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 int 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_DATA_ALIGN(hh_len - skb_headroom(skb)),
  68                                 0, GFP_ATOMIC))
  69                 return -1;
  70
  71         return 0;
  72 }
  73 EXPORT_SYMBOL(ip_route_me_harder);
  74
  75 #ifdef CONFIG_XFRM
  76 int ip_xfrm_me_harder(struct sk_buff *skb)
  77 {
  78         struct flowi fl;
  79         unsigned int hh_len;
  80         struct dst_entry *dst;
  81
  82         if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
  83                 return 0;
  84         if (xfrm_decode_session(skb, &fl, AF_INET) < 0)
  85                 return -1;
  86
  87         dst = skb_dst(skb);
  88         if (dst->xfrm)
  89                 dst = ((struct xfrm_dst *)dst)->route;
  90         dst_hold(dst);
  91
  92         dst = xfrm_lookup(dev_net(dst->dev), dst, &fl, skb->sk, 0);
  93         if (IS_ERR(dst))
  94                 return -1;
  95
  96         skb_dst_drop(skb);
  97         skb_dst_set(skb, dst);
  98
  99         /* Change in oif may mean change in hh_len. */
 100         hh_len = skb_dst(skb)->dev->hard_header_len;
 101         if (skb_headroom(skb) < hh_len &&
 102             pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
 103                 return -1;
 104         return 0;
 105 }
 106 EXPORT_SYMBOL(ip_xfrm_me_harder);
 107 #endif
 108
 109 void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 110 EXPORT_SYMBOL(ip_nat_decode_session);
 111
 112 /*
 113  * Extra routing may needed on local out, as the QUEUE target never
 114  * returns control to the table.
 115  */
 116
 117 struct ip_rt_info {
 118         __be32 daddr;
 119         __be32 saddr;
 120         u_int8_t tos;
 121         u_int32_t mark;
 122 };
 123
 124 static void nf_ip_saveroute(const struct sk_buff *skb,
 125                             struct nf_queue_entry *entry)
 126 {
 127         struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 128
 129         if (entry->hook == NF_INET_LOCAL_OUT) {
 130                 const struct iphdr *iph = ip_hdr(skb);
 131
 132                 rt_info->tos = iph->tos;
 133                 rt_info->daddr = iph->daddr;
 134                 rt_info->saddr = iph->saddr;
 135                 rt_info->mark = skb->mark;
 136         }
 137 }
 138
 139 static int nf_ip_reroute(struct sk_buff *skb,
 140                          const struct nf_queue_entry *entry)
 141 {
 142         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
 143
 144         if (entry->hook == NF_INET_LOCAL_OUT) {
 145                 const struct iphdr *iph = ip_hdr(skb);
 146
 147                 if (!(iph->tos == rt_info->tos &&
 148                       skb->mark == rt_info->mark &&
 149                       iph->daddr == rt_info->daddr &&
 150                       iph->saddr == rt_info->saddr))
 151                         return ip_route_me_harder(skb, RTN_UNSPEC);
 152         }
 153         return 0;
 154 }
 155
 156 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 157                             unsigned int dataoff, 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 (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
 165                         break;
 166                 if ((protocol == 0 && !csum_fold(skb->csum)) ||
 167                     !csum_tcpudp_magic(iph->saddr, iph->daddr,
 168                                        skb->len - dataoff, protocol,
 169                                        skb->csum)) {
 170                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 171                         break;
 172                 }
 173                 /* fall through */
 174         case CHECKSUM_NONE:
 175                 if (protocol == 0)
 176                         skb->csum = 0;
 177                 else
 178                         skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 179                                                        skb->len - dataoff,
 180                                                        protocol, 0);
 181                 csum = __skb_checksum_complete(skb);
 182         }
 183         return csum;
 184 }
 185 EXPORT_SYMBOL(nf_ip_checksum);
 186
 187 static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 188                                       unsigned int dataoff, unsigned int len,
 189                                       u_int8_t protocol)
 190 {
 191         const struct iphdr *iph = ip_hdr(skb);
 192         __sum16 csum = 0;
 193
 194         switch (skb->ip_summed) {
 195         case CHECKSUM_COMPLETE:
 196                 if (len == skb->len - dataoff)
 197                         return nf_ip_checksum(skb, hook, dataoff, protocol);
 198                 /* fall through */
 199         case CHECKSUM_NONE:
 200                 skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
 201                                                skb->len - dataoff, 0);
 202                 skb->ip_summed = CHECKSUM_NONE;
 203                 return __skb_checksum_complete_head(skb, dataoff + len);
 204         }
 205         return csum;
 206 }
 207
 208 static int nf_ip_route(struct net *net, struct dst_entry **dst,
 209                        struct flowi *fl, bool strict __always_unused)
 210 {
 211         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 212         if (IS_ERR(rt))
 213                 return PTR_ERR(rt);
 214         *dst = &rt->dst;
 215         return 0;
 216 }
 217
 218 static const struct nf_afinfo nf_ip_afinfo = {
 219         .family                 = AF_INET,
 220         .checksum               = nf_ip_checksum,
 221         .checksum_partial       = nf_ip_checksum_partial,
 222         .route                  = nf_ip_route,
 223         .saveroute              = nf_ip_saveroute,
 224         .reroute                = nf_ip_reroute,
 225         .route_key_size         = sizeof(struct ip_rt_info),
 226 };
 227
 228 static int ipv4_netfilter_init(void)
 229 {
 230         return nf_register_afinfo(&nf_ip_afinfo);
 231 }
 232
 233 static void ipv4_netfilter_fini(void)
 234 {
 235         nf_unregister_afinfo(&nf_ip_afinfo);
 236 }
 237
 238 module_init(ipv4_netfilter_init);
 239 module_exit(ipv4_netfilter_fini);