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 flowi4 fl4 = {};
  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                 fl4.daddr = iph->daddr;
  35                 if (type == RTN_LOCAL)
  36                         fl4.saddr = iph->saddr;
  37                 fl4.flowi4_tos = RT_TOS(iph->tos);
  38                 fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
  39                 fl4.flowi4_mark = skb->mark;
  40                 fl4.flowi4_flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
  41                 rt = ip_route_output_key(net, &fl4);
  42                 if (IS_ERR(rt))
  43                         return -1;
  44
  45                 /* Drop old route. */
  46                 skb_dst_drop(skb);
  47                 skb_dst_set(skb, &rt->dst);
  48         } else {
  49                 /* non-local src, find valid iif to satisfy
  50                  * rp-filter when calling ip_route_input. */
  51                 fl4.daddr = iph->saddr;
  52                 rt = ip_route_output_key(net, &fl4);
  53                 if (IS_ERR(rt))
  54                         return -1;
  55
  56                 orefdst = skb->_skb_refdst;
  57                 if (ip_route_input(skb, iph->daddr, iph->saddr,
  58                                    RT_TOS(iph->tos), rt->dst.dev) != 0) {
  59                         dst_release(&rt->dst);
  60                         return -1;
  61                 }
  62                 dst_release(&rt->dst);
  63                 refdst_drop(orefdst);
  64         }
  65
  66         if (skb_dst(skb)->error)
  67                 return -1;
  68
  69 #ifdef CONFIG_XFRM
  70         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  71             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
  72                 struct dst_entry *dst = skb_dst(skb);
  73                 skb_dst_set(skb, NULL);
  74                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
  75                 if (IS_ERR(dst))
  76                         return -1;
  77                 skb_dst_set(skb, dst);
  78         }
  79 #endif
  80
  81         /* Change in oif may mean change in hh_len. */
  82         hh_len = skb_dst(skb)->dev->hard_header_len;
  83         if (skb_headroom(skb) < hh_len &&
  84             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
  85                 return -1;
  86
  87         return 0;
  88 }
  89 EXPORT_SYMBOL(ip_route_me_harder);
  90
  91 #ifdef CONFIG_XFRM
  92 int ip_xfrm_me_harder(struct sk_buff *skb)
  93 {
  94         struct flowi fl;
  95         unsigned int hh_len;
  96         struct dst_entry *dst;
  97
  98         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  99                 return 0;
 100         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
 101                 return -1;
 102
 103         dst = skb_dst(skb);
 104         if (dst->xfrm)
 105                 dst = ((struct xfrm_dst *)dst)->route;
 106         dst_hold(dst);
 107
 108         dst = xfrm_lookup(dev_net(dst->dev), dst, &fl, skb->sk, 0);
 109         if (IS_ERR(dst))
 110                 return -1;
 111
 112         skb_dst_drop(skb);
 113         skb_dst_set(skb, dst);
 114
 115         /* Change in oif may mean change in hh_len. */
 116         hh_len = skb_dst(skb)->dev->hard_header_len;
 117         if (skb_headroom(skb) < hh_len &&
 118             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 119                 return -1;
 120         return 0;
 121 }
 122 EXPORT_SYMBOL(ip_xfrm_me_harder);
 123 #endif
 124
 125 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 126 EXPORT_SYMBOL(ip_nat_decode_session);
 127
 128 /*
 129  * Extra routing may needed on local out, as the QUEUE target never
 130  * returns control to the table.
 131  */
 132
 133 struct ip_rt_info {
 134         __be32 daddr;
 135         __be32 saddr;
 136         u_int8_t tos;
 137         u_int32_t mark;
 138 };
 139
 140 static void nf_ip_saveroute(const struct sk_buff *skb,
 141                             struct nf_queue_entry *entry)
 142 {
 143         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 144
 145         if (entry->hook == NF_INET_LOCAL_OUT) {
 146                 const struct iphdr *iph = ip_hdr(skb);
 147
 148                 rt_info->tos = iph->tos;
 149                 rt_info->daddr = iph->daddr;
 150                 rt_info->saddr = iph->saddr;
 151                 rt_info->mark = skb->mark;
 152         }
 153 }
 154
 155 static int nf_ip_reroute(struct sk_buff *skb,
 156                          const struct nf_queue_entry *entry)
 157 {
 158         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 159
 160         if (entry->hook == NF_INET_LOCAL_OUT) {
 161                 const struct iphdr *iph = ip_hdr(skb);
 162
 163                 if (!(iph->tos == rt_info->tos &&
 164                       skb->mark == rt_info->mark &&
 165                       iph->daddr == rt_info->daddr &&
 166                       iph->saddr == rt_info->saddr))
 167                         return ip_route_me_harder(skb, RTN_UNSPEC);
 168         }
 169         return 0;
 170 }
 171
 172 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 173                             unsigned int dataoff, u_int8_t protocol)
 174 {
 175         const struct iphdr *iph = ip_hdr(skb);
 176         __sum16 csum = 0;
 177
 178         switch (skb->ip_summed) {
 179         case CHECKSUM_COMPLETE:
 180                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 181                         break;
 182                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 183                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 184                                        skb->len - dataoff, protocol,
 185                                        skb->csum)) {
 186                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 187                         break;
 188                 }
 189                 /* fall through */
 190         case CHECKSUM_NONE:
 191                 if (protocol == 0)
 192                         skb->csum = 0;
 193                 else
 194                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 195                                                        skb->len - dataoff,
 196                                                        protocol, 0);
 197                 csum = __skb_checksum_complete(skb);
 198         }
 199         return csum;
 200 }
 201 EXPORT_SYMBOL(nf_ip_checksum);
 202
 203 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 204                                       unsigned int dataoff, unsigned int len,
 205                                       u_int8_t protocol)
 206 {
 207         const struct iphdr *iph = ip_hdr(skb);
 208         __sum16 csum = 0;
 209
 210         switch (skb->ip_summed) {
 211         case CHECKSUM_COMPLETE:
 212                 if (len == skb->len - dataoff)
 213                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 214                 /* fall through */
 215         case CHECKSUM_NONE:
 216                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 217                                                skb->len - dataoff, 0);
 218                 skb->ip_summed = CHECKSUM_NONE;
 219                 return __skb_checksum_complete_head(skb, dataoff + len);
 220         }
 221         return csum;
 222 }
 223
 224 static int nf_ip_route(struct net *net, struct dst_entry **dst,
 225                        struct flowi *fl, bool strict __always_unused)
 226 {
 227         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 228         if (IS_ERR(rt))
 229                 return PTR_ERR(rt);
 230         *dst = &rt->dst;
 231         return 0;
 232 }
 233
 234 static const struct nf_afinfo nf_ip_afinfo = {
 235         .family                 = AF_INET,
 236         .checksum               = nf_ip_checksum,
 237         .checksum_partial       = nf_ip_checksum_partial,
 238         .route                  = nf_ip_route,
 239         .saveroute              = nf_ip_saveroute,
 240         .reroute                = nf_ip_reroute,
 241         .route_key_size         = sizeof(struct ip_rt_info),
 242 };
 243
 244 static int ipv4_netfilter_init(void)
 245 {
 246         return nf_register_afinfo(&nf_ip_afinfo);
 247 }
 248
 249 static void ipv4_netfilter_fini(void)
 250 {
 251         nf_unregister_afinfo(&nf_ip_afinfo);
 252 }
 253
 254 module_init(ipv4_netfilter_init);
 255 module_exit(ipv4_netfilter_fini);
 256
 257 #ifdef CONFIG_SYSCTL
 258 struct ctl_path nf_net_ipv4_netfilter_sysctl_path[] = {
 259         { .procname = "net", },
 260         { .procname = "ipv4", },
 261         { .procname = "netfilter", },
 262         { }
 263 };
 264 EXPORT_SYMBOL_GPL(nf_net_ipv4_netfilter_sysctl_path);
 265 #endif /* CONFIG_SYSCTL */