linux/net/ipv4/netfilter.c
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   1/* IPv4 specific functions of netfilter core */
   2#include <linux/kernel.h>
   3#include <linux/netfilter.h>
   4#include <linux/netfilter_ipv4.h>
   5#include <linux/ip.h>
   6#include <linux/skbuff.h>
   7#include <linux/gfp.h>
   8#include <linux/export.h>
   9#include <net/route.h>
  10#include <net/xfrm.h>
  11#include <net/ip.h>
  12#include <net/netfilter/nf_queue.h>
  13
  14/* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  15int ip_route_me_harder(struct sk_buff *skb, unsigned int addr_type)
  16{
  17        struct net *net = dev_net(skb_dst(skb)->dev);
  18        const struct iphdr *iph = ip_hdr(skb);
  19        struct rtable *rt;
  20        struct flowi4 fl4 = {};
  21        __be32 saddr = iph->saddr;
  22        __u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
  23        unsigned int hh_len;
  24
  25        if (addr_type == RTN_UNSPEC)
  26                addr_type = inet_addr_type(net, saddr);
  27        if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
  28                flags |= FLOWI_FLAG_ANYSRC;
  29        else
  30                saddr = 0;
  31
  32        /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  33         * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  34         */
  35        fl4.daddr = iph->daddr;
  36        fl4.saddr = saddr;
  37        fl4.flowi4_tos = RT_TOS(iph->tos);
  38        fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
  39        fl4.flowi4_mark = skb->mark;
  40        fl4.flowi4_flags = flags;
  41        rt = ip_route_output_key(net, &fl4);
  42        if (IS_ERR(rt))
  43                return -1;
  44
  45        /* Drop old route. */
  46        skb_dst_drop(skb);
  47        skb_dst_set(skb, &rt->dst);
  48
  49        if (skb_dst(skb)->error)
  50                return -1;
  51
  52#ifdef CONFIG_XFRM
  53        if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  54            xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
  55                struct dst_entry *dst = skb_dst(skb);
  56                skb_dst_set(skb, NULL);
  57                dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
  58                if (IS_ERR(dst))
  59                        return -1;
  60                skb_dst_set(skb, dst);
  61        }
  62#endif
  63
  64        /* Change in oif may mean change in hh_len. */
  65        hh_len = skb_dst(skb)->dev->hard_header_len;
  66        if (skb_headroom(skb) < hh_len &&
  67            pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
  68                                0, GFP_ATOMIC))
  69                return -1;
  70
  71        return 0;
  72}
  73EXPORT_SYMBOL(ip_route_me_harder);
  74
  75/*
  76 * Extra routing may needed on local out, as the QUEUE target never
  77 * returns control to the table.
  78 */
  79
  80struct ip_rt_info {
  81        __be32 daddr;
  82        __be32 saddr;
  83        u_int8_t tos;
  84        u_int32_t mark;
  85};
  86
  87static void nf_ip_saveroute(const struct sk_buff *skb,
  88                            struct nf_queue_entry *entry)
  89{
  90        struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
  91
  92        if (entry->hook == NF_INET_LOCAL_OUT) {
  93                const struct iphdr *iph = ip_hdr(skb);
  94
  95                rt_info->tos = iph->tos;
  96                rt_info->daddr = iph->daddr;
  97                rt_info->saddr = iph->saddr;
  98                rt_info->mark = skb->mark;
  99        }
 100}
 101
 102static int nf_ip_reroute(struct sk_buff *skb,
 103                         const struct nf_queue_entry *entry)
 104{
 105        const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 106
 107        if (entry->hook == NF_INET_LOCAL_OUT) {
 108                const struct iphdr *iph = ip_hdr(skb);
 109
 110                if (!(iph->tos == rt_info->tos &&
 111                      skb->mark == rt_info->mark &&
 112                      iph->daddr == rt_info->daddr &&
 113                      iph->saddr == rt_info->saddr))
 114                        return ip_route_me_harder(skb, RTN_UNSPEC);
 115        }
 116        return 0;
 117}
 118
 119__sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 120                            unsigned int dataoff, u_int8_t protocol)
 121{
 122        const struct iphdr *iph = ip_hdr(skb);
 123        __sum16 csum = 0;
 124
 125        switch (skb->ip_summed) {
 126        case CHECKSUM_COMPLETE:
 127                if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 128                        break;
 129                if ((protocol == 0 && !csum_fold(skb->csum)) ||
 130                    !csum_tcpudp_magic(iph->saddr, iph->daddr,
 131                                       skb->len - dataoff, protocol,
 132                                       skb->csum)) {
 133                        skb->ip_summed = CHECKSUM_UNNECESSARY;
 134                        break;
 135                }
 136                /* fall through */
 137        case CHECKSUM_NONE:
 138                if (protocol == 0)
 139                        skb->csum = 0;
 140                else
 141                        skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 142                                                       skb->len - dataoff,
 143                                                       protocol, 0);
 144                csum = __skb_checksum_complete(skb);
 145        }
 146        return csum;
 147}
 148EXPORT_SYMBOL(nf_ip_checksum);
 149
 150static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 151                                      unsigned int dataoff, unsigned int len,
 152                                      u_int8_t protocol)
 153{
 154        const struct iphdr *iph = ip_hdr(skb);
 155        __sum16 csum = 0;
 156
 157        switch (skb->ip_summed) {
 158        case CHECKSUM_COMPLETE:
 159                if (len == skb->len - dataoff)
 160                        return nf_ip_checksum(skb, hook, dataoff, protocol);
 161                /* fall through */
 162        case CHECKSUM_NONE:
 163                skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 164                                               skb->len - dataoff, 0);
 165                skb->ip_summed = CHECKSUM_NONE;
 166                return __skb_checksum_complete_head(skb, dataoff + len);
 167        }
 168        return csum;
 169}
 170
 171static int nf_ip_route(struct net *net, struct dst_entry **dst,
 172                       struct flowi *fl, bool strict __always_unused)
 173{
 174        struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 175        if (IS_ERR(rt))
 176                return PTR_ERR(rt);
 177        *dst = &rt->dst;
 178        return 0;
 179}
 180
 181static const struct nf_afinfo nf_ip_afinfo = {
 182        .family                 = AF_INET,
 183        .checksum               = nf_ip_checksum,
 184        .checksum_partial       = nf_ip_checksum_partial,
 185        .route                  = nf_ip_route,
 186        .saveroute              = nf_ip_saveroute,
 187        .reroute                = nf_ip_reroute,
 188        .route_key_size         = sizeof(struct ip_rt_info),
 189};
 190
 191static int __init ipv4_netfilter_init(void)
 192{
 193        return nf_register_afinfo(&nf_ip_afinfo);
 194}
 195
 196static void __exit ipv4_netfilter_fini(void)
 197{
 198        nf_unregister_afinfo(&nf_ip_afinfo);
 199}
 200
 201module_init(ipv4_netfilter_init);
 202module_exit(ipv4_netfilter_fini);
 203
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