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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 | |
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 | __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 | |
89 | static 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 | |
98 | static 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 | |
107 | static int __init u32_mt_init(void) |
108 | { |
109 | return xt_register_match(&xt_u32_mt_reg); |
110 | } |
111 | |
112 | static void __exit u32_mt_exit(void) |
113 | { |
114 | xt_unregister_match(&xt_u32_mt_reg); |
115 | } |
116 | |
117 | module_init(u32_mt_init); |
118 | module_exit(u32_mt_exit); |
119 | MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>"); |
120 | MODULE_DESCRIPTION("Xtables: arbitrary byte matching"); |
121 | MODULE_LICENSE("GPL"); |
122 | MODULE_ALIAS("ipt_u32"); |
123 | MODULE_ALIAS("ip6t_u32"); |
124 |
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