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login_access.c

/* Taken from logdaemon-5.0, only minimal changes.  --marekm */

/************************************************************************
* Copyright 1995 by Wietse Venema.  All rights reserved. Individual files
* may be covered by other copyrights (as noted in the file itself.)
*
* This material was originally written and compiled by Wietse Venema at
* Eindhoven University of Technology, The Netherlands, in 1990, 1991,
* 1992, 1993, 1994 and 1995.
*
* Redistribution and use in source and binary forms are permitted
* provided that this entire copyright notice is duplicated in all such
* copies.  
*
* This software is provided "as is" and without any expressed or implied
* warranties, including, without limitation, the implied warranties of
* merchantibility and fitness for any particular purpose.
************************************************************************/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#ifdef LOGIN_ACCESS
#include "rcsid.h"
RCSID("$Id: login_access.c 6 2005-03-20 15:34:28Z bubulle $")
#include "prototypes.h"

 /*
  * This module implements a simple but effective form of login access
  * control based on login names and on host (or domain) names, internet
  * addresses (or network numbers), or on terminal line names in case of
  * non-networked logins. Diagnostics are reported through syslog(3).
  * 
  * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
  */

#include <sys/types.h>
#include <stdio.h>
#include <syslog.h>
#include <ctype.h>
#include <netdb.h>
#include <grp.h>
#ifdef PRIMARY_GROUP_MATCH
#include <pwd.h>
#endif
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>  /* for inet_ntoa() */

extern struct group *getgrnam();
extern int innetgr();
#if 0  /* should be defined by <errno.h> */
extern int errno;
#endif

#if !defined(MAXHOSTNAMELEN) || (MAXHOSTNAMELEN < 64)
#undef MAXHOSTNAMELEN
#define MAXHOSTNAMELEN 256
#endif

 /* Path name of the access control file. */

#ifndef     TABLE
#define TABLE     "/etc/login.access"
#endif

 /* Delimiters for fields and for lists of users, ttys or hosts. */

static char fs[] = ":";             /* field separator */
static char sep[] = ", \t";         /* list-element separator */

 /* Constants to be used in assignments only, not in comparisons... */

#define YES             1
#define NO              0

static int list_match();
static int user_match();
static int from_match();
static int string_match();

/* login_access - match username/group and host/tty with access control file */

int
login_access(const char *user, const char *from)
{
    FILE   *fp;
    char    line[BUFSIZ];
    char   *perm;             /* becomes permission field */
    char   *users;                  /* becomes list of login names */
    char   *froms;                  /* becomes list of terminals or hosts */
    int     match = NO;
    int     end;
    int     lineno = 0;             /* for diagnostics */

    /*
     * Process the table one line at a time and stop at the first match.
     * Blank lines and lines that begin with a '#' character are ignored.
     * Non-comment lines are broken at the ':' character. All fields are
     * mandatory. The first field should be a "+" or "-" character. A
     * non-existing table means no access control.
     */

    if ((fp = fopen(TABLE, "r"))) {
      while (!match && fgets(line, sizeof(line), fp)) {
          lineno++;
          if (line[end = strlen(line) - 1] != '\n') {
            syslog(LOG_ERR, "%s: line %d: missing newline or line too long",
                   TABLE, lineno);
            continue;
          }
          if (line[0] == '#')
            continue;               /* comment line */
          while (end > 0 && isspace(line[end - 1]))
            end--;
          line[end] = 0;                  /* strip trailing whitespace */
          if (line[0] == 0)               /* skip blank lines */
            continue;
          if (!(perm = strtok(line, fs))
            || !(users = strtok((char *) 0, fs))
            || !(froms = strtok((char *) 0, fs))
            || strtok((char *) 0, fs)) {
            syslog(LOG_ERR, "%s: line %d: bad field count", TABLE, lineno);
            continue;
          }
          if (perm[0] != '+' && perm[0] != '-') {
            syslog(LOG_ERR, "%s: line %d: bad first field", TABLE, lineno);
            continue;
          }
          match = (list_match(froms, from, from_match)
                 && list_match(users, user, user_match));
      }
      (void) fclose(fp);
    } else if (errno != ENOENT) {
      syslog(LOG_ERR, "cannot open %s: %m", TABLE);
    }
    return (match == 0 || (line[0] == '+'));
}

/* list_match - match an item against a list of tokens with exceptions */

static int
list_match(char *list, const char *item, int (*match_fn)())
{
    char   *tok;
    int     match = NO;

    /*
     * Process tokens one at a time. We have exhausted all possible matches
     * when we reach an "EXCEPT" token or the end of the list. If we do find
     * a match, look for an "EXCEPT" list and recurse to determine whether
     * the match is affected by any exceptions.
     */

    for (tok = strtok(list, sep); tok != 0; tok = strtok((char *) 0, sep)) {
      if (strcasecmp(tok, "EXCEPT") == 0) /* EXCEPT: give up */
          break;
      if ((match = (*match_fn) (tok, item)))    /* YES */
          break;
    }
    /* Process exceptions to matches. */

    if (match != NO) {
      while ((tok = strtok((char *) 0, sep)) && strcasecmp(tok, "EXCEPT"))
           /* VOID */ ;
      if (tok == 0 || list_match((char *) 0, item, match_fn) == NO)
          return (match);
    }
    return (NO);
}

/* myhostname - figure out local machine name */

static char *
myhostname(void)
{
    static char name[MAXHOSTNAMELEN + 1] = "";

    if (name[0] == 0) {
      gethostname(name, sizeof(name));
      name[MAXHOSTNAMELEN] = 0;
    }
    return (name);
}

/* netgroup_match - match group against machine or user */

static int
netgroup_match(const char *group, const char *machine, const char *user)
{
#if 0  /* original code */
#ifdef NIS
    static char *mydomain = 0;

    if (mydomain == 0)
      yp_get_default_domain(&mydomain);
    return (innetgr(group, machine, user, mydomain));
#else
    syslog(LOG_ERR, "NIS netgroup support not configured");
    return (NO);
#endif
#else  /* works better with glibc? */
      static char *mydomain = 0;

      if (mydomain == 0) {
            static char domain[MAXHOSTNAMELEN+1];

            getdomainname(domain, MAXHOSTNAMELEN);
            mydomain = domain;
      }

      return innetgr(group, machine, user, mydomain);
#endif
}

/* user_match - match a username against one token */

static int
user_match(const char *tok, const char *string)
{
    struct group *group;
#ifdef PRIMARY_GROUP_MATCH
    struct passwd *userinf;
#endif
    int     i;
    char   *at;

    /*
     * If a token has the magic value "ALL" the match always succeeds.
     * Otherwise, return YES if the token fully matches the username, or if
     * the token is a group that contains the username.
     */

    if ((at = strchr(tok + 1, '@')) != 0) {     /* split user@host pattern */
      *at = 0;
      return (user_match(tok, string) && from_match(at + 1, myhostname()));
    } else if (tok[0] == '@') {                 /* netgroup */
      return (netgroup_match(tok + 1, (char *) 0, string));
    } else if (string_match(tok, string)) {     /* ALL or exact match */
      return (YES);
    } else if ((group = getgrnam(tok))) { /* try group membership */
      for (i = 0; group->gr_mem[i]; i++)
          if (strcasecmp(string, group->gr_mem[i]) == 0)
            return (YES);
#ifdef PRIMARY_GROUP_MATCH
      /*
       * If the sting is an user whose initial GID matches the token,
       * accept it. May avoid excessively long lines in /etc/group.
       * Radu-Adrian Feurdean <raf@licj.soroscj.ro>
       *
       * XXX - disabled by default for now.  Need to verify that
       * getpwnam() doesn't have some nasty side effects.  --marekm
       */
      if ((userinf = getpwnam(string)))
          if (userinf->pw_gid == group->gr_gid)
            return (YES);
#endif
    }
    return (NO);
}

static char *
resolve_hostname(string)
    char *string;
{
#if 1
    /*
     * Resolve hostname to numeric IP address, as suggested
     * by Dave Hagewood <admin@arrowweb.com>.  --marekm
     */
    struct hostent *hp;

    hp = gethostbyname(string);
    if (hp)
      return inet_ntoa(*((struct in_addr *) *(hp->h_addr_list)));

    syslog(LOG_ERR, "%s - unknown host", string);
#endif
    return string;
}

/* from_match - match a host or tty against a list of tokens */

static int
from_match(const char *tok, const char *string)
{
    int     tok_len;
    int     str_len;

    /*
     * If a token has the magic value "ALL" the match always succeeds. Return
     * YES if the token fully matches the string. If the token is a domain
     * name, return YES if it matches the last fields of the string. If the
     * token has the magic value "LOCAL", return YES if the string does not
     * contain a "." character. If the token is a network number, return YES
     * if it matches the head of the string.
     */

    if (tok[0] == '@') {                  /* netgroup */
      return (netgroup_match(tok + 1, string, (char *) 0));
    } else if (string_match(tok, string)) {     /* ALL or exact match */
      return (YES);
    } else if (tok[0] == '.') {                 /* domain: match last fields */
      if ((str_len = strlen(string)) > (tok_len = strlen(tok))
          && strcasecmp(tok, string + str_len - tok_len) == 0)
          return (YES);
    } else if (strcasecmp(tok, "LOCAL") == 0) { /* local: no dots */
      if (strchr(string, '.') == 0)
          return (YES);
    } else if (tok[(tok_len = strlen(tok)) - 1] == '.'      /* network */
             && strncmp(tok, resolve_hostname(string), tok_len) == 0) {
      return (YES);
    }
    return (NO);
}

/* string_match - match a string against one token */

static int
string_match(const char *tok, const char *string)
{

    /*
     * If the token has the magic value "ALL" the match always succeeds.
     * Otherwise, return YES if the token fully matches the string.
     */

    if (strcasecmp(tok, "ALL") == 0) {          /* all: always matches */
      return (YES);
    } else if (strcasecmp(tok, string) == 0) {  /* try exact match */
      return (YES);
    }
    return (NO);
}
#endif  /* LOGIN_ACCESS */

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