| 1 | /* TTL modification target for IP tables |
| 2 | * (C) 2000,2005 by Harald Welte <laforge@netfilter.org> |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or modify |
| 5 | * it under the terms of the GNU General Public License version 2 as |
| 6 | * published by the Free Software Foundation. |
| 7 | * |
| 8 | */ |
| 9 | |
| 10 | #include <linux/module.h> |
| 11 | #include <linux/skbuff.h> |
| 12 | #include <linux/ip.h> |
| 13 | #include <net/checksum.h> |
| 14 | |
| 15 | #include <linux/netfilter/x_tables.h> |
| 16 | #include <linux/netfilter_ipv4/ipt_TTL.h> |
| 17 | |
| 18 | MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); |
| 19 | MODULE_DESCRIPTION("IP tables TTL modification module"); |
| 20 | MODULE_LICENSE("GPL"); |
| 21 | |
| 22 | static unsigned int |
| 23 | ipt_ttl_target(struct sk_buff **pskb, |
| 24 | const struct net_device *in, const struct net_device *out, |
| 25 | unsigned int hooknum, const struct xt_target *target, |
| 26 | const void *targinfo) |
| 27 | { |
| 28 | struct iphdr *iph; |
| 29 | const struct ipt_TTL_info *info = targinfo; |
| 30 | int new_ttl; |
| 31 | |
| 32 | if (!skb_make_writable(pskb, (*pskb)->len)) |
| 33 | return NF_DROP; |
| 34 | |
| 35 | iph = ip_hdr(*pskb); |
| 36 | |
| 37 | switch (info->mode) { |
| 38 | case IPT_TTL_SET: |
| 39 | new_ttl = info->ttl; |
| 40 | break; |
| 41 | case IPT_TTL_INC: |
| 42 | new_ttl = iph->ttl + info->ttl; |
| 43 | if (new_ttl > 255) |
| 44 | new_ttl = 255; |
| 45 | break; |
| 46 | case IPT_TTL_DEC: |
| 47 | new_ttl = iph->ttl - info->ttl; |
| 48 | if (new_ttl < 0) |
| 49 | new_ttl = 0; |
| 50 | break; |
| 51 | default: |
| 52 | new_ttl = iph->ttl; |
| 53 | break; |
| 54 | } |
| 55 | |
| 56 | if (new_ttl != iph->ttl) { |
| 57 | nf_csum_replace2(&iph->check, htons(iph->ttl << 8), |
| 58 | htons(new_ttl << 8)); |
| 59 | iph->ttl = new_ttl; |
| 60 | } |
| 61 | |
| 62 | return XT_CONTINUE; |
| 63 | } |
| 64 | |
| 65 | static bool ipt_ttl_checkentry(const char *tablename, |
| 66 | const void *e, |
| 67 | const struct xt_target *target, |
| 68 | void *targinfo, |
| 69 | unsigned int hook_mask) |
| 70 | { |
| 71 | struct ipt_TTL_info *info = targinfo; |
| 72 | |
| 73 | if (info->mode > IPT_TTL_MAXMODE) { |
| 74 | printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n", |
| 75 | info->mode); |
| 76 | return false; |
| 77 | } |
| 78 | if ((info->mode != IPT_TTL_SET) && (info->ttl == 0)) |
| 79 | return false; |
| 80 | return true; |
| 81 | } |
| 82 | |
| 83 | static struct xt_target ipt_TTL = { |
| 84 | .name = "TTL", |
| 85 | .family = AF_INET, |
| 86 | .target = ipt_ttl_target, |
| 87 | .targetsize = sizeof(struct ipt_TTL_info), |
| 88 | .table = "mangle", |
| 89 | .checkentry = ipt_ttl_checkentry, |
| 90 | .me = THIS_MODULE, |
| 91 | }; |
| 92 | |
| 93 | static int __init ipt_ttl_init(void) |
| 94 | { |
| 95 | return xt_register_target(&ipt_TTL); |
| 96 | } |
| 97 | |
| 98 | static void __exit ipt_ttl_fini(void) |
| 99 | { |
| 100 | xt_unregister_target(&ipt_TTL); |
| 101 | } |
| 102 | |
| 103 | module_init(ipt_ttl_init); |
| 104 | module_exit(ipt_ttl_fini); |