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 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
  82 EXPORT_SYMBOL(ip_nat_decode_session);
  83
  84 /*
  85  * Extra routing may needed on local out, as the QUEUE target never
  86  * returns control to the table.
  87  */
  88
  89 struct ip_rt_info {
  90         u_int32_t daddr;
  91         u_int32_t saddr;
  92         u_int8_t tos;
  93 };
  94
  95 static void queue_save(const struct sk_buff *skb, struct nf_info *info)
  96 {
  97         struct ip_rt_info *rt_info = nf_info_reroute(info);
  98
  99         if (info->hook == NF_IP_LOCAL_OUT) {
 100                 const struct iphdr *iph = skb->nh.iph;
 101
 102                 rt_info->tos = iph->tos;
 103                 rt_info->daddr = iph->daddr;
 104                 rt_info->saddr = iph->saddr;
 105         }
 106 }
 107
 108 static int queue_reroute(struct sk_buff **pskb, const struct nf_info *info)
 109 {
 110         const struct ip_rt_info *rt_info = nf_info_reroute(info);
 111
 112         if (info->hook == NF_IP_LOCAL_OUT) {
 113                 struct iphdr *iph = (*pskb)->nh.iph;
 114
 115                 if (!(iph->tos == rt_info->tos
 116                       && iph->daddr == rt_info->daddr
 117                       && iph->saddr == rt_info->saddr))
 118                         return ip_route_me_harder(pskb);
 119         }
 120         return 0;
 121 }
 122
 123 static struct nf_queue_rerouter ip_reroute = {
 124         .rer_size       = sizeof(struct ip_rt_info),
 125         .save           = queue_save,
 126         .reroute        = queue_reroute,
 127 };
 128
 129 static int init(void)
 130 {
 131         return nf_register_queue_rerouter(PF_INET, &ip_reroute);
 132 }
 133
 134 static void fini(void)
 135 {
 136         nf_unregister_queue_rerouter(PF_INET);
 137 }
 138
 139 module_init(init);
 140 module_exit(fini);