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 net *net, struct sk_buff *skb, unsigned int addr_type)
  21 {
  22         const struct iphdr *iph = ip_hdr(skb);
  23         struct rtable *rt;
  24         struct flowi4 fl4 = {};
  25         __be32 saddr = iph->saddr;
  26         const struct sock *sk = skb_to_full_sk(skb);
  27         __u8 flags = sk ? inet_sk_flowi_flags(sk) : 0;
  28         struct net_device *dev = skb_dst(skb)->dev;
  29         unsigned int hh_len;
  30
  31         if (addr_type == RTN_UNSPEC)
  32                 addr_type = inet_addr_type_dev_table(net, dev, saddr);
  33         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
  34                 flags |= FLOWI_FLAG_ANYSRC;
  35         else
  36                 saddr = 0;
  37
  38         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  39          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  40          */
  41         fl4.daddr = iph->daddr;
  42         fl4.saddr = saddr;
  43         fl4.flowi4_tos = RT_TOS(iph->tos);
  44         fl4.flowi4_oif = sk ? sk->sk_bound_dev_if : 0;
  45         if (!fl4.flowi4_oif)
  46                 fl4.flowi4_oif = l3mdev_master_ifindex(dev);
  47         fl4.flowi4_mark = skb->mark;
  48         fl4.flowi4_flags = flags;
  49         rt = ip_route_output_key(net, &fl4);
  50         if (IS_ERR(rt))
  51                 return PTR_ERR(rt);
  52
  53         /* Drop old route. */
  54         skb_dst_drop(skb);
  55         skb_dst_set(skb, &rt->dst);
  56
  57         if (skb_dst(skb)->error)
  58                 return skb_dst(skb)->error;
  59
  60 #ifdef CONFIG_XFRM
  61         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  62             xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
  63                 struct dst_entry *dst = skb_dst(skb);
  64                 skb_dst_set(skb, NULL);
  65                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), sk, 0);
  66                 if (IS_ERR(dst))
  67                         return PTR_ERR(dst);
  68                 skb_dst_set(skb, dst);
  69         }
  70 #endif
  71
  72         /* Change in oif may mean change in hh_len. */
  73         hh_len = skb_dst(skb)->dev->hard_header_len;
  74         if (skb_headroom(skb) < hh_len &&
  75             pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
  76                                 0, GFP_ATOMIC))
  77                 return -ENOMEM;
  78
  79         return 0;
  80 }
  81 EXPORT_SYMBOL(ip_route_me_harder);
  82
  83 int nf_ip_reroute(struct sk_buff *skb, const struct nf_queue_entry *entry)
  84 {
  85         const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
  86
  87         if (entry->state.hook == NF_INET_LOCAL_OUT) {
  88                 const struct iphdr *iph = ip_hdr(skb);
  89
  90                 if (!(iph->tos == rt_info->tos &&
  91                       skb->mark == rt_info->mark &&
  92                       iph->daddr == rt_info->daddr &&
  93                       iph->saddr == rt_info->saddr))
  94                         return ip_route_me_harder(entry->state.net, skb,
  95                                                   RTN_UNSPEC);
  96         }
  97         return 0;
  98 }
  99 EXPORT_SYMBOL_GPL(nf_ip_reroute);
 100
 101 int nf_ip_route(struct net *net, struct dst_entry **dst, struct flowi *fl,
 102                 bool strict __always_unused)
 103 {
 104         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 105         if (IS_ERR(rt))
 106                 return PTR_ERR(rt);
 107         *dst = &rt->dst;
 108         return 0;
 109 }
 110 EXPORT_SYMBOL_GPL(nf_ip_route);