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         struct net *net = dev_net(skb->dst->dev);
  16         const struct iphdr *iph = ip_hdr(skb);
  17         struct rtable *rt;
  18         struct flowi fl = {};
  19         struct dst_entry *odst;
  20         unsigned int hh_len;
  21         unsigned int type;
  22
  23         type = inet_addr_type(net, iph->saddr);
  24         if (skb->sk && inet_sk(skb->sk)->transparent)
  25                 type = RTN_LOCAL;
  26         if (addr_type == RTN_UNSPEC)
  27                 addr_type = type;
  28
  29         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  30          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  31          */
  32         if (addr_type == RTN_LOCAL) {
  33                 fl.nl_u.ip4_u.daddr = iph->daddr;
  34                 if (type == RTN_LOCAL)
  35                         fl.nl_u.ip4_u.saddr = iph->saddr;
  36                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  37                 fl.oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
  38                 fl.mark = skb->mark;
  39                 fl.flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
  40                 if (ip_route_output_key(net, &rt, &fl) != 0)
  41                         return -1;
  42
  43                 /* Drop old route. */
  44                 dst_release(skb->dst);
  45                 skb->dst = &rt->u.dst;
  46         } else {
  47                 /* non-local src, find valid iif to satisfy
  48                  * rp-filter when calling ip_route_input. */
  49                 fl.nl_u.ip4_u.daddr = iph->saddr;
  50                 if (ip_route_output_key(net, &rt, &fl) != 0)
  51                         return -1;
  52
  53                 odst = skb->dst;
  54                 if (ip_route_input(skb, iph->daddr, iph->saddr,
  55                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  56                         dst_release(&rt->u.dst);
  57                         return -1;
  58                 }
  59                 dst_release(&rt->u.dst);
  60                 dst_release(odst);
  61         }
  62
  63         if (skb->dst->error)
  64                 return -1;
  65
  66 #ifdef CONFIG_XFRM
  67         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  68             xfrm_decode_session(skb, &fl, AF_INET) == 0)
  69                 if (xfrm_lookup(&skb->dst, &fl, skb->sk, 0))
  70                         return -1;
  71 #endif
  72
  73         /* Change in oif may mean change in hh_len. */
  74         hh_len = skb->dst->dev->hard_header_len;
  75         if (skb_headroom(skb) < hh_len &&
  76             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
  77                 return -1;
  78
  79         return 0;
  80 }
  81 EXPORT_SYMBOL(ip_route_me_harder);
  82
  83 #ifdef CONFIG_XFRM
  84 int ip_xfrm_me_harder(struct sk_buff *skb)
  85 {
  86         struct flowi fl;
  87         unsigned int hh_len;
  88         struct dst_entry *dst;
  89
  90         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  91                 return 0;
  92         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
  93                 return -1;
  94
  95         dst = skb->dst;
  96         if (dst->xfrm)
  97                 dst = ((struct xfrm_dst *)dst)->route;
  98         dst_hold(dst);
  99
 100         if (xfrm_lookup(&dst, &fl, skb->sk, 0) < 0)
 101                 return -1;
 102
 103         dst_release(skb->dst);
 104         skb->dst = dst;
 105
 106         /* Change in oif may mean change in hh_len. */
 107         hh_len = skb->dst->dev->hard_header_len;
 108         if (skb_headroom(skb) < hh_len &&
 109             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 110                 return -1;
 111         return 0;
 112 }
 113 EXPORT_SYMBOL(ip_xfrm_me_harder);
 114 #endif
 115
 116 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 117 EXPORT_SYMBOL(ip_nat_decode_session);
 118
 119 /*
 120  * Extra routing may needed on local out, as the QUEUE target never
 121  * returns control to the table.
 122  */
 123
 124 struct ip_rt_info {
 125         __be32 daddr;
 126         __be32 saddr;
 127         u_int8_t tos;
 128 };
 129
 130 static void nf_ip_saveroute(const struct sk_buff *skb,
 131                             struct nf_queue_entry *entry)
 132 {
 133         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 134
 135         if (entry->hook == NF_INET_LOCAL_OUT) {
 136                 const struct iphdr *iph = ip_hdr(skb);
 137
 138                 rt_info->tos = iph->tos;
 139                 rt_info->daddr = iph->daddr;
 140                 rt_info->saddr = iph->saddr;
 141         }
 142 }
 143
 144 static int nf_ip_reroute(struct sk_buff *skb,
 145                          const struct nf_queue_entry *entry)
 146 {
 147         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 148
 149         if (entry->hook == NF_INET_LOCAL_OUT) {
 150                 const struct iphdr *iph = ip_hdr(skb);
 151
 152                 if (!(iph->tos == rt_info->tos
 153                       && iph->daddr == rt_info->daddr
 154                       && iph->saddr == rt_info->saddr))
 155                         return ip_route_me_harder(skb, RTN_UNSPEC);
 156         }
 157         return 0;
 158 }
 159
 160 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 161                             unsigned int dataoff, u_int8_t protocol)
 162 {
 163         const struct iphdr *iph = ip_hdr(skb);
 164         __sum16 csum = 0;
 165
 166         switch (skb->ip_summed) {
 167         case CHECKSUM_COMPLETE:
 168                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 169                         break;
 170                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 171                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 172                                        skb->len - dataoff, protocol,
 173                                        skb->csum)) {
 174                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 175                         break;
 176                 }
 177                 /* fall through */
 178         case CHECKSUM_NONE:
 179                 if (protocol == 0)
 180                         skb->csum = 0;
 181                 else
 182                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 183                                                        skb->len - dataoff,
 184                                                        protocol, 0);
 185                 csum = __skb_checksum_complete(skb);
 186         }
 187         return csum;
 188 }
 189 EXPORT_SYMBOL(nf_ip_checksum);
 190
 191 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 192                                       unsigned int dataoff, unsigned int len,
 193                                       u_int8_t protocol)
 194 {
 195         const struct iphdr *iph = ip_hdr(skb);
 196         __sum16 csum = 0;
 197
 198         switch (skb->ip_summed) {
 199         case CHECKSUM_COMPLETE:
 200                 if (len == skb->len - dataoff)
 201                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 202                 /* fall through */
 203         case CHECKSUM_NONE:
 204                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 205                                                skb->len - dataoff, 0);
 206                 skb->ip_summed = CHECKSUM_NONE;
 207                 csum = __skb_checksum_complete_head(skb, dataoff + len);
 208                 if (!csum)
 209                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 210         }
 211         return csum;
 212 }
 213
 214 static int nf_ip_route(struct dst_entry **dst, struct flowi *fl)
 215 {
 216         return ip_route_output_key(&init_net, (struct rtable **)dst, fl);
 217 }
 218
 219 static const struct nf_afinfo nf_ip_afinfo = {
 220         .family                 = AF_INET,
 221         .checksum               = nf_ip_checksum,
 222         .checksum_partial       = nf_ip_checksum_partial,
 223         .route                  = nf_ip_route,
 224         .saveroute              = nf_ip_saveroute,
 225         .reroute                = nf_ip_reroute,
 226         .route_key_size         = sizeof(struct ip_rt_info),
 227 };
 228
 229 static int ipv4_netfilter_init(void)
 230 {
 231         return nf_register_afinfo(&nf_ip_afinfo);
 232 }
 233
 234 static void ipv4_netfilter_fini(void)
 235 {
 236         nf_unregister_afinfo(&nf_ip_afinfo);
 237 }
 238
 239 module_init(ipv4_netfilter_init);
 240 module_exit(ipv4_netfilter_fini);
 241
 242 #ifdef CONFIG_SYSCTL
 243 struct ctl_path nf_net_ipv4_netfilter_sysctl_path[] = {
 244         { .procname = "net", .ctl_name = CTL_NET, },
 245         { .procname = "ipv4", .ctl_name = NET_IPV4, },
 246         { .procname = "netfilter", .ctl_name = NET_IPV4_NETFILTER, },
 247         { }
 248 };
 249 EXPORT_SYMBOL_GPL(nf_net_ipv4_netfilter_sysctl_path);
 250 #endif /* CONFIG_SYSCTL */