auth.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
  */

 #include "includes.h"
 RCSID("$OpenBSD: auth.c,v 1.1 2000/03/28 21:15:45 markus Exp $");

 #include "xmalloc.h"
 #include "rsa.h"
 #include "ssh.h"
 #include "pty.h"
 #include "packet.h"
 #include "buffer.h"
 #include "cipher.h"
 #include "mpaux.h"
 #include "servconf.h"
 #include "channels.h"
 #include "match.h"

 #include "session.h"
 #include "dispatch.h"

 /* import */
 extern ServerOptions options;
 extern char *forced_command;

 /*
  * Check if the user is allowed to log in via ssh. If user is listed in
  * DenyUsers or user's primary group 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 user isn't listed there, false will be
  * returned.
  * If the user's shell is not executable, false will be returned.
  * Otherwise true is returned.
  */
 static int
 allowed_user(struct passwd * pw)
 {
 	struct stat st;
 	struct group *grp;
 	int i;
 #ifdef WITH_AIXAUTHENTICATE
 	char *loginmsg;
 #endif /* WITH_AIXAUTHENTICATE */

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

 	/* deny if shell does not exists or is not executable */
 	if (stat(pw->pw_shell, &st) != 0)
 		return 0;
 	if (!((st.st_mode & S_IFREG) && (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP))))
 		return 0;

 	/* Return false if user is listed in DenyUsers */
 	if (options.num_deny_users > 0) {
 		if (!pw->pw_name)
 			return 0;
 		for (i = 0; i < options.num_deny_users; i++)
 			if (match_pattern(pw->pw_name, options.deny_users[i]))
 				return 0;
 	}
 	/* Return false if AllowUsers isn't empty and user isn't listed there */
 	if (options.num_allow_users > 0) {
 		if (!pw->pw_name)
 			return 0;
 		for (i = 0; i < options.num_allow_users; i++)
 			if (match_pattern(pw->pw_name, options.allow_users[i]))
 				break;
 		/* i < options.num_allow_users iff we break for loop */
 		if (i >= options.num_allow_users)
 			return 0;
 	}
 	/* Get the primary group name if we need it. Return false if it fails */
 	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 		grp = getgrgid(pw->pw_gid);
 		if (!grp)
 			return 0;

 		/* Return false if user's group is listed in DenyGroups */
 		if (options.num_deny_groups > 0) {
 			if (!grp->gr_name)
 				return 0;
 			for (i = 0; i < options.num_deny_groups; i++)
 				if (match_pattern(grp->gr_name, options.deny_groups[i]))
 					return 0;
 		}
 		/*
 		 * Return false if AllowGroups isn't empty and user's group
 		 * isn't listed there
 		 */
 		if (options.num_allow_groups > 0) {
 			if (!grp->gr_name)
 				return 0;
 			for (i = 0; i < options.num_allow_groups; i++)
 				if (match_pattern(grp->gr_name, options.allow_groups[i]))
 					break;
 			/* i < options.num_allow_groups iff we break for
 			   loop */
 			if (i >= options.num_allow_groups)
 				return 0;
 		}
 	}

 #ifdef WITH_AIXAUTHENTICATE
 	if (loginrestrictions(pw->pw_name,S_LOGIN,NULL,&loginmsg) != 0)
 		return 0;
 #endif /* WITH_AIXAUTHENTICATE */

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

 /*
  * convert ssh auth msg type into description
  */
 char *
 get_authname(int type)
 {
 	static char buf[1024];
 	switch (type) {
 	case SSH_CMSG_AUTH_PASSWORD:
 		return "password";
 	case SSH_CMSG_AUTH_RSA:
 		return "rsa";
 	case SSH_CMSG_AUTH_RHOSTS_RSA:
 		return "rhosts-rsa";
 	case SSH_CMSG_AUTH_RHOSTS:
 		return "rhosts";
 #ifdef KRB4
 	case SSH_CMSG_AUTH_KERBEROS:
 		return "kerberos";
 #endif
 #ifdef SKEY
 	case SSH_CMSG_AUTH_TIS_RESPONSE:
 		return "s/key";
 #endif
 	}
 	snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
 	return buf;
 }

 #define AUTH_FAIL_MAX 6
 #define AUTH_FAIL_LOG (AUTH_FAIL_MAX/2)
 #define AUTH_FAIL_MSG "Too many authentication failures for %.100s"

 /*
  * The user does not exist or access is denied,
  * but fake indication that authentication is needed.
  */
 void
 do_fake_authloop1(char *user)
 {
 	int attempt = 0;

 	log("Faking authloop for illegal user %.200s from %.200s port %d",
 	    user,
 	    get_remote_ipaddr(),
 	    get_remote_port());

 #ifdef WITH_AIXAUTHENTICATE
 		if (strncmp(get_authname(type),"password",
 		    strlen(get_authname(type))) == 0)
 			loginfailed(pw->pw_name,get_canonical_hostname(),"ssh");
 #endif /* WITH_AIXAUTHENTICATE */

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

 	/*
 	 * Keep reading packets, and always respond with a failure.  This is
 	 * to avoid disclosing whether such a user really exists.
 	 */
 	for (attempt = 1;; attempt++) {
 		/* Read a packet.  This will not return if the client disconnects. */
 		int plen;
 #ifndef SKEY
 		(void)packet_read(&plen);
 #else /* SKEY */
 		int type = packet_read(&plen);
 		unsigned int dlen;
 		char *password, *skeyinfo;
 		/* Try to send a fake s/key challenge. */
 		if (options.skey_authentication == 1 &&
 		    (skeyinfo = skey_fake_keyinfo(user)) != NULL) {
 			password = NULL;
 			if (type == SSH_CMSG_AUTH_TIS) {
 				packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 				packet_put_string(skeyinfo, strlen(skeyinfo));
 				packet_send();
 				packet_write_wait();
 				continue;
 			} else if (type == SSH_CMSG_AUTH_PASSWORD &&
 			           options.password_authentication &&
 			           (password = packet_get_string(&dlen)) != NULL &&
 			           dlen == 5 &&
 			           strncasecmp(password, "s/key", 5) == 0 ) {
 				packet_send_debug(skeyinfo);
 			}
 			if (password != NULL)
 				xfree(password);
 		}
 #endif
 		if (attempt > AUTH_FAIL_MAX)
 			packet_disconnect(AUTH_FAIL_MSG, user);

 		/*
 		 * Send failure.  This should be indistinguishable from a
 		 * failed authentication.
 		 */
 		packet_start(SSH_SMSG_FAILURE);
 		packet_send();
 		packet_write_wait();
 	}
 	/* NOTREACHED */
 	abort();
 }

 /*
  * read packets and try to authenticate local user *pw.
  * return if authentication is successfull
  */
 void
 do_authloop(struct passwd * pw)
 {
 	int attempt = 0;
 	unsigned int bits;
 	RSA *client_host_key;
 	BIGNUM *n;
 	char *client_user = NULL, *password = NULL;
 	char user[1024];
 	unsigned int dlen;
 	int plen, nlen, elen;
 	unsigned int ulen;
 	int type = 0;
 	void (*authlog) (const char *fmt,...) = verbose;

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

 	for (attempt = 1;; attempt++) {
 		int authenticated = 0;
 		strlcpy(user, "", sizeof user);

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

 		/* Process the packet. */
 		switch (type) {
 #ifdef AFS
 		case SSH_CMSG_HAVE_KERBEROS_TGT:
 			if (!options.kerberos_tgt_passing) {
 				/* packet_get_all(); */
 				verbose("Kerberos tgt passing disabled.");
 				break;
 			} else {
 				/* Accept Kerberos tgt. */
 				char *tgt = packet_get_string(&dlen);
 				packet_integrity_check(plen, 4 + dlen, type);
 				if (!auth_kerberos_tgt(pw, tgt))
 					verbose("Kerberos tgt REFUSED for %s", pw->pw_name);
 				xfree(tgt);
 			}
 			continue;

 		case SSH_CMSG_HAVE_AFS_TOKEN:
 			if (!options.afs_token_passing || !k_hasafs()) {
 				/* packet_get_all(); */
 				verbose("AFS token passing disabled.");
 				break;
 			} else {
 				/* Accept AFS token. */
 				char *token_string = packet_get_string(&dlen);
 				packet_integrity_check(plen, 4 + dlen, type);
 				if (!auth_afs_token(pw, token_string))
 					verbose("AFS token REFUSED for %s", pw->pw_name);
 				xfree(token_string);
 			}
 			continue;
 #endif /* AFS */
 #ifdef KRB4
 		case SSH_CMSG_AUTH_KERBEROS:
 			if (!options.kerberos_authentication) {
 				/* packet_get_all(); */
 				verbose("Kerberos authentication disabled.");
 				break;
 			} else {
 				/* Try Kerberos v4 authentication. */
 				KTEXT_ST auth;
 				char *tkt_user = NULL;
 				char *kdata = packet_get_string((unsigned int *) &auth.length);
 				packet_integrity_check(plen, 4 + auth.length, type);

 				if (auth.length < MAX_KTXT_LEN)
 					memcpy(auth.dat, kdata, auth.length);
 				xfree(kdata);

 				authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user);

 				if (authenticated) {
 					snprintf(user, sizeof user, " tktuser %s", tkt_user);
 					xfree(tkt_user);
 				}
 			}
 			break;
 #endif /* KRB4 */

 		case SSH_CMSG_AUTH_RHOSTS:
 			if (!options.rhosts_authentication) {
 				verbose("Rhosts authentication disabled.");
 				break;
 			}
 			/*
 			 * Get client user name.  Note that we just have to
 			 * trust the client; this is one reason why rhosts
 			 * authentication is insecure. (Another is
 			 * IP-spoofing on a local network.)
 			 */
 			client_user = packet_get_string(&ulen);
 			packet_integrity_check(plen, 4 + ulen, type);

 			/* Try to authenticate using /etc/hosts.equiv and
 			   .rhosts. */
 			authenticated = auth_rhosts(pw, client_user);

 			snprintf(user, sizeof user, " ruser %s", client_user);
 			break;

 		case SSH_CMSG_AUTH_RHOSTS_RSA:
 			if (!options.rhosts_rsa_authentication) {
 				verbose("Rhosts with RSA authentication disabled.");
 				break;
 			}
 			/*
 			 * 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 = RSA_new();
 			if (client_host_key == NULL)
 				fatal("RSA_new failed");
 			client_host_key->e = BN_new();
 			client_host_key->n = BN_new();
 			if (client_host_key->e == NULL || client_host_key->n == NULL)
 				fatal("BN_new failed");
 			bits = packet_get_int();
 			packet_get_bignum(client_host_key->e, &elen);
 			packet_get_bignum(client_host_key->n, &nlen);

 			if (bits != BN_num_bits(client_host_key->n))
 				error("Warning: keysize mismatch for client_host_key: "
 				      "actual %d, announced %d", BN_num_bits(client_host_key->n), bits);
 			packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);

 			authenticated = auth_rhosts_rsa(pw, client_user, client_host_key);
 			RSA_free(client_host_key);

 			snprintf(user, sizeof user, " ruser %s", client_user);
 			break;

 		case SSH_CMSG_AUTH_RSA:
 			if (!options.rsa_authentication) {
 				verbose("RSA authentication disabled.");
 				break;
 			}
 			/* RSA authentication requested. */
 			n = BN_new();
 			packet_get_bignum(n, &nlen);
 			packet_integrity_check(plen, nlen, type);
 			authenticated = auth_rsa(pw, n);
 			BN_clear_free(n);
 			break;

 		case SSH_CMSG_AUTH_PASSWORD:
 			if (!options.password_authentication) {
 				verbose("Password authentication disabled.");
 				break;
 			}
 			/*
 			 * 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_integrity_check(plen, 4 + dlen, type);

 #ifdef USE_PAM
 			/* Do PAM auth with password */
 			authenticated = auth_pam_password(pw, password);
 #else /* USE_PAM */
 			/* Try authentication with the password. */
 			authenticated = auth_password(pw, password);
 #endif /* USE_PAM */
 			memset(password, 0, strlen(password));
 			xfree(password);
 			break;

 #ifdef SKEY
 		case SSH_CMSG_AUTH_TIS:
 			debug("rcvd SSH_CMSG_AUTH_TIS");
 			if (options.skey_authentication == 1) {
 				char *skeyinfo = skey_keyinfo(pw->pw_name);
 				if (skeyinfo == NULL) {
 					debug("generating fake skeyinfo for %.100s.", pw->pw_name);
 					skeyinfo = skey_fake_keyinfo(pw->pw_name);
 				}
 				if (skeyinfo != NULL) {
 					/* we send our s/key- in tis-challenge messages */
 					debug("sending challenge '%s'", skeyinfo);
 					packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 					packet_put_string(skeyinfo, strlen(skeyinfo));
 					packet_send();
 					packet_write_wait();
 					continue;
 				}
 			}
 			break;
 		case SSH_CMSG_AUTH_TIS_RESPONSE:
 			debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 			if (options.skey_authentication == 1) {
 				char *response = packet_get_string(&dlen);
 				debug("skey response == '%s'", response);
 				packet_integrity_check(plen, 4 + dlen, type);
 				authenticated = (skey_haskey(pw->pw_name) == 0 &&
 						 skey_passcheck(pw->pw_name, response) != -1);
 				xfree(response);
 			}
 			break;
 #else
 		case SSH_CMSG_AUTH_TIS:
 			/* TIS Authentication is unsupported */
 			log("TIS authentication unsupported.");
 			break;
 #endif

 		default:
 			/*
 			 * Any unknown messages will be ignored (and failure
 			 * returned) during authentication.
 			 */
 			log("Unknown message during authentication: type %d", type);
 			break;
 		}

  		/*
  		 * Check if the user is logging in as root and root logins
  		 * are disallowed.
  		 * Note that root login is allowed for forced commands.
  		 */
  		if (authenticated && pw->pw_uid == 0 && !options.permit_root_login) {
  			if (forced_command) {
  				log("Root login accepted for forced command.");
  			} else {
  				authenticated = 0;
  				log("ROOT LOGIN REFUSED FROM %.200s",
  				    get_canonical_hostname());
  			}
   		}

 		/* Raise logging level */
 		if (authenticated ||
 		    attempt == AUTH_FAIL_LOG ||
 		    type == SSH_CMSG_AUTH_PASSWORD)
 			authlog = log;

 		authlog("%s %s for %.200s from %.200s port %d%s",
 			authenticated ? "Accepted" : "Failed",
 			get_authname(type),
 			pw->pw_uid == 0 ? "ROOT" : pw->pw_name,
 			get_remote_ipaddr(),
 			get_remote_port(),
 			user);

 #ifdef USE_PAM
 		if (authenticated) {
 			if (!do_pam_account(pw->pw_name, client_user)) {
 				if (client_user != NULL) {
 					xfree(client_user);
 					client_user = NULL;
 				}
 				do_fake_authloop1(pw->pw_name);
 			}
 			return;
 		}
 #else /* USE_PAM */
 		if (authenticated) {
 			return;
 		}
 #endif /* USE_PAM */

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

 		if (attempt > AUTH_FAIL_MAX)
 			packet_disconnect(AUTH_FAIL_MSG, pw->pw_name);

 		/* Send a message indicating that the authentication attempt failed. */
 		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()
 {
 	struct passwd *pw, pwcopy;
 	int plen;
 	unsigned int ulen;
 	char *user;
 #ifdef WITH_AIXAUTHENTICATE
 	char *loginmsg;
 #endif /* WITH_AIXAUTHENTICATE */

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

 	/* Get the user name. */
 	user = packet_get_string(&ulen);
 	packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);

 	setproctitle("%s", user);

 #ifdef AFS
 	/* If machine has AFS, set process authentication group. */
 	if (k_hasafs()) {
 		k_setpag();
 		k_unlog();
 	}
 #endif /* AFS */

 	/* Verify that the user is a valid user. */
 	pw = getpwnam(user);
 	if (!pw || !allowed_user(pw))
 		do_fake_authloop1(user);
 	xfree(user);

 	/* Take a copy of the returned structure. */
 	memset(&pwcopy, 0, sizeof(pwcopy));
 	pwcopy.pw_name = xstrdup(pw->pw_name);
 	pwcopy.pw_passwd = xstrdup(pw->pw_passwd);
 	pwcopy.pw_uid = pw->pw_uid;
 	pwcopy.pw_gid = pw->pw_gid;
 	pwcopy.pw_dir = xstrdup(pw->pw_dir);
 	pwcopy.pw_shell = xstrdup(pw->pw_shell);
 	pw = &pwcopy;

 #ifdef USE_PAM
 	start_pam(pw);
 #endif

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

 	debug("Attempting authentication for %.100s.", pw->pw_name);

 	/* If the user has no password, accept authentication immediately. */
 	if (options.password_authentication &&
 #ifdef KRB4
 	    (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 #endif /* KRB4 */
 #ifdef USE_PAM
 	    auth_pam_password(pw, "")) {
 #else /* USE_PAM */
 	    auth_password(pw, "")) {
 #endif /* USE_PAM */
 		/* Authentication with empty password succeeded. */
 		log("Login for user %s from %.100s, accepted without authentication.",
 		    pw->pw_name, get_remote_ipaddr());
 	} else {
 		/* Loop until the user has been authenticated or the
 		   connection is closed, do_authloop() returns only if
 		   authentication is successfull */
 		do_authloop(pw);
 	}

 	/* The user has been authenticated and accepted. */
 #ifdef WITH_AIXAUTHENTICATE
 	loginsuccess(user,get_canonical_hostname(),"ssh",&loginmsg);
 #endif /* WITH_AIXAUTHENTICATE */
 	packet_start(SSH_SMSG_SUCCESS);
 	packet_send();
 	packet_write_wait();

 	/* Perform session preparation. */
 	do_authenticated(pw);
 }
	/*
	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	* All rights reserved
	*/

	#include "includes.h"
	RCSID("$OpenBSD: auth.c,v 1.1 2000/03/28 21:15:45 markus Exp $");

	#include "xmalloc.h"
	#include "rsa.h"
	#include "ssh.h"
	#include "pty.h"
	#include "packet.h"
	#include "buffer.h"
	#include "cipher.h"
	#include "mpaux.h"
	#include "servconf.h"
	#include "channels.h"
	#include "match.h"

	#include "session.h"
	#include "dispatch.h"

	/* import */
	extern ServerOptions options;
	extern char *forced_command;

	/*
	* Check if the user is allowed to log in via ssh. If user is listed in
	* DenyUsers or user's primary group 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 user isn't listed there, false will be
	* returned.
	* If the user's shell is not executable, false will be returned.
	* Otherwise true is returned.
	*/
	static int
	allowed_user(struct passwd * pw)
	{
	struct stat st;
	struct group *grp;
	int i;
	#ifdef WITH_AIXAUTHENTICATE
	char *loginmsg;
	#endif /* WITH_AIXAUTHENTICATE */

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

	/* deny if shell does not exists or is not executable */
	if (stat(pw->pw_shell, &st) != 0)
	return 0;
	if (!((st.st_mode & S_IFREG) && (st.st_mode & (S_IXOTH\|S_IXUSR\|S_IXGRP))))
	return 0;

	/* Return false if user is listed in DenyUsers */
	if (options.num_deny_users > 0) {
	if (!pw->pw_name)
	return 0;
	for (i = 0; i < options.num_deny_users; i++)
	if (match_pattern(pw->pw_name, options.deny_users[i]))
	return 0;
	}
	/* Return false if AllowUsers isn't empty and user isn't listed there */
	if (options.num_allow_users > 0) {
	if (!pw->pw_name)
	return 0;
	for (i = 0; i < options.num_allow_users; i++)
	if (match_pattern(pw->pw_name, options.allow_users[i]))
	break;
	/* i < options.num_allow_users iff we break for loop */
	if (i >= options.num_allow_users)
	return 0;
	}
	/* Get the primary group name if we need it. Return false if it fails */
	if (options.num_deny_groups > 0 \|\| options.num_allow_groups > 0) {
	grp = getgrgid(pw->pw_gid);
	if (!grp)
	return 0;

	/* Return false if user's group is listed in DenyGroups */
	if (options.num_deny_groups > 0) {
	if (!grp->gr_name)
	return 0;
	for (i = 0; i < options.num_deny_groups; i++)
	if (match_pattern(grp->gr_name, options.deny_groups[i]))
	return 0;
	}
	/*
	* Return false if AllowGroups isn't empty and user's group
	* isn't listed there
	*/
	if (options.num_allow_groups > 0) {
	if (!grp->gr_name)
	return 0;
	for (i = 0; i < options.num_allow_groups; i++)
	if (match_pattern(grp->gr_name, options.allow_groups[i]))
	break;
	/* i < options.num_allow_groups iff we break for
	loop */
	if (i >= options.num_allow_groups)
	return 0;
	}
	}

	#ifdef WITH_AIXAUTHENTICATE
	if (loginrestrictions(pw->pw_name,S_LOGIN,NULL,&loginmsg) != 0)
	return 0;
	#endif /* WITH_AIXAUTHENTICATE */

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

	/*
	* convert ssh auth msg type into description
	*/
	char *
	get_authname(int type)
	{
	static char buf[1024];
	switch (type) {
	case SSH_CMSG_AUTH_PASSWORD:
	return "password";
	case SSH_CMSG_AUTH_RSA:
	return "rsa";
	case SSH_CMSG_AUTH_RHOSTS_RSA:
	return "rhosts-rsa";
	case SSH_CMSG_AUTH_RHOSTS:
	return "rhosts";
	#ifdef KRB4
	case SSH_CMSG_AUTH_KERBEROS:
	return "kerberos";
	#endif
	#ifdef SKEY
	case SSH_CMSG_AUTH_TIS_RESPONSE:
	return "s/key";
	#endif
	}
	snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
	return buf;
	}

	#define AUTH_FAIL_MAX 6
	#define AUTH_FAIL_LOG (AUTH_FAIL_MAX/2)
	#define AUTH_FAIL_MSG "Too many authentication failures for %.100s"

	/*
	* The user does not exist or access is denied,
	* but fake indication that authentication is needed.
	*/
	void
	do_fake_authloop1(char *user)
	{
	int attempt = 0;

	log("Faking authloop for illegal user %.200s from %.200s port %d",
	user,
	get_remote_ipaddr(),
	get_remote_port());

	#ifdef WITH_AIXAUTHENTICATE
	if (strncmp(get_authname(type),"password",
	strlen(get_authname(type))) == 0)
	loginfailed(pw->pw_name,get_canonical_hostname(),"ssh");
	#endif /* WITH_AIXAUTHENTICATE */

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

	/*
	* Keep reading packets, and always respond with a failure. This is
	* to avoid disclosing whether such a user really exists.
	*/
	for (attempt = 1;; attempt++) {
	/* Read a packet. This will not return if the client disconnects. */
	int plen;
	#ifndef SKEY
	(void)packet_read(&plen);
	#else /* SKEY */
	int type = packet_read(&plen);
	unsigned int dlen;
	char password, skeyinfo;
	/* Try to send a fake s/key challenge. */
	if (options.skey_authentication == 1 &&
	(skeyinfo = skey_fake_keyinfo(user)) != NULL) {
	password = NULL;
	if (type == SSH_CMSG_AUTH_TIS) {
	packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
	packet_put_string(skeyinfo, strlen(skeyinfo));
	packet_send();
	packet_write_wait();
	continue;
	} else if (type == SSH_CMSG_AUTH_PASSWORD &&
	options.password_authentication &&
	(password = packet_get_string(&dlen)) != NULL &&
	dlen == 5 &&
	strncasecmp(password, "s/key", 5) == 0 ) {
	packet_send_debug(skeyinfo);
	}
	if (password != NULL)
	xfree(password);
	}
	#endif
	if (attempt > AUTH_FAIL_MAX)
	packet_disconnect(AUTH_FAIL_MSG, user);

	/*
	* Send failure. This should be indistinguishable from a
	* failed authentication.
	*/
	packet_start(SSH_SMSG_FAILURE);
	packet_send();
	packet_write_wait();
	}
	/* NOTREACHED */
	abort();
	}

	/*
	* read packets and try to authenticate local user *pw.
	* return if authentication is successfull
	*/
	void
	do_authloop(struct passwd * pw)
	{
	int attempt = 0;
	unsigned int bits;
	RSA *client_host_key;
	BIGNUM *n;
	char client_user = NULL, password = NULL;
	char user[1024];
	unsigned int dlen;
	int plen, nlen, elen;
	unsigned int ulen;
	int type = 0;
	void (authlog) (const char fmt,...) = verbose;

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

	for (attempt = 1;; attempt++) {
	int authenticated = 0;
	strlcpy(user, "", sizeof user);

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

	/* Process the packet. */
	switch (type) {
	#ifdef AFS
	case SSH_CMSG_HAVE_KERBEROS_TGT:
	if (!options.kerberos_tgt_passing) {
	/* packet_get_all(); */
	verbose("Kerberos tgt passing disabled.");
	break;
	} else {
	/* Accept Kerberos tgt. */
	char *tgt = packet_get_string(&dlen);
	packet_integrity_check(plen, 4 + dlen, type);
	if (!auth_kerberos_tgt(pw, tgt))
	verbose("Kerberos tgt REFUSED for %s", pw->pw_name);
	xfree(tgt);
	}
	continue;

	case SSH_CMSG_HAVE_AFS_TOKEN:
	if (!options.afs_token_passing \|\| !k_hasafs()) {
	/* packet_get_all(); */
	verbose("AFS token passing disabled.");
	break;
	} else {
	/* Accept AFS token. */
	char *token_string = packet_get_string(&dlen);
	packet_integrity_check(plen, 4 + dlen, type);
	if (!auth_afs_token(pw, token_string))
	verbose("AFS token REFUSED for %s", pw->pw_name);
	xfree(token_string);
	}
	continue;
	#endif /* AFS */
	#ifdef KRB4
	case SSH_CMSG_AUTH_KERBEROS:
	if (!options.kerberos_authentication) {
	/* packet_get_all(); */
	verbose("Kerberos authentication disabled.");
	break;
	} else {
	/* Try Kerberos v4 authentication. */
	KTEXT_ST auth;
	char *tkt_user = NULL;
	char kdata = packet_get_string((unsigned int ) &auth.length);
	packet_integrity_check(plen, 4 + auth.length, type);

	if (auth.length < MAX_KTXT_LEN)
	memcpy(auth.dat, kdata, auth.length);
	xfree(kdata);

	authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user);

	if (authenticated) {
	snprintf(user, sizeof user, " tktuser %s", tkt_user);
	xfree(tkt_user);
	}
	}
	break;
	#endif /* KRB4 */

	case SSH_CMSG_AUTH_RHOSTS:
	if (!options.rhosts_authentication) {
	verbose("Rhosts authentication disabled.");
	break;
	}
	/*
	* Get client user name. Note that we just have to
	* trust the client; this is one reason why rhosts
	* authentication is insecure. (Another is
	* IP-spoofing on a local network.)
	*/
	client_user = packet_get_string(&ulen);
	packet_integrity_check(plen, 4 + ulen, type);

	/* Try to authenticate using /etc/hosts.equiv and
	.rhosts. */
	authenticated = auth_rhosts(pw, client_user);

	snprintf(user, sizeof user, " ruser %s", client_user);
	break;

	case SSH_CMSG_AUTH_RHOSTS_RSA:
	if (!options.rhosts_rsa_authentication) {
	verbose("Rhosts with RSA authentication disabled.");
	break;
	}
	/*
	* 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 = RSA_new();
	if (client_host_key == NULL)
	fatal("RSA_new failed");
	client_host_key->e = BN_new();
	client_host_key->n = BN_new();
	if (client_host_key->e == NULL \|\| client_host_key->n == NULL)
	fatal("BN_new failed");
	bits = packet_get_int();
	packet_get_bignum(client_host_key->e, &elen);
	packet_get_bignum(client_host_key->n, &nlen);

	if (bits != BN_num_bits(client_host_key->n))
	error("Warning: keysize mismatch for client_host_key: "
	"actual %d, announced %d", BN_num_bits(client_host_key->n), bits);
	packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);

	authenticated = auth_rhosts_rsa(pw, client_user, client_host_key);
	RSA_free(client_host_key);

	snprintf(user, sizeof user, " ruser %s", client_user);
	break;

	case SSH_CMSG_AUTH_RSA:
	if (!options.rsa_authentication) {
	verbose("RSA authentication disabled.");
	break;
	}
	/* RSA authentication requested. */
	n = BN_new();
	packet_get_bignum(n, &nlen);
	packet_integrity_check(plen, nlen, type);
	authenticated = auth_rsa(pw, n);
	BN_clear_free(n);
	break;

	case SSH_CMSG_AUTH_PASSWORD:
	if (!options.password_authentication) {
	verbose("Password authentication disabled.");
	break;
	}
	/*
	* 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_integrity_check(plen, 4 + dlen, type);

	#ifdef USE_PAM
	/* Do PAM auth with password */
	authenticated = auth_pam_password(pw, password);
	#else /* USE_PAM */
	/* Try authentication with the password. */
	authenticated = auth_password(pw, password);
	#endif /* USE_PAM */
	memset(password, 0, strlen(password));
	xfree(password);
	break;

	#ifdef SKEY
	case SSH_CMSG_AUTH_TIS:
	debug("rcvd SSH_CMSG_AUTH_TIS");
	if (options.skey_authentication == 1) {
	char *skeyinfo = skey_keyinfo(pw->pw_name);
	if (skeyinfo == NULL) {
	debug("generating fake skeyinfo for %.100s.", pw->pw_name);
	skeyinfo = skey_fake_keyinfo(pw->pw_name);
	}
	if (skeyinfo != NULL) {
	/* we send our s/key- in tis-challenge messages */
	debug("sending challenge '%s'", skeyinfo);
	packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
	packet_put_string(skeyinfo, strlen(skeyinfo));
	packet_send();
	packet_write_wait();
	continue;
	}
	}
	break;
	case SSH_CMSG_AUTH_TIS_RESPONSE:
	debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
	if (options.skey_authentication == 1) {
	char *response = packet_get_string(&dlen);
	debug("skey response == '%s'", response);
	packet_integrity_check(plen, 4 + dlen, type);
	authenticated = (skey_haskey(pw->pw_name) == 0 &&
	skey_passcheck(pw->pw_name, response) != -1);
	xfree(response);
	}
	break;
	#else
	case SSH_CMSG_AUTH_TIS:
	/* TIS Authentication is unsupported */
	log("TIS authentication unsupported.");
	break;
	#endif

	default:
	/*
	* Any unknown messages will be ignored (and failure
	* returned) during authentication.
	*/
	log("Unknown message during authentication: type %d", type);
	break;
	}

	/*
	* Check if the user is logging in as root and root logins
	* are disallowed.
	* Note that root login is allowed for forced commands.
	*/
	if (authenticated && pw->pw_uid == 0 && !options.permit_root_login) {
	if (forced_command) {
	log("Root login accepted for forced command.");
	} else {
	authenticated = 0;
	log("ROOT LOGIN REFUSED FROM %.200s",
	get_canonical_hostname());
	}
	}

	/* Raise logging level */
	if (authenticated \|\|
	attempt == AUTH_FAIL_LOG \|\|
	type == SSH_CMSG_AUTH_PASSWORD)
	authlog = log;

	authlog("%s %s for %.200s from %.200s port %d%s",
	authenticated ? "Accepted" : "Failed",
	get_authname(type),
	pw->pw_uid == 0 ? "ROOT" : pw->pw_name,
	get_remote_ipaddr(),
	get_remote_port(),
	user);

	#ifdef USE_PAM
	if (authenticated) {
	if (!do_pam_account(pw->pw_name, client_user)) {
	if (client_user != NULL) {
	xfree(client_user);
	client_user = NULL;
	}
	do_fake_authloop1(pw->pw_name);
	}
	return;
	}
	#else /* USE_PAM */
	if (authenticated) {
	return;
	}
	#endif /* USE_PAM */

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

	if (attempt > AUTH_FAIL_MAX)
	packet_disconnect(AUTH_FAIL_MSG, pw->pw_name);

	/* Send a message indicating that the authentication attempt failed. */
	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()
	{
	struct passwd *pw, pwcopy;
	int plen;
	unsigned int ulen;
	char *user;
	#ifdef WITH_AIXAUTHENTICATE
	char *loginmsg;
	#endif /* WITH_AIXAUTHENTICATE */

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

	/* Get the user name. */
	user = packet_get_string(&ulen);
	packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);

	setproctitle("%s", user);

	#ifdef AFS
	/* If machine has AFS, set process authentication group. */
	if (k_hasafs()) {
	k_setpag();
	k_unlog();
	}
	#endif /* AFS */

	/* Verify that the user is a valid user. */
	pw = getpwnam(user);
	if (!pw \|\| !allowed_user(pw))
	do_fake_authloop1(user);
	xfree(user);

	/* Take a copy of the returned structure. */
	memset(&pwcopy, 0, sizeof(pwcopy));
	pwcopy.pw_name = xstrdup(pw->pw_name);
	pwcopy.pw_passwd = xstrdup(pw->pw_passwd);
	pwcopy.pw_uid = pw->pw_uid;
	pwcopy.pw_gid = pw->pw_gid;
	pwcopy.pw_dir = xstrdup(pw->pw_dir);
	pwcopy.pw_shell = xstrdup(pw->pw_shell);
	pw = &pwcopy;

	#ifdef USE_PAM
	start_pam(pw);
	#endif

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

	debug("Attempting authentication for %.100s.", pw->pw_name);

	/* If the user has no password, accept authentication immediately. */
	if (options.password_authentication &&
	#ifdef KRB4
	(!options.kerberos_authentication \|\| options.kerberos_or_local_passwd) &&
	#endif /* KRB4 */
	#ifdef USE_PAM
	auth_pam_password(pw, "")) {
	#else /* USE_PAM */
	auth_password(pw, "")) {
	#endif /* USE_PAM */
	/* Authentication with empty password succeeded. */
	log("Login for user %s from %.100s, accepted without authentication.",
	pw->pw_name, get_remote_ipaddr());
	} else {
	/* Loop until the user has been authenticated or the
	connection is closed, do_authloop() returns only if
	authentication is successfull */
	do_authloop(pw);
	}

	/* The user has been authenticated and accepted. */
	#ifdef WITH_AIXAUTHENTICATE
	loginsuccess(user,get_canonical_hostname(),"ssh",&loginmsg);
	#endif /* WITH_AIXAUTHENTICATE */
	packet_start(SSH_SMSG_SUCCESS);
	packet_send();
	packet_write_wait();

	/* Perform session preparation. */
	do_authenticated(pw);
	}