1 // SPDX-License-Identifier: GPL-2.0-only
2 /* Kernel module to match FRAG parameters. */
3 
4 /* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
5  */
6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
7 #include <linux/module.h>
8 #include <linux/skbuff.h>
9 #include <linux/ipv6.h>
10 #include <linux/types.h>
11 #include <net/checksum.h>
12 #include <net/ipv6.h>
13 
14 #include <linux/netfilter/x_tables.h>
15 #include <linux/netfilter_ipv6/ip6_tables.h>
16 #include <linux/netfilter_ipv6/ip6t_frag.h>
17 
18 MODULE_LICENSE("GPL");
19 MODULE_DESCRIPTION("Xtables: IPv6 fragment match");
20 MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");
21 
22 /* Returns 1 if the id is matched by the range, 0 otherwise */
23 static inline bool
id_match(u_int32_t min,u_int32_t max,u_int32_t id,bool invert)24 id_match(u_int32_t min, u_int32_t max, u_int32_t id, bool invert)
25 {
26 	bool r;
27 	pr_debug("id_match:%c 0x%x <= 0x%x <= 0x%x\n", invert ? '!' : ' ',
28 		 min, id, max);
29 	r = (id >= min && id <= max) ^ invert;
30 	pr_debug(" result %s\n", r ? "PASS" : "FAILED");
31 	return r;
32 }
33 
34 static bool
frag_mt6(const struct sk_buff * skb,struct xt_action_param * par)35 frag_mt6(const struct sk_buff *skb, struct xt_action_param *par)
36 {
37 	struct frag_hdr _frag;
38 	const struct frag_hdr *fh;
39 	const struct ip6t_frag *fraginfo = par->matchinfo;
40 	unsigned int ptr = 0;
41 	int err;
42 
43 	err = ipv6_find_hdr(skb, &ptr, NEXTHDR_FRAGMENT, NULL, NULL);
44 	if (err < 0) {
45 		if (err != -ENOENT)
46 			par->hotdrop = true;
47 		return false;
48 	}
49 
50 	fh = skb_header_pointer(skb, ptr, sizeof(_frag), &_frag);
51 	if (fh == NULL) {
52 		par->hotdrop = true;
53 		return false;
54 	}
55 
56 	pr_debug("INFO %04X ", fh->frag_off);
57 	pr_debug("OFFSET %04X ", ntohs(fh->frag_off) & ~0x7);
58 	pr_debug("RES %02X %04X", fh->reserved, ntohs(fh->frag_off) & 0x6);
59 	pr_debug("MF %04X ", fh->frag_off & htons(IP6_MF));
60 	pr_debug("ID %u %08X\n", ntohl(fh->identification),
61 		 ntohl(fh->identification));
62 
63 	pr_debug("IPv6 FRAG id %02X ",
64 		 id_match(fraginfo->ids[0], fraginfo->ids[1],
65 			  ntohl(fh->identification),
66 			  !!(fraginfo->invflags & IP6T_FRAG_INV_IDS)));
67 	pr_debug("res %02X %02X%04X %02X ",
68 		 fraginfo->flags & IP6T_FRAG_RES, fh->reserved,
69 		 ntohs(fh->frag_off) & 0x6,
70 		 !((fraginfo->flags & IP6T_FRAG_RES) &&
71 		   (fh->reserved || (ntohs(fh->frag_off) & 0x06))));
72 	pr_debug("first %02X %02X %02X ",
73 		 fraginfo->flags & IP6T_FRAG_FST,
74 		 ntohs(fh->frag_off) & ~0x7,
75 		 !((fraginfo->flags & IP6T_FRAG_FST) &&
76 		   (ntohs(fh->frag_off) & ~0x7)));
77 	pr_debug("mf %02X %02X %02X ",
78 		 fraginfo->flags & IP6T_FRAG_MF,
79 		 ntohs(fh->frag_off) & IP6_MF,
80 		 !((fraginfo->flags & IP6T_FRAG_MF) &&
81 		   !((ntohs(fh->frag_off) & IP6_MF))));
82 	pr_debug("last %02X %02X %02X\n",
83 		 fraginfo->flags & IP6T_FRAG_NMF,
84 		 ntohs(fh->frag_off) & IP6_MF,
85 		 !((fraginfo->flags & IP6T_FRAG_NMF) &&
86 		   (ntohs(fh->frag_off) & IP6_MF)));
87 
88 	return id_match(fraginfo->ids[0], fraginfo->ids[1],
89 			 ntohl(fh->identification),
90 			 !!(fraginfo->invflags & IP6T_FRAG_INV_IDS)) &&
91 		!((fraginfo->flags & IP6T_FRAG_RES) &&
92 		  (fh->reserved || (ntohs(fh->frag_off) & 0x6))) &&
93 		!((fraginfo->flags & IP6T_FRAG_FST) &&
94 		  (ntohs(fh->frag_off) & ~0x7)) &&
95 		!((fraginfo->flags & IP6T_FRAG_MF) &&
96 		  !(ntohs(fh->frag_off) & IP6_MF)) &&
97 		!((fraginfo->flags & IP6T_FRAG_NMF) &&
98 		  (ntohs(fh->frag_off) & IP6_MF));
99 }
100 
frag_mt6_check(const struct xt_mtchk_param * par)101 static int frag_mt6_check(const struct xt_mtchk_param *par)
102 {
103 	const struct ip6t_frag *fraginfo = par->matchinfo;
104 
105 	if (fraginfo->invflags & ~IP6T_FRAG_INV_MASK) {
106 		pr_debug("unknown flags %X\n", fraginfo->invflags);
107 		return -EINVAL;
108 	}
109 	return 0;
110 }
111 
112 static struct xt_match frag_mt6_reg __read_mostly = {
113 	.name		= "frag",
114 	.family		= NFPROTO_IPV6,
115 	.match		= frag_mt6,
116 	.matchsize	= sizeof(struct ip6t_frag),
117 	.checkentry	= frag_mt6_check,
118 	.me		= THIS_MODULE,
119 };
120 
frag_mt6_init(void)121 static int __init frag_mt6_init(void)
122 {
123 	return xt_register_match(&frag_mt6_reg);
124 }
125 
frag_mt6_exit(void)126 static void __exit frag_mt6_exit(void)
127 {
128 	xt_unregister_match(&frag_mt6_reg);
129 }
130 
131 module_init(frag_mt6_init);
132 module_exit(frag_mt6_exit);
133