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 | |
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, offset: pos, to: &n, len: 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, offset: at + pos, to: &n, |
70 | len: 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 | |
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 | |
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 | |
129 | static int __init u32_mt_init(void) |
130 | { |
131 | return xt_register_match(target: &xt_u32_mt_reg); |
132 | } |
133 | |
134 | static void __exit u32_mt_exit(void) |
135 | { |
136 | xt_unregister_match(target: &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 | |