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#if 0
11#ifndef lint
12static char sccsid[] = "%Z% %M% %I% %E% %U%";
13#endif
14#endif
15
16#include <sys/types.h>
17#include <sys/param.h>
18#include <ctype.h>
19#include <errno.h>
20#include <grp.h>
21#include <netdb.h>
22#include <pwd.h>
23#include <stdio.h>
24#include <stdlib.h>
25#include <string.h>
26#include <syslog.h>
27#include <unistd.h>
28
29#include "pam_login_access.h"
30
31 /* Constants to be used in assignments only, not in comparisons... */
32
33#define YES             1
34#define NO              0
35
36static int	from_match(const char *, const char *, struct pam_login_access_options *);
37static int	list_match(char *, const char *,
38				int (*)(const char *, const char *,
39				struct pam_login_access_options *),
40				struct pam_login_access_options *);
41static int	netgroup_match(const char *, const char *, const char *);
42static int	string_match(const char *, const char *);
43static int	user_match(const char *, const char *, struct pam_login_access_options *);
44static int	group_match(const char *, const char *);
45
46/* login_access - match username/group and host/tty with access control file */
47
48int
49login_access(const char *user, const char *from,
50	struct pam_login_access_options *login_access_opts)
51{
52    FILE   *fp;
53    char    line[BUFSIZ];
54    char   *perm;			/* becomes permission field */
55    char   *users;			/* becomes list of login names */
56    char   *froms;			/* becomes list of terminals or hosts */
57    int     match = NO;
58    int     end;
59    int     lineno = 0;			/* for diagnostics */
60    const char *fieldsep = login_access_opts->fieldsep;
61
62    /*
63     * Process the table one line at a time and stop at the first match.
64     * Blank lines and lines that begin with a '#' character are ignored.
65     * Non-comment lines are broken at the ':' character. All fields are
66     * mandatory. The first field should be a "+" or "-" character. A
67     * non-existing table means no access control.
68     */
69
70    if ((fp = fopen(login_access_opts->accessfile, "r")) != NULL) {
71	while (!match && fgets(line, sizeof(line), fp)) {
72	    lineno++;
73	    if (line[end = strlen(line) - 1] != '\n') {
74		syslog(LOG_ERR, "%s: line %d: missing newline or line too long",
75		       login_access_opts->accessfile, lineno);
76		continue;
77	    }
78	    if (line[0] == '#')
79		continue;			/* comment line */
80	    while (end > 0 && isspace(line[end - 1]))
81		end--;
82	    line[end] = 0;			/* strip trailing whitespace */
83	    if (line[0] == 0)			/* skip blank lines */
84		continue;
85	    if (!(perm = strtok(line, fieldsep))
86		|| !(users = strtok((char *) 0, fieldsep))
87		|| !(froms = strtok((char *) 0, fieldsep))
88		|| strtok((char *) 0, fieldsep)) {
89		syslog(LOG_ERR, "%s: line %d: bad field count", login_access_opts->accessfile,
90		       lineno);
91		continue;
92	    }
93	    if (perm[0] != '+' && perm[0] != '-') {
94		syslog(LOG_ERR, "%s: line %d: bad first field", login_access_opts->accessfile,
95		       lineno);
96		continue;
97	    }
98	    match = (list_match(froms, from, from_match, login_access_opts)
99		     && list_match(users, user, user_match, login_access_opts));
100	}
101	(void) fclose(fp);
102    } else if (errno != ENOENT) {
103	syslog(LOG_ERR, "cannot open %s: %m", login_access_opts->accessfile);
104    }
105    return (match == 0 || (line[0] == '+'));
106}
107
108/* list_match - match an item against a list of tokens with exceptions */
109
110static int
111list_match(char *list, const char *item,
112    int (*match_fn)(const char *, const char *, struct pam_login_access_options *),
113    struct pam_login_access_options *login_access_opts)
114{
115    char   *tok;
116    int     match = NO;
117    const char *listsep = login_access_opts->listsep;
118
119    /*
120     * Process tokens one at a time. We have exhausted all possible matches
121     * when we reach an "EXCEPT" token or the end of the list. If we do find
122     * a match, look for an "EXCEPT" list and recurse to determine whether
123     * the match is affected by any exceptions.
124     */
125
126    for (tok = strtok(list, listsep); tok != NULL; tok = strtok((char *) 0, listsep)) {
127	if (strcmp(tok, "EXCEPT") == 0)	/* EXCEPT: give up */
128	    break;
129	if ((match = (*match_fn)(tok, item, login_access_opts)) != 0)	/* YES */
130	    break;
131    }
132    /* Process exceptions to matches. */
133
134    if (match != NO) {
135	while ((tok = strtok((char *) 0, listsep)) && strcmp(tok, "EXCEPT")) {
136	     /* VOID */ ;
137	}
138	if (tok == NULL ||
139	    list_match((char *) 0, item, match_fn, login_access_opts) == NO) {
140		return (match);
141	}
142    }
143    return (NO);
144}
145
146/* netgroup_match - match group against machine or user */
147
148static int
149netgroup_match(const char *group, const char *machine, const char *user)
150{
151    char domain[1024];
152    unsigned int i;
153
154    if (getdomainname(domain, sizeof(domain)) != 0 || *domain == '\0') {
155	syslog(LOG_ERR, "NIS netgroup support disabled: no NIS domain");
156	return (NO);
157    }
158
159    /* getdomainname() does not reliably terminate the string */
160    for (i = 0; i < sizeof(domain); ++i)
161	if (domain[i] == '\0')
162	    break;
163    if (i == sizeof(domain)) {
164	syslog(LOG_ERR, "NIS netgroup support disabled: invalid NIS domain");
165	return (NO);
166    }
167
168    if (innetgr(group, machine, user, domain) == 1)
169	return (YES);
170    return (NO);
171}
172
173/* group_match - match a group against one token */
174
175int
176group_match(const char *tok, const char *username)
177{
178    struct group *group;
179    struct passwd *passwd;
180    gid_t *grouplist;
181    int i, ret, ngroups = NGROUPS;
182
183    if ((passwd = getpwnam(username)) == NULL)
184	return (NO);
185    errno = 0;
186    if ((group = getgrnam(tok)) == NULL) {
187	if (errno != 0)
188	    syslog(LOG_ERR, "getgrnam() failed for %s: %s", username, strerror(errno));
189	else
190	    syslog(LOG_NOTICE, "group not found: %s", username);
191	return (NO);
192    }
193    if ((grouplist = calloc(ngroups, sizeof(gid_t))) == NULL) {
194	syslog(LOG_ERR, "cannot allocate memory for grouplist: %s", username);
195	return (NO);
196    }
197    ret = NO;
198    if (getgrouplist(username, passwd->pw_gid, grouplist, &ngroups) != 0)
199	syslog(LOG_ERR, "getgrouplist() failed for %s", username);
200    for (i = 0; i < ngroups; i++)
201	if (grouplist[i] == group->gr_gid)
202	    ret = YES;
203    free(grouplist);
204    return (ret);
205}
206
207/* user_match - match a username against one token */
208
209static int
210user_match(const char *tok, const char *string,
211	struct pam_login_access_options *login_access_opts)
212{
213    size_t stringlen;
214    char *grpstr;
215    int rc;
216
217    /*
218     * If a token has the magic value "ALL" the match always succeeds.
219     * Otherwise, return YES if the token fully matches the username, or if
220     * the token is a group that contains the username.
221     */
222
223    if (tok[0] == '@') {			/* netgroup */
224	return (netgroup_match(tok + 1, (char *) 0, string));
225    } else if (tok[0] == '(' && tok[(stringlen = strlen(&tok[1]))] == ')') {		/* group */
226	if ((grpstr = strndup(&tok[1], stringlen - 1)) == NULL) {
227	    syslog(LOG_ERR, "cannot allocate memory for %s", string);
228	    return (NO);
229	}
230	rc = group_match(grpstr, string);
231	free(grpstr);
232	return (rc);
233    } else if (string_match(tok, string)) {	/* ALL or exact match */
234	return (YES);
235    } else if (login_access_opts->defgroup == true) {/* try group membership */
236	return (group_match(tok, string));
237    }
238    return (NO);
239}
240
241/* from_match - match a host or tty against a list of tokens */
242
243static int
244from_match(const char *tok, const char *string,
245	struct pam_login_access_options *login_access_opts __unused)
246{
247    int     tok_len;
248    int     str_len;
249
250    /*
251     * If a token has the magic value "ALL" the match always succeeds. Return
252     * YES if the token fully matches the string. If the token is a domain
253     * name, return YES if it matches the last fields of the string. If the
254     * token has the magic value "LOCAL", return YES if the string does not
255     * contain a "." character. If the token is a network number, return YES
256     * if it matches the head of the string.
257     */
258
259    if (tok[0] == '@') {			/* netgroup */
260	return (netgroup_match(tok + 1, string, (char *) 0));
261    } else if (string_match(tok, string)) {	/* ALL or exact match */
262	return (YES);
263    } else if (tok[0] == '.') {			/* domain: match last fields */
264	if ((str_len = strlen(string)) > (tok_len = strlen(tok))
265	    && strcasecmp(tok, string + str_len - tok_len) == 0)
266	    return (YES);
267    } else if (strcmp(tok, "LOCAL") == 0) {	/* local: no dots */
268	if (strchr(string, '.') == NULL)
269	    return (YES);
270    } else if (tok[(tok_len = strlen(tok)) - 1] == '.'	/* network */
271	       && strncmp(tok, string, tok_len) == 0) {
272	return (YES);
273    }
274    return (NO);
275}
276
277/* string_match - match a string against one token */
278
279static int
280string_match(const char *tok, const char *string)
281{
282
283    /*
284     * If the token has the magic value "ALL" the match always succeeds.
285     * Otherwise, return YES if the token fully matches the string.
286     */
287
288    if (strcmp(tok, "ALL") == 0) {		/* all: always matches */
289	return (YES);
290    } else if (strcasecmp(tok, string) == 0) {	/* try exact match */
291	return (YES);
292    }
293    return (NO);
294}
295