auth.c

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/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: auth.c,v 1.60 2005/06/17 02:44:32 djm Exp $");

#ifdef HAVE_LOGIN_H
#include <login.h>
#endif
#ifdef USE_SHADOW
#include <shadow.h>
#endif

#ifdef HAVE_LIBGEN_H
#include <libgen.h>
#endif

#include "xmalloc.h"
#include "match.h"
#include "groupaccess.h"
#include "log.h"
#include "servconf.h"
#include "auth.h"
#include "auth-options.h"
#include "canohost.h"
#include "buffer.h"
#include "bufaux.h"
#include "uidswap.h"
#include "misc.h"
#include "bufaux.h"
#include "packet.h"
#include "loginrec.h"
#include "monitor_wrap.h"

/* import */
extern ServerOptions options;
extern Buffer loginmsg;

/* Debugging messages */
Buffer auth_debug;
int auth_debug_init;

/*
 * Check if the user is allowed to log in via ssh. If user is listed
 * in DenyUsers or one of user's groups is listed in DenyGroups, false
 * will be returned. If AllowUsers isn't empty and user isn't listed
 * there, or if AllowGroups isn't empty and one of user's groups isn't
 * listed there, false will be returned.
 * If the user's shell is not executable, false will be returned.
 * Otherwise true is returned.
 */
int
allowed_user(struct passwd * pw)
{
        struct stat st;
        const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
        char *shell;
        u_int i;
#ifdef USE_SHADOW
        struct spwd *spw = NULL;
#endif

        /* Shouldn't be called if pw is NULL, but better safe than sorry... */
        if (!pw || !pw->pw_name)
                return 0;

#ifdef USE_SHADOW
        if (!options.use_pam)
                spw = getspnam(pw->pw_name);
#ifdef HAS_SHADOW_EXPIRE
        if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
                return 0;
#endif /* HAS_SHADOW_EXPIRE */
#endif /* USE_SHADOW */

        /* grab passwd field for locked account check */
#ifdef USE_SHADOW
        if (spw != NULL)
#if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
                passwd = get_iaf_password(pw);
#else
                passwd = spw->sp_pwdp;
#endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
#else
        passwd = pw->pw_passwd;
#endif

        /* check for locked account */
        if (!options.use_pam && passwd && *passwd) {
                int locked = 0;

#ifdef LOCKED_PASSWD_STRING
                if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
                         locked = 1;
#endif
#ifdef LOCKED_PASSWD_PREFIX
                if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
                    strlen(LOCKED_PASSWD_PREFIX)) == 0)
                         locked = 1;
#endif
#ifdef LOCKED_PASSWD_SUBSTR
                if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
                        locked = 1;
#endif
#if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
                free(passwd);
#endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
                if (locked) {
                        logit("User %.100s not allowed because account is locked",
                            pw->pw_name);
                        return 0;
                }
        }

        /*
         * Get the shell from the password data.  An empty shell field is
         * legal, and means /bin/sh.
         */
        shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;

        /* deny if shell does not exists or is not executable */
        if (stat(shell, &st) != 0) {
                logit("User %.100s not allowed because shell %.100s does not exist",
                    pw->pw_name, shell);
                return 0;
        }
        if (S_ISREG(st.st_mode) == 0 ||
            (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
                logit("User %.100s not allowed because shell %.100s is not executable",
                    pw->pw_name, shell);
                return 0;
        }

        if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
            options.num_deny_groups > 0 || options.num_allow_groups > 0) {
                hostname = get_canonical_hostname(options.use_dns);
                ipaddr = get_remote_ipaddr();
        }

        /* Return false if user is listed in DenyUsers */
        if (options.num_deny_users > 0) {
                for (i = 0; i < options.num_deny_users; i++)
                        if (match_user(pw->pw_name, hostname, ipaddr,
                            options.deny_users[i])) {
                                logit("User %.100s from %.100s not allowed "
                                    "because listed in DenyUsers",
                                    pw->pw_name, hostname);
                                return 0;
                        }
        }
        /* Return false if AllowUsers isn't empty and user isn't listed there */
        if (options.num_allow_users > 0) {
                for (i = 0; i < options.num_allow_users; i++)
                        if (match_user(pw->pw_name, hostname, ipaddr,
                            options.allow_users[i]))
                                break;
                /* i < options.num_allow_users iff we break for loop */
                if (i >= options.num_allow_users) {
                        logit("User %.100s from %.100s not allowed because "
                            "not listed in AllowUsers", pw->pw_name, hostname);
                        return 0;
                }
        }
        if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
                /* Get the user's group access list (primary and supplementary) */
                if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
                        logit("User %.100s from %.100s not allowed because "
                            "not in any group", pw->pw_name, hostname);
                        return 0;
                }

                /* Return false if one of user's groups is listed in DenyGroups */
                if (options.num_deny_groups > 0)
                        if (ga_match(options.deny_groups,
                            options.num_deny_groups)) {
                                ga_free();
                                logit("User %.100s from %.100s not allowed "
                                    "because a group is listed in DenyGroups",
                                    pw->pw_name, hostname);
                                return 0;
                        }
                /*
                 * Return false if AllowGroups isn't empty and one of user's groups
                 * isn't listed there
                 */
                if (options.num_allow_groups > 0)
                        if (!ga_match(options.allow_groups,
                            options.num_allow_groups)) {
                                ga_free();
                                logit("User %.100s from %.100s not allowed "
                                    "because none of user's groups are listed "
                                    "in AllowGroups", pw->pw_name, hostname);
                                return 0;
                        }
                ga_free();
        }

#ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
        if (!sys_auth_allowed_user(pw, &loginmsg))
                return 0;
#endif

        /* We found no reason not to let this user try to log on... */
        return 1;
}

void
auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
{
        void (*authlog) (const char *fmt,...) = verbose;
        char *authmsg;

        /* Raise logging level */
        if (authenticated == 1 ||
            !authctxt->valid ||
            authctxt->failures >= options.max_authtries / 2 ||
            strcmp(method, "password") == 0)
                authlog = logit;

        if (authctxt->postponed)
                authmsg = "Postponed";
        else
                authmsg = authenticated ? "Accepted" : "Failed";

        authlog("%s %s for %s%.100s from %.200s port %d%s",
            authmsg,
            method,
            authctxt->valid ? "" : "invalid user ",
            authctxt->user,
            get_remote_ipaddr(),
            get_remote_port(),
            info);

#ifdef CUSTOM_FAILED_LOGIN
        if (authenticated == 0 && !authctxt->postponed &&
            (strcmp(method, "password") == 0 ||
            strncmp(method, "keyboard-interactive", 20) == 0 ||
            strcmp(method, "challenge-response") == 0))
                record_failed_login(authctxt->user,
                    get_canonical_hostname(options.use_dns), "ssh");
#endif
#ifdef SSH_AUDIT_EVENTS
        if (authenticated == 0 && !authctxt->postponed) {
                ssh_audit_event_t event;

                debug3("audit failed auth attempt, method %s euid %d",
                    method, (int)geteuid());
                /*
                 * Because the auth loop is used in both monitor and slave,
                 * we must be careful to send each event only once and with
                 * enough privs to write the event.
                 */
                event = audit_classify_auth(method);
                switch(event) {
                case SSH_AUTH_FAIL_NONE:
                case SSH_AUTH_FAIL_PASSWD:
                case SSH_AUTH_FAIL_KBDINT:
                        if (geteuid() == 0)
                                audit_event(event);
                        break;
                case SSH_AUTH_FAIL_PUBKEY:
                case SSH_AUTH_FAIL_HOSTBASED:
                case SSH_AUTH_FAIL_GSSAPI:
                        /*
                         * This is required to handle the case where privsep
                         * is enabled but it's root logging in, since
                         * use_privsep won't be cleared until after a
                         * successful login.
                         */
                        if (geteuid() == 0)
                                audit_event(event);
                        else
                                PRIVSEP(audit_event(event));
                        break;
                default:
                        error("unknown authentication audit event %d", event);
                }
        }
#endif
}

/*
 * Check whether root logins are disallowed.
 */
int
auth_root_allowed(char *method)
{
        switch (options.permit_root_login) {
        case PERMIT_YES:
                return 1;
                break;
        case PERMIT_NO_PASSWD:
                if (strcmp(method, "password") != 0)
                        return 1;
                break;
        case PERMIT_FORCED_ONLY:
                if (forced_command) {
                        logit("Root login accepted for forced command.");
                        return 1;
                }
                break;
        }
        logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
        return 0;
}


/*
 * Given a template and a passwd structure, build a filename
 * by substituting % tokenised options. Currently, %% becomes '%',
 * %h becomes the home directory and %u the username.
 *
 * This returns a buffer allocated by xmalloc.
 */
static char *
expand_authorized_keys(const char *filename, struct passwd *pw)
{
        char *file, *ret;

        file = percent_expand(filename, "h", pw->pw_dir,
            "u", pw->pw_name, (char *)NULL);

        /*
         * Ensure that filename starts anchored. If not, be backward
         * compatible and prepend the '%h/'
         */
        if (*file == '/')
                return (file);

        ret = xmalloc(MAXPATHLEN);
        if (strlcpy(ret, pw->pw_dir, MAXPATHLEN) >= MAXPATHLEN ||
            strlcat(ret, "/", MAXPATHLEN) >= MAXPATHLEN ||
            strlcat(ret, file, MAXPATHLEN) >= MAXPATHLEN)
                fatal("expand_authorized_keys: path too long");

        xfree(file);
        return (ret);
}

char *
authorized_keys_file(struct passwd *pw)
{
        return expand_authorized_keys(options.authorized_keys_file, pw);
}

char *
authorized_keys_file2(struct passwd *pw)
{
        return expand_authorized_keys(options.authorized_keys_file2, pw);
}

/* return ok if key exists in sysfile or userfile */
HostStatus
check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
    const char *sysfile, const char *userfile)
{
        Key *found;
        char *user_hostfile;
        struct stat st;
        HostStatus host_status;

        /* Check if we know the host and its host key. */
        found = key_new(key->type);
        host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);

        if (host_status != HOST_OK && userfile != NULL) {
                user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
                if (options.strict_modes &&
                    (stat(user_hostfile, &st) == 0) &&
                    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
                    (st.st_mode & 022) != 0)) {
                        logit("Authentication refused for %.100s: "
                            "bad owner or modes for %.200s",
                            pw->pw_name, user_hostfile);
                } else {
                        temporarily_use_uid(pw);
                        host_status = check_host_in_hostfile(user_hostfile,
                            host, key, found, NULL);
                        restore_uid();
                }
                xfree(user_hostfile);
        }
        key_free(found);

        debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
            "ok" : "not found", host);
        return host_status;
}


/*
 * Check a given file for security. This is defined as all components
 * of the path to the file must be owned by either the owner of
 * of the file or root and no directories must be group or world writable.
 *
 * XXX Should any specific check be done for sym links ?
 *
 * Takes an open file descriptor, the file name, a uid and and
 * error buffer plus max size as arguments.
 *
 * Returns 0 on success and -1 on failure
 */
int
secure_filename(FILE *f, const char *file, struct passwd *pw,
    char *err, size_t errlen)
{
        uid_t uid = pw->pw_uid;
        char buf[MAXPATHLEN], homedir[MAXPATHLEN];
        char *cp;
        int comparehome = 0;
        struct stat st;

        if (realpath(file, buf) == NULL) {
                snprintf(err, errlen, "realpath %s failed: %s", file,
                    strerror(errno));
                return -1;
        }
        if (realpath(pw->pw_dir, homedir) != NULL)
                comparehome = 1;

        /* check the open file to avoid races */
        if (fstat(fileno(f), &st) < 0 ||
            (st.st_uid != 0 && st.st_uid != uid) ||
            (st.st_mode & 022) != 0) {
                snprintf(err, errlen, "bad ownership or modes for file %s",
                    buf);
                return -1;
        }

        /* for each component of the canonical path, walking upwards */
        for (;;) {
                if ((cp = dirname(buf)) == NULL) {
                        snprintf(err, errlen, "dirname() failed");
                        return -1;
                }
                strlcpy(buf, cp, sizeof(buf));

                debug3("secure_filename: checking '%s'", buf);
                if (stat(buf, &st) < 0 ||
                    (st.st_uid != 0 && st.st_uid != uid) ||
                    (st.st_mode & 022) != 0) {
                        snprintf(err, errlen,
                            "bad ownership or modes for directory %s", buf);
                        return -1;
                }

                /* If are passed the homedir then we can stop */
                if (comparehome && strcmp(homedir, buf) == 0) {
                        debug3("secure_filename: terminating check at '%s'",
                            buf);
                        break;
                }
                /*
                 * dirname should always complete with a "/" path,
                 * but we can be paranoid and check for "." too
                 */
                if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
                        break;
        }
        return 0;
}

struct passwd *
getpwnamallow(const char *user)
{
#ifdef HAVE_LOGIN_CAP
        extern login_cap_t *lc;
#ifdef BSD_AUTH
        auth_session_t *as;
#endif
#endif
        struct passwd *pw;

        pw = getpwnam(user);
        if (pw == NULL) {
                logit("Invalid user %.100s from %.100s",
                    user, get_remote_ipaddr());
#ifdef CUSTOM_FAILED_LOGIN
                record_failed_login(user,
                    get_canonical_hostname(options.use_dns), "ssh");
#endif
#ifdef SSH_AUDIT_EVENTS
                audit_event(SSH_INVALID_USER);
#endif /* SSH_AUDIT_EVENTS */
                return (NULL);
        }
        if (!allowed_user(pw))
                return (NULL);
#ifdef HAVE_LOGIN_CAP
        if ((lc = login_getclass(pw->pw_class)) == NULL) {
                debug("unable to get login class: %s", user);
                return (NULL);
        }
#ifdef BSD_AUTH
        if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
            auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
                debug("Approval failure for %s", user);
                pw = NULL;
        }
        if (as != NULL)
                auth_close(as);
#endif
#endif
        if (pw != NULL)
                return (pwcopy(pw));
        return (NULL);
}

void
auth_debug_add(const char *fmt,...)
{
        char buf[1024];
        va_list args;

        if (!auth_debug_init)
                return;

        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);
        buffer_put_cstring(&auth_debug, buf);
}

void
auth_debug_send(void)
{
        char *msg;

        if (!auth_debug_init)
                return;
        while (buffer_len(&auth_debug)) {
                msg = buffer_get_string(&auth_debug, NULL);
                packet_send_debug("%s", msg);
                xfree(msg);
        }
}

void
auth_debug_reset(void)
{
        if (auth_debug_init)
                buffer_clear(&auth_debug);
        else {
                buffer_init(&auth_debug);
                auth_debug_init = 1;
        }
}

struct passwd *
fakepw(void)
{
        static struct passwd fake;

        memset(&fake, 0, sizeof(fake));
        fake.pw_name = "NOUSER";
        fake.pw_passwd =
            "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
        fake.pw_gecos = "NOUSER";
        fake.pw_uid = (uid_t)-1;
        fake.pw_gid = (gid_t)-1;
#ifdef HAVE_PW_CLASS_IN_PASSWD
        fake.pw_class = "";
#endif
        fake.pw_dir = "/nonexist";
        fake.pw_shell = "/nonexist";

        return (&fake);
}

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