/* IPv4 specific functions of netfilter core */
#include <linux/kernel.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>
#include <linux/skbuff.h>
#include <linux/gfp.h>
#include <net/route.h>
#include <net/xfrm.h>
#include <net/ip.h>
#include <net/netfilter/nf_queue.h>

/* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
int ip_route_me_harder(struct sk_buff *skb, unsigned addr_type)
{
        struct net *net = dev_net(skb_dst(skb)->dev);
        const struct iphdr *iph = ip_hdr(skb);
        struct rtable *rt;
        struct flowi fl = {};
        unsigned long orefdst;
        unsigned int hh_len;
        unsigned int type;

        type = inet_addr_type(net, iph->saddr);
        if (skb->sk && inet_sk(skb->sk)->transparent)
                type = RTN_LOCAL;
        if (addr_type == RTN_UNSPEC)
                addr_type = type;

        /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
         * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
         */
        if (addr_type == RTN_LOCAL) {
                fl.nl_u.ip4_u.daddr = iph->daddr;
                if (type == RTN_LOCAL)
                        fl.nl_u.ip4_u.saddr = iph->saddr;
                fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
                fl.oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
                fl.mark = skb->mark;
                fl.flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
                if (ip_route_output_key(net, &rt, &fl) != 0)
                        return -1;

                /* Drop old route. */
                skb_dst_drop(skb);
                skb_dst_set(skb, &rt->u.dst);
        } else {
                /* non-local src, find valid iif to satisfy
                 * rp-filter when calling ip_route_input. */
                fl.nl_u.ip4_u.daddr = iph->saddr;
                if (ip_route_output_key(net, &rt, &fl) != 0)
                        return -1;

                orefdst = skb->_skb_refdst;
                if (ip_route_input(skb, iph->daddr, iph->saddr,
                                   RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
                        dst_release(&rt->u.dst);
                        return -1;
                }
                dst_release(&rt->u.dst);
                refdst_drop(orefdst);
        }

        if (skb_dst(skb)->error)
                return -1;

#ifdef CONFIG_XFRM
        if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
            xfrm_decode_session(skb, &fl, AF_INET) == 0) {
                struct dst_entry *dst = skb_dst(skb);
                skb_dst_set(skb, NULL);
                if (xfrm_lookup(net, &dst, &fl, skb->sk, 0))
                        return -1;
                skb_dst_set(skb, dst);
        }
#endif

        /* Change in oif may mean change in hh_len. */
        hh_len = skb_dst(skb)->dev->hard_header_len;
        if (skb_headroom(skb) < hh_len &&
            pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
                return -1;

        return 0;
}
EXPORT_SYMBOL(ip_route_me_harder);

#ifdef CONFIG_XFRM
int ip_xfrm_me_harder(struct sk_buff *skb)
{
        struct flowi fl;
        unsigned int hh_len;
        struct dst_entry *dst;

        if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
                return 0;
        if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
                return -1;

        dst = skb_dst(skb);
        if (dst->xfrm)
                dst = ((struct xfrm_dst *)dst)->route;
        dst_hold(dst);

        if (xfrm_lookup(dev_net(dst->dev), &dst, &fl, skb->sk, 0) < 0)
                return -1;

        skb_dst_drop(skb);
        skb_dst_set(skb, dst);

        /* Change in oif may mean change in hh_len. */
        hh_len = skb_dst(skb)->dev->hard_header_len;
        if (skb_headroom(skb) < hh_len &&
            pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
                return -1;
        return 0;
}
EXPORT_SYMBOL(ip_xfrm_me_harder);
#endif

void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
EXPORT_SYMBOL(ip_nat_decode_session);

/*
 * Extra routing may needed on local out, as the QUEUE target never
 * returns control to the table.
 */

struct ip_rt_info {
        __be32 daddr;
        __be32 saddr;
        u_int8_t tos;
        u_int32_t mark;
};

static void nf_ip_saveroute(const struct sk_buff *skb,
                            struct nf_queue_entry *entry)
{
        struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);

        if (entry->hook == NF_INET_LOCAL_OUT) {
                const struct iphdr *iph = ip_hdr(skb);

                rt_info->tos = iph->tos;
                rt_info->daddr = iph->daddr;
                rt_info->saddr = iph->saddr;
                rt_info->mark = skb->mark;
        }
}

static int nf_ip_reroute(struct sk_buff *skb,
                         const struct nf_queue_entry *entry)
{
        const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);

        if (entry->hook == NF_INET_LOCAL_OUT) {
                const struct iphdr *iph = ip_hdr(skb);

                if (!(iph->tos == rt_info->tos &&
                      skb->mark == rt_info->mark &&
                      iph->daddr == rt_info->daddr &&
                      iph->saddr == rt_info->saddr))
                        return ip_route_me_harder(skb, RTN_UNSPEC);
        }
        return 0;
}

__sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
                            unsigned int dataoff, u_int8_t protocol)
{
        const struct iphdr *iph = ip_hdr(skb);
        __sum16 csum = 0;

        switch (skb->ip_summed) {
        case CHECKSUM_COMPLETE:
                if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
                        break;
                if ((protocol == 0 && !csum_fold(skb->csum)) ||
                    !csum_tcpudp_magic(iph->saddr, iph->daddr,
                                       skb->len - dataoff, protocol,
                                       skb->csum)) {
                        skb->ip_summed = CHECKSUM_UNNECESSARY;
                        break;
                }
                /* fall through */
        case CHECKSUM_NONE:
                if (protocol == 0)
                        skb->csum = 0;
                else
                        skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
                                                       skb->len - dataoff,
                                                       protocol, 0);
                csum = __skb_checksum_complete(skb);
        }
        return csum;
}
EXPORT_SYMBOL(nf_ip_checksum);

static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
                                      unsigned int dataoff, unsigned int len,
                                      u_int8_t protocol)
{
        const struct iphdr *iph = ip_hdr(skb);
        __sum16 csum = 0;

        switch (skb->ip_summed) {
        case CHECKSUM_COMPLETE:
                if (len == skb->len - dataoff)
                        return nf_ip_checksum(skb, hook, dataoff, protocol);
                /* fall through */
        case CHECKSUM_NONE:
                skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
                                               skb->len - dataoff, 0);
                skb->ip_summed = CHECKSUM_NONE;
                csum = __skb_checksum_complete_head(skb, dataoff + len);
                if (!csum)
                        skb->ip_summed = CHECKSUM_UNNECESSARY;
        }
        return csum;
}

static int nf_ip_route(struct dst_entry **dst, struct flowi *fl)
{
        return ip_route_output_key(&init_net, (struct rtable **)dst, fl);
}

static const struct nf_afinfo nf_ip_afinfo = {
        .family                 = AF_INET,
        .checksum               = nf_ip_checksum,
        .checksum_partial       = nf_ip_checksum_partial,
        .route                  = nf_ip_route,
        .saveroute              = nf_ip_saveroute,
        .reroute                = nf_ip_reroute,
        .route_key_size         = sizeof(struct ip_rt_info),
};

static int ipv4_netfilter_init(void)
{
        return nf_register_afinfo(&nf_ip_afinfo);
}

static void ipv4_netfilter_fini(void)
{
        nf_unregister_afinfo(&nf_ip_afinfo);
}

module_init(ipv4_netfilter_init);
module_exit(ipv4_netfilter_fini);

#ifdef CONFIG_SYSCTL
struct ctl_path nf_net_ipv4_netfilter_sysctl_path[] = {
        { .procname = "net", },
        { .procname = "ipv4", },
        { .procname = "netfilter", },
        { }
};
EXPORT_SYMBOL_GPL(nf_net_ipv4_netfilter_sysctl_path);
#endif /* CONFIG_SYSCTL */