xref: /freebsd/contrib/pam_modules/pam_passwdqc/passwdqc_check.c (revision 402783abd11a9f734cc08c6d9120347f316bdb3c)

/*
 * Copyright (c) 2000-2002 by Solar Designer. See LICENSE.
 */

#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <pwd.h>

#include "passwdqc.h"

#define REASON_ERROR \
	"check failed"

#define REASON_SAME \
	"is the same as the old one"
#define REASON_SIMILAR \
	"is based on the old one"

#define REASON_SHORT \
	"too short"
#define REASON_LONG \
	"too long"

#define REASON_SIMPLESHORT \
	"not enough different characters or classes for this length"
#define REASON_SIMPLE \
	"not enough different characters or classes"

#define REASON_PERSONAL \
	"based on personal login information"

#define REASON_WORD \
	"based on a dictionary word and not a passphrase"

#define FIXED_BITS			15

typedef unsigned long fixed;

/*
 * Calculates the expected number of different characters for a random
 * password of a given length. The result is rounded down. We use this
 * with the _requested_ minimum length (so longer passwords don't have
 * to meet this strict requirement for their length).
 */
static int expected_different(int charset, int length)
{
	fixed x, y, z;

	x = ((fixed)(charset - 1) << FIXED_BITS) / charset;
	y = x;
	while (--length > 0) y = (y * x) >> FIXED_BITS;
	z = (fixed)charset * (((fixed)1 << FIXED_BITS) - y);

	return (int)(z >> FIXED_BITS);
}

/*
 * A password is too simple if it is too short for its class, or doesn't
 * contain enough different characters for its class, or doesn't contain
 * enough words for a passphrase.
 */
static int is_simple(passwdqc_params_t *params, const char *newpass)
{
	int length, classes, words, chars;
	int digits, lowers, uppers, others, unknowns;
	int c, p;

	length = classes = words = chars = 0;
	digits = lowers = uppers = others = unknowns = 0;
	p = ' ';
	while ((c = (unsigned char)newpass[length])) {
		length++;

		if (!isascii(c)) unknowns++; else
		if (isdigit(c)) digits++; else
		if (islower(c)) lowers++; else
		if (isupper(c)) uppers++; else
			others++;

		if (isascii(c) && isalpha(c) && isascii(p) && !isalpha(p))
			words++;
		p = c;

		if (!strchr(&newpass[length], c))
			chars++;
	}

	if (!length) return 1;

/* Upper case characters and digits used in common ways don't increase the
 * strength of a password */
	c = (unsigned char)newpass[0];
	if (uppers && isascii(c) && isupper(c)) uppers--;
	c = (unsigned char)newpass[length - 1];
	if (digits && isascii(c) && isdigit(c)) digits--;

/* Count the number of different character classes we've seen. We assume
 * that there're no non-ASCII characters for digits. */
	classes = 0;
	if (digits) classes++;
	if (lowers) classes++;
	if (uppers) classes++;
	if (others) classes++;
	if (unknowns && (!classes || (digits && classes == 1))) classes++;

	for (; classes > 0; classes--)
	switch (classes) {
	case 1:
		if (length >= params->min[0] &&
		    chars >= expected_different(10, params->min[0]) - 1)
			return 0;
		return 1;

	case 2:
		if (length >= params->min[1] &&
		    chars >= expected_different(36, params->min[1]) - 1)
			return 0;
		if (!params->passphrase_words ||
		    words < params->passphrase_words)
			continue;
		if (length >= params->min[2] &&
		    chars >= expected_different(27, params->min[2]) - 1)
			return 0;
		continue;

	case 3:
		if (length >= params->min[3] &&
		    chars >= expected_different(62, params->min[3]) - 1)
			return 0;
		continue;

	case 4:
		if (length >= params->min[4] &&
		    chars >= expected_different(95, params->min[4]) - 1)
			return 0;
		continue;
	}

	return 1;
}

static char *unify(const char *src)
{
	const char *sptr;
	char *dst, *dptr;
	int c;

	if (!(dst = malloc(strlen(src) + 1)))
		return NULL;

	sptr = src;
	dptr = dst;
	do {
		c = (unsigned char)*sptr;
		if (isascii(c) && isupper(c))
			*dptr++ = tolower(c);
		else
			*dptr++ = *sptr;
	} while (*sptr++);

	return dst;
}

static char *reverse(const char *src)
{
	const char *sptr;
	char *dst, *dptr;

	if (!(dst = malloc(strlen(src) + 1)))
		return NULL;

	sptr = &src[strlen(src)];
	dptr = dst;
	while (sptr > src)
		*dptr++ = *--sptr;
	*dptr = '\0';

	return dst;
}

static void clean(char *dst)
{
	if (dst) {
		memset(dst, 0, strlen(dst));
		free(dst);
	}
}

/*
 * Needle is based on haystack if both contain a long enough common
 * substring and needle would be too simple for a password with the
 * substring removed.
 */
static int is_based(passwdqc_params_t *params,
    const char *haystack, const char *needle, const char *original)
{
	char *scratch;
	int length;
	int i, j;
	const char *p;
	int match;

	if (!params->match_length)	/* disabled */
		return 0;

	if (params->match_length < 0)	/* misconfigured */
		return 1;

	if (strstr(haystack, needle))	/* based on haystack entirely */
		return 1;

	scratch = NULL;

	length = strlen(needle);
	for (i = 0; i <= length - params->match_length; i++)
	for (j = params->match_length; i + j <= length; j++) {
		match = 0;
		for (p = haystack; *p; p++)
		if (*p == needle[i] && !strncmp(p, &needle[i], j)) {
			match = 1;
			if (!scratch) {
				if (!(scratch = malloc(length + 1)))
					return 1;
			}
			memcpy(scratch, original, i);
			memcpy(&scratch[i], &original[i + j],
			    length + 1 - (i + j));
			if (is_simple(params, scratch)) {
				clean(scratch);
				return 1;
			}
		}
		if (!match) break;
	}

	clean(scratch);

	return 0;
}

/*
 * This wordlist check is now the least important given the checks above
 * and the support for passphrases (which are based on dictionary words,
 * and checked by other means). It is still useful to trap simple short
 * passwords (if short passwords are allowed) that are word-based, but
 * passed the other checks due to uncommon capitalization, digits, and
 * special characters. We (mis)use the same set of words that are used
 * to generate random passwords. This list is much smaller than those
 * used for password crackers, and it doesn't contain common passwords
 * that aren't short English words. Perhaps support for large wordlists
 * should still be added, even though this is now of little importance.
 */
static int is_word_based(passwdqc_params_t *params,
    const char *needle, const char *original)
{
	char word[7];
	char *unified;
	int i;

	word[6] = '\0';
	for (i = 0; i < 0x1000; i++) {
		memcpy(word, _passwdqc_wordset_4k[i], 6);
		if ((int)strlen(word) < params->match_length) continue;
		unified = unify(word);
		if (is_based(params, unified, needle, original)) {
			clean(unified);
			return 1;
		}
		clean(unified);
	}

	return 0;
}

const char *_passwdqc_check(passwdqc_params_t *params,
    const char *newpass, const char *oldpass, struct passwd *pw)
{
	char truncated[9], *reversed;
	char *u_newpass, *u_reversed;
	char *u_oldpass;
	char *u_name, *u_gecos;
	const char *reason;
	int length;

	reversed = NULL;
	u_newpass = u_reversed = NULL;
	u_oldpass = NULL;
	u_name = u_gecos = NULL;

	reason = NULL;

	if (oldpass && !strcmp(oldpass, newpass))
		reason = REASON_SAME;

	length = strlen(newpass);

	if (!reason && length < params->min[4])
		reason = REASON_SHORT;

	if (!reason && length > params->max) {
		if (params->max == 8) {
			truncated[0] = '\0';
			strncat(truncated, newpass, 8);
			newpass = truncated;
			if (oldpass && !strncmp(oldpass, newpass, 8))
				reason = REASON_SAME;
		} else
			reason = REASON_LONG;
	}

	if (!reason && is_simple(params, newpass)) {
		if (length < params->min[1] && params->min[1] <= params->max)
			reason = REASON_SIMPLESHORT;
		else
			reason = REASON_SIMPLE;
	}

	if (!reason) {
		if ((reversed = reverse(newpass))) {
			u_newpass = unify(newpass);
			u_reversed = unify(reversed);
			if (oldpass)
				u_oldpass = unify(oldpass);
			if (pw) {
				u_name = unify(pw->pw_name);
				u_gecos = unify(pw->pw_gecos);
			}
		}
		if (!reversed ||
		    !u_newpass || !u_reversed ||
		    (oldpass && !u_oldpass) ||
		    (pw && (!u_name || !u_gecos)))
			reason = REASON_ERROR;
	}

	if (!reason && oldpass && params->similar_deny &&
	    (is_based(params, u_oldpass, u_newpass, newpass) ||
	    is_based(params, u_oldpass, u_reversed, reversed)))
		reason = REASON_SIMILAR;

	if (!reason && pw &&
	    (is_based(params, u_name, u_newpass, newpass) ||
	    is_based(params, u_name, u_reversed, reversed) ||
	    is_based(params, u_gecos, u_newpass, newpass) ||
	    is_based(params, u_gecos, u_reversed, reversed)))
		reason = REASON_PERSONAL;

	if (!reason && (int)strlen(newpass) < params->min[2] &&
	    (is_word_based(params, u_newpass, newpass) ||
	    is_word_based(params, u_reversed, reversed)))
		reason = REASON_WORD;

	memset(truncated, 0, sizeof(truncated));
	clean(reversed);
	clean(u_newpass); clean(u_reversed);
	clean(u_oldpass);
	clean(u_name); clean(u_gecos);

	return reason;
}