net/ipv4/netfilter.c

   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 **pskb, unsigned addr_type)
  13 {
  14         const struct iphdr *iph = ip_hdr(*pskb);
  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_IP_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 = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
  34                 fl.mark = (*pskb)->mark;
  35                 if (ip_route_output_key(&rt, &fl) != 0)
  36                         return -1;
  37
  38                 /* Drop old route. */
  39                 dst_release((*pskb)->dst);
  40                 (*pskb)->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 = (*pskb)->dst;
  49                 if (ip_route_input(*pskb, 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 ((*pskb)->dst->error)
  59                 return -1;
  60
  61 #ifdef CONFIG_XFRM
  62         if (!(IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  63             xfrm_decode_session(*pskb, &fl, AF_INET) == 0)
  64                 if (xfrm_lookup(&(*pskb)->dst, &fl, (*pskb)->sk, 0))
  65                         return -1;
  66 #endif
  67
  68         /* Change in oif may mean change in hh_len. */
  69         hh_len = (*pskb)->dst->dev->hard_header_len;
  70         if (skb_headroom(*pskb) < hh_len &&
  71             pskb_expand_head(*pskb, hh_len - skb_headroom(*pskb), 0,
  72                              GFP_ATOMIC))
  73                 return -1;
  74
  75         return 0;
  76 }
  77 EXPORT_SYMBOL(ip_route_me_harder);
  78
  79 #ifdef CONFIG_XFRM
  80 int ip_xfrm_me_harder(struct sk_buff **pskb)
  81 {
  82         struct flowi fl;
  83         unsigned int hh_len;
  84         struct dst_entry *dst;
  85
  86         if (IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED)
  87                 return 0;
  88         if (xfrm_decode_session(*pskb, &fl, AF_INET) < 0)
  89                 return -1;
  90
  91         dst = (*pskb)->dst;
  92         if (dst->xfrm)
  93                 dst = ((struct xfrm_dst *)dst)->route;
  94         dst_hold(dst);
  95
  96         if (xfrm_lookup(&dst, &fl, (*pskb)->sk, 0) < 0)
  97                 return -1;
  98
  99         dst_release((*pskb)->dst);
 100         (*pskb)->dst = dst;
 101
 102         /* Change in oif may mean change in hh_len. */
 103         hh_len = (*pskb)->dst->dev->hard_header_len;
 104         if (skb_headroom(*pskb) < hh_len &&
 105             pskb_expand_head(*pskb, hh_len - skb_headroom(*pskb), 0,
 106                              GFP_ATOMIC))
 107                 return -1;
 108         return 0;
 109 }
 110 EXPORT_SYMBOL(ip_xfrm_me_harder);
 111 #endif
 112
 113 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 114 EXPORT_SYMBOL(ip_nat_decode_session);
 115
 116 /*
 117  * Extra routing may needed on local out, as the QUEUE target never
 118  * returns control to the table.
 119  */
 120
 121 struct ip_rt_info {
 122         __be32 daddr;
 123         __be32 saddr;
 124         u_int8_t tos;
 125 };
 126
 127 static void nf_ip_saveroute(const struct sk_buff *skb, struct nf_info *info)
 128 {
 129         struct ip_rt_info *rt_info = nf_info_reroute(info);
 130
 131         if (info->hook == NF_IP_LOCAL_OUT) {
 132                 const struct iphdr *iph = ip_hdr(skb);
 133
 134                 rt_info->tos = iph->tos;
 135                 rt_info->daddr = iph->daddr;
 136                 rt_info->saddr = iph->saddr;
 137         }
 138 }
 139
 140 static int nf_ip_reroute(struct sk_buff **pskb, const struct nf_info *info)
 141 {
 142         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 143
 144         if (info->hook == NF_IP_LOCAL_OUT) {
 145                 const struct iphdr *iph = ip_hdr(*pskb);
 146
 147                 if (!(iph->tos == rt_info->tos
 148                       && iph->daddr == rt_info->daddr
 149                       && iph->saddr == rt_info->saddr))
 150                         return ip_route_me_harder(pskb, RTN_UNSPEC);
 151         }
 152         return 0;
 153 }
 154
 155 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 156                             unsigned int dataoff, u_int8_t protocol)
 157 {
 158         const struct iphdr *iph = ip_hdr(skb);
 159         __sum16 csum = 0;
 160
 161         switch (skb->ip_summed) {
 162         case CHECKSUM_COMPLETE:
 163                 if (hook != NF_IP_PRE_ROUTING && hook != NF_IP_LOCAL_IN)
 164                         break;
 165                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 166                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 167                                        skb->len - dataoff, protocol,
 168                                        skb->csum)) {
 169                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 170                         break;
 171                 }
 172                 /* fall through */
 173         case CHECKSUM_NONE:
 174                 if (protocol == 0)
 175                         skb->csum = 0;
 176                 else
 177                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 178                                                        skb->len - dataoff,
 179                                                        protocol, 0);
 180                 csum = __skb_checksum_complete(skb);
 181         }
 182         return csum;
 183 }
 184
 185 EXPORT_SYMBOL(nf_ip_checksum);
 186
 187 static struct nf_afinfo nf_ip_afinfo = {
 188         .family         = AF_INET,
 189         .checksum       = nf_ip_checksum,
 190         .saveroute      = nf_ip_saveroute,
 191         .reroute        = nf_ip_reroute,
 192         .route_key_size = sizeof(struct ip_rt_info),
 193 };
 194
 195 static int ipv4_netfilter_init(void)
 196 {
 197         return nf_register_afinfo(&nf_ip_afinfo);
 198 }
 199
 200 static void ipv4_netfilter_fini(void)
 201 {
 202         nf_unregister_afinfo(&nf_ip_afinfo);
 203 }
 204
 205 module_init(ipv4_netfilter_init);
 206 module_exit(ipv4_netfilter_fini);