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