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)
  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         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  20          * packets with foreign saddr to appear on the NF_IP_LOCAL_OUT hook.
  21          */
  22         if (inet_addr_type(iph->saddr) == RTN_LOCAL) {
  23                 fl.nl_u.ip4_u.daddr = iph->daddr;
  24                 fl.nl_u.ip4_u.saddr = iph->saddr;
  25                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  26                 fl.oif = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
  27 #ifdef CONFIG_IP_ROUTE_FWMARK
  28                 fl.nl_u.ip4_u.fwmark = (*pskb)->nfmark;
  29 #endif
  30                 if (ip_route_output_key(&rt, &fl) != 0)
  31                         return -1;
  32
  33                 /* Drop old route. */
  34                 dst_release((*pskb)->dst);
  35                 (*pskb)->dst = &rt->u.dst;
  36         } else {
  37                 /* non-local src, find valid iif to satisfy
  38                  * rp-filter when calling ip_route_input. */
  39                 fl.nl_u.ip4_u.daddr = iph->saddr;
  40                 if (ip_route_output_key(&rt, &fl) != 0)
  41                         return -1;
  42
  43                 odst = (*pskb)->dst;
  44                 if (ip_route_input(*pskb, iph->daddr, iph->saddr,
  45                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  46                         dst_release(&rt->u.dst);
  47                         return -1;
  48                 }
  49                 dst_release(&rt->u.dst);
  50                 dst_release(odst);
  51         }
  52
  53         if ((*pskb)->dst->error)
  54                 return -1;
  55
  56 #ifdef CONFIG_XFRM
  57         if (!(IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  58             xfrm_decode_session(*pskb, &fl, AF_INET) == 0)
  59                 if (xfrm_lookup(&(*pskb)->dst, &fl, (*pskb)->sk, 0))
  60                         return -1;
  61 #endif
  62
  63         /* Change in oif may mean change in hh_len. */
  64         hh_len = (*pskb)->dst->dev->hard_header_len;
  65         if (skb_headroom(*pskb) < hh_len) {
  66                 struct sk_buff *nskb;
  67
  68                 nskb = skb_realloc_headroom(*pskb, hh_len);
  69                 if (!nskb)
  70                         return -1;
  71                 if ((*pskb)->sk)
  72                         skb_set_owner_w(nskb, (*pskb)->sk);
  73                 kfree_skb(*pskb);
  74                 *pskb = nskb;
  75         }
  76
  77         return 0;
  78 }
  79 EXPORT_SYMBOL(ip_route_me_harder);
  80
  81 #ifdef CONFIG_XFRM
  82 int ip_xfrm_me_harder(struct sk_buff **pskb)
  83 {
  84         struct flowi fl;
  85         unsigned int hh_len;
  86         struct dst_entry *dst;
  87
  88         if (IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED)
  89                 return 0;
  90         if (xfrm_decode_session(*pskb, &fl, AF_INET) < 0)
  91                 return -1;
  92
  93         dst = (*pskb)->dst;
  94         if (dst->xfrm)
  95                 dst = ((struct xfrm_dst *)dst)->route;
  96         dst_hold(dst);
  97
  98         if (xfrm_lookup(&dst, &fl, (*pskb)->sk, 0) < 0)
  99                 return -1;
 100
 101         dst_release((*pskb)->dst);
 102         (*pskb)->dst = dst;
 103
 104         /* Change in oif may mean change in hh_len. */
 105         hh_len = (*pskb)->dst->dev->hard_header_len;
 106         if (skb_headroom(*pskb) < hh_len) {
 107                 struct sk_buff *nskb;
 108
 109                 nskb = skb_realloc_headroom(*pskb, hh_len);
 110                 if (!nskb)
 111                         return -1;
 112                 if ((*pskb)->sk)
 113                         skb_set_owner_w(nskb, (*pskb)->sk);
 114                 kfree_skb(*pskb);
 115                 *pskb = nskb;
 116         }
 117         return 0;
 118 }
 119 EXPORT_SYMBOL(ip_xfrm_me_harder);
 120 #endif
 121
 122 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 123 EXPORT_SYMBOL(ip_nat_decode_session);
 124
 125 /*
 126  * Extra routing may needed on local out, as the QUEUE target never
 127  * returns control to the table.
 128  */
 129
 130 struct ip_rt_info {
 131         u_int32_t daddr;
 132         u_int32_t saddr;
 133         u_int8_t tos;
 134 };
 135
 136 static void nf_ip_saveroute(const struct sk_buff *skb, struct nf_info *info)
 137 {
 138         struct ip_rt_info *rt_info = nf_info_reroute(info);
 139
 140         if (info->hook == NF_IP_LOCAL_OUT) {
 141                 const struct iphdr *iph = skb->nh.iph;
 142
 143                 rt_info->tos = iph->tos;
 144                 rt_info->daddr = iph->daddr;
 145                 rt_info->saddr = iph->saddr;
 146         }
 147 }
 148
 149 static int nf_ip_reroute(struct sk_buff **pskb, const struct nf_info *info)
 150 {
 151         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 152
 153         if (info->hook == NF_IP_LOCAL_OUT) {
 154                 struct iphdr *iph = (*pskb)->nh.iph;
 155
 156                 if (!(iph->tos == rt_info->tos
 157                       && iph->daddr == rt_info->daddr
 158                       && iph->saddr == rt_info->saddr))
 159                         return ip_route_me_harder(pskb);
 160         }
 161         return 0;
 162 }
 163
 164 unsigned int nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 165                             unsigned int dataoff, u_int8_t protocol)
 166 {
 167         struct iphdr *iph = skb->nh.iph;
 168         unsigned int csum = 0;
 169
 170         switch (skb->ip_summed) {
 171         case CHECKSUM_HW:
 172                 if (hook != NF_IP_PRE_ROUTING && hook != NF_IP_LOCAL_IN)
 173                         break;
 174                 if ((protocol == 0 && !(u16)csum_fold(skb->csum)) ||
 175                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 176                                        skb->len - dataoff, protocol,
 177                                        skb->csum)) {
 178                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 179                         break;
 180                 }
 181                 /* fall through */
 182         case CHECKSUM_NONE:
 183                 if (protocol == 0)
 184                         skb->csum = 0;
 185                 else
 186                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 187                                                        skb->len - dataoff,
 188                                                        protocol, 0);
 189                 csum = __skb_checksum_complete(skb);
 190         }
 191         return csum;
 192 }
 193
 194 EXPORT_SYMBOL(nf_ip_checksum);
 195
 196 static struct nf_afinfo nf_ip_afinfo = {
 197         .family         = AF_INET,
 198         .checksum       = nf_ip_checksum,
 199         .saveroute      = nf_ip_saveroute,
 200         .reroute        = nf_ip_reroute,
 201         .route_key_size = sizeof(struct ip_rt_info),
 202 };
 203
 204 static int ipv4_netfilter_init(void)
 205 {
 206         return nf_register_afinfo(&nf_ip_afinfo);
 207 }
 208
 209 static void ipv4_netfilter_fini(void)
 210 {
 211         nf_unregister_afinfo(&nf_ip_afinfo);
 212 }
 213
 214 module_init(ipv4_netfilter_init);
 215 module_exit(ipv4_netfilter_fini);