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