ip_forward.c 3.0 KB

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  1. /*
  2. * INET An implementation of the TCP/IP protocol suite for the LINUX
  3. * operating system. INET is implemented using the BSD Socket
  4. * interface as the means of communication with the user level.
  5. *
  6. * The IP forwarding functionality.
  7. *
  8. * Version: $Id: ip_forward.c,v 1.1.1.1 2007/06/12 07:27:14 eyryu Exp $
  9. *
  10. * Authors: see ip.c
  11. *
  12. * Fixes:
  13. * Many : Split from ip.c , see ip_input.c for
  14. * history.
  15. * Dave Gregorich : NULL ip_rt_put fix for multicast
  16. * routing.
  17. * Jos Vos : Add call_out_firewall before sending,
  18. * use output device for accounting.
  19. * Jos Vos : Call forward firewall after routing
  20. * (always use output device).
  21. * Mike McLagan : Routing by source
  22. */
  23. #include <linux/types.h>
  24. #include <linux/mm.h>
  25. #include <linux/skbuff.h>
  26. #include <linux/ip.h>
  27. #include <linux/icmp.h>
  28. #include <linux/netdevice.h>
  29. #include <net/sock.h>
  30. #include <net/ip.h>
  31. #include <net/tcp.h>
  32. #include <net/udp.h>
  33. #include <net/icmp.h>
  34. #include <linux/tcp.h>
  35. #include <linux/udp.h>
  36. #include <linux/netfilter_ipv4.h>
  37. #include <net/checksum.h>
  38. #include <linux/route.h>
  39. #include <net/route.h>
  40. #include <net/xfrm.h>
  41. static inline int ip_forward_finish(struct sk_buff *skb)
  42. {
  43. struct ip_options * opt = &(IPCB(skb)->opt);
  44. IP_INC_STATS_BH(IPSTATS_MIB_OUTFORWDATAGRAMS);
  45. if (unlikely(opt->optlen))
  46. ip_forward_options(skb);
  47. return dst_output(skb);
  48. }
  49. int ip_forward(struct sk_buff *skb)
  50. {
  51. struct iphdr *iph; /* Our header */
  52. struct rtable *rt; /* Route we use */
  53. struct ip_options * opt = &(IPCB(skb)->opt);
  54. if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
  55. goto drop;
  56. if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
  57. return NET_RX_SUCCESS;
  58. if (skb->pkt_type != PACKET_HOST)
  59. goto drop;
  60. skb->ip_summed = CHECKSUM_NONE;
  61. /*
  62. * According to the RFC, we must first decrease the TTL field. If
  63. * that reaches zero, we must reply an ICMP control message telling
  64. * that the packet's lifetime expired.
  65. */
  66. if (skb->nh.iph->ttl <= 1)
  67. goto too_many_hops;
  68. if (!xfrm4_route_forward(skb))
  69. goto drop;
  70. rt = (struct rtable*)skb->dst;
  71. if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
  72. goto sr_failed;
  73. /* We are about to mangle packet. Copy it! */
  74. if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len))
  75. goto drop;
  76. iph = skb->nh.iph;
  77. /* Decrease ttl after skb cow done */
  78. ip_decrease_ttl(iph);
  79. /*
  80. * We now generate an ICMP HOST REDIRECT giving the route
  81. * we calculated.
  82. */
  83. if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)
  84. ip_rt_send_redirect(skb);
  85. skb->priority = rt_tos2priority(iph->tos);
  86. return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev,
  87. ip_forward_finish);
  88. sr_failed:
  89. /*
  90. * Strict routing permits no gatewaying
  91. */
  92. icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
  93. goto drop;
  94. too_many_hops:
  95. /* Tell the sender its packet died... */
  96. IP_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS);
  97. icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
  98. drop:
  99. kfree_skb(skb);
  100. return NET_RX_DROP;
  101. }