(in_no_route);
        res->type = RTN_UNREACHABLE;
        res->fi = NULL;
        res->table = NULL;
        goto local_input;

        /*
         *      Do not cache martian addresses: they should be logged (RFC1812)
         */
martian_destination:
        RT_CACHE_STAT_INC(in_martian_dst);
#ifdef CONFIG_IP_ROUTE_VERBOSE
        if (IN_DEV_LOG_MARTIANS(in_dev))
                net_warn_ratelimited("martian destination %pI4 from %pI4, dev %s\n",
                                     &daddr, &saddr, dev->name);
#endif

e_inval:
        err = -EINVAL;
        goto out;

e_nobufs:
        err = -ENOBUFS;
        goto out;

martian_source:
        ip_handle_martian_source(dev, in_dev, skb, daddr, saddr);
        goto out;
}

int ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                         u8 tos, struct net_device *dev)
{
        struct fib_result res;
        int err;

        tos &= IPTOS_RT_MASK;
        rcu_read_lock();
        err = ip_route_input_rcu(skb, daddr, saddr, tos, dev, &res);
        rcu_read_unlock();

        return err;
}
EXPORT_SYMBOL(ip_route_input_noref);

/* called with rcu_read_lock held */
int ip_route_input_rcu(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                       u8 tos, struct net_device *dev, struct fib_result *res)
{
        /* Multicast recognition logic is moved from route cache to here.
         * The problem was that too many Ethernet cards have broken/missing
         * hardware multicast filters :-( As result the host on multicasting
         * network acquires a lot of useless route cache entries, sort of
         * SDR messages from all the world. Now we try to get rid of them.
         * Really, provided software IP multicast filter is organized
         * reasonably (at least, hashed), it does not result in a slowdown
         * comparing with route cache reject entries.
         * Note, that multicast routers are not affected, because
         * route cache entry is created eventually.
         */
        if (ipv4_is_multicast(daddr)) {
                struct in_device *in_dev = __in_dev_get_rcu(dev);
                int our = 0;
                int err = -EINVAL;

                if (!in_dev)
                        return err;
                our = ip_check_mc_rcu(in_dev, daddr, saddr,
                                      ip_hdr(skb)->protocol);

                /* check l3 master if no match yet */
                if (!our && netif_is_l3_slave(dev)) {
                        struct in_device *l3_in_dev;

                        l3_in_dev = __in_dev_get_rcu(skb->dev);
                        if (l3_in_dev)
                                our = ip_check_mc_rcu(l3_in_dev, daddr, saddr,
                                                      ip_hdr(skb)->protocol);
                }

                if (our
#ifdef CONFIG_IP_MROUTE
                        ||
                    (!ipv4_is_local_multicast(daddr) &&
                     IN_DEV_MFORWARD(in_dev))
#endif
                   ) {
                        err = ip_route_input_mc(skb, daddr, saddr,
                                                tos, dev, our);
                }
                return err;
        }

        return ip_route_input_slow(skb, daddr, saddr, tos, dev, res);
}

/* called with rcu_read_lock() */
static struct rtable *__mkroute_output(const struct fib_result *res,
                                       const struct flowi4 *fl4, int orig_oif,
                                       struct net_device *dev_out,
                                       unsigned int flags)
{
        struct fib_info *fi = res->fi;
        struct fib_nh_exception *fnhe;
        struct in_device *in_dev;
        u16 type = res->type;
        struct rtable *rth;
        bool do_cache;

        in_dev = __in_dev_get_rcu(dev_out);
        if (!in_dev)
                return ERR_PTR(-EINVAL);

        if (likely(!IN_DEV_ROUTE_LOCALNET(in_dev)))
                if (ipv4_is_loopback(fl4->saddr) &&
                    !(dev_out->flags & IFF_LOOPBACK) &&
                    !netif_is_l3_master(dev_out))
                        return ERR_PTR(-EINVAL);

        if (ipv4_is_lbcast(fl4->daddr))
                type = RTN_BROADCAST;
        else if (ipv4_is_multicast(fl4->daddr))
                type = RTN_MULTICAST;
        else if (ipv4_is_zeronet(fl4->daddr))
                return ERR_PTR(-EINVAL);

        if (dev_out->flags & IFF_LOOPBACK)
                flags |= RTCF_LOCAL;

        do_cache = true;
        if (type == RTN_BROADCAST) {
                flags |= RTCF_BROADCAST | RTCF_LOCAL;
                fi = NULL;
        } else if (type == RTN_MULTICAST) {
                flags |= RTCF_MULTICAST | RTCF_LOCAL;
                if (!ip_check_mc_rcu(in_dev, fl4->daddr, fl4->saddr,
                                     fl4->flowi4_proto))
                        flags &= ~RTCF_LOCAL;
                else
                        do_cache = false;
                /* If multicast route do not exist use
                 * default one, but do not gateway in this case.
                 * Yes, it is hack.
                 */
                if (fi && res->prefixlen < 4)
                        fi = NULL;
        } else if ((type == RTN_LOCAL) && (orig_oif != 0) &&
                   (orig_oif != dev_out->ifindex)) {
                /* For local routes that require a particular output interface
                 * we do not want to cache the result.  Caching the result
                 * causes incorrect behaviour when there are multiple source
                 * addresses on the interface, the end result being that if the
                 * intended recipient is waiting on that interface for the
                 * packet he won't receive it because it will be delivered on
                 * the loopback interface and the IP_PKTINFO ipi_ifindex will
                 * be set to the loopback interface as well.
                 */
                do_cache = false;
        }

        fnhe = NULL;
        do_cache &= fi != NULL;
        if (fi) {
                struct fib_nh_common *nhc = FIB_RES_NHC(*res);
                struct rtable __rcu **prth;

                fnhe = find_exception(nhc, fl4->daddr);
                if (!do_cache)
                        goto add;
                if (fnhe) {
                        prth = &fnhe->fnhe_rth_output;
                } else {
                        if (unlikely(fl4->flowi4_flags &
                                     FLOWI_FLAG_KNOWN_NH &&
                                     !(nhc->nhc_gw_family &&
                                       nhc->nhc_scope == RT_SCOPE_LINK))) {
                                do_cache = false;
                                goto add;
                        }
                        prth = raw_cpu_ptr(nhc->nhc_pcpu_rth_output);
                }
                rth = rcu_dereference(*prth);
                if (rt_cache_valid(rth) && dst_hold_safe(&rth->dst))
                        return rth;
        }

add:
        rth = rt_dst_alloc(dev_out, flags, type,
                           IN_DEV_ORCONF(in_dev, NOPOLICY),
                           IN_DEV_ORCONF(in_dev, NOXFRM));
        if (!rth)
                return ERR_PTR(-ENOBUFS);

        rth->rt_iif = orig_oif;

        RT_CACHE_STAT_INC(out_slow_tot);

        if (flags & (RTCF_BROADCAST | RTCF_MULTICAST)) {
                if (flags & RTCF_LOCAL &&
                    !(dev_out->flags & IFF_LOOPBACK)) {
                        rth->dst.output = ip_mc_output;
                        RT_CACHE_STAT_INC(out_slow_mc);
                }
#ifdef CONFIG_IP_MROUTE
                if (type == RTN_MULTICAST) {
                        if (IN_DEV_MFORWARD(in_dev) &&
                            !ipv4_is_local_multicast(fl4->daddr)) {
                                rth->dst.input = ip_mr_input;
                                rth->dst.output = ip_mc_output;
                        }
                }
#endif
        }

        rt_set_nexthop(rth, fl4->daddr, res, fnhe, fi, type, 0, do_cache);
        lwtunnel_set_redirect(&rth->dst);

        return rth;
}

/*
 * Major route resolver routine.
 */

struct rtable *ip_route_output_key_hash(struct net *net, struct flowi4 *fl4,
                                        const struct sk_buff *skb)
{
        __u8 tos = RT_FL_TOS(fl4);
        struct fib_result res = {
                .type           = RTN_UNSPEC,
                .fi             = NULL,
                .table          = NULL,
                .tclassid       = 0,
        };
        struct rtable *rth;

        fl4->flowi4_iif = LOOPBACK_IFINDEX;
        fl4->flowi4_tos = tos & IPTOS_RT_MASK;
        fl4->flowi4_scope = ((tos & RTO_ONLINK) ?
                         RT_SCOPE_LINK : RT_SCOPE_UNIVERSE);

        rcu_read_lock();
        rth = ip_route_output_key_hash_rcu(net, fl4, &res, skb);
        rcu_read_unlock();

        return rth;
}
EXPORT_SYMBOL_GPL(ip_route_output_key_hash);

struct rtable *ip_route_output_key_hash_rcu(struct net *net, struct flowi4 *fl4,
                                            struct fib_result *res,
                                            const struct sk_buff *skb)
{
        struct net_device *dev_out = NULL;
        int orig_oif = fl4->flowi4_oif;
        unsigned int flags = 0;
        struct rtable *rth;
        int err;

        if (fl4->saddr) {
                if (ipv4_is_multicast(fl4->saddr) ||
                    ipv4_is_lbcast(fl4->saddr) ||
                    ipv4_is_zeronet(fl4->saddr)) {
                        rth = ERR_PTR(-EINVAL);
                        goto out;
                }

                rth = ERR_PTR(-ENETUNREACH);

                /* I removed check for oif == dev_out->oif here.
                 * It was wrong for two reasons:
                 * 1. ip_dev_find(net, saddr) can return wrong iface, if saddr
                 *    is assigned to multiple interfaces.
                 * 2. Moreover, we are allowed to send packets with saddr
                 *    of another iface. --ANK
                 */

                if (fl4->flowi4_oif == 0 &&
                    (ipv4_is_multicast(fl4->daddr) ||
                     ipv4_is_lbcast(fl4->daddr))) {
                        /* It is equivalent to inet_addr_type(saddr) == RTN_LOCAL */
                        dev_out = __ip_dev_find(net, fl4->saddr, false);
                        if (!dev_out)
                                goto out;

                        /* Special hack: user can direct multicasts
                         * and limited broadcast via necessary interface
                         * without fiddling with IP_MULTICAST_IF or IP_PKTINFO.
                         * This hack is not just for fun, it allows
                         * vic,vat and friends to work.
                         * They bind socket to loopback, set ttl to zero
                         * and expect that it will work.
                         * From the viewpoint of routing cache they are broken,
                         * because we are not allowed to build multicast path
                         * with loopback source addr (look, routing cache
                         * cannot know, that ttl is zero, so that packet
                         * will not leave this host and route is valid).
                         * Luckily, this hack is good workaround.
                         */

                        fl4->flowi4_oif = dev_out->ifindex;
                        goto make_route;
                }

                if (!(fl4->flowi4_flags & FLOWI_FLAG_ANYSRC)) {
                        /* It is equivalent to inet_addr_type(saddr) == RTN_LOCAL */
                        if (!__ip_dev_find(net, fl4->saddr, false))
                                goto out;
                }
        }


        if (fl4->flowi4_oif) {
                dev_out = dev_get_by_index_rcu(net, fl4->flowi4_oif);
                rth = ERR_PTR(-ENODEV);
                if (!dev_out)
                        goto out;

                /* RACE: Check return value of inet_select_addr instead. */
                if (!(dev_out->flags & IFF_UP) || !__in_dev_get_rcu(dev_out)) {
                        rth = ERR_PTR(-ENETUNREACH);
                        goto out;
                }
                if (ipv4_is_local_multicast(fl4->daddr) ||
                    ipv4_is_lbcast(fl4->daddr) ||
                    fl4->flowi4_proto == IPPROTO_IGMP) {
                        if (!fl4->saddr)
                                fl4->saddr = inet_select_addr(dev_out, 0,
                                                              RT_SCOPE_LINK);
                        goto make_route;
                }
                if (!fl4->saddr) {
                        if (ipv4_is_multicast(fl4->daddr))
                                fl4->saddr = inet_select_addr(dev_out, 0,
                                                              fl4->flowi4_scope);
                        else if (!fl4->daddr)
                                fl4->saddr = inet_select_addr(dev_out, 0,
                                                              RT_SCOPE_HOST);
                }
        }

        if (!fl4->daddr) {
                fl4->daddr = fl4->saddr;
                if (!fl4->daddr)
                        fl4->daddr = fl4->saddr = htonl(INADDR_LOOPBACK);
                dev_out = net->loopback_dev;
                fl4->flowi4_oif = LOOPBACK_IFINDEX;
                res->type = RTN_LOCAL;
                flags |= RTCF_LOCAL;
                goto make_route;
        }

        err = fib_lookup(net, fl4, res, 0);
        if (err) {
                res->fi = NULL;
                res->table = NULL;
                if (fl4->flowi4_oif &&
                    (ipv4_is_multicast(fl4->daddr) ||
                    !netif_index_is_l3_master(net, fl4->flowi4_oif))) {
                        /* Apparently, routing tables are wrong. Assume,
                         * that the destination is on link.
                         *
                         * WHY? DW.
                         * Because we are allowed to send to iface
                         * even if it has NO routes and NO assigned
                         * addresses. When oif is specified, routing
                         * tables are looked up with only one purpose:
                         * to catch if destination is gatewayed, rather than
                         * direct. Moreover, if MSG_DONTROUTE is set,
                         * we send packet, ignoring both routing tables
                         * and ifaddr state. --ANK
                         *
                         *
                         * We could make it even if oif is unknown,
                         * likely IPv6, but we do not.
                         */

                        if (fl4->saddr == 0)
                                fl4->saddr = inet_select_addr(dev_out, 0,
                                                              RT_SCOPE_LINK);
                        res->type = RTN_UNICAST;
                        goto make_route;
                }
                rth = ERR_PTR(err);
                goto out;
        }

        if (res->type == RTN_LOCAL) {
                if (!fl4->saddr) {
                        if (res->fi->fib_prefsrc)
                                fl4->saddr = res->fi->fib_prefsrc;
                        else
                                fl4->saddr = fl4->daddr;
                }

                /* L3 master device is the loopback for that domain */
                dev_out = l3mdev_master_dev_rcu(FIB_RES_DEV(*res)) ? :
                        net->loopback_dev;

                /* make sure orig_oif points to fib result device even
                 * though packet rx/tx happens over loopback or l3mdev
                 */
                orig_oif = FIB_RES_OIF(*res);

                fl4->flowi4_oif = dev_out->ifindex;
                flags |= RTCF_LOCAL;
                goto make_route;
        }

        fib_select_path(net, res, fl4, skb);

        dev_out = FIB_RES_DEV(*res);

make_route:
        rth = __mkroute_output(res, fl4, orig_oif, dev_out, flags);

out:
        return rth;
}

static struct dst_ops ipv4_dst_blackhole_ops = {
        .family                 = AF_INET,
        .default_advmss         = ipv4_default_advmss,
        .neigh_lookup           = ipv4_neigh_lookup,
        .check                  = dst_blackhole_check,
        .cow_metrics            = dst_blackhole_cow_metrics,
        .update_pmtu            = dst_blackhole_update_pmtu,
        .redirect               = dst_blackhole_redirect,
        .mtu                    = dst_blackhole_mtu,
};

struct dst_entry *ipv4_blackhole_route(struct net *net, struct dst_entry *dst_orig)
{
        struct rtable *ort = (struct rtable *) dst_orig;
        struct rtable *rt;

        rt = dst_alloc(&ipv4_dst_blackhole_ops, NULL, 1, DST_OBSOLETE_DEAD, 0);
        if (rt) {
                struct dst_entry *new = &rt->dst;

                new->__use = 1;
                new->input = dst_discard;
                new->output = dst_discard_out;

                new->dev = net->loopback_dev;
                if (new->dev)
                        dev_hold(new->dev);

                rt->rt_is_input = ort->rt_is_input;
                rt->rt_iif = ort->rt_iif;
                rt->rt_pmtu = ort->rt_pmtu;
                rt->rt_mtu_locked = ort->rt_mtu_locked;

                rt->rt_genid = rt_genid_ipv4(net);
                rt->rt_flags = ort->rt_flags;
                rt->rt_type = ort->rt_type;
                rt->rt_uses_gateway = ort->rt_uses_gateway;
                rt->rt_gw_family = ort->rt_gw_family;
                if (rt->rt_gw_family == AF_INET)
                        rt->rt_gw4 = ort->rt_gw4;
                else if (rt->rt_gw_family == AF_INET6)
                        rt->rt_gw6 = ort->rt_gw6;

                INIT_LIST_HEAD(&rt->rt_uncached);
        }

        dst_release(dst_orig);

        return rt ? &rt->dst : ERR_PTR(-ENOMEM);
}

struct rtable *ip_route_output_flow(struct net *net, struct flowi4 *flp4,
                                    const struct sock *sk)
{
        struct rtable *rt = __ip_route_output_key(net, flp4);

        if (IS_ERR(rt))
                return rt;

        if (flp4->flowi4_proto) {
                flp4->flowi4_oif = rt->dst.dev->ifindex;
                rt = (struct rtable *)xfrm_lookup_route(net, &rt->dst,
                                                        flowi4_to_flowi(flp4),
                                                        sk, 0);
        }

        return rt;
}
EXPORT_SYMBOL_GPL(ip_route_output_flow);

struct rtable *ip_route_output_tunnel(struct sk_buff *skb,
                                      struct net_device *dev,
                                      struct net *net, __be32 *saddr,
                                      const struct ip_tunnel_info *info,
                                      u8 protocol, bool use_cache)
{
#ifdef CONFIG_DST_CACHE
        struct dst_cache *dst_cache;
#endif
        struct rtable *rt = NULL;
        struct flowi4 fl4;
        __u8 tos;

#ifdef CONFIG_DST_CACHE
        dst_cache = (struct dst_cache *)&info->dst_cache;
        if (use_cache) {
                rt = dst_cache_get_ip4(dst_cache, saddr);
                if (rt)
                        return rt;
        }
#endif
        memset(&fl4, 0, sizeof(fl4));
        fl4.flowi4_mark = skb->mark;
        fl4.flowi4_proto = protocol;
        fl4.daddr = info->key.u.ipv4.dst;
        fl4.saddr = info->key.u.ipv4.src;
        tos = info->key.tos;
        fl4.flowi4_tos = RT_TOS(tos);

        rt = ip_route_output_key(net, &fl4);
        if (IS_ERR(rt)) {
                netdev_dbg(dev, "no route to %pI4\n", &fl4.daddr);
                return ERR_PTR(-ENETUNREACH);
        }
        if (rt->dst.dev == dev) { /* is this necessary? */
                netdev_dbg(dev, "circular route to %pI4\n", &fl4.daddr);
                ip_rt_put(rt);
                return ERR_PTR(-ELOOP);
        }
#ifdef CONFIG_DST_CACHE
        if (use_cache)
                dst_cache_set_ip4(dst_cache, &rt->dst, fl4.saddr);
#endif
        *saddr = fl4.saddr;
        return rt;
}
EXPORT_SYMBOL_GPL(ip_route_output_tunnel);

/* called with rcu_read_lock held */
static int rt_fill_info(struct net *net, __be32 dst, __be32 src,
                        struct rtable *rt, u32 table_id, struct flowi4 *fl4,
                        struct sk_buff *skb, u32 portid, u32 seq,
                        unsigned int flags)
{
        struct rtmsg *r;
        struct nlmsghdr *nlh;
        unsigned long expires = 0;
        u32 error;
        u32 metrics[RTAX_MAX];

        nlh = nlmsg_put(skb, portid, seq, RTM_NEWROUTE, sizeof(*r), flags);
        if (!nlh)
                return -EMSGSIZE;

        r = nlmsg_data(nlh);
        r->rtm_family    = AF_INET;
        r->rtm_dst_len  = 32;
        r->rtm_src_len  = 0;
        r->rtm_tos      = fl4 ? fl4->flowi4_tos : 0;
        r->rtm_table    = table_id < 256 ? table_id : RT_TABLE_COMPAT;
        if (nla_put_u32(skb, RTA_TABLE, table_id))
                goto nla_put_failure;
        r->rtm_type     = rt->rt_type;
        r->rtm_scope    = RT_SCOPE_UNIVERSE;
        r->rtm_protocol = RTPROT_UNSPEC;
        r->rtm_flags    = (rt->rt_flags & ~0xFFFF) | RTM_F_CLONED;
        if (rt->rt_flags & RTCF_NOTIFY)
                r->rtm_flags |= RTM_F_NOTIFY;
        if (IPCB(skb)->flags & IPSKB_DOREDIRECT)
                r->rtm_flags |= RTCF_DOREDIRECT;

        if (nla_put_in_addr(skb, RTA_DST, dst))
                goto nla_put_failure;
        if (src) {
                r->rtm_src_len = 32;
                if (nla_put_in_addr(skb, RTA_SRC, src))
                        goto nla_put_failure;
        }
        if (rt->dst.dev &&
            nla_put_u32(skb, RTA_OIF, rt->dst.dev->ifindex))
                goto nla_put_failure;
        if (rt->dst.lwtstate &&
            lwtunnel_fill_encap(skb, rt->dst.lwtstate, RTA_ENCAP, RTA_ENCAP_TYPE) < 0)
                goto nla_put_failure;
#ifdef CONFIG_IP_ROUTE_CLASSID
        if (rt->dst.tclassid &&
            nla_put_u32(skb, RTA_FLOW, rt->dst.tclassid))
                goto nla_put_failure;
#endif
        if (fl4 && !rt_is_input_route(rt) &&
            fl4->saddr != src) {
                if (nla_put_in_addr(skb, RTA_PREFSRC, fl4->saddr))
                        goto nla_put_failure;
        }
        if (rt->rt_uses_gateway) {
                if (rt->rt_gw_family == AF_INET &&
                    nla_put_in_addr(skb, RTA_GATEWAY, rt->rt_gw4)) {
                        goto nla_put_failure;
                } else if (rt->rt_gw_family == AF_INET6) {
                        int alen = sizeof(struct in6_addr);
                        struct nlattr *nla;
                        struct rtvia *via;

                        nla = nla_reserve(skb, RTA_VIA, alen + 2);
                        if (!nla)
                                goto nla_put_failure;

                        via = nla_data(nla);
                        via->rtvia_family = AF_INET6;
                        memcpy(via->rtvia_addr, &rt->rt_gw6, alen);
                }
        }