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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 <net/route.h>
   8 #include <net/xfrm.h>
   9 #include <net/ip.h>
  10
  11 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  12 int ip_route_me_harder(struct sk_buff *skb, unsigned addr_type)
  13 {
  14         const struct iphdr *iph = ip_hdr(skb);
  15         struct rtable *rt;
  16         struct flowi fl = {};
  17         struct dst_entry *odst;
  18         unsigned int hh_len;
  19         unsigned int type;
  20
  21         type = inet_addr_type(iph->saddr);
  22         if (addr_type == RTN_UNSPEC)
  23                 addr_type = type;
  24
  25         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  26          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  27          */
  28         if (addr_type == RTN_LOCAL) {
  29                 fl.nl_u.ip4_u.daddr = iph->daddr;
  30                 if (type == RTN_LOCAL)
  31                         fl.nl_u.ip4_u.saddr = iph->saddr;
  32                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  33                 fl.oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
  34                 fl.mark = skb->mark;
  35                 if (ip_route_output_key(&rt, &fl) != 0)
  36                         return -1;
  37
  38                 /* Drop old route. */
  39                 dst_release(skb->dst);
  40                 skb->dst = &rt->u.dst;
  41         } else {
  42                 /* non-local src, find valid iif to satisfy
  43                  * rp-filter when calling ip_route_input. */
  44                 fl.nl_u.ip4_u.daddr = iph->saddr;
  45                 if (ip_route_output_key(&rt, &fl) != 0)
  46                         return -1;
  47
  48                 odst = skb->dst;
  49                 if (ip_route_input(skb, iph->daddr, iph->saddr,
  50                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  51                         dst_release(&rt->u.dst);
  52                         return -1;
  53                 }
  54                 dst_release(&rt->u.dst);
  55                 dst_release(odst);
  56         }
  57
  58         if (skb->dst->error)
  59                 return -1;
  60
  61 #ifdef CONFIG_XFRM
  62         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  63             xfrm_decode_session(skb, &fl, AF_INET) == 0)
  64                 if (xfrm_lookup(&skb->dst, &fl, skb->sk, 0))
  65                         return -1;
  66 #endif
  67
  68         /* Change in oif may mean change in hh_len. */
  69         hh_len = skb->dst->dev->hard_header_len;
  70         if (skb_headroom(skb) < hh_len &&
  71             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
  72                 return -1;
  73
  74         return 0;
  75 }
  76 EXPORT_SYMBOL(ip_route_me_harder);
  77
  78 #ifdef CONFIG_XFRM
  79 int ip_xfrm_me_harder(struct sk_buff *skb)
  80 {
  81         struct flowi fl;
  82         unsigned int hh_len;
  83         struct dst_entry *dst;
  84
  85         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  86                 return 0;
  87         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
  88                 return -1;
  89
  90         dst = skb->dst;
  91         if (dst->xfrm)
  92                 dst = ((struct xfrm_dst *)dst)->route;
  93         dst_hold(dst);
  94
  95         if (xfrm_lookup(&dst, &fl, skb->sk, 0) < 0)
  96                 return -1;
  97
  98         dst_release(skb->dst);
  99         skb->dst = dst;
 100
 101         /* Change in oif may mean change in hh_len. */
 102         hh_len = skb->dst->dev->hard_header_len;
 103         if (skb_headroom(skb) < hh_len &&
 104             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 105                 return -1;
 106         return 0;
 107 }
 108 EXPORT_SYMBOL(ip_xfrm_me_harder);
 109 #endif
 110
 111 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 112 EXPORT_SYMBOL(ip_nat_decode_session);
 113
 114 /*
 115  * Extra routing may needed on local out, as the QUEUE target never
 116  * returns control to the table.
 117  */
 118
 119 struct ip_rt_info {
 120         __be32 daddr;
 121         __be32 saddr;
 122         u_int8_t tos;
 123 };
 124
 125 static void nf_ip_saveroute(const struct sk_buff *skb, struct nf_info *info)
 126 {
 127         struct ip_rt_info *rt_info = nf_info_reroute(info);
 128
 129         if (info->hook == NF_INET_LOCAL_OUT) {
 130                 const struct iphdr *iph = ip_hdr(skb);
 131
 132                 rt_info->tos = iph->tos;
 133                 rt_info->daddr = iph->daddr;
 134                 rt_info->saddr = iph->saddr;
 135         }
 136 }
 137
 138 static int nf_ip_reroute(struct sk_buff *skb, const struct nf_info *info)
 139 {
 140         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 141
 142         if (info->hook == NF_INET_LOCAL_OUT) {
 143                 const struct iphdr *iph = ip_hdr(skb);
 144
 145                 if (!(iph->tos == rt_info->tos
 146                       && iph->daddr == rt_info->daddr
 147                       && iph->saddr == rt_info->saddr))
 148                         return ip_route_me_harder(skb, RTN_UNSPEC);
 149         }
 150         return 0;
 151 }
 152
 153 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 154                             unsigned int dataoff, u_int8_t protocol)
 155 {
 156         const struct iphdr *iph = ip_hdr(skb);
 157         __sum16 csum = 0;
 158
 159         switch (skb->ip_summed) {
 160         case CHECKSUM_COMPLETE:
 161                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 162                         break;
 163                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 164                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 165                                        skb->len - dataoff, protocol,
 166                                        skb->csum)) {
 167                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 168                         break;
 169                 }
 170                 /* fall through */
 171         case CHECKSUM_NONE:
 172                 if (protocol == 0)
 173                         skb->csum = 0;
 174                 else
 175                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 176                                                        skb->len - dataoff,
 177                                                        protocol, 0);
 178                 csum = __skb_checksum_complete(skb);
 179         }
 180         return csum;
 181 }
 182
 183 EXPORT_SYMBOL(nf_ip_checksum);
 184
 185 static struct nf_afinfo nf_ip_afinfo = {
 186         .family         = AF_INET,
 187         .checksum       = nf_ip_checksum,
 188         .saveroute      = nf_ip_saveroute,
 189         .reroute        = nf_ip_reroute,
 190         .route_key_size = sizeof(struct ip_rt_info),
 191 };
 192
 193 static int ipv4_netfilter_init(void)
 194 {
 195         return nf_register_afinfo(&nf_ip_afinfo);
 196 }
 197
 198 static void ipv4_netfilter_fini(void)
 199 {
 200         nf_unregister_afinfo(&nf_ip_afinfo);
 201 }
 202
 203 module_init(ipv4_netfilter_init);
 204 module_exit(ipv4_netfilter_fini);