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 * $FreeBSD: head/lib/libpam/modules/pam_login_access/login_access.c 297755 2016-04-09 18:09:10Z pfg $
10 */
11
12 #include <sys/types.h>
13 #include <ctype.h>
14 #include <errno.h>
15 #include <grp.h>
16 #include <netdb.h>
17 #include <stdio.h>
18 #include <stdlib.h>
19 #include <string.h>
20 #include <syslog.h>
21 #include <unistd.h>
22
23 #include "pam_login_access.h"
24
25 #define _PATH_LOGACCESS "/etc/login.access"
26
27 /* Delimiters for fields and for lists of users, ttys or hosts. */
28
29 static char fs[] = ":"; /* field separator */
30 static 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
37 static int from_match(const char *, const char *);
38 static int list_match(char *, const char *,
39 int (*)(const char *, const char *));
40 static int netgroup_match(const char *, const char *, const char *);
41 static int string_match(const char *, const char *);
42 static int user_match(const char *, const char *);
43
44 /* login_access - match username/group and host/tty with access control file */
45
46 int
login_access(const char * user,const char * from)47 login_access(const char *user, const char *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(NULL, fs))
83 || !(froms = strtok(NULL, fs))
84 || strtok(NULL, 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 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
106 static int
list_match(char * list,const char * item,int (* match_fn)(const char *,const char *))107 list_match(char *list, const char *item,
108 int (*match_fn)(const char *, const char *))
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 != NULL; tok = strtok(NULL, sep)) {
121 if (strcasecmp(tok, "EXCEPT") == 0) /* EXCEPT: give up */
122 break;
123 if ((match = (*match_fn)(tok, item)) != 0) /* YES */
124 break;
125 }
126 /* Process exceptions to matches. */
127
128 if (match != NO) {
129 while ((tok = strtok(NULL, sep)) && strcasecmp(tok, "EXCEPT"))
130 /* VOID */ ;
131 if (tok == NULL || list_match(NULL, item, match_fn) == NO)
132 return (match);
133 }
134 return (NO);
135 }
136
137 /* netgroup_match - match group against machine or user */
138
139 static int
netgroup_match(const char * group,const char * machine,const char * user)140 netgroup_match(const char *group, const char *machine, const char *user)
141 {
142 char domain[1024];
143 unsigned int i;
144
145 if (getdomainname(domain, sizeof(domain)) != 0 || *domain == '\0') {
146 syslog(LOG_ERR, "NIS netgroup support disabled: no NIS domain");
147 return (NO);
148 }
149
150 /* getdomainname() does not reliably terminate the string */
151 for (i = 0; i < sizeof(domain); ++i)
152 if (domain[i] == '\0')
153 break;
154 if (i == sizeof(domain)) {
155 syslog(LOG_ERR, "NIS netgroup support disabled: invalid NIS domain");
156 return (NO);
157 }
158
159 if (innetgr(group, machine, user, domain) == 1)
160 return (YES);
161 return (NO);
162 }
163
164 /* user_match - match a username against one token */
165
166 static int
user_match(const char * tok,const char * string)167 user_match(const char *tok, const char *string)
168 {
169 struct group *group;
170 int i;
171
172 /*
173 * If a token has the magic value "ALL" the match always succeeds.
174 * Otherwise, return YES if the token fully matches the username, or if
175 * the token is a group that contains the username.
176 */
177
178 if (tok[0] == '@') { /* netgroup */
179 return (netgroup_match(tok + 1, NULL, string));
180 } else if (string_match(tok, string)) { /* ALL or exact match */
181 return (YES);
182 } else if ((group = getgrnam(tok)) != NULL) {/* try group membership */
183 for (i = 0; group->gr_mem[i]; i++)
184 if (strcasecmp(string, group->gr_mem[i]) == 0)
185 return (YES);
186 }
187 return (NO);
188 }
189
190 /* from_match - match a host or tty against a list of tokens */
191
192 static int
from_match(const char * tok,const char * string)193 from_match(const char *tok, const char *string)
194 {
195 int tok_len;
196 int str_len;
197
198 /*
199 * If a token has the magic value "ALL" the match always succeeds. Return
200 * YES if the token fully matches the string. If the token is a domain
201 * name, return YES if it matches the last fields of the string. If the
202 * token has the magic value "LOCAL", return YES if the string does not
203 * contain a "." character. If the token is a network number, return YES
204 * if it matches the head of the string.
205 */
206
207 if (tok[0] == '@') { /* netgroup */
208 return (netgroup_match(tok + 1, string, NULL));
209 } else if (string_match(tok, string)) { /* ALL or exact match */
210 return (YES);
211 } else if (tok[0] == '.') { /* domain: match last fields */
212 if ((str_len = strlen(string)) > (tok_len = strlen(tok))
213 && strcasecmp(tok, string + str_len - tok_len) == 0)
214 return (YES);
215 } else if (strcasecmp(tok, "LOCAL") == 0) { /* local: no dots */
216 if (strchr(string, '.') == 0)
217 return (YES);
218 } else if (tok[(tok_len = strlen(tok)) - 1] == '.' /* network */
219 && strncmp(tok, string, tok_len) == 0) {
220 return (YES);
221 }
222 return (NO);
223 }
224
225 /* string_match - match a string against one token */
226
227 static int
string_match(const char * tok,const char * string)228 string_match(const char *tok, const char *string)
229 {
230
231 /*
232 * If the token has the magic value "ALL" the match always succeeds.
233 * Otherwise, return YES if the token fully matches the string.
234 */
235
236 if (strcasecmp(tok, "ALL") == 0) { /* all: always matches */
237 return (YES);
238 } else if (strcasecmp(tok, string) == 0) { /* try exact match */
239 return (YES);
240 }
241 return (NO);
242 }
243