auth-options.c revision 215116 
1/* $OpenBSD: auth-options.c,v 1.52 2010/05/20 23:46:02 djm Exp $ */
2/*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 *                    All rights reserved
6 * As far as I am concerned, the code I have written for this software
7 * can be used freely for any purpose.  Any derived versions of this
8 * software must be clearly marked as such, and if the derived work is
9 * incompatible with the protocol description in the RFC file, it must be
10 * called by a name other than "ssh" or "Secure Shell".
11 */
12
13#include "includes.h"
14
15#include <sys/types.h>
16
17#include <netdb.h>
18#include <pwd.h>
19#include <string.h>
20#include <stdio.h>
21#include <stdarg.h>
22
23#include "openbsd-compat/sys-queue.h"
24#include "xmalloc.h"
25#include "match.h"
26#include "log.h"
27#include "canohost.h"
28#include "buffer.h"
29#include "channels.h"
30#include "servconf.h"
31#include "misc.h"
32#include "key.h"
33#include "auth-options.h"
34#include "hostfile.h"
35#include "auth.h"
36#ifdef GSSAPI
37#include "ssh-gss.h"
38#endif
39#include "monitor_wrap.h"
40
41/* Flags set authorized_keys flags */
42int no_port_forwarding_flag = 0;
43int no_agent_forwarding_flag = 0;
44int no_x11_forwarding_flag = 0;
45int no_pty_flag = 0;
46int no_user_rc = 0;
47int key_is_cert_authority = 0;
48
49/* "command=" option. */
50char *forced_command = NULL;
51
52/* "environment=" options. */
53struct envstring *custom_environment = NULL;
54
55/* "tunnel=" option. */
56int forced_tun_device = -1;
57
58/* "principals=" option. */
59char *authorized_principals = NULL;
60
61extern ServerOptions options;
62
63void
64auth_clear_options(void)
65{
66	no_agent_forwarding_flag = 0;
67	no_port_forwarding_flag = 0;
68	no_pty_flag = 0;
69	no_x11_forwarding_flag = 0;
70	no_user_rc = 0;
71	key_is_cert_authority = 0;
72	while (custom_environment) {
73		struct envstring *ce = custom_environment;
74		custom_environment = ce->next;
75		xfree(ce->s);
76		xfree(ce);
77	}
78	if (forced_command) {
79		xfree(forced_command);
80		forced_command = NULL;
81	}
82	if (authorized_principals) {
83		xfree(authorized_principals);
84		authorized_principals = NULL;
85	}
86	forced_tun_device = -1;
87	channel_clear_permitted_opens();
88}
89
90/*
91 * return 1 if access is granted, 0 if not.
92 * side effect: sets key option flags
93 */
94int
95auth_parse_options(struct passwd *pw, char *opts, char *file, u_long linenum)
96{
97	const char *cp;
98	int i;
99
100	/* reset options */
101	auth_clear_options();
102
103	if (!opts)
104		return 1;
105
106	while (*opts && *opts != ' ' && *opts != '\t') {
107		cp = "cert-authority";
108		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
109			key_is_cert_authority = 1;
110			opts += strlen(cp);
111			goto next_option;
112		}
113		cp = "no-port-forwarding";
114		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
115			auth_debug_add("Port forwarding disabled.");
116			no_port_forwarding_flag = 1;
117			opts += strlen(cp);
118			goto next_option;
119		}
120		cp = "no-agent-forwarding";
121		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
122			auth_debug_add("Agent forwarding disabled.");
123			no_agent_forwarding_flag = 1;
124			opts += strlen(cp);
125			goto next_option;
126		}
127		cp = "no-X11-forwarding";
128		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
129			auth_debug_add("X11 forwarding disabled.");
130			no_x11_forwarding_flag = 1;
131			opts += strlen(cp);
132			goto next_option;
133		}
134		cp = "no-pty";
135		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
136			auth_debug_add("Pty allocation disabled.");
137			no_pty_flag = 1;
138			opts += strlen(cp);
139			goto next_option;
140		}
141		cp = "no-user-rc";
142		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
143			auth_debug_add("User rc file execution disabled.");
144			no_user_rc = 1;
145			opts += strlen(cp);
146			goto next_option;
147		}
148		cp = "command=\"";
149		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
150			opts += strlen(cp);
151			if (forced_command != NULL)
152				xfree(forced_command);
153			forced_command = xmalloc(strlen(opts) + 1);
154			i = 0;
155			while (*opts) {
156				if (*opts == '"')
157					break;
158				if (*opts == '\\' && opts[1] == '"') {
159					opts += 2;
160					forced_command[i++] = '"';
161					continue;
162				}
163				forced_command[i++] = *opts++;
164			}
165			if (!*opts) {
166				debug("%.100s, line %lu: missing end quote",
167				    file, linenum);
168				auth_debug_add("%.100s, line %lu: missing end quote",
169				    file, linenum);
170				xfree(forced_command);
171				forced_command = NULL;
172				goto bad_option;
173			}
174			forced_command[i] = '\0';
175			auth_debug_add("Forced command: %.900s", forced_command);
176			opts++;
177			goto next_option;
178		}
179		cp = "principals=\"";
180		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
181			opts += strlen(cp);
182			if (authorized_principals != NULL)
183				xfree(authorized_principals);
184			authorized_principals = xmalloc(strlen(opts) + 1);
185			i = 0;
186			while (*opts) {
187				if (*opts == '"')
188					break;
189				if (*opts == '\\' && opts[1] == '"') {
190					opts += 2;
191					authorized_principals[i++] = '"';
192					continue;
193				}
194				authorized_principals[i++] = *opts++;
195			}
196			if (!*opts) {
197				debug("%.100s, line %lu: missing end quote",
198				    file, linenum);
199				auth_debug_add("%.100s, line %lu: missing end quote",
200				    file, linenum);
201				xfree(authorized_principals);
202				authorized_principals = NULL;
203				goto bad_option;
204			}
205			authorized_principals[i] = '\0';
206			auth_debug_add("principals: %.900s",
207			    authorized_principals);
208			opts++;
209			goto next_option;
210		}
211		cp = "environment=\"";
212		if (options.permit_user_env &&
213		    strncasecmp(opts, cp, strlen(cp)) == 0) {
214			char *s;
215			struct envstring *new_envstring;
216
217			opts += strlen(cp);
218			s = xmalloc(strlen(opts) + 1);
219			i = 0;
220			while (*opts) {
221				if (*opts == '"')
222					break;
223				if (*opts == '\\' && opts[1] == '"') {
224					opts += 2;
225					s[i++] = '"';
226					continue;
227				}
228				s[i++] = *opts++;
229			}
230			if (!*opts) {
231				debug("%.100s, line %lu: missing end quote",
232				    file, linenum);
233				auth_debug_add("%.100s, line %lu: missing end quote",
234				    file, linenum);
235				xfree(s);
236				goto bad_option;
237			}
238			s[i] = '\0';
239			auth_debug_add("Adding to environment: %.900s", s);
240			debug("Adding to environment: %.900s", s);
241			opts++;
242			new_envstring = xmalloc(sizeof(struct envstring));
243			new_envstring->s = s;
244			new_envstring->next = custom_environment;
245			custom_environment = new_envstring;
246			goto next_option;
247		}
248		cp = "from=\"";
249		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
250			const char *remote_ip = get_remote_ipaddr();
251			const char *remote_host = get_canonical_hostname(
252			    options.use_dns);
253			char *patterns = xmalloc(strlen(opts) + 1);
254
255			opts += strlen(cp);
256			i = 0;
257			while (*opts) {
258				if (*opts == '"')
259					break;
260				if (*opts == '\\' && opts[1] == '"') {
261					opts += 2;
262					patterns[i++] = '"';
263					continue;
264				}
265				patterns[i++] = *opts++;
266			}
267			if (!*opts) {
268				debug("%.100s, line %lu: missing end quote",
269				    file, linenum);
270				auth_debug_add("%.100s, line %lu: missing end quote",
271				    file, linenum);
272				xfree(patterns);
273				goto bad_option;
274			}
275			patterns[i] = '\0';
276			opts++;
277			switch (match_host_and_ip(remote_host, remote_ip,
278			    patterns)) {
279			case 1:
280				xfree(patterns);
281				/* Host name matches. */
282				goto next_option;
283			case -1:
284				debug("%.100s, line %lu: invalid criteria",
285				    file, linenum);
286				auth_debug_add("%.100s, line %lu: "
287				    "invalid criteria", file, linenum);
288				/* FALLTHROUGH */
289			case 0:
290				xfree(patterns);
291				logit("Authentication tried for %.100s with "
292				    "correct key but not from a permitted "
293				    "host (host=%.200s, ip=%.200s).",
294				    pw->pw_name, remote_host, remote_ip);
295				auth_debug_add("Your host '%.200s' is not "
296				    "permitted to use this key for login.",
297				    remote_host);
298				break;
299			}
300			/* deny access */
301			return 0;
302		}
303		cp = "permitopen=\"";
304		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
305			char *host, *p;
306			int port;
307			char *patterns = xmalloc(strlen(opts) + 1);
308
309			opts += strlen(cp);
310			i = 0;
311			while (*opts) {
312				if (*opts == '"')
313					break;
314				if (*opts == '\\' && opts[1] == '"') {
315					opts += 2;
316					patterns[i++] = '"';
317					continue;
318				}
319				patterns[i++] = *opts++;
320			}
321			if (!*opts) {
322				debug("%.100s, line %lu: missing end quote",
323				    file, linenum);
324				auth_debug_add("%.100s, line %lu: missing "
325				    "end quote", file, linenum);
326				xfree(patterns);
327				goto bad_option;
328			}
329			patterns[i] = '\0';
330			opts++;
331			p = patterns;
332			host = hpdelim(&p);
333			if (host == NULL || strlen(host) >= NI_MAXHOST) {
334				debug("%.100s, line %lu: Bad permitopen "
335				    "specification <%.100s>", file, linenum,
336				    patterns);
337				auth_debug_add("%.100s, line %lu: "
338				    "Bad permitopen specification", file,
339				    linenum);
340				xfree(patterns);
341				goto bad_option;
342			}
343			host = cleanhostname(host);
344			if (p == NULL || (port = a2port(p)) <= 0) {
345				debug("%.100s, line %lu: Bad permitopen port "
346				    "<%.100s>", file, linenum, p ? p : "");
347				auth_debug_add("%.100s, line %lu: "
348				    "Bad permitopen port", file, linenum);
349				xfree(patterns);
350				goto bad_option;
351			}
352			if (options.allow_tcp_forwarding)
353				channel_add_permitted_opens(host, port);
354			xfree(patterns);
355			goto next_option;
356		}
357		cp = "tunnel=\"";
358		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
359			char *tun = NULL;
360			opts += strlen(cp);
361			tun = xmalloc(strlen(opts) + 1);
362			i = 0;
363			while (*opts) {
364				if (*opts == '"')
365					break;
366				tun[i++] = *opts++;
367			}
368			if (!*opts) {
369				debug("%.100s, line %lu: missing end quote",
370				    file, linenum);
371				auth_debug_add("%.100s, line %lu: missing end quote",
372				    file, linenum);
373				xfree(tun);
374				forced_tun_device = -1;
375				goto bad_option;
376			}
377			tun[i] = '\0';
378			forced_tun_device = a2tun(tun, NULL);
379			xfree(tun);
380			if (forced_tun_device == SSH_TUNID_ERR) {
381				debug("%.100s, line %lu: invalid tun device",
382				    file, linenum);
383				auth_debug_add("%.100s, line %lu: invalid tun device",
384				    file, linenum);
385				forced_tun_device = -1;
386				goto bad_option;
387			}
388			auth_debug_add("Forced tun device: %d", forced_tun_device);
389			opts++;
390			goto next_option;
391		}
392next_option:
393		/*
394		 * Skip the comma, and move to the next option
395		 * (or break out if there are no more).
396		 */
397		if (!*opts)
398			fatal("Bugs in auth-options.c option processing.");
399		if (*opts == ' ' || *opts == '\t')
400			break;		/* End of options. */
401		if (*opts != ',')
402			goto bad_option;
403		opts++;
404		/* Process the next option. */
405	}
406
407	/* grant access */
408	return 1;
409
410bad_option:
411	logit("Bad options in %.100s file, line %lu: %.50s",
412	    file, linenum, opts);
413	auth_debug_add("Bad options in %.100s file, line %lu: %.50s",
414	    file, linenum, opts);
415
416	/* deny access */
417	return 0;
418}
419
420#define OPTIONS_CRITICAL	1
421#define OPTIONS_EXTENSIONS	2
422static int
423parse_option_list(u_char *optblob, size_t optblob_len, struct passwd *pw,
424    u_int which, int crit,
425    int *cert_no_port_forwarding_flag,
426    int *cert_no_agent_forwarding_flag,
427    int *cert_no_x11_forwarding_flag,
428    int *cert_no_pty_flag,
429    int *cert_no_user_rc,
430    char **cert_forced_command,
431    int *cert_source_address_done)
432{
433	char *command, *allowed;
434	const char *remote_ip;
435	u_char *name = NULL, *data_blob = NULL;
436	u_int nlen, dlen, clen;
437	Buffer c, data;
438	int ret = -1, found;
439
440	buffer_init(&data);
441
442	/* Make copy to avoid altering original */
443	buffer_init(&c);
444	buffer_append(&c, optblob, optblob_len);
445
446	while (buffer_len(&c) > 0) {
447		if ((name = buffer_get_string_ret(&c, &nlen)) == NULL ||
448		    (data_blob = buffer_get_string_ret(&c, &dlen)) == NULL) {
449			error("Certificate options corrupt");
450			goto out;
451		}
452		buffer_append(&data, data_blob, dlen);
453		debug3("found certificate option \"%.100s\" len %u",
454		    name, dlen);
455		if (strlen(name) != nlen) {
456			error("Certificate constraint name contains \\0");
457			goto out;
458		}
459		found = 0;
460		if ((which & OPTIONS_EXTENSIONS) != 0) {
461			if (strcmp(name, "permit-X11-forwarding") == 0) {
462				*cert_no_x11_forwarding_flag = 0;
463				found = 1;
464			} else if (strcmp(name,
465			    "permit-agent-forwarding") == 0) {
466				*cert_no_agent_forwarding_flag = 0;
467				found = 1;
468			} else if (strcmp(name,
469			    "permit-port-forwarding") == 0) {
470				*cert_no_port_forwarding_flag = 0;
471				found = 1;
472			} else if (strcmp(name, "permit-pty") == 0) {
473				*cert_no_pty_flag = 0;
474				found = 1;
475			} else if (strcmp(name, "permit-user-rc") == 0) {
476				*cert_no_user_rc = 0;
477				found = 1;
478			}
479		}
480		if (!found && (which & OPTIONS_CRITICAL) != 0) {
481			if (strcmp(name, "force-command") == 0) {
482				if ((command = buffer_get_string_ret(&data,
483				    &clen)) == NULL) {
484					error("Certificate constraint \"%s\" "
485					    "corrupt", name);
486					goto out;
487				}
488				if (strlen(command) != clen) {
489					error("force-command constraint "
490					    "contains \\0");
491					goto out;
492				}
493				if (*cert_forced_command != NULL) {
494					error("Certificate has multiple "
495					    "force-command options");
496					xfree(command);
497					goto out;
498				}
499				*cert_forced_command = command;
500				found = 1;
501			}
502			if (strcmp(name, "source-address") == 0) {
503				if ((allowed = buffer_get_string_ret(&data,
504				    &clen)) == NULL) {
505					error("Certificate constraint "
506					    "\"%s\" corrupt", name);
507					goto out;
508				}
509				if (strlen(allowed) != clen) {
510					error("source-address constraint "
511					    "contains \\0");
512					goto out;
513				}
514				if ((*cert_source_address_done)++) {
515					error("Certificate has multiple "
516					    "source-address options");
517					xfree(allowed);
518					goto out;
519				}
520				remote_ip = get_remote_ipaddr();
521				switch (addr_match_cidr_list(remote_ip,
522				    allowed)) {
523				case 1:
524					/* accepted */
525					xfree(allowed);
526					break;
527				case 0:
528					/* no match */
529					logit("Authentication tried for %.100s "
530					    "with valid certificate but not "
531					    "from a permitted host "
532					    "(ip=%.200s).", pw->pw_name,
533					    remote_ip);
534					auth_debug_add("Your address '%.200s' "
535					    "is not permitted to use this "
536					    "certificate for login.",
537					    remote_ip);
538					xfree(allowed);
539					goto out;
540				case -1:
541					error("Certificate source-address "
542					    "contents invalid");
543					xfree(allowed);
544					goto out;
545				}
546				found = 1;
547			}
548		}
549
550		if (!found) {
551			if (crit) {
552				error("Certificate critical option \"%s\" "
553				    "is not supported", name);
554				goto out;
555			} else {
556				logit("Certificate extension \"%s\" "
557				    "is not supported", name);
558			}
559		} else if (buffer_len(&data) != 0) {
560			error("Certificate option \"%s\" corrupt "
561			    "(extra data)", name);
562			goto out;
563		}
564		buffer_clear(&data);
565		xfree(name);
566		xfree(data_blob);
567		name = data_blob = NULL;
568	}
569	/* successfully parsed all options */
570	ret = 0;
571
572 out:
573	if (ret != 0 &&
574	    cert_forced_command != NULL &&
575	    *cert_forced_command != NULL) {
576		xfree(*cert_forced_command);
577		*cert_forced_command = NULL;
578	}
579	if (name != NULL)
580		xfree(name);
581	if (data_blob != NULL)
582		xfree(data_blob);
583	buffer_free(&data);
584	buffer_free(&c);
585	return ret;
586}
587
588/*
589 * Set options from critical certificate options. These supersede user key
590 * options so this must be called after auth_parse_options().
591 */
592int
593auth_cert_options(Key *k, struct passwd *pw)
594{
595	int cert_no_port_forwarding_flag = 1;
596	int cert_no_agent_forwarding_flag = 1;
597	int cert_no_x11_forwarding_flag = 1;
598	int cert_no_pty_flag = 1;
599	int cert_no_user_rc = 1;
600	char *cert_forced_command = NULL;
601	int cert_source_address_done = 0;
602
603	if (key_cert_is_legacy(k)) {
604		/* All options are in the one field for v00 certs */
605		if (parse_option_list(buffer_ptr(&k->cert->critical),
606		    buffer_len(&k->cert->critical), pw,
607		    OPTIONS_CRITICAL|OPTIONS_EXTENSIONS, 1,
608		    &cert_no_port_forwarding_flag,
609		    &cert_no_agent_forwarding_flag,
610		    &cert_no_x11_forwarding_flag,
611		    &cert_no_pty_flag,
612		    &cert_no_user_rc,
613		    &cert_forced_command,
614		    &cert_source_address_done) == -1)
615			return -1;
616	} else {
617		/* Separate options and extensions for v01 certs */
618		if (parse_option_list(buffer_ptr(&k->cert->critical),
619		    buffer_len(&k->cert->critical), pw,
620		    OPTIONS_CRITICAL, 1, NULL, NULL, NULL, NULL, NULL,
621		    &cert_forced_command,
622		    &cert_source_address_done) == -1)
623			return -1;
624		if (parse_option_list(buffer_ptr(&k->cert->extensions),
625		    buffer_len(&k->cert->extensions), pw,
626		    OPTIONS_EXTENSIONS, 1,
627		    &cert_no_port_forwarding_flag,
628		    &cert_no_agent_forwarding_flag,
629		    &cert_no_x11_forwarding_flag,
630		    &cert_no_pty_flag,
631		    &cert_no_user_rc,
632		    NULL, NULL) == -1)
633			return -1;
634	}
635
636	no_port_forwarding_flag |= cert_no_port_forwarding_flag;
637	no_agent_forwarding_flag |= cert_no_agent_forwarding_flag;
638	no_x11_forwarding_flag |= cert_no_x11_forwarding_flag;
639	no_pty_flag |= cert_no_pty_flag;
640	no_user_rc |= cert_no_user_rc;
641	/* CA-specified forced command supersedes key option */
642	if (cert_forced_command != NULL) {
643		if (forced_command != NULL)
644			xfree(forced_command);
645		forced_command = cert_forced_command;
646	}
647	return 0;
648}
649
650