1 /*
2  * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
3  * Use is subject to license terms.
4  */
5 
6 #pragma ident	"%Z%%M%	%I%	%E% SMI"
7 
8  /*
9   * This module implements a simple access control language that is based on
10   * host (or domain) names, NIS (host) netgroup names, IP addresses (or
11   * network numbers) and daemon process names. When a match is found the
12   * search is terminated, and depending on whether PROCESS_OPTIONS is defined,
13   * a list of options is executed or an optional shell command is executed.
14   *
15   * Host and user names are looked up on demand, provided that suitable endpoint
16   * information is available as sockaddr_in structures or TLI netbufs. As a
17   * side effect, the pattern matching process may change the contents of
18   * request structure fields.
19   *
20   * Diagnostics are reported through syslog(3).
21   *
22   * Compile with -DNETGROUP if your library provides support for netgroups.
23   *
24   * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
25   */
26 
27 #ifndef lint
28 static char sccsid[] = "@(#) hosts_access.c 1.21 97/02/12 02:13:22";
29 #endif
30 
31 /* System libraries. */
32 
33 #include <sys/types.h>
34 #include <sys/param.h>
35 #include <netinet/in.h>
36 #include <arpa/inet.h>
37 #include <rpcsvc/ypclnt.h>
38 #include <netdb.h>
39 #include <stdio.h>
40 #include <stdlib.h>
41 #include <unistd.h>
42 #include <syslog.h>
43 #include <ctype.h>
44 #include <errno.h>
45 #include <setjmp.h>
46 #include <string.h>
47 
48 extern char *fgets();
49 extern int errno;
50 
51 #ifndef	INADDR_NONE
52 #define	INADDR_NONE	(-1)		/* XXX should be 0xffffffff */
53 #endif
54 
55 /* Local stuff. */
56 
57 #include "tcpd.h"
58 
59 /* Error handling. */
60 
61 extern jmp_buf tcpd_buf;
62 
63 /* Delimiters for lists of daemons or clients. */
64 
65 static char sep[] = ", \t\r\n";
66 
67 /* Constants to be used in assignments only, not in comparisons... */
68 
69 #define	YES		1
70 #define	NO		0
71 
72  /*
73   * These variables are globally visible so that they can be redirected in
74   * verification mode.
75   */
76 
77 char   *hosts_allow_table = HOSTS_ALLOW;
78 char   *hosts_deny_table = HOSTS_DENY;
79 int     hosts_access_verbose = 0;
80 
81  /*
82   * In a long-running process, we are not at liberty to just go away.
83   */
84 
85 int     resident = (-1);		/* -1, 0: unknown; +1: yes */
86 
87 /* Forward declarations. */
88 
89 static int table_match();
90 static int list_match();
91 static int server_match();
92 static int client_match();
93 static int host_match();
94 static int string_match();
95 static int masked_match();
96 #ifdef HAVE_IPV6
97 static void ipv6_mask();
98 #endif
99 
100 /* Size of logical line buffer. */
101 
102 #define	BUFLEN 2048
103 
104 /* hosts_access - host access control facility */
105 
hosts_access(request)106 int     hosts_access(request)
107 struct request_info *request;
108 {
109     int     verdict;
110 
111     /*
112      * If the (daemon, client) pair is matched by an entry in the file
113      * /etc/hosts.allow, access is granted. Otherwise, if the (daemon,
114      * client) pair is matched by an entry in the file /etc/hosts.deny,
115      * access is denied. Otherwise, access is granted. A non-existent
116      * access-control file is treated as an empty file.
117      *
118      * After a rule has been matched, the optional language extensions may
119      * decide to grant or refuse service anyway. Or, while a rule is being
120      * processed, a serious error is found, and it seems better to play safe
121      * and deny service. All this is done by jumping back into the
122      * hosts_access() routine, bypassing the regular return from the
123      * table_match() function calls below.
124      */
125 
126     if (resident <= 0)
127 	resident++;
128     verdict = setjmp(tcpd_buf);
129     if (verdict != 0)
130 	return (verdict == AC_PERMIT);
131     if (table_match(hosts_allow_table, request))
132 	return (YES);
133     if (table_match(hosts_deny_table, request))
134 	return (NO);
135     return (YES);
136 }
137 
138 /* table_match - match table entries with (daemon, client) pair */
139 
table_match(table,request)140 static int table_match(table, request)
141 char   *table;
142 struct request_info *request;
143 {
144     FILE   *fp;
145     char    sv_list[BUFLEN];		/* becomes list of daemons */
146     char   *cl_list;			/* becomes list of clients */
147     char   *sh_cmd;			/* becomes optional shell command */
148     int     match = NO;
149     struct tcpd_context saved_context;
150 
151     saved_context = tcpd_context;		/* stupid compilers */
152 
153     /*
154      * Between the fopen() and fclose() calls, avoid jumps that may cause
155      * file descriptor leaks.
156      */
157 
158     if ((fp = fopen(table, "r")) != 0) {
159 	tcpd_context.file = table;
160 	tcpd_context.line = 0;
161 	while (match == NO && xgets(sv_list, sizeof(sv_list), fp) != 0) {
162 	    if (sv_list[strlen(sv_list) - 1] != '\n') {
163 		tcpd_warn("missing newline or line too long");
164 		continue;
165 	    }
166 	    if (sv_list[0] == '#' || sv_list[strspn(sv_list, " \t\r\n")] == 0)
167 		continue;
168 	    if ((cl_list = split_at(skip_ipv6_addrs(sv_list), ':')) == 0) {
169 		tcpd_warn("missing \":\" separator");
170 		continue;
171 	    }
172 	    sh_cmd = split_at(skip_ipv6_addrs(cl_list), ':');
173 	    match = list_match(sv_list, request, server_match)
174 		&& list_match(cl_list, request, client_match);
175 	}
176 	(void) fclose(fp);
177     } else if (errno != ENOENT) {
178 	tcpd_warn("cannot open %s: %m", table);
179     }
180     if (match) {
181 	if (hosts_access_verbose > 1)
182 	    syslog(LOG_DEBUG, "matched:  %s line %d",
183 		   tcpd_context.file, tcpd_context.line);
184 	if (sh_cmd) {
185 #ifdef PROCESS_OPTIONS
186 	    process_options(sh_cmd, request);
187 #else
188 	    char    cmd[BUFSIZ];
189 	    shell_cmd(percent_x(cmd, sizeof(cmd), sh_cmd, request));
190 #endif
191 	}
192     }
193     tcpd_context = saved_context;
194     return (match);
195 }
196 
197 /* list_match - match a request against a list of patterns with exceptions */
198 
list_match(list,request,match_fn)199 static int list_match(list, request, match_fn)
200 char   *list;
201 struct request_info *request;
202 int   (*match_fn) ();
203 {
204     char   *tok;
205 
206     /*
207      * Process tokens one at a time. We have exhausted all possible matches
208      * when we reach an "EXCEPT" token or the end of the list. If we do find
209      * a match, look for an "EXCEPT" list and recurse to determine whether
210      * the match is affected by any exceptions.
211      */
212 
213     for (tok = strtok(list, sep); tok != 0; tok = strtok((char *) 0, sep)) {
214 	if (STR_EQ(tok, "EXCEPT"))		/* EXCEPT: give up */
215 	    return (NO);
216 	if (match_fn(tok, request)) {		/* YES: look for exceptions */
217 	    while ((tok = strtok((char *) 0, sep)) && STR_NE(tok, "EXCEPT"))
218 		 /* VOID */ ;
219 	    return (tok == 0 || list_match((char *) 0, request, match_fn) == 0);
220 	}
221     }
222     return (NO);
223 }
224 
225 /* server_match - match server information */
226 
server_match(tok,request)227 static int server_match(tok, request)
228 char   *tok;
229 struct request_info *request;
230 {
231     char   *host;
232 
233     if ((host = split_at(tok + 1, '@')) == 0) {	/* plain daemon */
234 	return (string_match(tok, eval_daemon(request)));
235     } else {					/* daemon@host */
236 	return (string_match(tok, eval_daemon(request))
237 		&& host_match(host, request->server));
238     }
239 }
240 
241 /* client_match - match client information */
242 
client_match(tok,request)243 static int client_match(tok, request)
244 char   *tok;
245 struct request_info *request;
246 {
247     char   *host;
248 
249     if ((host = split_at(tok + 1, '@')) == 0) {	/* plain host */
250 	return (host_match(tok, request->client));
251     } else {					/* user@host */
252 	return (host_match(host, request->client)
253 		&& string_match(tok, eval_user(request)));
254     }
255 }
256 
257 /* host_match - match host name and/or address against pattern */
258 
host_match(tok,host)259 static int host_match(tok, host)
260 char   *tok;
261 struct host_info *host;
262 {
263     char   *mask;
264 
265     /*
266      * This code looks a little hairy because we want to avoid unnecessary
267      * hostname lookups.
268      *
269      * The KNOWN pattern requires that both address AND name be known; some
270      * patterns are specific to host names or to host addresses; all other
271      * patterns are satisfied when either the address OR the name match.
272      */
273 
274     if (tok[0] == '@') {			/* netgroup: look it up */
275 #ifdef  NETGROUP
276 	static char *mydomain = 0;
277 	if (mydomain == 0)
278 	    yp_get_default_domain(&mydomain);
279 	return (innetgr(tok + 1, eval_hostname(host), (char *) 0, mydomain));
280 #else
281 	tcpd_warn("netgroup support is disabled");	/* not tcpd_jump() */
282 	return (NO);
283 #endif
284     } else if (STR_EQ(tok, "KNOWN")) {		/* check address and name */
285 	char   *name = eval_hostname(host);
286 	return (STR_NE(eval_hostaddr(host), unknown) && HOSTNAME_KNOWN(name));
287     } else if (STR_EQ(tok, "LOCAL")) {		/* local: no dots in name */
288 	char   *name = eval_hostname(host);
289 	return (strchr(name, '.') == 0 && HOSTNAME_KNOWN(name));
290 #ifdef HAVE_IPV6
291     } else if (tok[0] == '[') {			/* IPv6 address */
292 	    struct in6_addr in6, hostin6, *hip;
293 	    char *cbr;
294 	    char *slash;
295 	    int mask = IPV6_ABITS;
296 
297 	    /*
298 	     * In some cases we don't get the sockaddr, only the addr.
299 	     * We use inet_pton to convert it to its binary representation
300 	     * and match against that.
301 	     */
302 	    if (host->sin == NULL) {
303 		if (host->addr == NULL ||
304 		    inet_pton(AF_INET6, host->addr, &hostin6) != 1) {
305 		    return (NO);
306 		}
307 		hip = &hostin6;
308 	    } else {
309 		if (SGFAM(host->sin) != AF_INET6)
310 		    return (NO);
311 		hip = &host->sin->sg_sin6.sin6_addr;
312 	    }
313 
314 	    if (cbr = strchr(tok, ']'))
315 		*cbr = '\0';
316 
317 	    /*
318 	     * A /nnn prefix specifies how many bits of the address we
319 	     * need to check.
320 	     */
321 	    if (slash = strchr(tok, '/')) {
322 		*slash = '\0';
323 		mask = atoi(slash+1);
324 		if (mask < 0 || mask > IPV6_ABITS) {
325 		    tcpd_warn("bad IP6 prefix specification");
326 		    return (NO);
327 		}
328 		/* Copy, because we need to modify it below */
329 		if (host->sin != NULL) {
330 		    hostin6 = host->sin->sg_sin6.sin6_addr;
331 		    hip = &hostin6;
332 		}
333 	    }
334 
335 	    if (cbr == NULL || inet_pton(AF_INET6, tok+1, &in6) != 1) {
336 		tcpd_warn("bad IP6 address specification");
337 		return (NO);
338 	    }
339 	    /*
340 	     * Zero the bits we're not interested in in both addresses
341 	     * then compare.  Note that we take a copy of the host info
342 	     * in that case.
343 	     */
344 	    if (mask != IPV6_ABITS) {
345 		ipv6_mask(&in6, mask);
346 		ipv6_mask(hip, mask);
347 	    }
348 	    if (memcmp(&in6, hip, sizeof(in6)) == 0)
349 		return (YES);
350 	    return (NO);
351 #endif
352     } else if ((mask = split_at(tok, '/')) != 0) {	/* net/mask */
353 	return (masked_match(tok, mask, eval_hostaddr(host)));
354     } else {					/* anything else */
355 	return (string_match(tok, eval_hostaddr(host))
356 	    || (NOT_INADDR(tok) && string_match(tok, eval_hostname(host))));
357     }
358 }
359 
360 /* string_match - match string against pattern */
361 
string_match(tok,string)362 static int string_match(tok, string)
363 char   *tok;
364 char   *string;
365 {
366     int     n;
367 
368     if (tok[0] == '.') {			/* suffix */
369 	n = strlen(string) - strlen(tok);
370 	return (n > 0 && STR_EQ(tok, string + n));
371     } else if (STR_EQ(tok, "ALL")) {		/* all: match any */
372 	return (YES);
373     } else if (STR_EQ(tok, "KNOWN")) {		/* not unknown */
374 	return (STR_NE(string, unknown));
375     } else if (tok[(n = strlen(tok)) - 1] == '.') {	/* prefix */
376 	return (STRN_EQ(tok, string, n));
377     } else {					/* exact match */
378 	return (STR_EQ(tok, string));
379     }
380 }
381 
382 /* masked_match - match address against netnumber/netmask */
383 
masked_match(net_tok,mask_tok,string)384 static int masked_match(net_tok, mask_tok, string)
385 char   *net_tok;
386 char   *mask_tok;
387 char   *string;
388 {
389     unsigned long net;
390     unsigned long mask;
391     unsigned long addr;
392 
393     /*
394      * Disallow forms other than dotted quad: the treatment that inet_addr()
395      * gives to forms with less than four components is inconsistent with the
396      * access control language. John P. Rouillard <rouilj@cs.umb.edu>.
397      */
398 
399     if ((addr = dot_quad_addr(string)) == INADDR_NONE)
400 	return (NO);
401     if ((net = dot_quad_addr(net_tok)) == INADDR_NONE
402 	|| (mask = dot_quad_addr(mask_tok)) == INADDR_NONE) {
403 	tcpd_warn("bad net/mask expression: %s/%s", net_tok, mask_tok);
404 	return (NO);				/* not tcpd_jump() */
405     }
406     return ((addr & mask) == net);
407 }
408 
409 #ifdef HAVE_IPV6
410 /*
411  * Function that zeros all but the first "maskbits" bits of the IPV6 address
412  * This function can be made generic by specifying an address length as
413  * extra parameter. (So Wietse can implement 1.2.3.4/16)
414  */
ipv6_mask(in6p,maskbits)415 static void ipv6_mask(in6p, maskbits)
416 struct in6_addr *in6p;
417 int maskbits;
418 {
419     uchar_t *p = (uchar_t*) in6p;
420 
421     if (maskbits < 0 || maskbits >= IPV6_ABITS)
422 	return;
423 
424     p += maskbits / 8;
425     maskbits %= 8;
426 
427     if (maskbits != 0)
428 	*p++ &= 0xff << (8 - maskbits);
429 
430     while (p < (((uchar_t*) in6p)) + sizeof(*in6p))
431 	*p++ = 0;
432 }
433 #endif
434