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 <net/route.h>
   7 #include <net/xfrm.h>
   8 #include <net/ip.h>
   9
  10 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  11 int ip_route_me_harder(struct sk_buff **pskb, unsigned addr_type)
  12 {
  13         struct iphdr *iph = (*pskb)->nh.iph;
  14         struct rtable *rt;
  15         struct flowi fl = {};
  16         struct dst_entry *odst;
  17         unsigned int hh_len;
  18         unsigned int type;
  19
  20         type = inet_addr_type(iph->saddr);
  21         if (addr_type == RTN_UNSPEC)
  22                 addr_type = type;
  23
  24         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  25          * packets with foreign saddr to appear on the NF_IP_LOCAL_OUT hook.
  26          */
  27         if (addr_type == RTN_LOCAL) {
  28                 fl.nl_u.ip4_u.daddr = iph->daddr;
  29                 if (type == RTN_LOCAL)
  30                         fl.nl_u.ip4_u.saddr = iph->saddr;
  31                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  32                 fl.oif = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
  33                 fl.mark = (*pskb)->mark;
  34                 if (ip_route_output_key(&rt, &fl) != 0)
  35                         return -1;
  36
  37                 /* Drop old route. */
  38                 dst_release((*pskb)->dst);
  39                 (*pskb)->dst = &rt->u.dst;
  40         } else {
  41                 /* non-local src, find valid iif to satisfy
  42                  * rp-filter when calling ip_route_input. */
  43                 fl.nl_u.ip4_u.daddr = iph->saddr;
  44                 if (ip_route_output_key(&rt, &fl) != 0)
  45                         return -1;
  46
  47                 odst = (*pskb)->dst;
  48                 if (ip_route_input(*pskb, iph->daddr, iph->saddr,
  49                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  50                         dst_release(&rt->u.dst);
  51                         return -1;
  52                 }
  53                 dst_release(&rt->u.dst);
  54                 dst_release(odst);
  55         }
  56
  57         if ((*pskb)->dst->error)
  58                 return -1;
  59
  60 #ifdef CONFIG_XFRM
  61         if (!(IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  62             xfrm_decode_session(*pskb, &fl, AF_INET) == 0)
  63                 if (xfrm_lookup(&(*pskb)->dst, &fl, (*pskb)->sk, 0))
  64                         return -1;
  65 #endif
  66
  67         /* Change in oif may mean change in hh_len. */
  68         hh_len = (*pskb)->dst->dev->hard_header_len;
  69         if (skb_headroom(*pskb) < hh_len) {
  70                 struct sk_buff *nskb;
  71
  72                 nskb = skb_realloc_headroom(*pskb, hh_len);
  73                 if (!nskb)
  74                         return -1;
  75                 if ((*pskb)->sk)
  76                         skb_set_owner_w(nskb, (*pskb)->sk);
  77                 kfree_skb(*pskb);
  78                 *pskb = nskb;
  79         }
  80
  81         return 0;
  82 }
  83 EXPORT_SYMBOL(ip_route_me_harder);
  84
  85 #ifdef CONFIG_XFRM
  86 int ip_xfrm_me_harder(struct sk_buff **pskb)
  87 {
  88         struct flowi fl;
  89         unsigned int hh_len;
  90         struct dst_entry *dst;
  91
  92         if (IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED)
  93                 return 0;
  94         if (xfrm_decode_session(*pskb, &fl, AF_INET) < 0)
  95                 return -1;
  96
  97         dst = (*pskb)->dst;
  98         if (dst->xfrm)
  99                 dst = ((struct xfrm_dst *)dst)->route;
 100         dst_hold(dst);
 101
 102         if (xfrm_lookup(&dst, &fl, (*pskb)->sk, 0) < 0)
 103                 return -1;
 104
 105         dst_release((*pskb)->dst);
 106         (*pskb)->dst = dst;
 107
 108         /* Change in oif may mean change in hh_len. */
 109         hh_len = (*pskb)->dst->dev->hard_header_len;
 110         if (skb_headroom(*pskb) < hh_len) {
 111                 struct sk_buff *nskb;
 112
 113                 nskb = skb_realloc_headroom(*pskb, hh_len);
 114                 if (!nskb)
 115                         return -1;
 116                 if ((*pskb)->sk)
 117                         skb_set_owner_w(nskb, (*pskb)->sk);
 118                 kfree_skb(*pskb);
 119                 *pskb = nskb;
 120         }
 121         return 0;
 122 }
 123 EXPORT_SYMBOL(ip_xfrm_me_harder);
 124 #endif
 125
 126 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 127 EXPORT_SYMBOL(ip_nat_decode_session);
 128
 129 /*
 130  * Extra routing may needed on local out, as the QUEUE target never
 131  * returns control to the table.
 132  */
 133
 134 struct ip_rt_info {
 135         __be32 daddr;
 136         __be32 saddr;
 137         u_int8_t tos;
 138 };
 139
 140 static void nf_ip_saveroute(const struct sk_buff *skb, struct nf_info *info)
 141 {
 142         struct ip_rt_info *rt_info = nf_info_reroute(info);
 143
 144         if (info->hook == NF_IP_LOCAL_OUT) {
 145                 const struct iphdr *iph = skb->nh.iph;
 146
 147                 rt_info->tos = iph->tos;
 148                 rt_info->daddr = iph->daddr;
 149                 rt_info->saddr = iph->saddr;
 150         }
 151 }
 152
 153 static int nf_ip_reroute(struct sk_buff **pskb, const struct nf_info *info)
 154 {
 155         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 156
 157         if (info->hook == NF_IP_LOCAL_OUT) {
 158                 struct iphdr *iph = (*pskb)->nh.iph;
 159
 160                 if (!(iph->tos == rt_info->tos
 161                       && iph->daddr == rt_info->daddr
 162                       && iph->saddr == rt_info->saddr))
 163                         return ip_route_me_harder(pskb, RTN_UNSPEC);
 164         }
 165         return 0;
 166 }
 167
 168 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 169                             unsigned int dataoff, u_int8_t protocol)
 170 {
 171         struct iphdr *iph = skb->nh.iph;
 172         __sum16 csum = 0;
 173
 174         switch (skb->ip_summed) {
 175         case CHECKSUM_COMPLETE:
 176                 if (hook != NF_IP_PRE_ROUTING && hook != NF_IP_LOCAL_IN)
 177                         break;
 178                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 179                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 180                                        skb->len - dataoff, protocol,
 181                                        skb->csum)) {
 182                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 183                         break;
 184                 }
 185                 /* fall through */
 186         case CHECKSUM_NONE:
 187                 if (protocol == 0)
 188                         skb->csum = 0;
 189                 else
 190                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 191                                                        skb->len - dataoff,
 192                                                        protocol, 0);
 193                 csum = __skb_checksum_complete(skb);
 194         }
 195         return csum;
 196 }
 197
 198 EXPORT_SYMBOL(nf_ip_checksum);
 199
 200 static struct nf_afinfo nf_ip_afinfo = {
 201         .family         = AF_INET,
 202         .checksum       = nf_ip_checksum,
 203         .saveroute      = nf_ip_saveroute,
 204         .reroute        = nf_ip_reroute,
 205         .route_key_size = sizeof(struct ip_rt_info),
 206 };
 207
 208 static int ipv4_netfilter_init(void)
 209 {
 210         return nf_register_afinfo(&nf_ip_afinfo);
 211 }
 212
 213 static void ipv4_netfilter_fini(void)
 214 {
 215         nf_unregister_afinfo(&nf_ip_afinfo);
 216 }
 217
 218 module_init(ipv4_netfilter_init);
 219 module_exit(ipv4_netfilter_fini);