1 // SPDX-License-Identifier: GPL-2.0-only
2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
3 #include <linux/types.h>
4 #include <linux/module.h>
5 #include <net/ip.h>
6 #include <linux/ipv6.h>
7 #include <net/ipv6.h>
8 #include <net/tcp.h>
9 #include <net/udp.h>
10 #include <linux/netfilter/x_tables.h>
11 #include <linux/netfilter/xt_tcpudp.h>
12 #include <linux/netfilter_ipv4/ip_tables.h>
13 #include <linux/netfilter_ipv6/ip6_tables.h>
14
15 MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
16 MODULE_LICENSE("GPL");
17 MODULE_ALIAS("xt_tcp");
18 MODULE_ALIAS("xt_udp");
19 MODULE_ALIAS("ipt_udp");
20 MODULE_ALIAS("ipt_tcp");
21 MODULE_ALIAS("ip6t_udp");
22 MODULE_ALIAS("ip6t_tcp");
23
24 /* Returns 1 if the port is matched by the range, 0 otherwise */
25 static inline bool
26 port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
27 {
28 return (port >= min && port <= max) ^ invert;
29 }
30
31 static bool
32 tcp_find_option(u_int8_t option,
33 const struct sk_buff *skb,
34 unsigned int protoff,
35 unsigned int optlen,
36 bool invert,
37 bool *hotdrop)
38 {
39 /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
40 const u_int8_t *op;
41 u_int8_t _opt[60 - sizeof(struct tcphdr)];
42 unsigned int i;
43
44 pr_debug("finding option\n");
45
46 if (!optlen)
47 return invert;
48
49 /* If we don't have the whole header, drop packet. */
50 op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
51 optlen, _opt);
52 if (op == NULL) {
53 *hotdrop = true;
54 return false;
55 }
56
57 for (i = 0; i < optlen; ) {
58 if (op[i] == option) return !invert;
59 if (op[i] < 2) i++;
60 else i += op[i+1]?:1;
61 }
62
63 return invert;
64 }
65
66 static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
67 {
68 const struct tcphdr *th;
69 struct tcphdr _tcph;
70 const struct xt_tcp *tcpinfo = par->matchinfo;
71
72 if (par->fragoff != 0) {
73 /* To quote Alan:
74
75 Don't allow a fragment of TCP 8 bytes in. Nobody normal
76 causes this. Its a cracker trying to break in by doing a
77 flag overwrite to pass the direction checks.
78 */
79 if (par->fragoff == 1) {
80 pr_debug("Dropping evil TCP offset=1 frag.\n");
81 par->hotdrop = true;
82 }
83 /* Must not be a fragment. */
84 return false;
85 }
86
87 th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
88 if (th == NULL) {
89 /* We've been asked to examine this packet, and we
90 can't. Hence, no choice but to drop. */
91 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
92 par->hotdrop = true;
93 return false;
94 }
95
96 if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
97 ntohs(th->source),
98 !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
99 return false;
100 if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
101 ntohs(th->dest),
102 !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
103 return false;
104 if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
105 (((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
106 return false;
107 if (tcpinfo->option) {
108 if (th->doff * 4 < sizeof(_tcph)) {
109 par->hotdrop = true;
110 return false;
111 }
112 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
113 th->doff*4 - sizeof(_tcph),
114 tcpinfo->invflags & XT_TCP_INV_OPTION,
115 &par->hotdrop))
116 return false;
117 }
118 return true;
119 }
120
121 static int tcp_mt_check(const struct xt_mtchk_param *par)
122 {
123 const struct xt_tcp *tcpinfo = par->matchinfo;
124
125 /* Must specify no unknown invflags */
126 return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
127 }
128
129 static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
130 {
131 const struct udphdr *uh;
132 struct udphdr _udph;
133 const struct xt_udp *udpinfo = par->matchinfo;
134
135 /* Must not be a fragment. */
136 if (par->fragoff != 0)
137 return false;
138
139 uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
140 if (uh == NULL) {
141 /* We've been asked to examine this packet, and we
142 can't. Hence, no choice but to drop. */
143 pr_debug("Dropping evil UDP tinygram.\n");
144 par->hotdrop = true;
145 return false;
146 }
147
148 return port_match(udpinfo->spts[0], udpinfo->spts[1],
149 ntohs(uh->source),
150 !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
151 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
152 ntohs(uh->dest),
153 !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
154 }
155
156 static int udp_mt_check(const struct xt_mtchk_param *par)
157 {
158 const struct xt_udp *udpinfo = par->matchinfo;
159
160 /* Must specify no unknown invflags */
161 return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
162 }
163
164 static struct xt_match tcpudp_mt_reg[] __read_mostly = {
165 {
166 .name = "tcp",
167 .family = NFPROTO_IPV4,
168 .checkentry = tcp_mt_check,
169 .match = tcp_mt,
170 .matchsize = sizeof(struct xt_tcp),
171 .proto = IPPROTO_TCP,
172 .me = THIS_MODULE,
173 },
174 {
175 .name = "tcp",
176 .family = NFPROTO_IPV6,
177 .checkentry = tcp_mt_check,
178 .match = tcp_mt,
179 .matchsize = sizeof(struct xt_tcp),
180 .proto = IPPROTO_TCP,
181 .me = THIS_MODULE,
182 },
183 {
184 .name = "udp",
185 .family = NFPROTO_IPV4,
186 .checkentry = udp_mt_check,
187 .match = udp_mt,
188 .matchsize = sizeof(struct xt_udp),
189 .proto = IPPROTO_UDP,
190 .me = THIS_MODULE,
191 },
192 {
193 .name = "udp",
194 .family = NFPROTO_IPV6,
195 .checkentry = udp_mt_check,
196 .match = udp_mt,
197 .matchsize = sizeof(struct xt_udp),
198 .proto = IPPROTO_UDP,
199 .me = THIS_MODULE,
200 },
201 {
202 .name = "udplite",
203 .family = NFPROTO_IPV4,
204 .checkentry = udp_mt_check,
205 .match = udp_mt,
206 .matchsize = sizeof(struct xt_udp),
207 .proto = IPPROTO_UDPLITE,
208 .me = THIS_MODULE,
209 },
210 {
211 .name = "udplite",
212 .family = NFPROTO_IPV6,
213 .checkentry = udp_mt_check,
214 .match = udp_mt,
215 .matchsize = sizeof(struct xt_udp),
216 .proto = IPPROTO_UDPLITE,
217 .me = THIS_MODULE,
218 },
219 };
220
221 static int __init tcpudp_mt_init(void)
222 {
223 return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
224 }
225
226 static void __exit tcpudp_mt_exit(void)
227 {
228 xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
229 }
230
231 module_init(tcpudp_mt_init);
232 module_exit(tcpudp_mt_exit);
233
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