1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * TTL modification target for IP tables 4 * (C) 2000,2005 by Harald Welte <laforge@netfilter.org> 5 * 6 * Hop Limit modification target for ip6tables 7 * Maciej Soltysiak <solt@dns.toxicfilms.tv> 8 */ 9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 10 #include <linux/module.h> 11 #include <linux/skbuff.h> 12 #include <linux/ip.h> 13 #include <linux/ipv6.h> 14 #include <net/checksum.h> 15 16 #include <linux/netfilter/x_tables.h> 17 #include <linux/netfilter_ipv4/ipt_TTL.h> 18 #include <linux/netfilter_ipv6/ip6t_HL.h> 19 20 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); 21 MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>"); 22 MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target"); 23 MODULE_LICENSE("GPL"); 24 25 static unsigned int 26 ttl_tg(struct sk_buff *skb, const struct xt_action_param *par) 27 { 28 struct iphdr *iph; 29 const struct ipt_TTL_info *info = par->targinfo; 30 int new_ttl; 31 32 if (skb_ensure_writable(skb, sizeof(*iph))) 33 return NF_DROP; 34 35 iph = ip_hdr(skb); 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 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 unsigned int 66 hl_tg6(struct sk_buff *skb, const struct xt_action_param *par) 67 { 68 struct ipv6hdr *ip6h; 69 const struct ip6t_HL_info *info = par->targinfo; 70 int new_hl; 71 72 if (skb_ensure_writable(skb, sizeof(*ip6h))) 73 return NF_DROP; 74 75 ip6h = ipv6_hdr(skb); 76 77 switch (info->mode) { 78 case IP6T_HL_SET: 79 new_hl = info->hop_limit; 80 break; 81 case IP6T_HL_INC: 82 new_hl = ip6h->hop_limit + info->hop_limit; 83 if (new_hl > 255) 84 new_hl = 255; 85 break; 86 case IP6T_HL_DEC: 87 new_hl = ip6h->hop_limit - info->hop_limit; 88 if (new_hl < 0) 89 new_hl = 0; 90 break; 91 default: 92 new_hl = ip6h->hop_limit; 93 break; 94 } 95 96 ip6h->hop_limit = new_hl; 97 98 return XT_CONTINUE; 99 } 100 101 static int ttl_tg_check(const struct xt_tgchk_param *par) 102 { 103 const struct ipt_TTL_info *info = par->targinfo; 104 105 if (info->mode > IPT_TTL_MAXMODE) 106 return -EINVAL; 107 if (info->mode != IPT_TTL_SET && info->ttl == 0) 108 return -EINVAL; 109 return 0; 110 } 111 112 static int hl_tg6_check(const struct xt_tgchk_param *par) 113 { 114 const struct ip6t_HL_info *info = par->targinfo; 115 116 if (info->mode > IP6T_HL_MAXMODE) 117 return -EINVAL; 118 if (info->mode != IP6T_HL_SET && info->hop_limit == 0) 119 return -EINVAL; 120 return 0; 121 } 122 123 static struct xt_target hl_tg_reg[] __read_mostly = { 124 { 125 .name = "TTL", 126 .revision = 0, 127 .family = NFPROTO_IPV4, 128 .target = ttl_tg, 129 .targetsize = sizeof(struct ipt_TTL_info), 130 .table = "mangle", 131 .checkentry = ttl_tg_check, 132 .me = THIS_MODULE, 133 }, 134 { 135 .name = "HL", 136 .revision = 0, 137 .family = NFPROTO_IPV6, 138 .target = hl_tg6, 139 .targetsize = sizeof(struct ip6t_HL_info), 140 .table = "mangle", 141 .checkentry = hl_tg6_check, 142 .me = THIS_MODULE, 143 }, 144 }; 145 146 static int __init hl_tg_init(void) 147 { 148 return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); 149 } 150 151 static void __exit hl_tg_exit(void) 152 { 153 xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); 154 } 155 156 module_init(hl_tg_init); 157 module_exit(hl_tg_exit); 158 MODULE_ALIAS("ipt_TTL"); 159 MODULE_ALIAS("ip6t_HL"); 160