xt_tcpudp.c

  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, protoff + sizeof(struct tcphdr),
 54				optlen, _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 == optlen - 1)
 63			i++;
 64		else
 65			i += op[i + 1] ? : 1;
 66	}
 67
 68	return invert;
 69}
 70
 71static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
 72{
 73	const struct tcphdr *th;
 74	struct tcphdr _tcph;
 75	const struct xt_tcp *tcpinfo = par->matchinfo;
 76
 77	if (par->fragoff != 0) {
 78		/* To quote Alan:
 79
 80		   Don't allow a fragment of TCP 8 bytes in. Nobody normal
 81		   causes this. Its a cracker trying to break in by doing a
 82		   flag overwrite to pass the direction checks.
 83		*/
 84		if (par->fragoff == 1) {
 85			pr_debug("Dropping evil TCP offset=1 frag.\n");
 86			par->hotdrop = true;
 87		}
 88		/* Must not be a fragment. */
 89		return false;
 90	}
 91
 92	th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
 93	if (th == NULL) {
 94		/* We've been asked to examine this packet, and we
 95		   can't.  Hence, no choice but to drop. */
 96		pr_debug("Dropping evil TCP offset=0 tinygram.\n");
 97		par->hotdrop = true;
 98		return false;
 99	}
100
101	if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
102			ntohs(th->source),
103			!!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
104		return false;
105	if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
106			ntohs(th->dest),
107			!!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
108		return false;
109	if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
110		     (((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
111		return false;
112	if (tcpinfo->option) {
113		if (th->doff * 4 < sizeof(_tcph)) {
114			par->hotdrop = true;
115			return false;
116		}
117		if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
118				     th->doff*4 - sizeof(_tcph),
119				     tcpinfo->invflags & XT_TCP_INV_OPTION,
120				     &par->hotdrop))
121			return false;
122	}
123	return true;
124}
125
126static int tcp_mt_check(const struct xt_mtchk_param *par)
127{
128	const struct xt_tcp *tcpinfo = par->matchinfo;
129
130	/* Must specify no unknown invflags */
131	return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
132}
133
134static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
135{
136	const struct udphdr *uh;
137	struct udphdr _udph;
138	const struct xt_udp *udpinfo = par->matchinfo;
139
140	/* Must not be a fragment. */
141	if (par->fragoff != 0)
142		return false;
143
144	uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
145	if (uh == NULL) {
146		/* We've been asked to examine this packet, and we
147		   can't.  Hence, no choice but to drop. */
148		pr_debug("Dropping evil UDP tinygram.\n");
149		par->hotdrop = true;
150		return false;
151	}
152
153	return port_match(udpinfo->spts[0], udpinfo->spts[1],
154			  ntohs(uh->source),
155			  !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
156		&& port_match(udpinfo->dpts[0], udpinfo->dpts[1],
157			      ntohs(uh->dest),
158			      !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
159}
160
161static int udp_mt_check(const struct xt_mtchk_param *par)
162{
163	const struct xt_udp *udpinfo = par->matchinfo;
164
165	/* Must specify no unknown invflags */
166	return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
167}
168
169/* Returns 1 if the type and code is matched by the range, 0 otherwise */
170static bool type_code_in_range(u8 test_type, u8 min_code, u8 max_code,
171			       u8 type, u8 code)
172{
173	return type == test_type && code >= min_code && code <= max_code;
174}
175
176static bool icmp_type_code_match(u8 test_type, u8 min_code, u8 max_code,
177				 u8 type, u8 code, bool invert)
178{
179	return (test_type == 0xFF ||
180		type_code_in_range(test_type, min_code, max_code, type, code))
181		^ invert;
182}
183
184static bool icmp6_type_code_match(u8 test_type, u8 min_code, u8 max_code,
185				  u8 type, u8 code, bool invert)
186{
187	return type_code_in_range(test_type, min_code, max_code, type, code) ^ invert;
188}
189
190static bool
191icmp_match(const struct sk_buff *skb, struct xt_action_param *par)
192{
193	const struct icmphdr *ic;
194	struct icmphdr _icmph;
195	const struct ipt_icmp *icmpinfo = par->matchinfo;
196
197	/* Must not be a fragment. */
198	if (par->fragoff != 0)
199		return false;
200
201	ic = skb_header_pointer(skb, par->thoff, sizeof(_icmph), &_icmph);
202	if (!ic) {
203		/* We've been asked to examine this packet, and we
204		 * can't.  Hence, no choice but to drop.
205		 */
206		par->hotdrop = true;
207		return false;
208	}
209
210	return icmp_type_code_match(icmpinfo->type,
211				    icmpinfo->code[0],
212				    icmpinfo->code[1],
213				    ic->type, ic->code,
214				    !!(icmpinfo->invflags & IPT_ICMP_INV));
215}
216
217static bool
218icmp6_match(const struct sk_buff *skb, struct xt_action_param *par)
219{
220	const struct icmp6hdr *ic;
221	struct icmp6hdr _icmph;
222	const struct ip6t_icmp *icmpinfo = par->matchinfo;
223
224	/* Must not be a fragment. */
225	if (par->fragoff != 0)
226		return false;
227
228	ic = skb_header_pointer(skb, par->thoff, sizeof(_icmph), &_icmph);
229	if (!ic) {
230		/* We've been asked to examine this packet, and we
231		 * can't.  Hence, no choice but to drop.
232		 */
233		par->hotdrop = true;
234		return false;
235	}
236
237	return icmp6_type_code_match(icmpinfo->type,
238				     icmpinfo->code[0],
239				     icmpinfo->code[1],
240				     ic->icmp6_type, ic->icmp6_code,
241				     !!(icmpinfo->invflags & IP6T_ICMP_INV));
242}
243
244static int icmp_checkentry(const struct xt_mtchk_param *par)
245{
246	const struct ipt_icmp *icmpinfo = par->matchinfo;
247
248	return (icmpinfo->invflags & ~IPT_ICMP_INV) ? -EINVAL : 0;
249}
250
251static int icmp6_checkentry(const struct xt_mtchk_param *par)
252{
253	const struct ip6t_icmp *icmpinfo = par->matchinfo;
254
255	return (icmpinfo->invflags & ~IP6T_ICMP_INV) ? -EINVAL : 0;
256}
257
258static struct xt_match tcpudp_mt_reg[] __read_mostly = {
259	{
260		.name		= "tcp",
261		.family		= NFPROTO_IPV4,
262		.checkentry	= tcp_mt_check,
263		.match		= tcp_mt,
264		.matchsize	= sizeof(struct xt_tcp),
265		.proto		= IPPROTO_TCP,
266		.me		= THIS_MODULE,
267	},
268	{
269		.name		= "tcp",
270		.family		= NFPROTO_IPV6,
271		.checkentry	= tcp_mt_check,
272		.match		= tcp_mt,
273		.matchsize	= sizeof(struct xt_tcp),
274		.proto		= IPPROTO_TCP,
275		.me		= THIS_MODULE,
276	},
277	{
278		.name		= "udp",
279		.family		= NFPROTO_IPV4,
280		.checkentry	= udp_mt_check,
281		.match		= udp_mt,
282		.matchsize	= sizeof(struct xt_udp),
283		.proto		= IPPROTO_UDP,
284		.me		= THIS_MODULE,
285	},
286	{
287		.name		= "udp",
288		.family		= NFPROTO_IPV6,
289		.checkentry	= udp_mt_check,
290		.match		= udp_mt,
291		.matchsize	= sizeof(struct xt_udp),
292		.proto		= IPPROTO_UDP,
293		.me		= THIS_MODULE,
294	},
295	{
296		.name		= "udplite",
297		.family		= NFPROTO_IPV4,
298		.checkentry	= udp_mt_check,
299		.match		= udp_mt,
300		.matchsize	= sizeof(struct xt_udp),
301		.proto		= IPPROTO_UDPLITE,
302		.me		= THIS_MODULE,
303	},
304	{
305		.name		= "udplite",
306		.family		= NFPROTO_IPV6,
307		.checkentry	= udp_mt_check,
308		.match		= udp_mt,
309		.matchsize	= sizeof(struct xt_udp),
310		.proto		= IPPROTO_UDPLITE,
311		.me		= THIS_MODULE,
312	},
313	{
314		.name       = "icmp",
315		.match      = icmp_match,
316		.matchsize  = sizeof(struct ipt_icmp),
317		.checkentry = icmp_checkentry,
318		.proto      = IPPROTO_ICMP,
319		.family     = NFPROTO_IPV4,
320		.me         = THIS_MODULE,
321	},
322	{
323		.name       = "icmp6",
324		.match      = icmp6_match,
325		.matchsize  = sizeof(struct ip6t_icmp),
326		.checkentry = icmp6_checkentry,
327		.proto      = IPPROTO_ICMPV6,
328		.family     = NFPROTO_IPV6,
329		.me	    = THIS_MODULE,
330	},
331};
332
333static int __init tcpudp_mt_init(void)
334{
335	return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
336}
337
338static void __exit tcpudp_mt_exit(void)
339{
340	xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
341}
342
343module_init(tcpudp_mt_init);
344module_exit(tcpudp_mt_exit);