/*
 * 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.
 *
 * $FreeBSD: head/lib/libpam/modules/pam_login_access/login_access.c 297755 2016-04-09 18:09:10Z pfg $
 */

#include <sys/types.h>
#include <ctype.h>
#include <errno.h>
#include <grp.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

#include "pam_login_access.h"

#define _PATH_LOGACCESS         "/etc/login.access"

 /* 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      from_match(const char *, const char *);
static int      list_match(char *, const char *,
                                int (*)(const char *, const char *));
static int      netgroup_match(const char *, const char *, const char *);
static int      string_match(const char *, const char *);
static int      user_match(const char *, const char *);

/* 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(_PATH_LOGACCESS, "r")) != NULL) {
        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",
                       _PATH_LOGACCESS, 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(NULL, fs))
                || !(froms = strtok(NULL, fs))
                || strtok(NULL, fs)) {
                syslog(LOG_ERR, "%s: line %d: bad field count", _PATH_LOGACCESS,
                       lineno);
                continue;
            }
            if (perm[0] != '+' && perm[0] != '-') {
                syslog(LOG_ERR, "%s: line %d: bad first field", _PATH_LOGACCESS,
                       lineno);
                continue;
            }
            match = (list_match(froms, from, from_match)
                     && list_match(users, user, user_match));
        }
        fclose(fp);
    } else if (errno != ENOENT) {
        syslog(LOG_ERR, "cannot open %s: %m", _PATH_LOGACCESS);
    }
    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)(const char *, const char *))
{
    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 != NULL; tok = strtok(NULL, sep)) {
        if (strcasecmp(tok, "EXCEPT") == 0)     /* EXCEPT: give up */
            break;
        if ((match = (*match_fn)(tok, item)) != 0)      /* YES */
            break;
    }
    /* Process exceptions to matches. */

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

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

static int
netgroup_match(const char *group, const char *machine, const char *user)
{
    char domain[1024];
    unsigned int i;

    if (getdomainname(domain, sizeof(domain)) != 0 || *domain == '\0') {
        syslog(LOG_ERR, "NIS netgroup support disabled: no NIS domain");
        return (NO);
    }

    /* getdomainname() does not reliably terminate the string */
    for (i = 0; i < sizeof(domain); ++i)
        if (domain[i] == '\0')
            break;
    if (i == sizeof(domain)) {
        syslog(LOG_ERR, "NIS netgroup support disabled: invalid NIS domain");
        return (NO);
    }

    if (innetgr(group, machine, user, domain) == 1)
        return (YES);
    return (NO);
}

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

static int
user_match(const char *tok, const char *string)
{
    struct group *group;
    int     i;

    /*
     * 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 (tok[0] == '@') {                        /* netgroup */
        return (netgroup_match(tok + 1, NULL, string));
    } else if (string_match(tok, string)) {     /* ALL or exact match */
        return (YES);
    } else if ((group = getgrnam(tok)) != NULL) {/* try group membership */
        for (i = 0; group->gr_mem[i]; i++)
            if (strcasecmp(string, group->gr_mem[i]) == 0)
                return (YES);
    }
    return (NO);
}

/* 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, NULL));
    } 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, 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);
}