login_access.c revision 2198 
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 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
44login_access(user, from)
45char   *user;
46char   *from;
47{
48    FILE   *fp;
49    char    line[BUFSIZ];
50    char   *perm;			/* becomes permission field */
51    char   *users;			/* becomes list of login names */
52    char   *froms;			/* becomes list of terminals or hosts */
53    int     match = NO;
54    int     end;
55    int     lineno = 0;			/* for diagnostics */
56
57    /*
58     * Process the table one line at a time and stop at the first match.
59     * Blank lines and lines that begin with a '#' character are ignored.
60     * Non-comment lines are broken at the ':' character. All fields are
61     * mandatory. The first field should be a "+" or "-" character. A
62     * non-existing table means no access control.
63     */
64
65    if (fp = fopen(_PATH_LOGACCESS, "r")) {
66	while (!match && fgets(line, sizeof(line), fp)) {
67	    lineno++;
68	    if (line[end = strlen(line) - 1] != '\n') {
69		syslog(LOG_ERR, "%s: line %d: missing newline or line too long",
70		       _PATH_LOGACCESS, lineno);
71		continue;
72	    }
73	    if (line[0] == '#')
74		continue;			/* comment line */
75	    while (end > 0 && isspace(line[end - 1]))
76		end--;
77	    line[end] = 0;			/* strip trailing whitespace */
78	    if (line[0] == 0)			/* skip blank lines */
79		continue;
80	    if (!(perm = strtok(line, fs))
81		|| !(users = strtok((char *) 0, fs))
82		|| !(froms = strtok((char *) 0, fs))
83		|| strtok((char *) 0, fs)) {
84		syslog(LOG_ERR, "%s: line %d: bad field count", _PATH_LOGACCESS,
85		       lineno);
86		continue;
87	    }
88	    if (perm[0] != '+' && perm[0] != '-') {
89		syslog(LOG_ERR, "%s: line %d: bad first field", _PATH_LOGACCESS,
90		       lineno);
91		continue;
92	    }
93	    match = (list_match(froms, from, from_match)
94		     && list_match(users, user, user_match));
95	}
96	(void) fclose(fp);
97    } else if (errno != ENOENT) {
98	syslog(LOG_ERR, "cannot open %s: %m", _PATH_LOGACCESS);
99    }
100    return (match == 0 || (line[0] == '+'));
101}
102
103/* list_match - match an item against a list of tokens with exceptions */
104
105static int list_match(list, item, match_fn)
106char   *list;
107char   *item;
108int   (*match_fn) ();
109{
110    char   *tok;
111    int     match = NO;
112
113    /*
114     * Process tokens one at a time. We have exhausted all possible matches
115     * when we reach an "EXCEPT" token or the end of the list. If we do find
116     * a match, look for an "EXCEPT" list and recurse to determine whether
117     * the match is affected by any exceptions.
118     */
119
120    for (tok = strtok(list, sep); tok != 0; tok = strtok((char *) 0, sep)) {
121	if (strcasecmp(tok, "EXCEPT") == 0)	/* EXCEPT: give up */
122	    break;
123	if (match = (*match_fn) (tok, item))	/* YES */
124	    break;
125    }
126    /* Process exceptions to matches. */
127
128    if (match != NO) {
129	while ((tok = strtok((char *) 0, sep)) && strcasecmp(tok, "EXCEPT"))
130	     /* VOID */ ;
131	if (tok == 0 || list_match((char *) 0, item, match_fn) == NO)
132	    return (match);
133    }
134    return (NO);
135}
136
137/* netgroup_match - match group against machine or user */
138
139static int netgroup_match(group, machine, user)
140char   *machine;
141char   *user;
142{
143#ifdef NIS
144    static char *mydomain = 0;
145
146    if (mydomain == 0)
147	yp_get_default_domain(&mydomain);
148    return (innetgr(group, machine, user, mydomain));
149#else
150    syslog(LOG_ERR, "NIS netgroup support not configured");
151#endif
152}
153
154/* user_match - match a username against one token */
155
156static int user_match(tok, string)
157char   *tok;
158char   *string;
159{
160    struct group *group;
161    int     i;
162
163    /*
164     * If a token has the magic value "ALL" the match always succeeds.
165     * Otherwise, return YES if the token fully matches the username, or if
166     * the token is a group that contains the username.
167     */
168
169    if (tok[0] == '@') {			/* netgroup */
170	return (netgroup_match(tok + 1, (char *) 0, string));
171    } else if (string_match(tok, string)) {	/* ALL or exact match */
172	return (YES);
173    } else if (group = getgrnam(tok)) {		/* try group membership */
174	for (i = 0; group->gr_mem[i]; i++)
175	    if (strcasecmp(string, group->gr_mem[i]) == 0)
176		return (YES);
177    }
178    return (NO);
179}
180
181/* from_match - match a host or tty against a list of tokens */
182
183static int from_match(tok, string)
184char   *tok;
185char   *string;
186{
187    int     tok_len;
188    int     str_len;
189
190    /*
191     * If a token has the magic value "ALL" the match always succeeds. Return
192     * YES if the token fully matches the string. If the token is a domain
193     * name, return YES if it matches the last fields of the string. If the
194     * token has the magic value "LOCAL", return YES if the string does not
195     * contain a "." character. If the token is a network number, return YES
196     * if it matches the head of the string.
197     */
198
199    if (tok[0] == '@') {			/* netgroup */
200	return (netgroup_match(tok + 1, string, (char *) 0));
201    } else if (string_match(tok, string)) {	/* ALL or exact match */
202	return (YES);
203    } else if (tok[0] == '.') {			/* domain: match last fields */
204	if ((str_len = strlen(string)) > (tok_len = strlen(tok))
205	    && strcasecmp(tok, string + str_len - tok_len) == 0)
206	    return (YES);
207    } else if (strcasecmp(tok, "LOCAL") == 0) {	/* local: no dots */
208	if (strchr(string, '.') == 0)
209	    return (YES);
210    } else if (tok[(tok_len = strlen(tok)) - 1] == '.'	/* network */
211	       && strncmp(tok, string, tok_len) == 0) {
212	return (YES);
213    }
214    return (NO);
215}
216
217/* string_match - match a string against one token */
218
219static int string_match(tok, string)
220char   *tok;
221char   *string;
222{
223
224    /*
225     * If the token has the magic value "ALL" the match always succeeds.
226     * Otherwise, return YES if the token fully matches the string.
227     */
228
229    if (strcasecmp(tok, "ALL") == 0) {		/* all: always matches */
230	return (YES);
231    } else if (strcasecmp(tok, string) == 0) {	/* try exact match */
232	return (YES);
233    }
234    return (NO);
235}
236#endif /* LOGIN_ACCES */
237