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 <linux/export.h>
   9 #include <net/route.h>
  10 #include <net/xfrm.h>
  11 #include <net/ip.h>
  12 #include <net/netfilter/nf_queue.h>
  13
  14 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  15 int ip_route_me_harder(struct sk_buff *skb, unsigned addr_type)
  16 {
  17         struct net *net = dev_net(skb_dst(skb)->dev);
  18         const struct iphdr *iph = ip_hdr(skb);
  19         struct rtable *rt;
  20         struct flowi4 fl4 = {};
  21         __be32 saddr = iph->saddr;
  22         __u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
  23         unsigned int hh_len;
  24
  25         if (addr_type == RTN_UNSPEC)
  26                 addr_type = inet_addr_type(net, saddr);
  27         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
  28                 flags |= FLOWI_FLAG_ANYSRC;
  29         else
  30                 saddr = 0;
  31
  32         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  33          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  34          */
  35         fl4.daddr = iph->daddr;
  36         fl4.saddr = 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 = flags;
  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
  49         if (skb_dst(skb)->error)
  50                 return -1;
  51
  52 #ifdef CONFIG_XFRM
  53         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  54             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
  55                 struct dst_entry *dst = skb_dst(skb);
  56                 skb_dst_set(skb, NULL);
  57                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
  58                 if (IS_ERR(dst))
  59                         return -1;
  60                 skb_dst_set(skb, dst);
  61         }
  62 #endif
  63
  64         /* Change in oif may mean change in hh_len. */
  65         hh_len = skb_dst(skb)->dev->hard_header_len;
  66         if (skb_headroom(skb) < hh_len &&
  67             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
  68                 return -1;
  69
  70         return 0;
  71 }
  72 EXPORT_SYMBOL(ip_route_me_harder);
  73
  74 #ifdef CONFIG_XFRM
  75 int ip_xfrm_me_harder(struct sk_buff *skb)
  76 {
  77         struct flowi fl;
  78         unsigned int hh_len;
  79         struct dst_entry *dst;
  80
  81         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  82                 return 0;
  83         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
  84                 return -1;
  85
  86         dst = skb_dst(skb);
  87         if (dst->xfrm)
  88                 dst = ((struct xfrm_dst *)dst)->route;
  89         dst_hold(dst);
  90
  91         dst = xfrm_lookup(dev_net(dst->dev), dst, &fl, skb->sk, 0);
  92         if (IS_ERR(dst))
  93                 return -1;
  94
  95         skb_dst_drop(skb);
  96         skb_dst_set(skb, dst);
  97
  98         /* Change in oif may mean change in hh_len. */
  99         hh_len = skb_dst(skb)->dev->hard_header_len;
 100         if (skb_headroom(skb) < hh_len &&
 101             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 102                 return -1;
 103         return 0;
 104 }
 105 EXPORT_SYMBOL(ip_xfrm_me_harder);
 106 #endif
 107
 108 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 109 EXPORT_SYMBOL(ip_nat_decode_session);
 110
 111 /*
 112  * Extra routing may needed on local out, as the QUEUE target never
 113  * returns control to the table.
 114  */
 115
 116 struct ip_rt_info {
 117         __be32 daddr;
 118         __be32 saddr;
 119         u_int8_t tos;
 120         u_int32_t mark;
 121 };
 122
 123 static void nf_ip_saveroute(const struct sk_buff *skb,
 124                             struct nf_queue_entry *entry)
 125 {
 126         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 127
 128         if (entry->hook == NF_INET_LOCAL_OUT) {
 129                 const struct iphdr *iph = ip_hdr(skb);
 130
 131                 rt_info->tos = iph->tos;
 132                 rt_info->daddr = iph->daddr;
 133                 rt_info->saddr = iph->saddr;
 134                 rt_info->mark = skb->mark;
 135         }
 136 }
 137
 138 static int nf_ip_reroute(struct sk_buff *skb,
 139                          const struct nf_queue_entry *entry)
 140 {
 141         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 142
 143         if (entry->hook == NF_INET_LOCAL_OUT) {
 144                 const struct iphdr *iph = ip_hdr(skb);
 145
 146                 if (!(iph->tos == rt_info->tos &&
 147                       skb->mark == rt_info->mark &&
 148                       iph->daddr == rt_info->daddr &&
 149                       iph->saddr == rt_info->saddr))
 150                         return ip_route_me_harder(skb, RTN_UNSPEC);
 151         }
 152         return 0;
 153 }
 154
 155 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 156                             unsigned int dataoff, u_int8_t protocol)
 157 {
 158         const struct iphdr *iph = ip_hdr(skb);
 159         __sum16 csum = 0;
 160
 161         switch (skb->ip_summed) {
 162         case CHECKSUM_COMPLETE:
 163                 if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 164                         break;
 165                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 166                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 167                                        skb->len - dataoff, protocol,
 168                                        skb->csum)) {
 169                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 170                         break;
 171                 }
 172                 /* fall through */
 173         case CHECKSUM_NONE:
 174                 if (protocol == 0)
 175                         skb->csum = 0;
 176                 else
 177                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 178                                                        skb->len - dataoff,
 179                                                        protocol, 0);
 180                 csum = __skb_checksum_complete(skb);
 181         }
 182         return csum;
 183 }
 184 EXPORT_SYMBOL(nf_ip_checksum);
 185
 186 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 187                                       unsigned int dataoff, unsigned int len,
 188                                       u_int8_t protocol)
 189 {
 190         const struct iphdr *iph = ip_hdr(skb);
 191         __sum16 csum = 0;
 192
 193         switch (skb->ip_summed) {
 194         case CHECKSUM_COMPLETE:
 195                 if (len == skb->len - dataoff)
 196                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 197                 /* fall through */
 198         case CHECKSUM_NONE:
 199                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 200                                                skb->len - dataoff, 0);
 201                 skb->ip_summed = CHECKSUM_NONE;
 202                 return __skb_checksum_complete_head(skb, dataoff + len);
 203         }
 204         return csum;
 205 }
 206
 207 static int nf_ip_route(struct net *net, struct dst_entry **dst,
 208                        struct flowi *fl, bool strict __always_unused)
 209 {
 210         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 211         if (IS_ERR(rt))
 212                 return PTR_ERR(rt);
 213         *dst = &rt->dst;
 214         return 0;
 215 }
 216
 217 static const struct nf_afinfo nf_ip_afinfo = {
 218         .family                 = AF_INET,
 219         .checksum               = nf_ip_checksum,
 220         .checksum_partial       = nf_ip_checksum_partial,
 221         .route                  = nf_ip_route,
 222         .saveroute              = nf_ip_saveroute,
 223         .reroute                = nf_ip_reroute,
 224         .route_key_size         = sizeof(struct ip_rt_info),
 225 };
 226
 227 static int ipv4_netfilter_init(void)
 228 {
 229         return nf_register_afinfo(&nf_ip_afinfo);
 230 }
 231
 232 static void ipv4_netfilter_fini(void)
 233 {
 234         nf_unregister_afinfo(&nf_ip_afinfo);
 235 }
 236
 237 module_init(ipv4_netfilter_init);
 238 module_exit(ipv4_netfilter_fini);
 239
 240 #ifdef CONFIG_SYSCTL
 241 struct ctl_path nf_net_ipv4_netfilter_sysctl_path[] = {
 242         { .procname = "net", },
 243         { .procname = "ipv4", },
 244         { .procname = "netfilter", },
 245         { }
 246 };
 247 EXPORT_SYMBOL_GPL(nf_net_ipv4_netfilter_sysctl_path);
 248 #endif /* CONFIG_SYSCTL */