xref: /openbsd-src/usr.sbin/snmpd/traphandler.c (revision 99fd087599a8791921855f21bd7e36130f39aadc) 
1 /*	$OpenBSD: traphandler.c,v 1.15 2019/10/24 12:39:27 tb Exp $	*/
2 
3 /*
4  * Copyright (c) 2014 Bret Stephen Lambert <blambert@openbsd.org>
5  *
6  * Permission to use, copy, modify, and distribute this software for any
7  * purpose with or without fee is hereby granted, provided that the above
8  * copyright notice and this permission notice appear in all copies.
9  *
10  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17  */
18 
19 #include <sys/queue.h>
20 #include <sys/socket.h>
21 #include <sys/stat.h>
22 #include <sys/types.h>
23 #include <sys/uio.h>
24 #include <sys/wait.h>
25 
26 #include <net/if.h>
27 #include <netinet/in.h>
28 #include <arpa/inet.h>
29 
30 #include <ber.h>
31 #include <event.h>
32 #include <fcntl.h>
33 #include <imsg.h>
34 #include <netdb.h>
35 #include <stdio.h>
36 #include <stdlib.h>
37 #include <string.h>
38 #include <syslog.h>
39 #include <unistd.h>
40 #include <pwd.h>
41 
42 #include "snmpd.h"
43 #include "mib.h"
44 
45 char	 trap_path[PATH_MAX];
46 
47 void	 traphandler_init(struct privsep *, struct privsep_proc *, void *arg);
48 int	 traphandler_dispatch_parent(int, struct privsep_proc *, struct imsg *);
49 int	 traphandler_bind(struct address *);
50 void	 traphandler_recvmsg(int, short, void *);
51 int	 traphandler_priv_recvmsg(struct privsep_proc *, struct imsg *);
52 int	 traphandler_fork_handler(struct privsep_proc *, struct imsg *);
53 int	 traphandler_parse(char *, size_t, struct ber_element **,
54 	    struct ber_element **, u_int *, struct ber_oid *);
55 void	 traphandler_v1translate(struct ber_oid *, u_int, u_int);
56 
57 int	 trapcmd_cmp(struct trapcmd *, struct trapcmd *);
58 void	 trapcmd_exec(struct trapcmd *, struct sockaddr *,
59 	    struct ber_element *, char *, u_int);
60 
61 char	*traphandler_hostname(struct sockaddr *, int);
62 
63 RB_PROTOTYPE(trapcmd_tree, trapcmd, cmd_entry, trapcmd_cmp)
64 RB_GENERATE(trapcmd_tree, trapcmd, cmd_entry, trapcmd_cmp)
65 
66 struct trapcmd_tree trapcmd_tree = RB_INITIALIZER(&trapcmd_tree);
67 
68 static struct privsep_proc procs[] = {
69 	{ "parent",	PROC_PARENT,	traphandler_dispatch_parent }
70 };
71 
72 void
73 traphandler(struct privsep *ps, struct privsep_proc *p)
74 {
75 	struct snmpd		*env = ps->ps_env;
76 	struct address		*h;
77 	struct listen_sock	*so;
78 
79 	if (env->sc_traphandler) {
80 		TAILQ_FOREACH(h, &env->sc_addresses, entry) {
81 			if (h->ipproto != IPPROTO_UDP)
82 				continue;
83 			if ((so = calloc(1, sizeof(*so))) == NULL)
84 				fatal("%s", __func__);
85 			if ((so->s_fd = traphandler_bind(h)) == -1)
86 				fatal("could not create trap listener socket");
87 			TAILQ_INSERT_TAIL(&env->sc_sockets, so, entry);
88 		}
89 	}
90 
91 	proc_run(ps, p, procs, nitems(procs), traphandler_init, NULL);
92 }
93 
94 void
95 traphandler_init(struct privsep *ps, struct privsep_proc *p, void *arg)
96 {
97 	struct snmpd		*env = ps->ps_env;
98 	struct listen_sock	*so;
99 
100 	if (pledge("stdio id proc recvfd exec", NULL) == -1)
101 		fatal("pledge");
102 
103 	if (!env->sc_traphandler)
104 		return;
105 
106 	/* listen for SNMP trap messages */
107 	TAILQ_FOREACH(so, &env->sc_sockets, entry) {
108 		event_set(&so->s_ev, so->s_fd, EV_READ|EV_PERSIST,
109 		    traphandler_recvmsg, ps);
110 		event_add(&so->s_ev, NULL);
111 	}
112 }
113 
114 int
115 traphandler_bind(struct address *addr)
116 {
117 	int			 s;
118 	char			 buf[512];
119 
120 	if ((s = snmpd_socket_af(&addr->ss, htons(SNMPD_TRAPPORT),
121 	    IPPROTO_UDP)) == -1)
122 		return (-1);
123 
124 	if (fcntl(s, F_SETFL, O_NONBLOCK) == -1)
125 		goto bad;
126 
127 	if (bind(s, (struct sockaddr *)&addr->ss, addr->ss.ss_len) == -1)
128 		goto bad;
129 
130 	if (print_host(&addr->ss, buf, sizeof(buf)) == NULL)
131 		goto bad;
132 
133 	log_info("traphandler: listening on %s:%d", buf, SNMPD_TRAPPORT);
134 
135 	return (s);
136  bad:
137 	close (s);
138 	return (-1);
139 }
140 
141 void
142 traphandler_shutdown(void)
143 {
144 	struct listen_sock	*so;
145 
146 	TAILQ_FOREACH(so, &snmpd_env->sc_sockets, entry) {
147 		event_del(&so->s_ev);
148 		close(so->s_fd);
149 	}
150 }
151 
152 int
153 traphandler_dispatch_parent(int fd, struct privsep_proc *p, struct imsg *imsg)
154 {
155 	switch (imsg->hdr.type) {
156 	default:
157 		break;
158 	}
159 
160 	return (-1);
161 }
162 
163 int
164 snmpd_dispatch_traphandler(int fd, struct privsep_proc *p, struct imsg *imsg)
165 {
166 	switch (imsg->hdr.type) {
167 	case IMSG_ALERT:
168 		return (traphandler_priv_recvmsg(p, imsg));
169 	default:
170 		break;
171 	}
172 
173 	return (-1);
174 }
175 
176 void
177 traphandler_recvmsg(int fd, short events, void *arg)
178 {
179 	struct privsep		*ps = arg;
180 	char			 buf[8196];
181 	struct iovec		 iov[2];
182 	struct sockaddr_storage	 ss;
183 	socklen_t		 slen;
184 	ssize_t			 n;
185 	struct ber_element	*req, *iter;
186 	struct ber_oid		 trapoid;
187 	u_int			 uptime;
188 
189 	slen = sizeof(ss);
190 	if ((n = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr *)&ss,
191 	    &slen)) == -1)
192 		return;
193 
194 	if (traphandler_parse(buf, n, &req, &iter, &uptime, &trapoid) == -1)
195 		goto done;
196 
197 	iov[0].iov_base = &ss;
198 	iov[0].iov_len = ss.ss_len;
199 	iov[1].iov_base = buf;
200 	iov[1].iov_len = n;
201 
202 	/* Forward it to the parent process */
203 	if (proc_composev(ps, PROC_PARENT, IMSG_ALERT, iov, 2) == -1)
204 		goto done;
205 
206  done:
207 	if (req != NULL)
208 		ober_free_elements(req);
209 	return;
210 }
211 
212 /*
213  * Validate received message
214  */
215 int
216 traphandler_parse(char *buf, size_t n, struct ber_element **req,
217     struct ber_element **vbinds, u_int *uptime, struct ber_oid *trapoid)
218 {
219 	struct ber		 ber;
220 	struct ber_element	*elm;
221 	u_int			 vers, gtype, etype;
222 
223 	bzero(&ber, sizeof(ber));
224 	ober_set_application(&ber, smi_application);
225 	ober_set_readbuf(&ber, buf, n);
226 
227 	if ((*req = ober_read_elements(&ber, NULL)) == NULL)
228 		goto done;
229 
230 	if (ober_scanf_elements(*req, "{dSe", &vers, &elm) == -1)
231 		goto done;
232 
233 	switch (vers) {
234 	case SNMP_V1:
235 		if (ober_scanf_elements(elm, "{oSddd",
236 		    trapoid, &gtype, &etype, uptime) == -1)
237 			goto done;
238 		traphandler_v1translate(trapoid, gtype, etype);
239 		break;
240 
241 	case SNMP_V2:
242 		if (ober_scanf_elements(elm, "{SSS{e}}", &elm) == -1 ||
243 		    ober_scanf_elements(elm, "{Sd}{So}",
244 		    uptime, trapoid) == -1)
245 			goto done;
246 		*vbinds = elm->be_next->be_next;
247 		break;
248 
249 	default:
250 		log_warnx("unsupported SNMP trap version '%d'", vers);
251 		goto done;
252 	}
253 
254 	ober_free(&ber);
255 	return (0);
256 
257  done:
258 	ober_free(&ber);
259 	if (*req)
260 		ober_free_elements(*req);
261 	*req = NULL;
262 	return (-1);
263 }
264 
265 void
266 traphandler_v1translate(struct ber_oid *oid, u_int gtype, u_int etype)
267 {
268 	/* append 'specific trap' number to 'enterprise specific' traps */
269 	if (gtype >= 6) {
270 		oid->bo_id[oid->bo_n] = 0;
271 		oid->bo_id[oid->bo_n + 1] = etype;
272 		oid->bo_n += 2;
273 	}
274 }
275 
276 int
277 traphandler_priv_recvmsg(struct privsep_proc *p, struct imsg *imsg)
278 {
279 	ssize_t			 n;
280 	pid_t			 pid;
281 
282 	if ((n = IMSG_DATA_SIZE(imsg)) <= 0)
283 		return (-1);			/* XXX */
284 
285 	switch ((pid = fork())) {
286 	case 0:
287 		traphandler_fork_handler(p, imsg);
288 		/* NOTREACHED */
289 	case -1:
290 		log_warn("%s: couldn't fork traphandler", __func__);
291 		return (0);
292 	default:
293 		log_debug("forked process %i to handle trap", pid);
294 		return (0);
295 	}
296 	/* NOTREACHED */
297 }
298 
299 int
300 traphandler_fork_handler(struct privsep_proc *p, struct imsg *imsg)
301 {
302 	struct privsep		*ps = p->p_ps;
303 	struct snmpd		*env = ps->ps_env;
304 	char			 oidbuf[SNMP_MAX_OID_STRLEN];
305 	struct sockaddr		*sa;
306 	char			*buf;
307 	ssize_t			 n;
308 	struct ber_element	*req, *iter;
309 	struct trapcmd		*cmd;
310 	struct ber_oid		 trapoid;
311 	u_int			 uptime;
312 	struct passwd		*pw;
313 	int			 verbose;
314 
315 	pw = ps->ps_pw;
316 	verbose = log_getverbose();
317 
318 	if (setgroups(1, &pw->pw_gid) ||
319 	    setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) ||
320 	    setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid))
321 		fatal("traphandler_fork_handler: cannot drop privileges");
322 
323 	closefrom(STDERR_FILENO + 1);
324 
325 	log_init((env->sc_flags & SNMPD_F_DEBUG) ? 1 : 0, LOG_DAEMON);
326 	log_setverbose(verbose);
327 	log_procinit(p->p_title);
328 
329 	n = IMSG_DATA_SIZE(imsg);
330 
331 	sa = imsg->data;
332 	n -= sa->sa_len;
333 	buf = (char *)imsg->data + sa->sa_len;
334 
335 	if (traphandler_parse(buf, n, &req, &iter, &uptime, &trapoid) == -1)
336 		fatalx("couldn't parse SNMP trap message");
337 
338 	smi_oid2string(&trapoid, oidbuf, sizeof(oidbuf), 0);
339 	if ((cmd = trapcmd_lookup(&trapoid)) != NULL)
340 		trapcmd_exec(cmd, sa, iter, oidbuf, uptime);
341 
342 	if (req != NULL)
343 		ober_free_elements(req);
344 
345 	exit(0);
346 }
347 
348 void
349 trapcmd_exec(struct trapcmd *cmd, struct sockaddr *sa,
350     struct ber_element *iter, char *trapoid, u_int uptime)
351 {
352 	char			 oidbuf[SNMP_MAX_OID_STRLEN];
353 	struct ber_oid		 oid;
354 	struct ber_element	*elm;
355 	int			 n, s[2], status = 0;
356 	char			*value, *host;
357 	pid_t			 child = -1;
358 
359 	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, s) == -1) {
360 		log_warn("could not create pipe for OID '%s'",
361 		    smi_oid2string(cmd->cmd_oid, oidbuf, sizeof(oidbuf), 0));
362 		return;
363 	}
364 
365 	switch (child = fork()) {
366 	case 0:
367 		dup2(s[1], STDIN_FILENO);
368 
369 		close(s[0]);
370 		close(s[1]);
371 
372 		closefrom(STDERR_FILENO + 1);
373 
374 		/* path to command is in argv[0], args follow */
375 		execve(cmd->cmd_argv[0], cmd->cmd_argv, NULL);
376 
377 		/* this shouldn't happen */
378 		log_warn("could not exec trap command for OID '%s'",
379 		    smi_oid2string(cmd->cmd_oid, oidbuf, sizeof(oidbuf), 0));
380 		_exit(1);
381 		/* NOTREACHED */
382 
383 	case -1:
384 		log_warn("could not fork trap command for OID '%s'",
385 		    smi_oid2string(cmd->cmd_oid, oidbuf, sizeof(oidbuf), 0));
386 		close(s[0]);
387 		close(s[1]);
388 		return;
389 	}
390 
391 	close(s[1]);
392 
393 	host = traphandler_hostname(sa, 0);
394 	if (dprintf(s[0], "%s\n", host) == -1)
395 		goto out;
396 
397 	host = traphandler_hostname(sa, 1);
398 	if (dprintf(s[0], "%s\n", host) == -1)
399 		goto out;
400 
401 	if (dprintf(s[0],
402 	    "iso.org.dod.internet.mgmt.mib-2.system.sysUpTime.0 %u\n",
403 	    uptime) == -1)
404 		goto out;
405 
406 	if (dprintf(s[0],
407 	    "iso.org.dod.internet.snmpV2.snmpModules.snmpMIB.snmpMIBObjects."
408 	    "snmpTrap.snmpTrapOID.0 %s\n", trapoid) == -1)
409 		goto out;
410 
411 	for (; iter != NULL; iter = iter->be_next) {
412 		if (ober_scanf_elements(iter, "{oe}", &oid, &elm) == -1)
413 			goto out;
414 		if ((value = smi_print_element(elm)) == NULL)
415 			goto out;
416 		smi_oid2string(&oid, oidbuf, sizeof(oidbuf), 0);
417 		n = dprintf(s[0], "%s %s\n", oidbuf, value);
418 		free(value);
419 		if (n == -1)
420 			goto out;
421 	}
422  out:
423 	close(s[0]);
424 	waitpid(child, &status, 0);
425 
426 	if (WIFSIGNALED(status)) {
427 		log_warnx("child %i exited due to receipt of signal %i",
428 		    child, WTERMSIG(status));
429 	} else if (WEXITSTATUS(status) != 0) {
430 		log_warnx("child %i exited with status %i",
431 		    child, WEXITSTATUS(status));
432 	} else {
433 		log_debug("child %i finished", child);
434 	}
435 		close(s[1]);
436 
437 	return;
438 }
439 
440 char *
441 traphandler_hostname(struct sockaddr *sa, int numeric)
442 {
443 	static char	 buf[NI_MAXHOST];
444 	int		 flag = 0;
445 
446 	if (numeric)
447 		flag = NI_NUMERICHOST;
448 
449 	bzero(buf, sizeof(buf));
450 	if (getnameinfo(sa, sa->sa_len, buf, sizeof(buf), NULL, 0, flag) != 0)
451 		return ("Unknown");
452 
453 	return (buf);
454 }
455 
456 struct trapcmd *
457 trapcmd_lookup(struct ber_oid *oid)
458 {
459 	struct trapcmd	key, *res;
460 
461 	bzero(&key, sizeof(key));
462 	key.cmd_oid = oid;
463 
464 	if ((res = RB_FIND(trapcmd_tree, &trapcmd_tree, &key)) == NULL)
465 		res = key.cmd_maybe;
466 	return (res);
467 }
468 
469 int
470 trapcmd_cmp(struct trapcmd *cmd1, struct trapcmd *cmd2)
471 {
472 	int ret;
473 
474 	ret = ober_oid_cmp(cmd2->cmd_oid, cmd1->cmd_oid);
475 	switch (ret) {
476 	case 2:
477 		/* cmd1 is a child of cmd2 */
478 		cmd1->cmd_maybe = cmd2;
479 		return (1);
480 	default:
481 		return (ret);
482 	}
483 	/* NOTREACHED */
484 }
485 
486 int
487 trapcmd_add(struct trapcmd *cmd)
488 {
489 	return (RB_INSERT(trapcmd_tree, &trapcmd_tree, cmd) != NULL);
490 }
491 
492 void
493 trapcmd_free(struct trapcmd *cmd)
494 {
495 	RB_REMOVE(trapcmd_tree, &trapcmd_tree, cmd);
496 	free(cmd->cmd_argv);
497 	free(cmd->cmd_oid);
498 	free(cmd);
499 }
500