1 /* 2 * TTL modification target for IP tables 3 * (C) 2000,2005 by Harald Welte <laforge@netfilter.org> 4 * 5 * Hop Limit modification target for ip6tables 6 * Maciej Soltysiak <solt@dns.toxicfilms.tv> 7 * 8 * This program is free software; you can redistribute it and/or modify 9 * it under the terms of the GNU General Public License version 2 as 10 * published by the Free Software Foundation. 11 */ 12 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 13 #include <linux/module.h> 14 #include <linux/skbuff.h> 15 #include <linux/ip.h> 16 #include <linux/ipv6.h> 17 #include <net/checksum.h> 18 19 #include <linux/netfilter/x_tables.h> 20 #include <linux/netfilter_ipv4/ipt_TTL.h> 21 #include <linux/netfilter_ipv6/ip6t_HL.h> 22 23 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); 24 MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>"); 25 MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target"); 26 MODULE_LICENSE("GPL"); 27 28 static unsigned int 29 ttl_tg(struct sk_buff *skb, const struct xt_action_param *par) 30 { 31 struct iphdr *iph; 32 const struct ipt_TTL_info *info = par->targinfo; 33 int new_ttl; 34 35 if (!skb_make_writable(skb, skb->len)) 36 return NF_DROP; 37 38 iph = ip_hdr(skb); 39 40 switch (info->mode) { 41 case IPT_TTL_SET: 42 new_ttl = info->ttl; 43 break; 44 case IPT_TTL_INC: 45 new_ttl = iph->ttl + info->ttl; 46 if (new_ttl > 255) 47 new_ttl = 255; 48 break; 49 case IPT_TTL_DEC: 50 new_ttl = iph->ttl - info->ttl; 51 if (new_ttl < 0) 52 new_ttl = 0; 53 break; 54 default: 55 new_ttl = iph->ttl; 56 break; 57 } 58 59 if (new_ttl != iph->ttl) { 60 csum_replace2(&iph->check, htons(iph->ttl << 8), 61 htons(new_ttl << 8)); 62 iph->ttl = new_ttl; 63 } 64 65 return XT_CONTINUE; 66 } 67 68 static unsigned int 69 hl_tg6(struct sk_buff *skb, const struct xt_action_param *par) 70 { 71 struct ipv6hdr *ip6h; 72 const struct ip6t_HL_info *info = par->targinfo; 73 int new_hl; 74 75 if (!skb_make_writable(skb, skb->len)) 76 return NF_DROP; 77 78 ip6h = ipv6_hdr(skb); 79 80 switch (info->mode) { 81 case IP6T_HL_SET: 82 new_hl = info->hop_limit; 83 break; 84 case IP6T_HL_INC: 85 new_hl = ip6h->hop_limit + info->hop_limit; 86 if (new_hl > 255) 87 new_hl = 255; 88 break; 89 case IP6T_HL_DEC: 90 new_hl = ip6h->hop_limit - info->hop_limit; 91 if (new_hl < 0) 92 new_hl = 0; 93 break; 94 default: 95 new_hl = ip6h->hop_limit; 96 break; 97 } 98 99 ip6h->hop_limit = new_hl; 100 101 return XT_CONTINUE; 102 } 103 104 static int ttl_tg_check(const struct xt_tgchk_param *par) 105 { 106 const struct ipt_TTL_info *info = par->targinfo; 107 108 if (info->mode > IPT_TTL_MAXMODE) { 109 pr_info("TTL: invalid or unknown mode %u\n", info->mode); 110 return -EINVAL; 111 } 112 if (info->mode != IPT_TTL_SET && info->ttl == 0) 113 return -EINVAL; 114 return 0; 115 } 116 117 static int hl_tg6_check(const struct xt_tgchk_param *par) 118 { 119 const struct ip6t_HL_info *info = par->targinfo; 120 121 if (info->mode > IP6T_HL_MAXMODE) { 122 pr_info("invalid or unknown mode %u\n", info->mode); 123 return -EINVAL; 124 } 125 if (info->mode != IP6T_HL_SET && info->hop_limit == 0) { 126 pr_info("increment/decrement does not " 127 "make sense with value 0\n"); 128 return -EINVAL; 129 } 130 return 0; 131 } 132 133 static struct xt_target hl_tg_reg[] __read_mostly = { 134 { 135 .name = "TTL", 136 .revision = 0, 137 .family = NFPROTO_IPV4, 138 .target = ttl_tg, 139 .targetsize = sizeof(struct ipt_TTL_info), 140 .table = "mangle", 141 .checkentry = ttl_tg_check, 142 .me = THIS_MODULE, 143 }, 144 { 145 .name = "HL", 146 .revision = 0, 147 .family = NFPROTO_IPV6, 148 .target = hl_tg6, 149 .targetsize = sizeof(struct ip6t_HL_info), 150 .table = "mangle", 151 .checkentry = hl_tg6_check, 152 .me = THIS_MODULE, 153 }, 154 }; 155 156 static int __init hl_tg_init(void) 157 { 158 return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); 159 } 160 161 static void __exit hl_tg_exit(void) 162 { 163 xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); 164 } 165 166 module_init(hl_tg_init); 167 module_exit(hl_tg_exit); 168 MODULE_ALIAS("ipt_TTL"); 169 MODULE_ALIAS("ip6t_HL"); 170