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 <linux/gfp.h>
   8 #include <net/route.h>
   9 #include <net/xfrm.h>
  10 #include <net/ip.h>
  11 #include <net/netfilter/nf_queue.h>
  12
  13 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  14 int ip_route_me_harder(struct sk_buff *skb, unsigned addr_type)
  15 {
  16         struct net *net = dev_net(skb_dst(skb)->dev);
  17         const struct iphdr *iph = ip_hdr(skb);
  18         struct rtable *rt;
  19         struct flowi fl = {};
  20         unsigned long orefdst;
  21         unsigned int hh_len;
  22         unsigned int type;
  23
  24         type = inet_addr_type(net, iph->saddr);
  25         if (skb->sk && inet_sk(skb->sk)->transparent)
  26                 type = RTN_LOCAL;
  27         if (addr_type == RTN_UNSPEC)
  28                 addr_type = type;
  29
  30         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  31          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  32          */
  33         if (addr_type == RTN_LOCAL) {
  34                 fl.fl4_dst = iph->daddr;
  35                 if (type == RTN_LOCAL)
  36                         fl.fl4_src = iph->saddr;
  37                 fl.fl4_tos = RT_TOS(iph->tos);
  38                 fl.oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
  39                 fl.mark = skb->mark;
  40                 fl.flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
  41                 if (ip_route_output_key(net, &rt, &fl) != 0)
  42                         return -1;
  43
  44                 /* Drop old route. */
  45                 skb_dst_drop(skb);
  46                 skb_dst_set(skb, &rt->dst);
  47         } else {
  48                 /* non-local src, find valid iif to satisfy
  49                  * rp-filter when calling ip_route_input. */
  50                 fl.fl4_dst = iph->saddr;
  51                 if (ip_route_output_key(net, &rt, &fl) != 0)
  52                         return -1;
  53
  54                 orefdst = skb->_skb_refdst;
  55                 if (ip_route_input(skb, iph->daddr, iph->saddr,
  56                                    RT_TOS(iph->tos), rt->dst.dev) != 0) {
  57                         dst_release(&rt->dst);
  58                         return -1;
  59                 }
  60                 dst_release(&rt->dst);
  61                 refdst_drop(orefdst);
  62         }
  63
  64         if (skb_dst(skb)->error)
  65                 return -1;
  66
  67 #ifdef CONFIG_XFRM
  68         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  69             xfrm_decode_session(skb, &fl, AF_INET) == 0) {
  70                 struct dst_entry *dst = skb_dst(skb);
  71                 skb_dst_set(skb, NULL);
  72                 if (xfrm_lookup(net, &dst, &fl, skb->sk, 0))
  73                         return -1;
  74                 skb_dst_set(skb, dst);
  75         }
  76 #endif
  77
  78         /* Change in oif may mean change in hh_len. */
  79         hh_len = skb_dst(skb)->dev->hard_header_len;
  80         if (skb_headroom(skb) < hh_len &&
  81             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
  82                 return -1;
  83
  84         return 0;
  85 }
  86 EXPORT_SYMBOL(ip_route_me_harder);
  87
  88 #ifdef CONFIG_XFRM
  89 int ip_xfrm_me_harder(struct sk_buff *skb)
  90 {
  91         struct flowi fl;
  92         unsigned int hh_len;
  93         struct dst_entry *dst;
  94
  95         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  96                 return 0;
  97         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
  98                 return -1;
  99
 100         dst = skb_dst(skb);
 101         if (dst->xfrm)
 102                 dst = ((struct xfrm_dst *)dst)->route;
 103         dst_hold(dst);
 104
 105         if (xfrm_lookup(dev_net(dst->dev), &dst, &fl, skb->sk, 0) < 0)
 106                 return -1;
 107
 108         skb_dst_drop(skb);
 109         skb_dst_set(skb, dst);
 110
 111         /* Change in oif may mean change in hh_len. */
 112         hh_len = skb_dst(skb)->dev->hard_header_len;
 113         if (skb_headroom(skb) < hh_len &&
 114             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 115                 return -1;
 116         return 0;
 117 }
 118 EXPORT_SYMBOL(ip_xfrm_me_harder);
 119 #endif
 120
 121 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 122 EXPORT_SYMBOL(ip_nat_decode_session);
 123
 124 /*
 125  * Extra routing may needed on local out, as the QUEUE target never
 126  * returns control to the table.
 127  */
 128
 129 struct ip_rt_info {
 130         __be32 daddr;
 131         __be32 saddr;
 132         u_int8_t tos;
 133         u_int32_t mark;
 134 };
 135
 136 static void nf_ip_saveroute(const struct sk_buff *skb,
 137                             struct nf_queue_entry *entry)
 138 {
 139         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 140
 141         if (entry->hook == NF_INET_LOCAL_OUT) {
 142                 const struct iphdr *iph = ip_hdr(skb);
 143
 144                 rt_info->tos = iph->tos;
 145                 rt_info->daddr = iph->daddr;
 146                 rt_info->saddr = iph->saddr;
 147                 rt_info->mark = skb->mark;
 148         }
 149 }
 150
 151 static int nf_ip_reroute(struct sk_buff *skb,
 152                          const struct nf_queue_entry *entry)
 153 {
 154         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 155
 156         if (entry->hook == NF_INET_LOCAL_OUT) {
 157                 const struct iphdr *iph = ip_hdr(skb);
 158
 159                 if (!(iph->tos == rt_info->tos &&
 160                       skb->mark == rt_info->mark &&
 161                       iph->daddr == rt_info->daddr &&
 162                       iph->saddr == rt_info->saddr))
 163                         return ip_route_me_harder(skb, RTN_UNSPEC);
 164         }
 165         return 0;
 166 }
 167
 168 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 169                             unsigned int dataoff, u_int8_t protocol)
 170 {
 171         const struct iphdr *iph = ip_hdr(skb);
 172         __sum16 csum = 0;
 173
 174         switch (skb->ip_summed) {
 175         case CHECKSUM_COMPLETE:
 176                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 177                         break;
 178                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 179                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 180                                        skb->len - dataoff, protocol,
 181                                        skb->csum)) {
 182                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 183                         break;
 184                 }
 185                 /* fall through */
 186         case CHECKSUM_NONE:
 187                 if (protocol == 0)
 188                         skb->csum = 0;
 189                 else
 190                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 191                                                        skb->len - dataoff,
 192                                                        protocol, 0);
 193                 csum = __skb_checksum_complete(skb);
 194         }
 195         return csum;
 196 }
 197 EXPORT_SYMBOL(nf_ip_checksum);
 198
 199 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 200                                       unsigned int dataoff, unsigned int len,
 201                                       u_int8_t protocol)
 202 {
 203         const struct iphdr *iph = ip_hdr(skb);
 204         __sum16 csum = 0;
 205
 206         switch (skb->ip_summed) {
 207         case CHECKSUM_COMPLETE:
 208                 if (len == skb->len - dataoff)
 209                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 210                 /* fall through */
 211         case CHECKSUM_NONE:
 212                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 213                                                skb->len - dataoff, 0);
 214                 skb->ip_summed = CHECKSUM_NONE;
 215                 return __skb_checksum_complete_head(skb, dataoff + len);
 216         }
 217         return csum;
 218 }
 219
 220 static int nf_ip_route(struct dst_entry **dst, struct flowi *fl)
 221 {
 222         return ip_route_output_key(&init_net, (struct rtable **)dst, fl);
 223 }
 224
 225 static const struct nf_afinfo nf_ip_afinfo = {
 226         .family                 = AF_INET,
 227         .checksum               = nf_ip_checksum,
 228         .checksum_partial       = nf_ip_checksum_partial,
 229         .route                  = nf_ip_route,
 230         .saveroute              = nf_ip_saveroute,
 231         .reroute                = nf_ip_reroute,
 232         .route_key_size         = sizeof(struct ip_rt_info),
 233 };
 234
 235 static int ipv4_netfilter_init(void)
 236 {
 237         return nf_register_afinfo(&nf_ip_afinfo);
 238 }
 239
 240 static void ipv4_netfilter_fini(void)
 241 {
 242         nf_unregister_afinfo(&nf_ip_afinfo);
 243 }
 244
 245 module_init(ipv4_netfilter_init);
 246 module_exit(ipv4_netfilter_fini);
 247
 248 #ifdef CONFIG_SYSCTL
 249 struct ctl_path nf_net_ipv4_netfilter_sysctl_path[] = {
 250         { .procname = "net", },
 251         { .procname = "ipv4", },
 252         { .procname = "netfilter", },
 253         { }
 254 };
 255 EXPORT_SYMBOL_GPL(nf_net_ipv4_netfilter_sysctl_path);
 256 #endif /* CONFIG_SYSCTL */