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