passwordcheck.c

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/*-------------------------------------------------------------------------
 *
 * passwordcheck.c
 *
 *
 * Copyright (c) 2009-2025, PostgreSQL Global Development Group
 *
 * Author: Laurenz Albe <laurenz.albe@wien.gv.at>
 *
 * IDENTIFICATION
 *    contrib/passwordcheck/passwordcheck.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <ctype.h>
#include <limits.h>
 
#ifdef USE_CRACKLIB
#include <crack.h>
#endif
 
#include "commands/user.h"
#include "fmgr.h"
#include "libpq/crypt.h"
 
PG_MODULE_MAGIC_EXT(
                    .name = "passwordcheck",
                    .version = PG_VERSION
);
 
/* Saved hook value */
static check_password_hook_type prev_check_password_hook = NULL;
 
/* GUC variables */
static int  min_password_length = 8;
 
/*
 * check_password
 *
 * performs checks on an encrypted or unencrypted password
 * ereport's if not acceptable
 *
 * username: name of role being created or changed
 * password: new password (possibly already encrypted)
 * password_type: PASSWORD_TYPE_* code, to indicate if the password is
 *          in plaintext or encrypted form.
 * validuntil_time: password expiration time, as a timestamptz Datum
 * validuntil_null: true if password expiration time is NULL
 *
 * This sample implementation doesn't pay any attention to the password
 * expiration time, but you might wish to insist that it be non-null and
 * not too far in the future.
 */
static void
check_password(const char *username,
               const char *shadow_pass,
               PasswordType password_type,
               Datum validuntil_time,
               bool validuntil_null)
{
    if (prev_check_password_hook)
        prev_check_password_hook(username, shadow_pass,
                                 password_type, validuntil_time,
                                 validuntil_null);
 
    if (password_type != PASSWORD_TYPE_PLAINTEXT)
    {
        /*
         * Unfortunately we cannot perform exhaustive checks on encrypted
         * passwords - we are restricted to guessing. (Alternatively, we could
         * insist on the password being presented non-encrypted, but that has
         * its own security disadvantages.)
         *
         * We only check for username = password.
         */
        const char *logdetail = NULL;
 
        if (plain_crypt_verify(username, shadow_pass, username, &logdetail) == STATUS_OK)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("password must not equal user name")));
    }
    else
    {
        /*
         * For unencrypted passwords we can perform better checks
         */
        const char *password = shadow_pass;
        int         pwdlen = strlen(password);
        int         i;
        bool        pwd_has_letter,
                    pwd_has_nonletter;
#ifdef USE_CRACKLIB
        const char *reason;
#endif
 
        /* enforce minimum length */
        if (pwdlen < min_password_length)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("password is too short"),
                     errdetail("password must be at least \"passwordcheck.min_password_length\" (%d) bytes long",
                               min_password_length)));
 
        /* check if the password contains the username */
        if (strstr(password, username))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("password must not contain user name")));
 
        /* check if the password contains both letters and non-letters */
        pwd_has_letter = false;
        pwd_has_nonletter = false;
        for (i = 0; i < pwdlen; i++)
        {
            /*
             * isalpha() does not work for multibyte encodings but let's
             * consider non-ASCII characters non-letters
             */
            if (isalpha((unsigned char) password[i]))
                pwd_has_letter = true;
            else
                pwd_has_nonletter = true;
        }
        if (!pwd_has_letter || !pwd_has_nonletter)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("password must contain both letters and nonletters")));
 
#ifdef USE_CRACKLIB
        /* call cracklib to check password */
        if ((reason = FascistCheck(password, CRACKLIB_DICTPATH)))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("password is easily cracked"),
                     errdetail_log("cracklib diagnostic: %s", reason)));
#endif
    }
 
    /* all checks passed, password is ok */
}
 
/*
 * Module initialization function
 */
void
_PG_init(void)
{
    /* Define custom GUC variables. */
    DefineCustomIntVariable("passwordcheck.min_password_length",
                            "Minimum allowed password length.",
                            NULL,
                            &min_password_length,
                            8,
                            0, INT_MAX,
                            PGC_SUSET,
                            GUC_UNIT_BYTE,
                            NULL, NULL, NULL);
 
    MarkGUCPrefixReserved("passwordcheck");
 
    /* activate password checks when the module is loaded */
    prev_check_password_hook = check_password_hook;
    check_password_hook = check_password;
}