login_access.c revision 29922 
1 /*
2  * This module implements a simple but effective form of login access
3  * control based on login names and on host (or domain) names, internet
4  * addresses (or network numbers), or on terminal line names in case of
5  * non-networked logins. Diagnostics are reported through syslog(3).
6  *
7  * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
8  */
9
10#ifdef LOGIN_ACCESS
11#ifndef lint
12static const char sccsid[] = "%Z% %M% %I% %E% %U%";
13#endif
14
15#include <stdio.h>
16#include <syslog.h>
17#include <ctype.h>
18#include <sys/types.h>
19#include <grp.h>
20#include <errno.h>
21#include <string.h>
22#include <unistd.h>
23#include <stdlib.h>
24
25#include "pathnames.h"
26
27 /* Delimiters for fields and for lists of users, ttys or hosts. */
28
29static char fs[] = ":";			/* field separator */
30static char sep[] = ", \t";		/* list-element separator */
31
32 /* Constants to be used in assignments only, not in comparisons... */
33
34#define YES             1
35#define NO              0
36
37static int list_match();
38static int user_match();
39static int from_match();
40static int string_match();
41
42/* login_access - match username/group and host/tty with access control file */
43
44int
45login_access(user, from)
46char   *user;
47char   *from;
48{
49    FILE   *fp;
50    char    line[BUFSIZ];
51    char   *perm;			/* becomes permission field */
52    char   *users;			/* becomes list of login names */
53    char   *froms;			/* becomes list of terminals or hosts */
54    int     match = NO;
55    int     end;
56    int     lineno = 0;			/* for diagnostics */
57
58    /*
59     * Process the table one line at a time and stop at the first match.
60     * Blank lines and lines that begin with a '#' character are ignored.
61     * Non-comment lines are broken at the ':' character. All fields are
62     * mandatory. The first field should be a "+" or "-" character. A
63     * non-existing table means no access control.
64     */
65
66    if ((fp = fopen(_PATH_LOGACCESS, "r")) != NULL) {
67	while (!match && fgets(line, sizeof(line), fp)) {
68	    lineno++;
69	    if (line[end = strlen(line) - 1] != '\n') {
70		syslog(LOG_ERR, "%s: line %d: missing newline or line too long",
71		       _PATH_LOGACCESS, lineno);
72		continue;
73	    }
74	    if (line[0] == '#')
75		continue;			/* comment line */
76	    while (end > 0 && isspace(line[end - 1]))
77		end--;
78	    line[end] = 0;			/* strip trailing whitespace */
79	    if (line[0] == 0)			/* skip blank lines */
80		continue;
81	    if (!(perm = strtok(line, fs))
82		|| !(users = strtok((char *) 0, fs))
83		|| !(froms = strtok((char *) 0, fs))
84		|| strtok((char *) 0, fs)) {
85		syslog(LOG_ERR, "%s: line %d: bad field count", _PATH_LOGACCESS,
86		       lineno);
87		continue;
88	    }
89	    if (perm[0] != '+' && perm[0] != '-') {
90		syslog(LOG_ERR, "%s: line %d: bad first field", _PATH_LOGACCESS,
91		       lineno);
92		continue;
93	    }
94	    match = (list_match(froms, from, from_match)
95		     && list_match(users, user, user_match));
96	}
97	(void) fclose(fp);
98    } else if (errno != ENOENT) {
99	syslog(LOG_ERR, "cannot open %s: %m", _PATH_LOGACCESS);
100    }
101    return (match == 0 || (line[0] == '+'));
102}
103
104/* list_match - match an item against a list of tokens with exceptions */
105
106static int list_match(list, item, match_fn)
107char   *list;
108char   *item;
109int   (*match_fn) ();
110{
111    char   *tok;
112    int     match = NO;
113
114    /*
115     * Process tokens one at a time. We have exhausted all possible matches
116     * when we reach an "EXCEPT" token or the end of the list. If we do find
117     * a match, look for an "EXCEPT" list and recurse to determine whether
118     * the match is affected by any exceptions.
119     */
120
121    for (tok = strtok(list, sep); tok != 0; tok = strtok((char *) 0, sep)) {
122	if (strcasecmp(tok, "EXCEPT") == 0)	/* EXCEPT: give up */
123	    break;
124	if ((match = (*match_fn)(tok, item)) != NULL)	/* YES */
125	    break;
126    }
127    /* Process exceptions to matches. */
128
129    if (match != NO) {
130	while ((tok = strtok((char *) 0, sep)) && strcasecmp(tok, "EXCEPT"))
131	     /* VOID */ ;
132	if (tok == 0 || list_match((char *) 0, item, match_fn) == NO)
133	    return (match);
134    }
135    return (NO);
136}
137
138/* netgroup_match - match group against machine or user */
139
140static int netgroup_match(group, machine, user)
141gid_t   group;
142char   *machine;
143char   *user;
144{
145#ifdef NIS
146    static char *mydomain = 0;
147
148    if (mydomain == 0)
149	yp_get_default_domain(&mydomain);
150    return (innetgr(group, machine, user, mydomain));
151#else
152    syslog(LOG_ERR, "NIS netgroup support not configured");
153    return 0;
154#endif
155}
156
157/* user_match - match a username against one token */
158
159static int user_match(tok, string)
160char   *tok;
161char   *string;
162{
163    struct group *group;
164    int     i;
165
166    /*
167     * If a token has the magic value "ALL" the match always succeeds.
168     * Otherwise, return YES if the token fully matches the username, or if
169     * the token is a group that contains the username.
170     */
171
172    if (tok[0] == '@') {			/* netgroup */
173	return (netgroup_match(tok + 1, (char *) 0, string));
174    } else if (string_match(tok, string)) {	/* ALL or exact match */
175	return (YES);
176    } else if ((group = getgrnam(tok)) != NULL) {/* try group membership */
177	for (i = 0; group->gr_mem[i]; i++)
178	    if (strcasecmp(string, group->gr_mem[i]) == 0)
179		return (YES);
180    }
181    return (NO);
182}
183
184/* from_match - match a host or tty against a list of tokens */
185
186static int from_match(tok, string)
187char   *tok;
188char   *string;
189{
190    int     tok_len;
191    int     str_len;
192
193    /*
194     * If a token has the magic value "ALL" the match always succeeds. Return
195     * YES if the token fully matches the string. If the token is a domain
196     * name, return YES if it matches the last fields of the string. If the
197     * token has the magic value "LOCAL", return YES if the string does not
198     * contain a "." character. If the token is a network number, return YES
199     * if it matches the head of the string.
200     */
201
202    if (tok[0] == '@') {			/* netgroup */
203	return (netgroup_match(tok + 1, string, (char *) 0));
204    } else if (string_match(tok, string)) {	/* ALL or exact match */
205	return (YES);
206    } else if (tok[0] == '.') {			/* domain: match last fields */
207	if ((str_len = strlen(string)) > (tok_len = strlen(tok))
208	    && strcasecmp(tok, string + str_len - tok_len) == 0)
209	    return (YES);
210    } else if (strcasecmp(tok, "LOCAL") == 0) {	/* local: no dots */
211	if (strchr(string, '.') == 0)
212	    return (YES);
213    } else if (tok[(tok_len = strlen(tok)) - 1] == '.'	/* network */
214	       && strncmp(tok, string, tok_len) == 0) {
215	return (YES);
216    }
217    return (NO);
218}
219
220/* string_match - match a string against one token */
221
222static int string_match(tok, string)
223char   *tok;
224char   *string;
225{
226
227    /*
228     * If the token has the magic value "ALL" the match always succeeds.
229     * Otherwise, return YES if the token fully matches the string.
230     */
231
232    if (strcasecmp(tok, "ALL") == 0) {		/* all: always matches */
233	return (YES);
234    } else if (strcasecmp(tok, string) == 0) {	/* try exact match */
235	return (YES);
236    }
237    return (NO);
238}
239#endif /* LOGIN_ACCES */
240