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Linux/net/netfilter/xt_HL.c

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  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 

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