auth1.c

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/*
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"
RCSID("$OpenBSD: auth1.c,v 1.62 2005/07/16 01:35:24 djm Exp $");

#include "xmalloc.h"
#include "rsa.h"
#include "ssh1.h"
#include "packet.h"
#include "buffer.h"
#include "log.h"
#include "servconf.h"
#include "compat.h"
#include "auth.h"
#include "channels.h"
#include "session.h"
#include "uidswap.h"
#include "monitor_wrap.h"
#include "buffer.h"

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

static int auth1_process_password(Authctxt *, char *, size_t);
static int auth1_process_rsa(Authctxt *, char *, size_t);
static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
static int auth1_process_tis_response(Authctxt *, char *, size_t);

static char *client_user = NULL;    /* Used to fill in remote user for PAM */

struct AuthMethod1 {
        int type;
        char *name;
        int *enabled;
        int (*method)(Authctxt *, char *, size_t);
};

const struct AuthMethod1 auth1_methods[] = {
        {
                SSH_CMSG_AUTH_PASSWORD, "password",
                &options.password_authentication, auth1_process_password
        },
        {
                SSH_CMSG_AUTH_RSA, "rsa",
                &options.rsa_authentication, auth1_process_rsa
        },
        {
                SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
                &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
        },
        {
                SSH_CMSG_AUTH_TIS, "challenge-response",
                &options.challenge_response_authentication,
                auth1_process_tis_challenge
        },
        {
                SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
                &options.challenge_response_authentication,
                auth1_process_tis_response
        },
        { -1, NULL, NULL, NULL}
};

static const struct AuthMethod1
*lookup_authmethod1(int type)
{
        int i;

        for(i = 0; auth1_methods[i].name != NULL; i++)
                if (auth1_methods[i].type == type)
                        return (&(auth1_methods[i]));

        return (NULL);
}

static char *
get_authname(int type)
{
        const struct AuthMethod1 *a;
        static char buf[64];

        if ((a = lookup_authmethod1(type)) != NULL)
                return (a->name);
        snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
        return (buf);
}

static int
auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
{
        int authenticated = 0;
        char *password;
        u_int dlen;

        /*
         * Read user password.  It is in plain text, but was
         * transmitted over the encrypted channel so it is
         * not visible to an outside observer.
         */
        password = packet_get_string(&dlen);
        packet_check_eom();

        /* Try authentication with the password. */
        authenticated = PRIVSEP(auth_password(authctxt, password));

        memset(password, 0, dlen);
        xfree(password);

        return (authenticated);
}

static int
auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
{
        int authenticated = 0;
        BIGNUM *n;

        /* RSA authentication requested. */
        if ((n = BN_new()) == NULL)
                fatal("do_authloop: BN_new failed");
        packet_get_bignum(n);
        packet_check_eom();
        authenticated = auth_rsa(authctxt, n);
        BN_clear_free(n);

        return (authenticated);
}

static int
auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
{
        int keybits, authenticated = 0;
        u_int bits;
        Key *client_host_key;
        u_int ulen;

        /*
         * Get client user name.  Note that we just have to
         * trust the client; root on the client machine can
         * claim to be any user.
         */
        client_user = packet_get_string(&ulen);

        /* Get the client host key. */
        client_host_key = key_new(KEY_RSA1);
        bits = packet_get_int();
        packet_get_bignum(client_host_key->rsa->e);
        packet_get_bignum(client_host_key->rsa->n);

        keybits = BN_num_bits(client_host_key->rsa->n);
        if (keybits < 0 || bits != (u_int)keybits) {
                verbose("Warning: keysize mismatch for client_host_key: "
                    "actual %d, announced %d",
                    BN_num_bits(client_host_key->rsa->n), bits);
        }
        packet_check_eom();

        authenticated = auth_rhosts_rsa(authctxt, client_user,
            client_host_key);
        key_free(client_host_key);

        snprintf(info, infolen, " ruser %.100s", client_user);

        return (authenticated);
}

static int
auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
{
        char *challenge;

        if ((challenge = get_challenge(authctxt)) == NULL)
                return (0);

        debug("sending challenge '%s'", challenge);
        packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
        packet_put_cstring(challenge);
        xfree(challenge);
        packet_send();
        packet_write_wait();

        return (-1);
}

static int
auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
{
        int authenticated = 0;
        char *response;
        u_int dlen;

        response = packet_get_string(&dlen);
        packet_check_eom();
        authenticated = verify_response(authctxt, response);
        memset(response, 'r', dlen);
        xfree(response);

        return (authenticated);
}

/*
 * read packets, try to authenticate the user and
 * return only if authentication is successful
 */
static void
do_authloop(Authctxt *authctxt)
{
        int authenticated = 0;
        char info[1024];
        int prev = 0, type = 0;
        const struct AuthMethod1 *meth;

        debug("Attempting authentication for %s%.100s.",
            authctxt->valid ? "" : "invalid user ", authctxt->user);

        /* If the user has no password, accept authentication immediately. */
        if (options.password_authentication &&
#ifdef KRB5
            (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
#endif
            PRIVSEP(auth_password(authctxt, ""))) {
#ifdef USE_PAM
                if (options.use_pam && (PRIVSEP(do_pam_account())))
#endif
                {
                        auth_log(authctxt, 1, "without authentication", "");
                        return;
                }
        }

        /* Indicate that authentication is needed. */
        packet_start(SSH_SMSG_FAILURE);
        packet_send();
        packet_write_wait();

        for (;;) {
                /* default to fail */
                authenticated = 0;

                info[0] = '\0';

                /* Get a packet from the client. */
                prev = type;
                type = packet_read();

                /*
                 * If we started challenge-response authentication but the
                 * next packet is not a response to our challenge, release
                 * the resources allocated by get_challenge() (which would
                 * normally have been released by verify_response() had we
                 * received such a response)
                 */
                if (prev == SSH_CMSG_AUTH_TIS &&
                    type != SSH_CMSG_AUTH_TIS_RESPONSE)
                        abandon_challenge_response(authctxt);

                if ((meth = lookup_authmethod1(type)) == NULL) {
                        logit("Unknown message during authentication: "
                            "type %d", type);
                        goto skip;
                }

                if (!*(meth->enabled)) {
                        verbose("%s authentication disabled.", meth->name);
                        goto skip;
                }

                authenticated = meth->method(authctxt, info, sizeof(info));
                if (authenticated == -1)
                        continue; /* "postponed" */

#ifdef BSD_AUTH
                if (authctxt->as) {
                        auth_close(authctxt->as);
                        authctxt->as = NULL;
                }
#endif
                if (!authctxt->valid && authenticated)
                        fatal("INTERNAL ERROR: authenticated invalid user %s",
                            authctxt->user);

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

#ifdef HAVE_CYGWIN
                if (authenticated &&
                    !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
                    authctxt->pw)) {
                        packet_disconnect("Authentication rejected for uid %d.",
                            authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
                        authenticated = 0;
                }
#else
                /* Special handling for root */
                if (authenticated && authctxt->pw->pw_uid == 0 &&
                    !auth_root_allowed(meth->name)) {
                        authenticated = 0;
# ifdef SSH_AUDIT_EVENTS
                        PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
# endif
                }
#endif

#ifdef USE_PAM
                if (options.use_pam && authenticated &&
                    !PRIVSEP(do_pam_account())) {
                        char *msg;
                        size_t len;

                        error("Access denied for user %s by PAM account "
                            "configuration", authctxt->user);
                        len = buffer_len(&loginmsg);
                        buffer_append(&loginmsg, "\0", 1);
                        msg = buffer_ptr(&loginmsg);
                        /* strip trailing newlines */
                        if (len > 0)
                                while (len > 0 && msg[--len] == '\n')
                                        msg[len] = '\0';
                        else
                                msg = "Access denied.";
                        packet_disconnect(msg);
                }
#endif

 skip:
                /* Log before sending the reply */
                auth_log(authctxt, authenticated, get_authname(type), info);

                if (client_user != NULL) {
                        xfree(client_user);
                        client_user = NULL;
                }

                if (authenticated)
                        return;

                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);
                }

                packet_start(SSH_SMSG_FAILURE);
                packet_send();
                packet_write_wait();
        }
}

/*
 * Performs authentication of an incoming connection.  Session key has already
 * been exchanged and encryption is enabled.
 */
void
do_authentication(Authctxt *authctxt)
{
        u_int ulen;
        char *user, *style = NULL;

        /* Get the name of the user that we wish to log in as. */
        packet_read_expect(SSH_CMSG_USER);

        /* Get the user name. */
        user = packet_get_string(&ulen);
        packet_check_eom();

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

        authctxt->user = user;
        authctxt->style = style;

        /* Verify that the user is a valid user. */
        if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
                authctxt->valid = 1;
        else {
                debug("do_authentication: invalid user %s", user);
                authctxt->pw = fakepw();
        }

        setproctitle("%s%s", authctxt->valid ? user : "unknown",
            use_privsep ? " [net]" : "");

#ifdef USE_PAM
        if (options.use_pam)
                PRIVSEP(start_pam(authctxt));
#endif

        /*
         * If we are not running as root, the user must have the same uid as
         * the server.
         */
#ifndef HAVE_CYGWIN
        if (!use_privsep && getuid() != 0 && authctxt->pw &&
            authctxt->pw->pw_uid != getuid())
                packet_disconnect("Cannot change user when server not running as root.");
#endif

        /*
         * Loop until the user has been authenticated or the connection is
         * closed, do_authloop() returns only if authentication is successful
         */
        do_authloop(authctxt);

        /* The user has been authenticated and accepted. */
        packet_start(SSH_SMSG_SUCCESS);
        packet_send();
        packet_write_wait();
}

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