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 <linux/icmp.h>
8#include <net/ipv6.h>
9#include <net/tcp.h>
10#include <net/udp.h>
11#include <linux/netfilter/x_tables.h>
12#include <linux/netfilter/xt_tcpudp.h>
13#include <linux/netfilter_ipv4/ip_tables.h>
14#include <linux/netfilter_ipv6/ip6_tables.h>
15
16MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
17MODULE_LICENSE("GPL");
18MODULE_ALIAS("xt_tcp");
19MODULE_ALIAS("xt_udp");
20MODULE_ALIAS("ipt_udp");
21MODULE_ALIAS("ipt_tcp");
22MODULE_ALIAS("ip6t_udp");
23MODULE_ALIAS("ip6t_tcp");
24MODULE_ALIAS("ipt_icmp");
25MODULE_ALIAS("ip6t_icmp6");
26
27/* Returns 1 if the port is matched by the range, 0 otherwise */
28static inline bool
29port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
30{
31 return (port >= min && port <= max) ^ invert;
32}
33
34static bool
35tcp_find_option(u_int8_t option,
36 const struct sk_buff *skb,
37 unsigned int protoff,
38 unsigned int optlen,
39 bool invert,
40 bool *hotdrop)
41{
42 /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
43 const u_int8_t *op;
44 u_int8_t _opt[60 - sizeof(struct tcphdr)];
45 unsigned int i;
46
47 pr_debug("finding option\n");
48
49 if (!optlen)
50 return invert;
51
52 /* If we don't have the whole header, drop packet. */
53 op = skb_header_pointer(skb, offset: protoff + sizeof(struct tcphdr),
54 len: optlen, buffer: _opt);
55 if (op == NULL) {
56 *hotdrop = true;
57 return false;
58 }
59
60 for (i = 0; i < optlen; ) {
61 if (op[i] == option) return !invert;
62 if (op[i] < 2) i++;
63 else i += op[i+1]?:1;
64 }
65
66 return invert;
67}
68
69static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
70{
71 const struct tcphdr *th;
72 struct tcphdr _tcph;
73 const struct xt_tcp *tcpinfo = par->matchinfo;
74
75 if (par->fragoff != 0) {
76 /* To quote Alan:
77
78 Don't allow a fragment of TCP 8 bytes in. Nobody normal
79 causes this. Its a cracker trying to break in by doing a
80 flag overwrite to pass the direction checks.
81 */
82 if (par->fragoff == 1) {
83 pr_debug("Dropping evil TCP offset=1 frag.\n");
84 par->hotdrop = true;
85 }
86 /* Must not be a fragment. */
87 return false;
88 }
89
90 th = skb_header_pointer(skb, offset: par->thoff, len: sizeof(_tcph), buffer: &_tcph);
91 if (th == NULL) {
92 /* We've been asked to examine this packet, and we
93 can't. Hence, no choice but to drop. */
94 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
95 par->hotdrop = true;
96 return false;
97 }
98
99 if (!port_match(min: tcpinfo->spts[0], max: tcpinfo->spts[1],
100 ntohs(th->source),
101 invert: !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
102 return false;
103 if (!port_match(min: tcpinfo->dpts[0], max: tcpinfo->dpts[1],
104 ntohs(th->dest),
105 invert: !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
106 return false;
107 if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
108 (((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
109 return false;
110 if (tcpinfo->option) {
111 if (th->doff * 4 < sizeof(_tcph)) {
112 par->hotdrop = true;
113 return false;
114 }
115 if (!tcp_find_option(option: tcpinfo->option, skb, protoff: par->thoff,
116 optlen: th->doff*4 - sizeof(_tcph),
117 invert: tcpinfo->invflags & XT_TCP_INV_OPTION,
118 hotdrop: &par->hotdrop))
119 return false;
120 }
121 return true;
122}
123
124static int tcp_mt_check(const struct xt_mtchk_param *par)
125{
126 const struct xt_tcp *tcpinfo = par->matchinfo;
127
128 /* Must specify no unknown invflags */
129 return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
130}
131
132static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
133{
134 const struct udphdr *uh;
135 struct udphdr _udph;
136 const struct xt_udp *udpinfo = par->matchinfo;
137
138 /* Must not be a fragment. */
139 if (par->fragoff != 0)
140 return false;
141
142 uh = skb_header_pointer(skb, offset: par->thoff, len: sizeof(_udph), buffer: &_udph);
143 if (uh == NULL) {
144 /* We've been asked to examine this packet, and we
145 can't. Hence, no choice but to drop. */
146 pr_debug("Dropping evil UDP tinygram.\n");
147 par->hotdrop = true;
148 return false;
149 }
150
151 return port_match(min: udpinfo->spts[0], max: udpinfo->spts[1],
152 ntohs(uh->source),
153 invert: !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
154 && port_match(min: udpinfo->dpts[0], max: udpinfo->dpts[1],
155 ntohs(uh->dest),
156 invert: !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
157}
158
159static int udp_mt_check(const struct xt_mtchk_param *par)
160{
161 const struct xt_udp *udpinfo = par->matchinfo;
162
163 /* Must specify no unknown invflags */
164 return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
165}
166
167/* Returns 1 if the type and code is matched by the range, 0 otherwise */
168static bool type_code_in_range(u8 test_type, u8 min_code, u8 max_code,
169 u8 type, u8 code)
170{
171 return type == test_type && code >= min_code && code <= max_code;
172}
173
174static bool icmp_type_code_match(u8 test_type, u8 min_code, u8 max_code,
175 u8 type, u8 code, bool invert)
176{
177 return (test_type == 0xFF ||
178 type_code_in_range(test_type, min_code, max_code, type, code))
179 ^ invert;
180}
181
182static bool icmp6_type_code_match(u8 test_type, u8 min_code, u8 max_code,
183 u8 type, u8 code, bool invert)
184{
185 return type_code_in_range(test_type, min_code, max_code, type, code) ^ invert;
186}
187
188static bool
189icmp_match(const struct sk_buff *skb, struct xt_action_param *par)
190{
191 const struct icmphdr *ic;
192 struct icmphdr _icmph;
193 const struct ipt_icmp *icmpinfo = par->matchinfo;
194
195 /* Must not be a fragment. */
196 if (par->fragoff != 0)
197 return false;
198
199 ic = skb_header_pointer(skb, offset: par->thoff, len: sizeof(_icmph), buffer: &_icmph);
200 if (!ic) {
201 /* We've been asked to examine this packet, and we
202 * can't. Hence, no choice but to drop.
203 */
204 par->hotdrop = true;
205 return false;
206 }
207
208 return icmp_type_code_match(test_type: icmpinfo->type,
209 min_code: icmpinfo->code[0],
210 max_code: icmpinfo->code[1],
211 type: ic->type, code: ic->code,
212 invert: !!(icmpinfo->invflags & IPT_ICMP_INV));
213}
214
215static bool
216icmp6_match(const struct sk_buff *skb, struct xt_action_param *par)
217{
218 const struct icmp6hdr *ic;
219 struct icmp6hdr _icmph;
220 const struct ip6t_icmp *icmpinfo = par->matchinfo;
221
222 /* Must not be a fragment. */
223 if (par->fragoff != 0)
224 return false;
225
226 ic = skb_header_pointer(skb, offset: par->thoff, len: sizeof(_icmph), buffer: &_icmph);
227 if (!ic) {
228 /* We've been asked to examine this packet, and we
229 * can't. Hence, no choice but to drop.
230 */
231 par->hotdrop = true;
232 return false;
233 }
234
235 return icmp6_type_code_match(test_type: icmpinfo->type,
236 min_code: icmpinfo->code[0],
237 max_code: icmpinfo->code[1],
238 type: ic->icmp6_type, code: ic->icmp6_code,
239 invert: !!(icmpinfo->invflags & IP6T_ICMP_INV));
240}
241
242static int icmp_checkentry(const struct xt_mtchk_param *par)
243{
244 const struct ipt_icmp *icmpinfo = par->matchinfo;
245
246 return (icmpinfo->invflags & ~IPT_ICMP_INV) ? -EINVAL : 0;
247}
248
249static int icmp6_checkentry(const struct xt_mtchk_param *par)
250{
251 const struct ip6t_icmp *icmpinfo = par->matchinfo;
252
253 return (icmpinfo->invflags & ~IP6T_ICMP_INV) ? -EINVAL : 0;
254}
255
256static struct xt_match tcpudp_mt_reg[] __read_mostly = {
257 {
258 .name = "tcp",
259 .family = NFPROTO_IPV4,
260 .checkentry = tcp_mt_check,
261 .match = tcp_mt,
262 .matchsize = sizeof(struct xt_tcp),
263 .proto = IPPROTO_TCP,
264 .me = THIS_MODULE,
265 },
266 {
267 .name = "tcp",
268 .family = NFPROTO_IPV6,
269 .checkentry = tcp_mt_check,
270 .match = tcp_mt,
271 .matchsize = sizeof(struct xt_tcp),
272 .proto = IPPROTO_TCP,
273 .me = THIS_MODULE,
274 },
275 {
276 .name = "udp",
277 .family = NFPROTO_IPV4,
278 .checkentry = udp_mt_check,
279 .match = udp_mt,
280 .matchsize = sizeof(struct xt_udp),
281 .proto = IPPROTO_UDP,
282 .me = THIS_MODULE,
283 },
284 {
285 .name = "udp",
286 .family = NFPROTO_IPV6,
287 .checkentry = udp_mt_check,
288 .match = udp_mt,
289 .matchsize = sizeof(struct xt_udp),
290 .proto = IPPROTO_UDP,
291 .me = THIS_MODULE,
292 },
293 {
294 .name = "udplite",
295 .family = NFPROTO_IPV4,
296 .checkentry = udp_mt_check,
297 .match = udp_mt,
298 .matchsize = sizeof(struct xt_udp),
299 .proto = IPPROTO_UDPLITE,
300 .me = THIS_MODULE,
301 },
302 {
303 .name = "udplite",
304 .family = NFPROTO_IPV6,
305 .checkentry = udp_mt_check,
306 .match = udp_mt,
307 .matchsize = sizeof(struct xt_udp),
308 .proto = IPPROTO_UDPLITE,
309 .me = THIS_MODULE,
310 },
311 {
312 .name = "icmp",
313 .match = icmp_match,
314 .matchsize = sizeof(struct ipt_icmp),
315 .checkentry = icmp_checkentry,
316 .proto = IPPROTO_ICMP,
317 .family = NFPROTO_IPV4,
318 .me = THIS_MODULE,
319 },
320 {
321 .name = "icmp6",
322 .match = icmp6_match,
323 .matchsize = sizeof(struct ip6t_icmp),
324 .checkentry = icmp6_checkentry,
325 .proto = IPPROTO_ICMPV6,
326 .family = NFPROTO_IPV6,
327 .me = THIS_MODULE,
328 },
329};
330
331static int __init tcpudp_mt_init(void)
332{
333 return xt_register_matches(match: tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
334}
335
336static void __exit tcpudp_mt_exit(void)
337{
338 xt_unregister_matches(match: tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
339}
340
341module_init(tcpudp_mt_init);
342module_exit(tcpudp_mt_exit);
343