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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 <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
  19         if (addr_type == RTN_UNSPEC)
  20                 addr_type = inet_addr_type(iph->saddr);
  21
  22         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  23          * packets with foreign saddr to appear on the NF_IP_LOCAL_OUT hook.
  24          */
  25         if (addr_type == RTN_LOCAL) {
  26                 fl.nl_u.ip4_u.daddr = iph->daddr;
  27                 fl.nl_u.ip4_u.saddr = iph->saddr;
  28                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  29                 fl.oif = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
  30                 fl.mark = (*pskb)->mark;
  31                 if (ip_route_output_key(&rt, &fl) != 0)
  32                         return -1;
  33
  34                 /* Drop old route. */
  35                 dst_release((*pskb)->dst);
  36                 (*pskb)->dst = &rt->u.dst;
  37         } else {
  38                 /* non-local src, find valid iif to satisfy
  39                  * rp-filter when calling ip_route_input. */
  40                 fl.nl_u.ip4_u.daddr = iph->saddr;
  41                 if (ip_route_output_key(&rt, &fl) != 0)
  42                         return -1;
  43
  44                 odst = (*pskb)->dst;
  45                 if (ip_route_input(*pskb, iph->daddr, iph->saddr,
  46                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  47                         dst_release(&rt->u.dst);
  48                         return -1;
  49                 }
  50                 dst_release(&rt->u.dst);
  51                 dst_release(odst);
  52         }
  53
  54         if ((*pskb)->dst->error)
  55                 return -1;
  56
  57 #ifdef CONFIG_XFRM
  58         if (!(IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  59             xfrm_decode_session(*pskb, &fl, AF_INET) == 0)
  60                 if (xfrm_lookup(&(*pskb)->dst, &fl, (*pskb)->sk, 0))
  61                         return -1;
  62 #endif
  63
  64         /* Change in oif may mean change in hh_len. */
  65         hh_len = (*pskb)->dst->dev->hard_header_len;
  66         if (skb_headroom(*pskb) < hh_len) {
  67                 struct sk_buff *nskb;
  68
  69                 nskb = skb_realloc_headroom(*pskb, hh_len);
  70                 if (!nskb)
  71                         return -1;
  72                 if ((*pskb)->sk)
  73                         skb_set_owner_w(nskb, (*pskb)->sk);
  74                 kfree_skb(*pskb);
  75                 *pskb = nskb;
  76         }
  77
  78         return 0;
  79 }
  80 EXPORT_SYMBOL(ip_route_me_harder);
  81
  82 #ifdef CONFIG_XFRM
  83 int ip_xfrm_me_harder(struct sk_buff **pskb)
  84 {
  85         struct flowi fl;
  86         unsigned int hh_len;
  87         struct dst_entry *dst;
  88
  89         if (IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED)
  90                 return 0;
  91         if (xfrm_decode_session(*pskb, &fl, AF_INET) < 0)
  92                 return -1;
  93
  94         dst = (*pskb)->dst;
  95         if (dst->xfrm)
  96                 dst = ((struct xfrm_dst *)dst)->route;
  97         dst_hold(dst);
  98
  99         if (xfrm_lookup(&dst, &fl, (*pskb)->sk, 0) < 0)
 100                 return -1;
 101
 102         dst_release((*pskb)->dst);
 103         (*pskb)->dst = dst;
 104
 105         /* Change in oif may mean change in hh_len. */
 106         hh_len = (*pskb)->dst->dev->hard_header_len;
 107         if (skb_headroom(*pskb) < hh_len) {
 108                 struct sk_buff *nskb;
 109
 110                 nskb = skb_realloc_headroom(*pskb, hh_len);
 111                 if (!nskb)
 112                         return -1;
 113                 if ((*pskb)->sk)
 114                         skb_set_owner_w(nskb, (*pskb)->sk);
 115                 kfree_skb(*pskb);
 116                 *pskb = nskb;
 117         }
 118         return 0;
 119 }
 120 EXPORT_SYMBOL(ip_xfrm_me_harder);
 121 #endif
 122
 123 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 124 EXPORT_SYMBOL(ip_nat_decode_session);
 125
 126 /*
 127  * Extra routing may needed on local out, as the QUEUE target never
 128  * returns control to the table.
 129  */
 130
 131 struct ip_rt_info {
 132         __be32 daddr;
 133         __be32 saddr;
 134         u_int8_t tos;
 135 };
 136
 137 static void nf_ip_saveroute(const struct sk_buff *skb, struct nf_info *info)
 138 {
 139         struct ip_rt_info *rt_info = nf_info_reroute(info);
 140
 141         if (info->hook == NF_IP_LOCAL_OUT) {
 142                 const struct iphdr *iph = skb->nh.iph;
 143
 144                 rt_info->tos = iph->tos;
 145                 rt_info->daddr = iph->daddr;
 146                 rt_info->saddr = iph->saddr;
 147         }
 148 }
 149
 150 static int nf_ip_reroute(struct sk_buff **pskb, const struct nf_info *info)
 151 {
 152         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 153
 154         if (info->hook == NF_IP_LOCAL_OUT) {
 155                 struct iphdr *iph = (*pskb)->nh.iph;
 156
 157                 if (!(iph->tos == rt_info->tos
 158                       && iph->daddr == rt_info->daddr
 159                       && iph->saddr == rt_info->saddr))
 160                         return ip_route_me_harder(pskb, RTN_UNSPEC);
 161         }
 162         return 0;
 163 }
 164
 165 unsigned int nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 166                             unsigned int dataoff, u_int8_t protocol)
 167 {
 168         struct iphdr *iph = skb->nh.iph;
 169         unsigned int csum = 0;
 170
 171         switch (skb->ip_summed) {
 172         case CHECKSUM_COMPLETE:
 173                 if (hook != NF_IP_PRE_ROUTING && hook != NF_IP_LOCAL_IN)
 174                         break;
 175                 if ((protocol == 0 && !(u16)csum_fold(skb->csum)) ||
 176                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 177                                        skb->len - dataoff, protocol,
 178                                        skb->csum)) {
 179                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 180                         break;
 181                 }
 182                 /* fall through */
 183         case CHECKSUM_NONE:
 184                 if (protocol == 0)
 185                         skb->csum = 0;
 186                 else
 187                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 188                                                        skb->len - dataoff,
 189                                                        protocol, 0);
 190                 csum = __skb_checksum_complete(skb);
 191         }
 192         return csum;
 193 }
 194
 195 EXPORT_SYMBOL(nf_ip_checksum);
 196
 197 static struct nf_afinfo nf_ip_afinfo = {
 198         .family         = AF_INET,
 199         .checksum       = nf_ip_checksum,
 200         .saveroute      = nf_ip_saveroute,
 201         .reroute        = nf_ip_reroute,
 202         .route_key_size = sizeof(struct ip_rt_info),
 203 };
 204
 205 static int ipv4_netfilter_init(void)
 206 {
 207         return nf_register_afinfo(&nf_ip_afinfo);
 208 }
 209
 210 static void ipv4_netfilter_fini(void)
 211 {
 212         nf_unregister_afinfo(&nf_ip_afinfo);
 213 }
 214
 215 module_init(ipv4_netfilter_init);
 216 module_exit(ipv4_netfilter_fini);