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
17static 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
90static 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
99static 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
119static 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
129static int __init u32_mt_init(void)
130{
131 return xt_register_match(target: &xt_u32_mt_reg);
132}
133
134static void __exit u32_mt_exit(void)
135{
136 xt_unregister_match(target: &xt_u32_mt_reg);
137}
138
139module_init(u32_mt_init);
140module_exit(u32_mt_exit);
141MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
142MODULE_DESCRIPTION("Xtables: arbitrary byte matching");
143MODULE_LICENSE("GPL");
144MODULE_ALIAS("ipt_u32");
145MODULE_ALIAS("ip6t_u32");
146

source code of linux/net/netfilter/xt_u32.c