auth2.c

Go to the documentation of this file.

/*
 * 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: auth2.c,v 1.107 2004/07/28 09:40:29 markus Exp $");

#include "ssh2.h"
#include "xmalloc.h"
#include "packet.h"
#include "log.h"
#include "servconf.h"
#include "compat.h"
#include "auth.h"
#include "dispatch.h"
#include "pathnames.h"
#include "monitor_wrap.h"
#include "buffer.h"

#ifdef GSSAPI
#include "ssh-gss.h"
#endif

/* import */
extern ServerOptions options;
extern u_char *session_id2;
extern u_int session_id2_len;
extern Buffer loginmsg;

/* methods */

extern Authmethod method_none;
extern Authmethod method_pubkey;
extern Authmethod method_passwd;
extern Authmethod method_kbdint;
extern Authmethod method_hostbased;
#ifdef GSSAPI
extern Authmethod method_gssapi;
#endif

Authmethod *authmethods[] = {
        &method_none,
        &method_pubkey,
#ifdef GSSAPI
        &method_gssapi,
#endif
        &method_passwd,
        &method_kbdint,
        &method_hostbased,
        NULL
};

/* protocol */

static void input_service_request(int, u_int32_t, void *);
static void input_userauth_request(int, u_int32_t, void *);

/* helper */
static Authmethod *authmethod_lookup(const char *);
static char *authmethods_get(void);
int user_key_allowed(struct passwd *, Key *);

/*
 * loop until authctxt->success == TRUE
 */

void
do_authentication2(Authctxt *authctxt)
{
        /* challenge-response is implemented via keyboard interactive */
        if (options.challenge_response_authentication)
                options.kbd_interactive_authentication = 1;

        dispatch_init(&dispatch_protocol_error);
        dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
        dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
}

static void
input_service_request(int type, u_int32_t seq, void *ctxt)
{
        Authctxt *authctxt = ctxt;
        u_int len;
        int acceptit = 0;
        char *service = packet_get_string(&len);
        packet_check_eom();

        if (authctxt == NULL)
                fatal("input_service_request: no authctxt");

        if (strcmp(service, "ssh-userauth") == 0) {
                if (!authctxt->success) {
                        acceptit = 1;
                        /* now we can handle user-auth requests */
                        dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
                }
        }
        /* XXX all other service requests are denied */

        if (acceptit) {
                packet_start(SSH2_MSG_SERVICE_ACCEPT);
                packet_put_cstring(service);
                packet_send();
                packet_write_wait();
        } else {
                debug("bad service request %s", service);
                packet_disconnect("bad service request %s", service);
        }
        xfree(service);
}

static void
input_userauth_request(int type, u_int32_t seq, void *ctxt)
{
        Authctxt *authctxt = ctxt;
        Authmethod *m = NULL;
        char *user, *service, *method, *style = NULL;
        int authenticated = 0;

        if (authctxt == NULL)
                fatal("input_userauth_request: no authctxt");

        user = packet_get_string(NULL);
        service = packet_get_string(NULL);
        method = packet_get_string(NULL);
        debug("userauth-request for user %s service %s method %s", user, service, method);
        debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);

        if ((style = strchr(user, ':')) != NULL)
                *style++ = 0;

        if (authctxt->attempt++ == 0) {
                /* setup auth context */
                authctxt->pw = PRIVSEP(getpwnamallow(user));
                authctxt->user = xstrdup(user);
                if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
                        authctxt->valid = 1;
                        debug2("input_userauth_request: setting up authctxt for %s", user);
                } else {
                        logit("input_userauth_request: invalid user %s", user);
                        authctxt->pw = fakepw();
#ifdef SSH_AUDIT_EVENTS
                        PRIVSEP(audit_event(SSH_INVALID_USER));
#endif
                }
#ifdef USE_PAM
                if (options.use_pam)
                        PRIVSEP(start_pam(authctxt));
#endif
                setproctitle("%s%s", authctxt->valid ? user : "unknown",
                    use_privsep ? " [net]" : "");
                authctxt->service = xstrdup(service);
                authctxt->style = style ? xstrdup(style) : NULL;
                if (use_privsep)
                        mm_inform_authserv(service, style);
        } else if (strcmp(user, authctxt->user) != 0 ||
            strcmp(service, authctxt->service) != 0) {
                packet_disconnect("Change of username or service not allowed: "
                    "(%s,%s) -> (%s,%s)",
                    authctxt->user, authctxt->service, user, service);
        }
        /* reset state */
        auth2_challenge_stop(authctxt);

#ifdef GSSAPI
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
#endif

        authctxt->postponed = 0;

        /* try to authenticate user */
        m = authmethod_lookup(method);
        if (m != NULL) {
                debug2("input_userauth_request: try method %s", method);
                authenticated = m->userauth(authctxt);
        }
        userauth_finish(authctxt, authenticated, method);

        xfree(service);
        xfree(user);
        xfree(method);
}

void
userauth_finish(Authctxt *authctxt, int authenticated, char *method)
{
        char *methods;

        if (!authctxt->valid && authenticated)
                fatal("INTERNAL ERROR: authenticated invalid user %s",
                    authctxt->user);

        /* Special handling for root */
        if (authenticated && authctxt->pw->pw_uid == 0 &&
            !auth_root_allowed(method)) {
                authenticated = 0;
#ifdef SSH_AUDIT_EVENTS
                PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
#endif
        }

#ifdef USE_PAM
        if (options.use_pam && authenticated) {
                if (!PRIVSEP(do_pam_account())) {
                        /* if PAM returned a message, send it to the user */
                        if (buffer_len(&loginmsg) > 0) {
                                buffer_append(&loginmsg, "\0", 1);
                                userauth_send_banner(buffer_ptr(&loginmsg));
                                packet_write_wait();
                        }
                        fatal("Access denied for user %s by PAM account "
                            "configuration", authctxt->user);
                }
        }
#endif

#ifdef _UNICOS
        if (authenticated && cray_access_denied(authctxt->user)) {
                authenticated = 0;
                fatal("Access denied for user %s.",authctxt->user);
        }
#endif /* _UNICOS */

        /* Log before sending the reply */
        auth_log(authctxt, authenticated, method, " ssh2");

        if (authctxt->postponed)
                return;

        /* XXX todo: check if multiple auth methods are needed */
        if (authenticated == 1) {
                /* turn off userauth */
                dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
                packet_start(SSH2_MSG_USERAUTH_SUCCESS);
                packet_send();
                packet_write_wait();
                /* now we can break out */
                authctxt->success = 1;
        } else {
                if (authctxt->failures++ > options.max_authtries) {
#ifdef SSH_AUDIT_EVENTS
                        PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
#endif
                        packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
                }
                methods = authmethods_get();
                packet_start(SSH2_MSG_USERAUTH_FAILURE);
                packet_put_cstring(methods);
                packet_put_char(0);     /* XXX partial success, unused */
                packet_send();
                packet_write_wait();
                xfree(methods);
        }
}

#define DELIM   ","

static char *
authmethods_get(void)
{
        Buffer b;
        char *list;
        int i;

        buffer_init(&b);
        for (i = 0; authmethods[i] != NULL; i++) {
                if (strcmp(authmethods[i]->name, "none") == 0)
                        continue;
                if (authmethods[i]->enabled != NULL &&
                    *(authmethods[i]->enabled) != 0) {
                        if (buffer_len(&b) > 0)
                                buffer_append(&b, ",", 1);
                        buffer_append(&b, authmethods[i]->name,
                            strlen(authmethods[i]->name));
                }
        }
        buffer_append(&b, "\0", 1);
        list = xstrdup(buffer_ptr(&b));
        buffer_free(&b);
        return list;
}

static Authmethod *
authmethod_lookup(const char *name)
{
        int i;

        if (name != NULL)
                for (i = 0; authmethods[i] != NULL; i++)
                        if (authmethods[i]->enabled != NULL &&
                            *(authmethods[i]->enabled) != 0 &&
                            strcmp(name, authmethods[i]->name) == 0)
                                return authmethods[i];
        debug2("Unrecognized authentication method name: %s",
            name ? name : "NULL");
        return NULL;
}

---

© sourcejam.com 2005-2008