1/*-
2 * Copyright (c) 2003-2004 Networks Associates Technology, Inc.
3 * Copyright (c) 2006 SPARTA, Inc.
4 * All rights reserved.
5 *
6 * This software was developed for the FreeBSD Project by Network
7 * Associates Laboratories, the Security Research Division of Network
8 * Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"),
9 * as part of the DARPA CHATS research program.
10 *
11 * This software was enhanced by SPARTA ISSO under SPAWAR contract
12 * N66001-04-C-6019 ("SEFOS").
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 * 1. Redistributions of source code must retain the above copyright
18 *    notice, this list of conditions and the following disclaimer.
19 * 2. Redistributions in binary form must reproduce the above copyright
20 *    notice, this list of conditions and the following disclaimer in the
21 *    documentation and/or other materials provided with the distribution.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 *
35 * $FreeBSD$
36 */
37
38/*
39 * Developed by the TrustedBSD Project.
40 *
41 * Administratively limit access to local UDP/TCP ports for binding purposes.
42 * Intended to be combined with net.inet.ip.portrange.reservedhigh to allow
43 * specific uids and gids to bind specific ports for specific purposes,
44 * while not opening the door to any user replacing an "official" service
45 * while you're restarting it.  This only affects ports explicitly bound by
46 * the user process (either for listen/outgoing socket for TCP, or send/
47 * receive for UDP).  This module will not limit ports bound implicitly for
48 * out-going connections where the process hasn't explicitly selected a port:
49 * these are automatically selected by the IP stack.
50 *
51 * To use this module, security.mac.enforce_socket must be enabled, and you
52 * will probably want to twiddle the net.inet sysctl listed above.  Then use
53 * sysctl(8) to modify the rules string:
54 *
55 * # sysctl security.mac.portacl.rules="uid:425:tcp:80,uid:425:tcp:79"
56 *
57 * This ruleset, for example, permits uid 425 to bind TCP ports 80 (http) and
58 * 79 (finger).  User names and group names can't be used directly because
59 * the kernel only knows about uids and gids.
60 */
61
62#include <sys/param.h>
63#include <sys/domain.h>
64#include <sys/kernel.h>
65#include <sys/lock.h>
66#include <sys/malloc.h>
67#include <sys/module.h>
68#include <sys/mutex.h>
69#include <sys/priv.h>
70#include <sys/proc.h>
71#include <sys/protosw.h>
72#include <sys/queue.h>
73#include <sys/systm.h>
74#include <sys/sbuf.h>
75#include <sys/socket.h>
76#include <sys/socketvar.h>
77#include <sys/sysctl.h>
78
79#include <netinet/in.h>
80#include <netinet/in_pcb.h>
81
82#include <security/mac/mac_policy.h>
83
84SYSCTL_DECL(_security_mac);
85
86static SYSCTL_NODE(_security_mac, OID_AUTO, portacl, CTLFLAG_RW, 0,
87    "TrustedBSD mac_portacl policy controls");
88
89static int	portacl_enabled = 1;
90SYSCTL_INT(_security_mac_portacl, OID_AUTO, enabled, CTLFLAG_RWTUN,
91    &portacl_enabled, 0, "Enforce portacl policy");
92
93static int	portacl_suser_exempt = 1;
94SYSCTL_INT(_security_mac_portacl, OID_AUTO, suser_exempt, CTLFLAG_RWTUN,
95    &portacl_suser_exempt, 0, "Privilege permits binding of any port");
96
97static int	portacl_autoport_exempt = 1;
98SYSCTL_INT(_security_mac_portacl, OID_AUTO, autoport_exempt, CTLFLAG_RWTUN,
99    &portacl_autoport_exempt, 0, "Allow automatic allocation through "
100    "binding port 0 if not IP_PORTRANGELOW");
101
102static int	portacl_port_high = 1023;
103SYSCTL_INT(_security_mac_portacl, OID_AUTO, port_high, CTLFLAG_RWTUN,
104    &portacl_port_high, 0, "Highest port to enforce for");
105
106static MALLOC_DEFINE(M_PORTACL, "portacl_rule", "Rules for mac_portacl");
107
108#define	MAC_RULE_STRING_LEN	1024
109
110#define	RULE_GID	1
111#define	RULE_UID	2
112#define	RULE_PROTO_TCP	1
113#define	RULE_PROTO_UDP	2
114struct rule {
115	id_t			r_id;
116	int			r_idtype;
117	u_int16_t		r_port;
118	int			r_protocol;
119
120	TAILQ_ENTRY(rule)	r_entries;
121};
122
123#define	GID_STRING	"gid"
124#define	TCP_STRING	"tcp"
125#define	UID_STRING	"uid"
126#define	UDP_STRING	"udp"
127
128/*
129 * Text format for the rule string is that a rule consists of a
130 * comma-separated list of elements.  Each element is in the form
131 * idtype:id:protocol:portnumber, and constitutes granting of permission
132 * for the specified binding.
133 */
134
135static struct mtx			rule_mtx;
136static TAILQ_HEAD(rulehead, rule)	rule_head;
137static char				rule_string[MAC_RULE_STRING_LEN];
138
139static void
140toast_rules(struct rulehead *head)
141{
142	struct rule *rule;
143
144	while ((rule = TAILQ_FIRST(head)) != NULL) {
145		TAILQ_REMOVE(head, rule, r_entries);
146		free(rule, M_PORTACL);
147	}
148}
149
150/*
151 * Note that there is an inherent race condition in the unload of modules
152 * and access via sysctl.
153 */
154static void
155destroy(struct mac_policy_conf *mpc)
156{
157
158	mtx_destroy(&rule_mtx);
159	toast_rules(&rule_head);
160}
161
162static void
163init(struct mac_policy_conf *mpc)
164{
165
166	mtx_init(&rule_mtx, "rule_mtx", NULL, MTX_DEF);
167	TAILQ_INIT(&rule_head);
168}
169
170/*
171 * Note: parsing routines are destructive on the passed string.
172 */
173static int
174parse_rule_element(char *element, struct rule **rule)
175{
176	char *idtype, *id, *protocol, *portnumber, *p;
177	struct rule *new;
178	int error;
179
180	error = 0;
181	new = malloc(sizeof(*new), M_PORTACL, M_ZERO | M_WAITOK);
182
183	idtype = strsep(&element, ":");
184	if (idtype == NULL) {
185		error = EINVAL;
186		goto out;
187	}
188	id = strsep(&element, ":");
189	if (id == NULL) {
190		error = EINVAL;
191		goto out;
192	}
193	new->r_id = strtol(id, &p, 10);
194	if (*p != '\0') {
195		error = EINVAL;
196		goto out;
197	}
198	if (strcmp(idtype, UID_STRING) == 0)
199		new->r_idtype = RULE_UID;
200	else if (strcmp(idtype, GID_STRING) == 0)
201		new->r_idtype = RULE_GID;
202	else {
203		error = EINVAL;
204		goto out;
205	}
206	protocol = strsep(&element, ":");
207	if (protocol == NULL) {
208		error = EINVAL;
209		goto out;
210	}
211	if (strcmp(protocol, TCP_STRING) == 0)
212		new->r_protocol = RULE_PROTO_TCP;
213	else if (strcmp(protocol, UDP_STRING) == 0)
214		new->r_protocol = RULE_PROTO_UDP;
215	else {
216		error = EINVAL;
217		goto out;
218	}
219	portnumber = element;
220	if (portnumber == NULL) {
221		error = EINVAL;
222		goto out;
223	}
224	new->r_port = strtol(portnumber, &p, 10);
225	if (*p != '\0') {
226		error = EINVAL;
227		goto out;
228	}
229
230out:
231	if (error != 0) {
232		free(new, M_PORTACL);
233		*rule = NULL;
234	} else
235		*rule = new;
236	return (error);
237}
238
239static int
240parse_rules(char *string, struct rulehead *head)
241{
242	struct rule *new;
243	char *element;
244	int error;
245
246	error = 0;
247	while ((element = strsep(&string, ",")) != NULL) {
248		if (strlen(element) == 0)
249			continue;
250		error = parse_rule_element(element, &new);
251		if (error)
252			goto out;
253		TAILQ_INSERT_TAIL(head, new, r_entries);
254	}
255out:
256	if (error != 0)
257		toast_rules(head);
258	return (error);
259}
260
261/*
262 * rule_printf() and rules_to_string() are unused currently because they rely
263 * on sbufs with auto-extension, which may sleep while holding a mutex.
264 * Instead, the non-canonical user-generated rule string is returned to the
265 * user when the rules are queried, which is faster anyway.
266 */
267#if 0
268static void
269rule_printf(struct sbuf *sb, struct rule *rule)
270{
271	const char *idtype, *protocol;
272
273	switch(rule->r_idtype) {
274	case RULE_GID:
275		idtype = GID_STRING;
276		break;
277	case RULE_UID:
278		idtype = UID_STRING;
279		break;
280	default:
281		panic("rule_printf: unknown idtype (%d)\n", rule->r_idtype);
282	}
283
284	switch (rule->r_protocol) {
285	case RULE_PROTO_TCP:
286		protocol = TCP_STRING;
287		break;
288	case RULE_PROTO_UDP:
289		protocol = UDP_STRING;
290		break;
291	default:
292		panic("rule_printf: unknown protocol (%d)\n",
293		    rule->r_protocol);
294	}
295	sbuf_printf(sb, "%s:%jd:%s:%d", idtype, (intmax_t)rule->r_id,
296	    protocol, rule->r_port);
297}
298
299static char *
300rules_to_string(void)
301{
302	struct rule *rule;
303	struct sbuf *sb;
304	int needcomma;
305	char *temp;
306
307	sb = sbuf_new_auto();
308	needcomma = 0;
309	mtx_lock(&rule_mtx);
310	for (rule = TAILQ_FIRST(&rule_head); rule != NULL;
311	    rule = TAILQ_NEXT(rule, r_entries)) {
312		if (!needcomma)
313			needcomma = 1;
314		else
315			sbuf_printf(sb, ",");
316		rule_printf(sb, rule);
317	}
318	mtx_unlock(&rule_mtx);
319	sbuf_finish(sb);
320	temp = strdup(sbuf_data(sb), M_PORTACL);
321	sbuf_delete(sb);
322	return (temp);
323}
324#endif
325
326/*
327 * Note: due to races, there is not a single serializable order
328 * between parallel calls to the sysctl.
329 */
330static int
331sysctl_rules(SYSCTL_HANDLER_ARGS)
332{
333	char *string, *copy_string, *new_string;
334	struct rulehead head, save_head;
335	int error;
336
337	new_string = NULL;
338	if (req->newptr != NULL) {
339		new_string = malloc(MAC_RULE_STRING_LEN, M_PORTACL,
340		    M_WAITOK | M_ZERO);
341		mtx_lock(&rule_mtx);
342		strcpy(new_string, rule_string);
343		mtx_unlock(&rule_mtx);
344		string = new_string;
345	} else
346		string = rule_string;
347
348	error = sysctl_handle_string(oidp, string, MAC_RULE_STRING_LEN, req);
349	if (error)
350		goto out;
351
352	if (req->newptr != NULL) {
353		copy_string = strdup(string, M_PORTACL);
354		TAILQ_INIT(&head);
355		error = parse_rules(copy_string, &head);
356		free(copy_string, M_PORTACL);
357		if (error)
358			goto out;
359
360		TAILQ_INIT(&save_head);
361		mtx_lock(&rule_mtx);
362		TAILQ_CONCAT(&save_head, &rule_head, r_entries);
363		TAILQ_CONCAT(&rule_head, &head, r_entries);
364		strcpy(rule_string, string);
365		mtx_unlock(&rule_mtx);
366		toast_rules(&save_head);
367	}
368out:
369	if (new_string != NULL)
370		free(new_string, M_PORTACL);
371	return (error);
372}
373
374SYSCTL_PROC(_security_mac_portacl, OID_AUTO, rules,
375       CTLTYPE_STRING|CTLFLAG_RW, 0, 0, sysctl_rules, "A", "Rules");
376
377static int
378rules_check(struct ucred *cred, int family, int type, u_int16_t port)
379{
380	struct rule *rule;
381	int error;
382
383#if 0
384	printf("Check requested for euid %d, family %d, type %d, port %d\n",
385	    cred->cr_uid, family, type, port);
386#endif
387
388	if (port > portacl_port_high)
389		return (0);
390
391	error = EPERM;
392	mtx_lock(&rule_mtx);
393	for (rule = TAILQ_FIRST(&rule_head);
394	    rule != NULL;
395	    rule = TAILQ_NEXT(rule, r_entries)) {
396		if (type == SOCK_DGRAM && rule->r_protocol != RULE_PROTO_UDP)
397			continue;
398		if (type == SOCK_STREAM && rule->r_protocol != RULE_PROTO_TCP)
399			continue;
400		if (port != rule->r_port)
401			continue;
402		if (rule->r_idtype == RULE_UID) {
403			if (cred->cr_uid == rule->r_id) {
404				error = 0;
405				break;
406			}
407		} else if (rule->r_idtype == RULE_GID) {
408			if (cred->cr_gid == rule->r_id) {
409				error = 0;
410				break;
411			} else if (groupmember(rule->r_id, cred)) {
412				error = 0;
413				break;
414			}
415		} else
416			panic("rules_check: unknown rule type %d",
417			    rule->r_idtype);
418	}
419	mtx_unlock(&rule_mtx);
420
421	if (error != 0 && portacl_suser_exempt != 0)
422		error = priv_check_cred(cred, PRIV_NETINET_RESERVEDPORT, 0);
423
424	return (error);
425}
426
427/*
428 * Note, this only limits the ability to explicitly bind a port, it
429 * doesn't limit implicitly bound ports for outgoing connections where
430 * the source port is left up to the IP stack to determine automatically.
431 */
432static int
433socket_check_bind(struct ucred *cred, struct socket *so,
434    struct label *solabel, struct sockaddr *sa)
435{
436	struct sockaddr_in *sin;
437	struct inpcb *inp;
438	int family, type;
439	u_int16_t port;
440
441	/* Only run if we are enabled. */
442	if (portacl_enabled == 0)
443		return (0);
444
445	/* Only interested in IPv4 and IPv6 sockets. */
446	if (so->so_proto->pr_domain->dom_family != PF_INET &&
447	    so->so_proto->pr_domain->dom_family != PF_INET6)
448		return (0);
449
450	/* Currently, we don't attempt to deal with SOCK_RAW, etc. */
451	if (so->so_type != SOCK_DGRAM &&
452	    so->so_type != SOCK_STREAM)
453		return (0);
454
455	/* Reject addresses we don't understand; fail closed. */
456	if (sa->sa_family != AF_INET && sa->sa_family != AF_INET6)
457		return (EINVAL);
458
459	family = so->so_proto->pr_domain->dom_family;
460	type = so->so_type;
461	sin = (struct sockaddr_in *) sa;
462	port = ntohs(sin->sin_port);
463
464	/*
465	 * Sockets are frequently bound with a specific IP address but a port
466	 * number of '0' to request automatic port allocation.  This is often
467	 * desirable as long as IP_PORTRANGELOW isn't set, which might permit
468	 * automatic allocation of a "privileged" port.  The autoport exempt
469	 * flag exempts port 0 allocation from rule checking as long as a low
470	 * port isn't required.
471	 */
472	if (portacl_autoport_exempt && port == 0) {
473		inp = sotoinpcb(so);
474		if ((inp->inp_flags & INP_LOWPORT) == 0)
475			return (0);
476	}
477
478	return (rules_check(cred, family, type, port));
479}
480
481static struct mac_policy_ops portacl_ops =
482{
483	.mpo_destroy = destroy,
484	.mpo_init = init,
485	.mpo_socket_check_bind = socket_check_bind,
486};
487
488MAC_POLICY_SET(&portacl_ops, mac_portacl, "TrustedBSD MAC/portacl",
489    MPC_LOADTIME_FLAG_UNLOADOK, NULL);
490MODULE_VERSION(mac_portacl, 1);
491