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