net/ipv4/netfilter.c

   1 /* IPv4 specific functions of netfilter core */
   2
   3 #include <linux/config.h>
   4 #ifdef CONFIG_NETFILTER
   5
   6 #include <linux/kernel.h>
   7 #include <linux/netfilter.h>
   8 #include <linux/netfilter_ipv4.h>
   9
  10 #include <linux/ip.h>
  11 #include <linux/tcp.h>
  12 #include <linux/udp.h>
  13 #include <linux/icmp.h>
  14 #include <net/route.h>
  15 #include <net/xfrm.h>
  16 #include <net/ip.h>
  17
  18 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  19 int ip_route_me_harder(struct sk_buff **pskb)
  20 {
  21         struct iphdr *iph = (*pskb)->nh.iph;
  22         struct rtable *rt;
  23         struct flowi fl = {};
  24         struct dst_entry *odst;
  25         unsigned int hh_len;
  26
  27         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  28          * packets with foreign saddr to appear on the NF_IP_LOCAL_OUT hook.
  29          */
  30         if (inet_addr_type(iph->saddr) == RTN_LOCAL) {
  31                 fl.nl_u.ip4_u.daddr = iph->daddr;
  32                 fl.nl_u.ip4_u.saddr = iph->saddr;
  33                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  34                 fl.oif = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
  35 #ifdef CONFIG_IP_ROUTE_FWMARK
  36                 fl.nl_u.ip4_u.fwmark = (*pskb)->nfmark;
  37 #endif
  38                 if (ip_route_output_key(&rt, &fl) != 0)
  39                         return -1;
  40
  41                 /* Drop old route. */
  42                 dst_release((*pskb)->dst);
  43                 (*pskb)->dst = &rt->u.dst;
  44         } else {
  45                 /* non-local src, find valid iif to satisfy
  46                  * rp-filter when calling ip_route_input. */
  47                 fl.nl_u.ip4_u.daddr = iph->saddr;
  48                 if (ip_route_output_key(&rt, &fl) != 0)
  49                         return -1;
  50
  51                 odst = (*pskb)->dst;
  52                 if (ip_route_input(*pskb, iph->daddr, iph->saddr,
  53                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  54                         dst_release(&rt->u.dst);
  55                         return -1;
  56                 }
  57                 dst_release(&rt->u.dst);
  58                 dst_release(odst);
  59         }
  60
  61         if ((*pskb)->dst->error)
  62                 return -1;
  63
  64 #ifdef CONFIG_XFRM
  65         if (!(IPCB(*pskb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  66             xfrm_decode_session(*pskb, &fl, AF_INET) == 0)
  67                 if (xfrm_lookup(&(*pskb)->dst, &fl, (*pskb)->sk, 0))
  68                         return -1;
  69 #endif
  70
  71         /* Change in oif may mean change in hh_len. */
  72         hh_len = (*pskb)->dst->dev->hard_header_len;
  73         if (skb_headroom(*pskb) < hh_len) {
  74                 struct sk_buff *nskb;
  75
  76                 nskb = skb_realloc_headroom(*pskb, hh_len);
  77                 if (!nskb)
  78                         return -1;
  79                 if ((*pskb)->sk)
  80                         skb_set_owner_w(nskb, (*pskb)->sk);
  81                 kfree_skb(*pskb);
  82                 *pskb = nskb;
  83         }
  84
  85         return 0;
  86 }
  87 EXPORT_SYMBOL(ip_route_me_harder);
  88
  89 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
  90 EXPORT_SYMBOL(ip_nat_decode_session);
  91
  92 /*
  93  * Extra routing may needed on local out, as the QUEUE target never
  94  * returns control to the table.
  95  */
  96
  97 struct ip_rt_info {
  98         u_int32_t daddr;
  99         u_int32_t saddr;
 100         u_int8_t tos;
 101 };
 102
 103 static void queue_save(const struct sk_buff *skb, struct nf_info *info)
 104 {
 105         struct ip_rt_info *rt_info = nf_info_reroute(info);
 106
 107         if (info->hook == NF_IP_LOCAL_OUT) {
 108                 const struct iphdr *iph = skb->nh.iph;
 109
 110                 rt_info->tos = iph->tos;
 111                 rt_info->daddr = iph->daddr;
 112                 rt_info->saddr = iph->saddr;
 113         }
 114 }
 115
 116 static int queue_reroute(struct sk_buff **pskb, const struct nf_info *info)
 117 {
 118         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 119
 120         if (info->hook == NF_IP_LOCAL_OUT) {
 121                 struct iphdr *iph = (*pskb)->nh.iph;
 122
 123                 if (!(iph->tos == rt_info->tos
 124                       && iph->daddr == rt_info->daddr
 125                       && iph->saddr == rt_info->saddr))
 126                         return ip_route_me_harder(pskb);
 127         }
 128         return 0;
 129 }
 130
 131 static struct nf_queue_rerouter ip_reroute = {
 132         .rer_size       = sizeof(struct ip_rt_info),
 133         .save           = queue_save,
 134         .reroute        = queue_reroute,
 135 };
 136
 137 static int init(void)
 138 {
 139         return nf_register_queue_rerouter(PF_INET, &ip_reroute);
 140 }
 141
 142 static void fini(void)
 143 {
 144         nf_unregister_queue_rerouter(PF_INET);
 145 }
 146
 147 module_init(init);
 148 module_exit(fini);
 149
 150 #endif /* CONFIG_NETFILTER */