1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *	xt_u32 - kernel module to match u32 packet content
4  *
5  *	Original author: Don Cohen <don@isis.cs3-inc.com>
6  *	(C) CC Computer Consultants GmbH, 2007
7  */
8 
9 #include <linux/module.h>
10 #include <linux/moduleparam.h>
11 #include <linux/spinlock.h>
12 #include <linux/skbuff.h>
13 #include <linux/types.h>
14 #include <linux/netfilter/x_tables.h>
15 #include <linux/netfilter/xt_u32.h>
16 
u32_match_it(const struct xt_u32 * data,const struct sk_buff * skb)17 static bool u32_match_it(const struct xt_u32 *data,
18 			 const struct sk_buff *skb)
19 {
20 	const struct xt_u32_test *ct;
21 	unsigned int testind;
22 	unsigned int nnums;
23 	unsigned int nvals;
24 	unsigned int i;
25 	__be32 n;
26 	u_int32_t pos;
27 	u_int32_t val;
28 	u_int32_t at;
29 
30 	/*
31 	 * Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17"
32 	 * (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands.
33 	 */
34 	for (testind = 0; testind < data->ntests; ++testind) {
35 		ct  = &data->tests[testind];
36 		at  = 0;
37 		pos = ct->location[0].number;
38 
39 		if (skb->len < 4 || pos > skb->len - 4)
40 			return false;
41 
42 		if (skb_copy_bits(skb, pos, &n, sizeof(n)) < 0)
43 			BUG();
44 		val   = ntohl(n);
45 		nnums = ct->nnums;
46 
47 		/* Inner loop runs over "&", "<<", ">>" and "@" operands */
48 		for (i = 1; i < nnums; ++i) {
49 			u_int32_t number = ct->location[i].number;
50 			switch (ct->location[i].nextop) {
51 			case XT_U32_AND:
52 				val &= number;
53 				break;
54 			case XT_U32_LEFTSH:
55 				val <<= number;
56 				break;
57 			case XT_U32_RIGHTSH:
58 				val >>= number;
59 				break;
60 			case XT_U32_AT:
61 				if (at + val < at)
62 					return false;
63 				at += val;
64 				pos = number;
65 				if (at + 4 < at || skb->len < at + 4 ||
66 				    pos > skb->len - at - 4)
67 					return false;
68 
69 				if (skb_copy_bits(skb, at + pos, &n,
70 						    sizeof(n)) < 0)
71 					BUG();
72 				val = ntohl(n);
73 				break;
74 			}
75 		}
76 
77 		/* Run over the "," and ":" operands */
78 		nvals = ct->nvalues;
79 		for (i = 0; i < nvals; ++i)
80 			if (ct->value[i].min <= val && val <= ct->value[i].max)
81 				break;
82 
83 		if (i >= ct->nvalues)
84 			return false;
85 	}
86 
87 	return true;
88 }
89 
u32_mt(const struct sk_buff * skb,struct xt_action_param * par)90 static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par)
91 {
92 	const struct xt_u32 *data = par->matchinfo;
93 	bool ret;
94 
95 	ret = u32_match_it(data, skb);
96 	return ret ^ data->invert;
97 }
98 
u32_mt_checkentry(const struct xt_mtchk_param * par)99 static int u32_mt_checkentry(const struct xt_mtchk_param *par)
100 {
101 	const struct xt_u32 *data = par->matchinfo;
102 	const struct xt_u32_test *ct;
103 	unsigned int i;
104 
105 	if (data->ntests > ARRAY_SIZE(data->tests))
106 		return -EINVAL;
107 
108 	for (i = 0; i < data->ntests; ++i) {
109 		ct = &data->tests[i];
110 
111 		if (ct->nnums > ARRAY_SIZE(ct->location) ||
112 		    ct->nvalues > ARRAY_SIZE(ct->value))
113 			return -EINVAL;
114 	}
115 
116 	return 0;
117 }
118 
119 static struct xt_match xt_u32_mt_reg __read_mostly = {
120 	.name       = "u32",
121 	.revision   = 0,
122 	.family     = NFPROTO_UNSPEC,
123 	.match      = u32_mt,
124 	.checkentry = u32_mt_checkentry,
125 	.matchsize  = sizeof(struct xt_u32),
126 	.me         = THIS_MODULE,
127 };
128 
u32_mt_init(void)129 static int __init u32_mt_init(void)
130 {
131 	return xt_register_match(&xt_u32_mt_reg);
132 }
133 
u32_mt_exit(void)134 static void __exit u32_mt_exit(void)
135 {
136 	xt_unregister_match(&xt_u32_mt_reg);
137 }
138 
139 module_init(u32_mt_init);
140 module_exit(u32_mt_exit);
141 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
142 MODULE_DESCRIPTION("Xtables: arbitrary byte matching");
143 MODULE_LICENSE("GPL");
144 MODULE_ALIAS("ipt_u32");
145 MODULE_ALIAS("ip6t_u32");
146