/* vi: set sw=4 ts=4: */
/*
 * Mini weak password checker implementation for busybox
 *
 * Copyright (C) 2006 Tito Ragusa <farmatito@tiscali.it>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

/*      A good password:
        1)      should contain at least six characters (man passwd);
        2)      empty passwords are not permitted;
        3)      should contain a mix of four different types of characters
                upper case letters,
                lower case letters,
                numbers,
                special characters such as !@#$%^&*,;".
        This password types should not  be permitted:
        a)      pure numbers: birthdates, social security number, license plate, phone numbers;
        b)      words and all letters only passwords (uppercase, lowercase or mixed)
                as palindromes, consecutive or repetitive letters
                or adjacent letters on your keyboard;
        c)      username, real name, company name or (e-mail?) address
                in any form (as-is, reversed, capitalized, doubled, etc.).
                (we can check only against username, gecos and hostname)
        d)      common and obvious letter-number replacements
                (e.g. replace the letter O with number 0)
                such as "M1cr0$0ft" or "P@ssw0rd" (CAVEAT: we cannot check for them
                without the use of a dictionary).

        For each missing type of characters an increase of password length is
        requested.

        If user is root we warn only.

        CAVEAT: some older versions of crypt() truncates passwords to 8 chars,
        so that aaaaaaaa1Q$ is equal to aaaaaaaa making it possible to fool
        some of our checks. We don't test for this special case as newer versions
        of crypt do not truncate passwords.
*/

#include "libbb.h"

static int string_checker_helper(const char *p1, const char *p2) __attribute__ ((__pure__));

static int string_checker_helper(const char *p1, const char *p2)
{
        /* as sub-string */
        if (strcasestr(p2, p1) != NULL
        /* invert in case haystack is shorter than needle */
         || strcasestr(p1, p2) != NULL
        /* as-is or capitalized */
        /* || strcasecmp(p1, p2) == 0 - 1st strcasestr should catch this too */
        ) {
                return 1;
        }
        return 0;
}

static int string_checker(const char *p1, const char *p2)
{
        int size, i;
        /* check string */
        int ret = string_checker_helper(p1, p2);
        /* make our own copy */
        char *p = xstrdup(p1);

        /* reverse string */
        i = size = strlen(p1);
        while (--i >= 0) {
                *p++ = p1[i];
        }
        p -= size; /* restore pointer */

        /* check reversed string */
        ret |= string_checker_helper(p, p2);

        /* clean up */
        memset(p, 0, size);
        free(p);

        return ret;
}

#define CATEGORIES  4

#define LOWERCASE   1
#define UPPERCASE   2
#define NUMBERS     4
#define SPECIAL     8

#define LAST_CAT    8

static const char *obscure_msg(const char *old_p, const char *new_p, const struct passwd *pw)
{
        unsigned length;
        unsigned size;
        unsigned mixed;
        unsigned c;
        unsigned i;
        const char *p;
        char *hostname;

        /* size */
        if (!new_p || (length = strlen(new_p)) < CONFIG_PASSWORD_MINLEN)
                return "too short";

        /* no username as-is, as sub-string, reversed, capitalized, doubled */
        if (string_checker(new_p, pw->pw_name)) {
                return "similar to username";
        }
        /* no gecos as-is, as sub-string, reversed, capitalized, doubled */
        if (pw->pw_gecos[0] && string_checker(new_p, pw->pw_gecos)) {
                return "similar to gecos";
        }
        /* hostname as-is, as sub-string, reversed, capitalized, doubled */
        hostname = safe_gethostname();
        i = string_checker(new_p, hostname);
        free(hostname);
        if (i)
                return "similar to hostname";

        /* Should / Must contain a mix of: */
        mixed = 0;
        for (i = 0; i < length; i++) {
                if (islower(new_p[i])) {        /* a-z */
                        mixed |= LOWERCASE;
                } else if (isupper(new_p[i])) { /* A-Z */
                        mixed |= UPPERCASE;
                } else if (isdigit(new_p[i])) { /* 0-9 */
                        mixed |= NUMBERS;
                } else  {                       /* special characters */
                        mixed |= SPECIAL;
                }
                /* Count i'th char */
                c = 0;
                p = new_p;
                while (1) {
                        p = strchr(p, new_p[i]);
                        if (p == NULL) {
                                break;
                        }
                        c++;
                        p++;
                        if (!*p) {
                                break;
                        }
                }
                /* More than 50% similar characters ? */
                if (c*2 >= length) {
                        return "too many similar characters";
                }
        }

        size = CONFIG_PASSWORD_MINLEN + 2*CATEGORIES;
        for (i = 1; i <= LAST_CAT; i <<= 1)
                if (mixed & i)
                        size -= 2;
        if (length < size)
                return "too weak";

        if (old_p && old_p[0]) {
                /* check vs. old password */
                if (string_checker(new_p, old_p)) {
                        return "similar to old password";
                }
        }

        return NULL;
}

int FAST_FUNC obscure(const char *old, const char *newval, const struct passwd *pw)
{
        const char *msg;

        msg = obscure_msg(old, newval, pw);
        if (msg) {
                printf("Bad password: %s\n", msg);
                return 1;
        }
        return 0;
}