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/inet_dscp.h>
  18 #include <net/netfilter/nf_queue.h>
  19
  20 /* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
  21 int ip_route_me_harder(struct net *net, struct sock *sk, struct sk_buff *skb, unsigned int addr_type)
  22 {
  23         const struct iphdr *iph = ip_hdr(skb);
  24         struct rtable *rt;
  25         struct flowi4 fl4 = {};
  26         __be32 saddr = iph->saddr;
  27         __u8 flags;
  28         struct net_device *dev = skb_dst(skb)->dev;
  29         struct flow_keys flkeys;
  30         unsigned int hh_len;
  31
  32         sk = sk_to_full_sk(sk);
  33         flags = sk ? inet_sk_flowi_flags(sk) : 0;
  34
  35         if (addr_type == RTN_UNSPEC)
  36                 addr_type = inet_addr_type_dev_table(net, dev, saddr);
  37         if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
  38                 flags |= FLOWI_FLAG_ANYSRC;
  39         else
  40                 saddr = 0;
  41
  42         /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
  43          * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
  44          */
  45         fl4.daddr = iph->daddr;
  46         fl4.saddr = saddr;
  47         fl4.flowi4_tos = inet_dscp_to_dsfield(ip4h_dscp(iph));
  48         fl4.flowi4_oif = sk ? sk->sk_bound_dev_if : 0;
  49         fl4.flowi4_l3mdev = l3mdev_master_ifindex(dev);
  50         fl4.flowi4_mark = skb->mark;
  51         fl4.flowi4_flags = flags;
  52         fib4_rules_early_flow_dissect(net, skb, &fl4, &flkeys);
  53         rt = ip_route_output_key(net, &fl4);
  54         if (IS_ERR(rt))
  55                 return PTR_ERR(rt);
  56
  57         /* Drop old route. */
  58         skb_dst_drop(skb);
  59         skb_dst_set(skb, &rt->dst);
  60
  61         if (skb_dst(skb)->error)
  62                 return skb_dst(skb)->error;
  63
  64 #ifdef CONFIG_XFRM
  65         if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
  66             xfrm_decode_session(net, skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
  67                 struct dst_entry *dst = skb_dst(skb);
  68                 skb_dst_set(skb, NULL);
  69                 dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), sk, 0);
  70                 if (IS_ERR(dst))
  71                         return PTR_ERR(dst);
  72                 skb_dst_set(skb, dst);
  73         }
  74 #endif
  75
  76         /* Change in oif may mean change in hh_len. */
  77         hh_len = skb_dst(skb)->dev->hard_header_len;
  78         if (skb_headroom(skb) < hh_len &&
  79             pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
  80                                 0, GFP_ATOMIC))
  81                 return -ENOMEM;
  82
  83         return 0;
  84 }
  85 EXPORT_SYMBOL(ip_route_me_harder);
  86
  87 int nf_ip_route(struct net *net, struct dst_entry **dst, struct flowi *fl,
  88                 bool strict __always_unused)
  89 {
  90         struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
  91         if (IS_ERR(rt))
  92                 return PTR_ERR(rt);
  93         *dst = &rt->dst;
  94         return 0;
  95 }
  96 EXPORT_SYMBOL_GPL(nf_ip_route);