lib/pam_module/pam_login_access/login_access.c

   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: src/lib/libpam/modules/pam_login_access/login_access.c,v 1.13 2007/05/25 07:50:18 des Exp $
  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
  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((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         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
 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 != 0; tok = strtok((char *) 0, 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((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
 139 static int
 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
 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, (char *) 0, 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
 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, (char *) 0));
 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
 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 }