net/ipv4/netfilter.c

   1 /*
   2  * IPv4 specific functions of netfilter core
   3  *
   4  * Rusty Russell (C) 2000 -- This code is GPL.
   5  * Patrick McHardy (C) 2006-2012
   6  */
   7 #include <linux/kernel.h>
   8 #include <linux/netfilter.h>
   9 #include <linux/netfilter_ipv4.h>
  10 #include <linux/ip.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/gfp.h>
  13 #include <linux/export.h>
  14 #include <net/route.h>
  15 #include <net/xfrm.h>
  16 #include <net/ip.h>
  17 #include <net/netfilter/nf_queue.h>
  18
  19 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  20 int ip_route_me_harder(struct sk_buff *skb, unsigned int addr_type)
  21 {
  22         struct net *net = dev_net(skb_dst(skb)->dev);
  23         const struct iphdr *iph = ip_hdr(skb);
  24         struct rtable *rt;
  25         struct flowi4 fl4 = {};
  26         __be32 saddr = iph->saddr;
  27         __u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
  28         unsigned int hh_len;
  29
  30         if (addr_type == RTN_UNSPEC)
  31                 addr_type = inet_addr_type(net, saddr);
  32         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
  33                 flags |= FLOWI_FLAG_ANYSRC;
  34         else
  35                 saddr = 0;
  36
  37         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  38          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  39          */
  40         fl4.daddr = iph->daddr;
  41         fl4.saddr = saddr;
  42         fl4.flowi4_tos = RT_TOS(iph->tos);
  43         fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
  44         fl4.flowi4_mark = skb->mark;
  45         fl4.flowi4_flags = flags;
  46         rt = ip_route_output_key(net, &fl4);
  47         if (IS_ERR(rt))
  48                 return PTR_ERR(rt);
  49
  50         /* Drop old route. */
  51         skb_dst_drop(skb);
  52         skb_dst_set(skb, &rt->dst);
  53
  54         if (skb_dst(skb)->error)
  55                 return skb_dst(skb)->error;
  56
  57 #ifdef CONFIG_XFRM
  58         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  59             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
  60                 struct dst_entry *dst = skb_dst(skb);
  61                 skb_dst_set(skb, NULL);
  62                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
  63                 if (IS_ERR(dst))
  64                         return PTR_ERR(dst);;
  65                 skb_dst_set(skb, dst);
  66         }
  67 #endif
  68
  69         /* Change in oif may mean change in hh_len. */
  70         hh_len = skb_dst(skb)->dev->hard_header_len;
  71         if (skb_headroom(skb) < hh_len &&
  72             pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
  73                                 0, GFP_ATOMIC))
  74                 return -ENOMEM;
  75
  76         return 0;
  77 }
  78 EXPORT_SYMBOL(ip_route_me_harder);
  79
  80 /*
  81  * Extra routing may needed on local out, as the QUEUE target never
  82  * returns control to the table.
  83  */
  84
  85 struct ip_rt_info {
  86         __be32 daddr;
  87         __be32 saddr;
  88         u_int8_t tos;
  89         u_int32_t mark;
  90 };
  91
  92 static void nf_ip_saveroute(const struct sk_buff *skb,
  93                             struct nf_queue_entry *entry)
  94 {
  95         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
  96
  97         if (entry->hook == NF_INET_LOCAL_OUT) {
  98                 const struct iphdr *iph = ip_hdr(skb);
  99
 100                 rt_info->tos = iph->tos;
 101                 rt_info->daddr = iph->daddr;
 102                 rt_info->saddr = iph->saddr;
 103                 rt_info->mark = skb->mark;
 104         }
 105 }
 106
 107 static int nf_ip_reroute(struct sk_buff *skb,
 108                          const struct nf_queue_entry *entry)
 109 {
 110         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 111
 112         if (entry->hook == NF_INET_LOCAL_OUT) {
 113                 const struct iphdr *iph = ip_hdr(skb);
 114
 115                 if (!(iph->tos == rt_info->tos &&
 116                       skb->mark == rt_info->mark &&
 117                       iph->daddr == rt_info->daddr &&
 118                       iph->saddr == rt_info->saddr))
 119                         return ip_route_me_harder(skb, RTN_UNSPEC);
 120         }
 121         return 0;
 122 }
 123
 124 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 125                             unsigned int dataoff, u_int8_t protocol)
 126 {
 127         const struct iphdr *iph = ip_hdr(skb);
 128         __sum16 csum = 0;
 129
 130         switch (skb->ip_summed) {
 131         case CHECKSUM_COMPLETE:
 132                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 133                         break;
 134                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 135                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 136                                        skb->len - dataoff, protocol,
 137                                        skb->csum)) {
 138                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 139                         break;
 140                 }
 141                 /* fall through */
 142         case CHECKSUM_NONE:
 143                 if (protocol == 0)
 144                         skb->csum = 0;
 145                 else
 146                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 147                                                        skb->len - dataoff,
 148                                                        protocol, 0);
 149                 csum = __skb_checksum_complete(skb);
 150         }
 151         return csum;
 152 }
 153 EXPORT_SYMBOL(nf_ip_checksum);
 154
 155 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 156                                       unsigned int dataoff, unsigned int len,
 157                                       u_int8_t protocol)
 158 {
 159         const struct iphdr *iph = ip_hdr(skb);
 160         __sum16 csum = 0;
 161
 162         switch (skb->ip_summed) {
 163         case CHECKSUM_COMPLETE:
 164                 if (len == skb->len - dataoff)
 165                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 166                 /* fall through */
 167         case CHECKSUM_NONE:
 168                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 169                                                skb->len - dataoff, 0);
 170                 skb->ip_summed = CHECKSUM_NONE;
 171                 return __skb_checksum_complete_head(skb, dataoff + len);
 172         }
 173         return csum;
 174 }
 175
 176 static int nf_ip_route(struct net *net, struct dst_entry **dst,
 177                        struct flowi *fl, bool strict __always_unused)
 178 {
 179         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 180         if (IS_ERR(rt))
 181                 return PTR_ERR(rt);
 182         *dst = &rt->dst;
 183         return 0;
 184 }
 185
 186 static const struct nf_afinfo nf_ip_afinfo = {
 187         .family                 = AF_INET,
 188         .checksum               = nf_ip_checksum,
 189         .checksum_partial       = nf_ip_checksum_partial,
 190         .route                  = nf_ip_route,
 191         .saveroute              = nf_ip_saveroute,
 192         .reroute                = nf_ip_reroute,
 193         .route_key_size         = sizeof(struct ip_rt_info),
 194 };
 195
 196 static int __init ipv4_netfilter_init(void)
 197 {
 198         return nf_register_afinfo(&nf_ip_afinfo);
 199 }
 200
 201 static void __exit ipv4_netfilter_fini(void)
 202 {
 203         nf_unregister_afinfo(&nf_ip_afinfo);
 204 }
 205
 206 module_init(ipv4_netfilter_init);
 207 module_exit(ipv4_netfilter_fini);