| /* TTL modification target for IP tables |
| * (C) 2000,2005 by Harald Welte <laforge@netfilter.org> |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License version 2 as |
| * published by the Free Software Foundation. |
| * |
| */ |
| |
| #include <linux/module.h> |
| #include <linux/skbuff.h> |
| #include <linux/ip.h> |
| #include <net/checksum.h> |
| |
| #include <linux/netfilter/x_tables.h> |
| #include <linux/netfilter_ipv4/ipt_TTL.h> |
| |
| MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); |
| MODULE_DESCRIPTION("Xtables: IPv4 TTL field modification target"); |
| MODULE_LICENSE("GPL"); |
| |
| static unsigned int |
| ttl_tg(struct sk_buff *skb, const struct xt_target_param *par) |
| { |
| struct iphdr *iph; |
| const struct ipt_TTL_info *info = par->targinfo; |
| int new_ttl; |
| |
| if (!skb_make_writable(skb, skb->len)) |
| return NF_DROP; |
| |
| iph = ip_hdr(skb); |
| |
| switch (info->mode) { |
| case IPT_TTL_SET: |
| new_ttl = info->ttl; |
| break; |
| case IPT_TTL_INC: |
| new_ttl = iph->ttl + info->ttl; |
| if (new_ttl > 255) |
| new_ttl = 255; |
| break; |
| case IPT_TTL_DEC: |
| new_ttl = iph->ttl - info->ttl; |
| if (new_ttl < 0) |
| new_ttl = 0; |
| break; |
| default: |
| new_ttl = iph->ttl; |
| break; |
| } |
| |
| if (new_ttl != iph->ttl) { |
| csum_replace2(&iph->check, htons(iph->ttl << 8), |
| htons(new_ttl << 8)); |
| iph->ttl = new_ttl; |
| } |
| |
| return XT_CONTINUE; |
| } |
| |
| static bool |
| ttl_tg_check(const char *tablename, const void *e, |
| const struct xt_target *target, void *targinfo, |
| unsigned int hook_mask) |
| { |
| const struct ipt_TTL_info *info = targinfo; |
| |
| if (info->mode > IPT_TTL_MAXMODE) { |
| printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n", |
| info->mode); |
| return false; |
| } |
| if (info->mode != IPT_TTL_SET && info->ttl == 0) |
| return false; |
| return true; |
| } |
| |
| static struct xt_target ttl_tg_reg __read_mostly = { |
| .name = "TTL", |
| .family = NFPROTO_IPV4, |
| .target = ttl_tg, |
| .targetsize = sizeof(struct ipt_TTL_info), |
| .table = "mangle", |
| .checkentry = ttl_tg_check, |
| .me = THIS_MODULE, |
| }; |
| |
| static int __init ttl_tg_init(void) |
| { |
| return xt_register_target(&ttl_tg_reg); |
| } |
| |
| static void __exit ttl_tg_exit(void) |
| { |
| xt_unregister_target(&ttl_tg_reg); |
| } |
| |
| module_init(ttl_tg_init); |
| module_exit(ttl_tg_exit); |