| /* 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_ipv4/ip_tables.h> |
| #include <linux/netfilter_ipv4/ipt_TTL.h> |
| |
| MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); |
| MODULE_DESCRIPTION("IP tables TTL modification module"); |
| MODULE_LICENSE("GPL"); |
| |
| static unsigned int |
| ipt_ttl_target(struct sk_buff **pskb, const struct net_device *in, |
| const struct net_device *out, unsigned int hooknum, |
| const void *targinfo, void *userinfo) |
| { |
| struct iphdr *iph; |
| const struct ipt_TTL_info *info = targinfo; |
| u_int16_t diffs[2]; |
| int new_ttl; |
| |
| if (!skb_make_writable(pskb, (*pskb)->len)) |
| return NF_DROP; |
| |
| iph = (*pskb)->nh.iph; |
| |
| 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) { |
| diffs[0] = htons(((unsigned)iph->ttl) << 8) ^ 0xFFFF; |
| iph->ttl = new_ttl; |
| diffs[1] = htons(((unsigned)iph->ttl) << 8); |
| iph->check = csum_fold(csum_partial((char *)diffs, |
| sizeof(diffs), |
| iph->check^0xFFFF)); |
| } |
| |
| return IPT_CONTINUE; |
| } |
| |
| static int ipt_ttl_checkentry(const char *tablename, |
| const void *e, |
| void *targinfo, |
| unsigned int targinfosize, |
| unsigned int hook_mask) |
| { |
| struct ipt_TTL_info *info = targinfo; |
| |
| if (targinfosize != IPT_ALIGN(sizeof(struct ipt_TTL_info))) { |
| printk(KERN_WARNING "ipt_TTL: targinfosize %u != %Zu\n", |
| targinfosize, |
| IPT_ALIGN(sizeof(struct ipt_TTL_info))); |
| return 0; |
| } |
| |
| if (strcmp(tablename, "mangle")) { |
| printk(KERN_WARNING "ipt_TTL: can only be called from " |
| "\"mangle\" table, not \"%s\"\n", tablename); |
| return 0; |
| } |
| |
| if (info->mode > IPT_TTL_MAXMODE) { |
| printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n", |
| info->mode); |
| return 0; |
| } |
| |
| if ((info->mode != IPT_TTL_SET) && (info->ttl == 0)) |
| return 0; |
| |
| return 1; |
| } |
| |
| static struct ipt_target ipt_TTL = { |
| .name = "TTL", |
| .target = ipt_ttl_target, |
| .checkentry = ipt_ttl_checkentry, |
| .me = THIS_MODULE, |
| }; |
| |
| static int __init init(void) |
| { |
| return ipt_register_target(&ipt_TTL); |
| } |
| |
| static void __exit fini(void) |
| { |
| ipt_unregister_target(&ipt_TTL); |
| } |
| |
| module_init(init); |
| module_exit(fini); |