auth1.c - security/openssh-library - Rivoreo Source Code Repositories

 /* $OpenBSD: auth1.c,v 1.73 2008/07/04 23:30:16 djm Exp $ */
 /*
  * 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"

 #include <sys/types.h>

 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
 #include <pwd.h>

 #include "openbsd-compat/sys-queue.h"
 #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 "key.h"
 #include "hostfile.h"
 #include "auth.h"
 #include "channels.h"
 #include "session.h"
 #include "uidswap.h"
 #ifdef GSSAPI
 #include "ssh-gss.h"
 #endif
 #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);
 }

 /*ARGSUSED*/
 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);
 }

 /*ARGSUSED*/
 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);
 }

 /*ARGSUSED*/
 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);
 }

 /*ARGSUSED*/
 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);
 }

 /*ARGSUSED*/
 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 (authctxt->failures >= options.max_authtries)
 			goto skip;
 		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("%s", 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();
 }
	/* $OpenBSD: auth1.c,v 1.73 2008/07/04 23:30:16 djm Exp $ */
	/*
	* 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"

	#include <sys/types.h>

	#include <stdarg.h>
	#include <stdio.h>
	#include <string.h>
	#include <unistd.h>
	#include <pwd.h>

	#include "openbsd-compat/sys-queue.h"
	#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 "key.h"
	#include "hostfile.h"
	#include "auth.h"
	#include "channels.h"
	#include "session.h"
	#include "uidswap.h"
	#ifdef GSSAPI
	#include "ssh-gss.h"
	#endif
	#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);
	}

	/ARGSUSED/
	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);
	}

	/ARGSUSED/
	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);
	}

	/ARGSUSED/
	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);
	}

	/ARGSUSED/
	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);
	}

	/ARGSUSED/
	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 (authctxt->failures >= options.max_authtries)
	goto skip;
	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("%s", 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();
	}