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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
23MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
24MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
25MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
26MODULE_LICENSE("GPL");
27
28static unsigned int
29ttl_tg(struct sk_buff *skb, const struct xt_target_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
68static unsigned int
69hl_tg6(struct sk_buff *skb, const struct xt_target_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
104static bool 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 printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
110 info->mode);
111 return false;
112 }
113 if (info->mode != IPT_TTL_SET && info->ttl == 0)
114 return false;
115 return true;
116}
117
118static bool hl_tg6_check(const struct xt_tgchk_param *par)
119{
120 const struct ip6t_HL_info *info = par->targinfo;
121
122 if (info->mode > IP6T_HL_MAXMODE) {
123 printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
124 info->mode);
125 return false;
126 }
127 if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
128 printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
129 "make sense with value 0\n");
130 return false;
131 }
132 return true;
133}
134
135static struct xt_target hl_tg_reg[] __read_mostly = {
136 {
137 .name = "TTL",
138 .revision = 0,
139 .family = NFPROTO_IPV4,
140 .target = ttl_tg,
141 .targetsize = sizeof(struct ipt_TTL_info),
142 .table = "mangle",
143 .checkentry = ttl_tg_check,
144 .me = THIS_MODULE,
145 },
146 {
147 .name = "HL",
148 .revision = 0,
149 .family = NFPROTO_IPV6,
150 .target = hl_tg6,
151 .targetsize = sizeof(struct ip6t_HL_info),
152 .table = "mangle",
153 .checkentry = hl_tg6_check,
154 .me = THIS_MODULE,
155 },
156};
157
158static int __init hl_tg_init(void)
159{
160 return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
161}
162
163static void __exit hl_tg_exit(void)
164{
165 xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
166}
167
168module_init(hl_tg_init);
169module_exit(hl_tg_exit);
170MODULE_ALIAS("ipt_TTL");
171MODULE_ALIAS("ip6t_HL");
172
