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   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(skb)->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                 skb_dst_drop(skb);
  45                 skb_dst_set(skb, &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(skb);
  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(skb)->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                 struct dst_entry *dst = skb_dst(skb);
  70                 skb_dst_set(skb, NULL);
  71                 if (xfrm_lookup(net, &dst, &fl, skb->sk, 0))
  72                         return -1;
  73                 skb_dst_set(skb, dst);
  74         }
  75 #endif
  76
  77         /* Change in oif may mean change in hh_len. */
  78         hh_len = skb_dst(skb)->dev->hard_header_len;
  79         if (skb_headroom(skb) < hh_len &&
  80             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
  81                 return -1;
  82
  83         return 0;
  84 }
  85 EXPORT_SYMBOL(ip_route_me_harder);
  86
  87 #ifdef CONFIG_XFRM
  88 int ip_xfrm_me_harder(struct sk_buff *skb)
  89 {
  90         struct flowi fl;
  91         unsigned int hh_len;
  92         struct dst_entry *dst;
  93
  94         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  95                 return 0;
  96         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
  97                 return -1;
  98
  99         dst = skb_dst(skb);
 100         if (dst->xfrm)
 101                 dst = ((struct xfrm_dst *)dst)->route;
 102         dst_hold(dst);
 103
 104         if (xfrm_lookup(dev_net(dst->dev), &dst, &fl, skb->sk, 0) < 0)
 105                 return -1;
 106
 107         skb_dst_drop(skb);
 108         skb_dst_set(skb, dst);
 109
 110         /* Change in oif may mean change in hh_len. */
 111         hh_len = skb_dst(skb)->dev->hard_header_len;
 112         if (skb_headroom(skb) < hh_len &&
 113             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 114                 return -1;
 115         return 0;
 116 }
 117 EXPORT_SYMBOL(ip_xfrm_me_harder);
 118 #endif
 119
 120 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 121 EXPORT_SYMBOL(ip_nat_decode_session);
 122
 123 /*
 124  * Extra routing may needed on local out, as the QUEUE target never
 125  * returns control to the table.
 126  */
 127
 128 struct ip_rt_info {
 129         __be32 daddr;
 130         __be32 saddr;
 131         u_int8_t tos;
 132         u_int32_t mark;
 133 };
 134
 135 static void nf_ip_saveroute(const struct sk_buff *skb,
 136                             struct nf_queue_entry *entry)
 137 {
 138         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 139
 140         if (entry->hook == NF_INET_LOCAL_OUT) {
 141                 const struct iphdr *iph = ip_hdr(skb);
 142
 143                 rt_info->tos = iph->tos;
 144                 rt_info->daddr = iph->daddr;
 145                 rt_info->saddr = iph->saddr;
 146                 rt_info->mark = skb->mark;
 147         }
 148 }
 149
 150 static int nf_ip_reroute(struct sk_buff *skb,
 151                          const struct nf_queue_entry *entry)
 152 {
 153         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 154
 155         if (entry->hook == NF_INET_LOCAL_OUT) {
 156                 const struct iphdr *iph = ip_hdr(skb);
 157
 158                 if (!(iph->tos == rt_info->tos &&
 159                       skb->mark == rt_info->mark &&
 160                       iph->daddr == rt_info->daddr &&
 161                       iph->saddr == rt_info->saddr))
 162                         return ip_route_me_harder(skb, RTN_UNSPEC);
 163         }
 164         return 0;
 165 }
 166
 167 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 168                             unsigned int dataoff, u_int8_t protocol)
 169 {
 170         const struct iphdr *iph = ip_hdr(skb);
 171         __sum16 csum = 0;
 172
 173         switch (skb->ip_summed) {
 174         case CHECKSUM_COMPLETE:
 175                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 176                         break;
 177                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 178                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 179                                        skb->len - dataoff, protocol,
 180                                        skb->csum)) {
 181                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 182                         break;
 183                 }
 184                 /* fall through */
 185         case CHECKSUM_NONE:
 186                 if (protocol == 0)
 187                         skb->csum = 0;
 188                 else
 189                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 190                                                        skb->len - dataoff,
 191                                                        protocol, 0);
 192                 csum = __skb_checksum_complete(skb);
 193         }
 194         return csum;
 195 }
 196 EXPORT_SYMBOL(nf_ip_checksum);
 197
 198 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 199                                       unsigned int dataoff, unsigned int len,
 200                                       u_int8_t protocol)
 201 {
 202         const struct iphdr *iph = ip_hdr(skb);
 203         __sum16 csum = 0;
 204
 205         switch (skb->ip_summed) {
 206         case CHECKSUM_COMPLETE:
 207                 if (len == skb->len - dataoff)
 208                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 209                 /* fall through */
 210         case CHECKSUM_NONE:
 211                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 212                                                skb->len - dataoff, 0);
 213                 skb->ip_summed = CHECKSUM_NONE;
 214                 csum = __skb_checksum_complete_head(skb, dataoff + len);
 215                 if (!csum)
 216                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 217         }
 218         return csum;
 219 }
 220
 221 static int nf_ip_route(struct dst_entry **dst, struct flowi *fl)
 222 {
 223         return ip_route_output_key(&init_net, (struct rtable **)dst, fl);
 224 }
 225
 226 static const struct nf_afinfo nf_ip_afinfo = {
 227         .family                 = AF_INET,
 228         .checksum               = nf_ip_checksum,
 229         .checksum_partial       = nf_ip_checksum_partial,
 230         .route                  = nf_ip_route,
 231         .saveroute              = nf_ip_saveroute,
 232         .reroute                = nf_ip_reroute,
 233         .route_key_size         = sizeof(struct ip_rt_info),
 234 };
 235
 236 static int ipv4_netfilter_init(void)
 237 {
 238         return nf_register_afinfo(&nf_ip_afinfo);
 239 }
 240
 241 static void ipv4_netfilter_fini(void)
 242 {
 243         nf_unregister_afinfo(&nf_ip_afinfo);
 244 }
 245
 246 module_init(ipv4_netfilter_init);
 247 module_exit(ipv4_netfilter_fini);
 248
 249 #ifdef CONFIG_SYSCTL
 250 struct ctl_path nf_net_ipv4_netfilter_sysctl_path[] = {
 251         { .procname = "net", },
 252         { .procname = "ipv4", },
 253         { .procname = "netfilter", },
 254         { }
 255 };
 256 EXPORT_SYMBOL_GPL(nf_net_ipv4_netfilter_sysctl_path);
 257 #endif /* CONFIG_SYSCTL */