linux/net/ipv4/netfilter.c
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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 <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 */
  15int 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}
  73EXPORT_SYMBOL(ip_route_me_harder);
  74
  75#ifdef CONFIG_XFRM
  76int 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}
 106EXPORT_SYMBOL(ip_xfrm_me_harder);
 107#endif
 108
 109void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 110EXPORT_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
 117struct ip_rt_info {
 118        __be32 daddr;
 119        __be32 saddr;
 120        u_int8_t tos;
 121        u_int32_t mark;
 122};
 123
 124static 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
 139static 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}
 185EXPORT_SYMBOL(nf_ip_checksum);
 186
 187static __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
 208static 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
 218static 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
 228static int ipv4_netfilter_init(void)
 229{
 230        return nf_register_afinfo(&nf_ip_afinfo);
 231}
 232
 233static void ipv4_netfilter_fini(void)
 234{
 235        nf_unregister_afinfo(&nf_ip_afinfo);
 236}
 237
 238module_init(ipv4_netfilter_init);
 239module_exit(ipv4_netfilter_fini);
 240
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