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1b50b8a3 JE |
1 | /* |
2 | * xt_u32 - kernel module to match u32 packet content | |
3 | * | |
4 | * Original author: Don Cohen <don@isis.cs3-inc.com> | |
5 | * © Jan Engelhardt <jengelh@gmx.de>, 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 | ||
16 | static 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 | u_int32_t pos; | |
25 | u_int32_t val; | |
26 | u_int32_t at; | |
27 | int ret; | |
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 | ret = skb_copy_bits(skb, pos, &val, sizeof(val)); | |
42 | BUG_ON(ret < 0); | |
43 | val = ntohl(val); | |
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 | ret = skb_copy_bits(skb, at + pos, &val, | |
69 | sizeof(val)); | |
70 | BUG_ON(ret < 0); | |
71 | val = ntohl(val); | |
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 | ||
89 | static bool u32_match(const struct sk_buff *skb, | |
90 | const struct net_device *in, | |
91 | const struct net_device *out, | |
92 | const struct xt_match *match, const void *matchinfo, | |
93 | int offset, unsigned int protoff, bool *hotdrop) | |
94 | { | |
95 | const struct xt_u32 *data = matchinfo; | |
96 | bool ret; | |
97 | ||
98 | ret = u32_match_it(data, skb); | |
99 | return ret ^ data->invert; | |
100 | } | |
101 | ||
9f15c530 | 102 | static struct xt_match u32_reg[] __read_mostly = { |
1b50b8a3 JE |
103 | { |
104 | .name = "u32", | |
105 | .family = AF_INET, | |
106 | .match = u32_match, | |
107 | .matchsize = sizeof(struct xt_u32), | |
108 | .me = THIS_MODULE, | |
109 | }, | |
110 | { | |
111 | .name = "u32", | |
112 | .family = AF_INET6, | |
113 | .match = u32_match, | |
114 | .matchsize = sizeof(struct xt_u32), | |
115 | .me = THIS_MODULE, | |
116 | }, | |
117 | }; | |
118 | ||
119 | static int __init xt_u32_init(void) | |
120 | { | |
121 | return xt_register_matches(u32_reg, ARRAY_SIZE(u32_reg)); | |
122 | } | |
123 | ||
124 | static void __exit xt_u32_exit(void) | |
125 | { | |
126 | xt_unregister_matches(u32_reg, ARRAY_SIZE(u32_reg)); | |
127 | } | |
128 | ||
129 | module_init(xt_u32_init); | |
130 | module_exit(xt_u32_exit); | |
131 | MODULE_AUTHOR("Jan Engelhardt <jengelh@gmx.de>"); | |
132 | MODULE_DESCRIPTION("netfilter u32 match module"); | |
133 | MODULE_LICENSE("GPL"); | |
134 | MODULE_ALIAS("ipt_u32"); | |
135 | MODULE_ALIAS("ip6t_u32"); |