1 /* ipv6header match - matches IPv6 packets based
2    on whether they contain certain headers */
3 
4 /* Original idea: Brad Chapman
5  * Rewritten by: Andras Kis-Szabo <kisza@sch.bme.hu> */
6 
7 /* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
8  *
9  * This program is free software; you can redistribute it and/or modify
10  * it under the terms of the GNU General Public License version 2 as
11  * published by the Free Software Foundation.
12  */
13 
14 #include <linux/module.h>
15 #include <linux/skbuff.h>
16 #include <linux/ipv6.h>
17 #include <linux/types.h>
18 #include <net/checksum.h>
19 #include <net/ipv6.h>
20 
21 #include <linux/netfilter/x_tables.h>
22 #include <linux/netfilter_ipv6/ip6_tables.h>
23 #include <linux/netfilter_ipv6/ip6t_ipv6header.h>
24 
25 MODULE_LICENSE("GPL");
26 MODULE_DESCRIPTION("Xtables: IPv6 header types match");
27 MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");
28 
29 static bool
30 ipv6header_mt6(const struct sk_buff *skb, struct xt_action_param *par)
31 {
32 	const struct ip6t_ipv6header_info *info = par->matchinfo;
33 	unsigned int temp;
34 	int len;
35 	u8 nexthdr;
36 	unsigned int ptr;
37 
38 	/* Make sure this isn't an evil packet */
39 
40 	/* type of the 1st exthdr */
41 	nexthdr = ipv6_hdr(skb)->nexthdr;
42 	/* pointer to the 1st exthdr */
43 	ptr = sizeof(struct ipv6hdr);
44 	/* available length */
45 	len = skb->len - ptr;
46 	temp = 0;
47 
48 	while (ip6t_ext_hdr(nexthdr)) {
49 		const struct ipv6_opt_hdr *hp;
50 		struct ipv6_opt_hdr _hdr;
51 		int hdrlen;
52 
53 		/* No more exthdr -> evaluate */
54 		if (nexthdr == NEXTHDR_NONE) {
55 			temp |= MASK_NONE;
56 			break;
57 		}
58 		/* Is there enough space for the next ext header? */
59 		if (len < (int)sizeof(struct ipv6_opt_hdr))
60 			return false;
61 		/* ESP -> evaluate */
62 		if (nexthdr == NEXTHDR_ESP) {
63 			temp |= MASK_ESP;
64 			break;
65 		}
66 
67 		hp = skb_header_pointer(skb, ptr, sizeof(_hdr), &_hdr);
68 		BUG_ON(hp == NULL);
69 
70 		/* Calculate the header length */
71 		if (nexthdr == NEXTHDR_FRAGMENT)
72 			hdrlen = 8;
73 		else if (nexthdr == NEXTHDR_AUTH)
74 			hdrlen = (hp->hdrlen + 2) << 2;
75 		else
76 			hdrlen = ipv6_optlen(hp);
77 
78 		/* set the flag */
79 		switch (nexthdr) {
80 		case NEXTHDR_HOP:
81 			temp |= MASK_HOPOPTS;
82 			break;
83 		case NEXTHDR_ROUTING:
84 			temp |= MASK_ROUTING;
85 			break;
86 		case NEXTHDR_FRAGMENT:
87 			temp |= MASK_FRAGMENT;
88 			break;
89 		case NEXTHDR_AUTH:
90 			temp |= MASK_AH;
91 			break;
92 		case NEXTHDR_DEST:
93 			temp |= MASK_DSTOPTS;
94 			break;
95 		default:
96 			return false;
97 		}
98 
99 		nexthdr = hp->nexthdr;
100 		len -= hdrlen;
101 		ptr += hdrlen;
102 		if (ptr > skb->len)
103 			break;
104 	}
105 
106 	if (nexthdr != NEXTHDR_NONE && nexthdr != NEXTHDR_ESP)
107 		temp |= MASK_PROTO;
108 
109 	if (info->modeflag)
110 		return !((temp ^ info->matchflags ^ info->invflags)
111 			 & info->matchflags);
112 	else {
113 		if (info->invflags)
114 			return temp != info->matchflags;
115 		else
116 			return temp == info->matchflags;
117 	}
118 }
119 
120 static int ipv6header_mt6_check(const struct xt_mtchk_param *par)
121 {
122 	const struct ip6t_ipv6header_info *info = par->matchinfo;
123 
124 	/* invflags is 0 or 0xff in hard mode */
125 	if ((!info->modeflag) && info->invflags != 0x00 &&
126 	    info->invflags != 0xFF)
127 		return -EINVAL;
128 
129 	return 0;
130 }
131 
132 static struct xt_match ipv6header_mt6_reg __read_mostly = {
133 	.name		= "ipv6header",
134 	.family		= NFPROTO_IPV6,
135 	.match		= ipv6header_mt6,
136 	.matchsize	= sizeof(struct ip6t_ipv6header_info),
137 	.checkentry	= ipv6header_mt6_check,
138 	.destroy	= NULL,
139 	.me		= THIS_MODULE,
140 };
141 
142 static int __init ipv6header_mt6_init(void)
143 {
144 	return xt_register_match(&ipv6header_mt6_reg);
145 }
146 
147 static void __exit ipv6header_mt6_exit(void)
148 {
149 	xt_unregister_match(&ipv6header_mt6_reg);
150 }
151 
152 module_init(ipv6header_mt6_init);
153 module_exit(ipv6header_mt6_exit);
154