auth2.c - security/openssh-library - Rivoreo Source Code Repositories

 /* $OpenBSD: auth2.c,v 1.128 2013/05/17 00:13:13 djm Exp $ */
 /*
  * 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"

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/uio.h>

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

 #include "atomicio.h"
 #include "xmalloc.h"
 #include "ssh2.h"
 #include "packet.h"
 #include "log.h"
 #include "buffer.h"
 #include "servconf.h"
 #include "compat.h"
 #include "key.h"
 #include "hostfile.h"
 #include "auth.h"
 #include "dispatch.h"
 #include "pathnames.h"
 #include "buffer.h"

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

 /* 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
 #ifdef JPAKE
 extern Authmethod method_jpake;
 #endif

 Authmethod *authmethods[] = {
 	&method_none,
 	&method_pubkey,
 #ifdef GSSAPI
 	&method_gssapi,
 #endif
 #ifdef JPAKE
 	&method_jpake,
 #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(Authctxt *, const char *);
 static char *authmethods_get(Authctxt *authctxt);

 #define MATCH_NONE	0	/* method or submethod mismatch */
 #define MATCH_METHOD	1	/* method matches (no submethod specified) */
 #define MATCH_BOTH	2	/* method and submethod match */
 #define MATCH_PARTIAL	3	/* method matches, submethod can't be checked */
 static int list_starts_with(const char *, const char *, const char *);

 char *
 auth2_read_banner(void)
 {
 	struct stat st;
 	char *banner = NULL;
 	size_t len, n;
 	int fd;

 	if ((fd = open(options.banner, O_RDONLY)) == -1)
 		return (NULL);
 	if (fstat(fd, &st) == -1) {
 		close(fd);
 		return (NULL);
 	}
 	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
 		close(fd);
 		return (NULL);
 	}

 	len = (size_t)st.st_size;		/* truncate */
 	banner = xmalloc(len + 1);
 	n = atomicio(read, fd, banner, len);
 	close(fd);

 	if (n != len) {
 		free(banner);
 		return (NULL);
 	}
 	banner[n] = '\0';

 	return (banner);
 }

 void
 userauth_send_banner(const char *msg)
 {
 	if (datafellows & SSH_BUG_BANNER)
 		return;

 	packet_start(SSH2_MSG_USERAUTH_BANNER);
 	packet_put_cstring(msg);
 	packet_put_cstring("");		/* language, unused */
 	packet_send();
 	debug("%s: sent", __func__);
 }

 static void
 userauth_banner(void)
 {
 	char *banner = NULL;

 	if (options.banner == NULL ||
 	    strcasecmp(options.banner, "none") == 0 ||
 	    (datafellows & SSH_BUG_BANNER) != 0)
 		return;

 	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
 		goto done;
 	userauth_send_banner(banner);

 done:
 	free(banner);
 }

 /*
  * loop until authctxt->success == TRUE
  */
 void
 do_authentication2(Authctxt *authctxt)
 {
 	dispatch_init(&dispatch_protocol_error);
 	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 }

 /*ARGSUSED*/
 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_cstring(&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);
 	}
 	free(service);
 }

 /*ARGSUSED*/
 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_cstring(NULL);
 	service = packet_get_cstring(NULL);
 	method = packet_get_cstring(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);
 		userauth_banner();
 		if (auth2_setup_methods_lists(authctxt) != 0)
 			packet_disconnect("no authentication methods enabled");
 	} 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 JPAKE
 	auth2_jpake_stop(authctxt);
 #endif

 #ifdef GSSAPI
 	/* XXX move to auth2_gssapi_stop() */
 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 #endif

 	authctxt->postponed = 0;
 	authctxt->server_caused_failure = 0;

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

 	free(service);
 	free(user);
 	free(method);
 }

 void
 userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
     const char *submethod)
 {
 	char *methods;
 	int partial = 0;

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

 	/* 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
 	}

 	if (authenticated && options.num_auth_methods != 0) {
 		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
 			authenticated = 0;
 			partial = 1;
 		}
 	}

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

 	if (authctxt->postponed)
 		return;

 #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 */

 	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 {

 		/* Allow initial try of "none" auth without failure penalty */
 		if (!authctxt->server_caused_failure &&
 		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
 			authctxt->failures++;
 		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(authctxt);
 		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
 		    partial, methods);
 		packet_start(SSH2_MSG_USERAUTH_FAILURE);
 		packet_put_cstring(methods);
 		packet_put_char(partial);
 		packet_send();
 		packet_write_wait();
 		free(methods);
 	}
 }

 /*
  * Checks whether method is allowed by at least one AuthenticationMethods
  * methods list. Returns 1 if allowed, or no methods lists configured.
  * 0 otherwise.
  */
 int
 auth2_method_allowed(Authctxt *authctxt, const char *method,
     const char *submethod)
 {
 	u_int i;

 	/*
 	 * NB. authctxt->num_auth_methods might be zero as a result of
 	 * auth2_setup_methods_lists(), so check the configuration.
 	 */
 	if (options.num_auth_methods == 0)
 		return 1;
 	for (i = 0; i < authctxt->num_auth_methods; i++) {
 		if (list_starts_with(authctxt->auth_methods[i], method,
 		    submethod) != MATCH_NONE)
 			return 1;
 	}
 	return 0;
 }

 static char *
 authmethods_get(Authctxt *authctxt)
 {
 	Buffer b;
 	char *list;
 	u_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)
 			continue;
 		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
 		    NULL))
 			continue;
 		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(Authctxt *authctxt, 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 &&
 			    auth2_method_allowed(authctxt,
 			    authmethods[i]->name, NULL))
 				return authmethods[i];
 	debug2("Unrecognized authentication method name: %s",
 	    name ? name : "NULL");
 	return NULL;
 }

 /*
  * Check a comma-separated list of methods for validity. Is need_enable is
  * non-zero, then also require that the methods are enabled.
  * Returns 0 on success or -1 if the methods list is invalid.
  */
 int
 auth2_methods_valid(const char *_methods, int need_enable)
 {
 	char *methods, *omethods, *method, *p;
 	u_int i, found;
 	int ret = -1;

 	if (*_methods == '\0') {
 		error("empty authentication method list");
 		return -1;
 	}
 	omethods = methods = xstrdup(_methods);
 	while ((method = strsep(&methods, ",")) != NULL) {
 		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
 			if ((p = strchr(method, ':')) != NULL)
 				*p = '\0';
 			if (strcmp(method, authmethods[i]->name) != 0)
 				continue;
 			if (need_enable) {
 				if (authmethods[i]->enabled == NULL ||
 				    *(authmethods[i]->enabled) == 0) {
 					error("Disabled method \"%s\" in "
 					    "AuthenticationMethods list \"%s\"",
 					    method, _methods);
 					goto out;
 				}
 			}
 			found = 1;
 			break;
 		}
 		if (!found) {
 			error("Unknown authentication method \"%s\" in list",
 			    method);
 			goto out;
 		}
 	}
 	ret = 0;
  out:
 	free(omethods);
 	return ret;
 }

 /*
  * Prune the AuthenticationMethods supplied in the configuration, removing
  * any methods lists that include disabled methods. Note that this might
  * leave authctxt->num_auth_methods == 0, even when multiple required auth
  * has been requested. For this reason, all tests for whether multiple is
  * enabled should consult options.num_auth_methods directly.
  */
 int
 auth2_setup_methods_lists(Authctxt *authctxt)
 {
 	u_int i;

 	if (options.num_auth_methods == 0)
 		return 0;
 	debug3("%s: checking methods", __func__);
 	authctxt->auth_methods = xcalloc(options.num_auth_methods,
 	    sizeof(*authctxt->auth_methods));
 	authctxt->num_auth_methods = 0;
 	for (i = 0; i < options.num_auth_methods; i++) {
 		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
 			logit("Authentication methods list \"%s\" contains "
 			    "disabled method, skipping",
 			    options.auth_methods[i]);
 			continue;
 		}
 		debug("authentication methods list %d: %s",
 		    authctxt->num_auth_methods, options.auth_methods[i]);
 		authctxt->auth_methods[authctxt->num_auth_methods++] =
 		    xstrdup(options.auth_methods[i]);
 	}
 	if (authctxt->num_auth_methods == 0) {
 		error("No AuthenticationMethods left after eliminating "
 		    "disabled methods");
 		return -1;
 	}
 	return 0;
 }

 static int
 list_starts_with(const char *methods, const char *method,
     const char *submethod)
 {
 	size_t l = strlen(method);
 	int match;
 	const char *p;

 	if (strncmp(methods, method, l) != 0)
 		return MATCH_NONE;
 	p = methods + l;
 	match = MATCH_METHOD;
 	if (*p == ':') {
 		if (!submethod)
 			return MATCH_PARTIAL;
 		l = strlen(submethod);
 		p += 1;
 		if (strncmp(submethod, p, l))
 			return MATCH_NONE;
 		p += l;
 		match = MATCH_BOTH;
 	}
 	if (*p != ',' && *p != '\0')
 		return MATCH_NONE;
 	return match;
 }

 /*
  * Remove method from the start of a comma-separated list of methods.
  * Returns 0 if the list of methods did not start with that method or 1
  * if it did.
  */
 static int
 remove_method(char **methods, const char *method, const char *submethod)
 {
 	char *omethods = *methods, *p;
 	size_t l = strlen(method);
 	int match;

 	match = list_starts_with(omethods, method, submethod);
 	if (match != MATCH_METHOD && match != MATCH_BOTH)
 		return 0;
 	p = omethods + l;
 	if (submethod && match == MATCH_BOTH)
 		p += 1 + strlen(submethod); /* include colon */
 	if (*p == ',')
 		p++;
 	*methods = xstrdup(p);
 	free(omethods);
 	return 1;
 }

 /*
  * Called after successful authentication. Will remove the successful method
  * from the start of each list in which it occurs. If it was the last method
  * in any list, then authentication is deemed successful.
  * Returns 1 if the method completed any authentication list or 0 otherwise.
  */
 int
 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
     const char *submethod)
 {
 	u_int i, found = 0;

 	debug3("%s: updating methods list after \"%s\"", __func__, method);
 	for (i = 0; i < authctxt->num_auth_methods; i++) {
 		if (!remove_method(&(authctxt->auth_methods[i]), method,
 		    submethod))
 			continue;
 		found = 1;
 		if (*authctxt->auth_methods[i] == '\0') {
 			debug2("authentication methods list %d complete", i);
 			return 1;
 		}
 		debug3("authentication methods list %d remaining: \"%s\"",
 		    i, authctxt->auth_methods[i]);
 	}
 	/* This should not happen, but would be bad if it did */
 	if (!found)
 		fatal("%s: method not in AuthenticationMethods", __func__);
 	return 0;
 }
	/* $OpenBSD: auth2.c,v 1.128 2013/05/17 00:13:13 djm Exp $ */
	/*
	* 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"

	#include <sys/types.h>
	#include <sys/stat.h>
	#include <sys/uio.h>

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

	#include "atomicio.h"
	#include "xmalloc.h"
	#include "ssh2.h"
	#include "packet.h"
	#include "log.h"
	#include "buffer.h"
	#include "servconf.h"
	#include "compat.h"
	#include "key.h"
	#include "hostfile.h"
	#include "auth.h"
	#include "dispatch.h"
	#include "pathnames.h"
	#include "buffer.h"

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

	/* 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
	#ifdef JPAKE
	extern Authmethod method_jpake;
	#endif

	Authmethod *authmethods[] = {
	&method_none,
	&method_pubkey,
	#ifdef GSSAPI
	&method_gssapi,
	#endif
	#ifdef JPAKE
	&method_jpake,
	#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(Authctxt , const char *);
	static char authmethods_get(Authctxt authctxt);

	#define MATCH_NONE 0 /* method or submethod mismatch */
	#define MATCH_METHOD 1 /* method matches (no submethod specified) */
	#define MATCH_BOTH 2 /* method and submethod match */
	#define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */
	static int list_starts_with(const char , const char , const char *);

	char *
	auth2_read_banner(void)
	{
	struct stat st;
	char *banner = NULL;
	size_t len, n;
	int fd;

	if ((fd = open(options.banner, O_RDONLY)) == -1)
	return (NULL);
	if (fstat(fd, &st) == -1) {
	close(fd);
	return (NULL);
	}
	if (st.st_size <= 0 \|\| st.st_size > 110241024) {
	close(fd);
	return (NULL);
	}

	len = (size_t)st.st_size; /* truncate */
	banner = xmalloc(len + 1);
	n = atomicio(read, fd, banner, len);
	close(fd);

	if (n != len) {
	free(banner);
	return (NULL);
	}
	banner[n] = '\0';

	return (banner);
	}

	void
	userauth_send_banner(const char *msg)
	{
	if (datafellows & SSH_BUG_BANNER)
	return;

	packet_start(SSH2_MSG_USERAUTH_BANNER);
	packet_put_cstring(msg);
	packet_put_cstring(""); /* language, unused */
	packet_send();
	debug("%s: sent", __func__);
	}

	static void
	userauth_banner(void)
	{
	char *banner = NULL;

	if (options.banner == NULL \|\|
	strcasecmp(options.banner, "none") == 0 \|\|
	(datafellows & SSH_BUG_BANNER) != 0)
	return;

	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
	goto done;
	userauth_send_banner(banner);

	done:
	free(banner);
	}

	/*
	* loop until authctxt->success == TRUE
	*/
	void
	do_authentication2(Authctxt *authctxt)
	{
	dispatch_init(&dispatch_protocol_error);
	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
	}

	/ARGSUSED/
	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_cstring(&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);
	}
	free(service);
	}

	/ARGSUSED/
	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_cstring(NULL);
	service = packet_get_cstring(NULL);
	method = packet_get_cstring(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);
	userauth_banner();
	if (auth2_setup_methods_lists(authctxt) != 0)
	packet_disconnect("no authentication methods enabled");
	} 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 JPAKE
	auth2_jpake_stop(authctxt);
	#endif

	#ifdef GSSAPI
	/* XXX move to auth2_gssapi_stop() */
	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
	#endif

	authctxt->postponed = 0;
	authctxt->server_caused_failure = 0;

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

	free(service);
	free(user);
	free(method);
	}

	void
	userauth_finish(Authctxt authctxt, int authenticated, const char method,
	const char *submethod)
	{
	char *methods;
	int partial = 0;

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

	/* 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
	}

	if (authenticated && options.num_auth_methods != 0) {
	if (!auth2_update_methods_lists(authctxt, method, submethod)) {
	authenticated = 0;
	partial = 1;
	}
	}

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

	if (authctxt->postponed)
	return;

	#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 */

	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 {

	/* Allow initial try of "none" auth without failure penalty */
	if (!authctxt->server_caused_failure &&
	(authctxt->attempt > 1 \|\| strcmp(method, "none") != 0))
	authctxt->failures++;
	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(authctxt);
	debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
	partial, methods);
	packet_start(SSH2_MSG_USERAUTH_FAILURE);
	packet_put_cstring(methods);
	packet_put_char(partial);
	packet_send();
	packet_write_wait();
	free(methods);
	}
	}

	/*
	* Checks whether method is allowed by at least one AuthenticationMethods
	* methods list. Returns 1 if allowed, or no methods lists configured.
	* 0 otherwise.
	*/
	int
	auth2_method_allowed(Authctxt authctxt, const char method,
	const char *submethod)
	{
	u_int i;

	/*
	* NB. authctxt->num_auth_methods might be zero as a result of
	* auth2_setup_methods_lists(), so check the configuration.
	*/
	if (options.num_auth_methods == 0)
	return 1;
	for (i = 0; i < authctxt->num_auth_methods; i++) {
	if (list_starts_with(authctxt->auth_methods[i], method,
	submethod) != MATCH_NONE)
	return 1;
	}
	return 0;
	}

	static char *
	authmethods_get(Authctxt *authctxt)
	{
	Buffer b;
	char *list;
	u_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)
	continue;
	if (!auth2_method_allowed(authctxt, authmethods[i]->name,
	NULL))
	continue;
	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(Authctxt authctxt, 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 &&
	auth2_method_allowed(authctxt,
	authmethods[i]->name, NULL))
	return authmethods[i];
	debug2("Unrecognized authentication method name: %s",
	name ? name : "NULL");
	return NULL;
	}

	/*
	* Check a comma-separated list of methods for validity. Is need_enable is
	* non-zero, then also require that the methods are enabled.
	* Returns 0 on success or -1 if the methods list is invalid.
	*/
	int
	auth2_methods_valid(const char *_methods, int need_enable)
	{
	char methods, omethods, method, p;
	u_int i, found;
	int ret = -1;

	if (*_methods == '\0') {
	error("empty authentication method list");
	return -1;
	}
	omethods = methods = xstrdup(_methods);
	while ((method = strsep(&methods, ",")) != NULL) {
	for (found = i = 0; !found && authmethods[i] != NULL; i++) {
	if ((p = strchr(method, ':')) != NULL)
	*p = '\0';
	if (strcmp(method, authmethods[i]->name) != 0)
	continue;
	if (need_enable) {
	if (authmethods[i]->enabled == NULL \|\|
	*(authmethods[i]->enabled) == 0) {
	error("Disabled method \"%s\" in "
	"AuthenticationMethods list \"%s\"",
	method, _methods);
	goto out;
	}
	}
	found = 1;
	break;
	}
	if (!found) {
	error("Unknown authentication method \"%s\" in list",
	method);
	goto out;
	}
	}
	ret = 0;
	out:
	free(omethods);
	return ret;
	}

	/*
	* Prune the AuthenticationMethods supplied in the configuration, removing
	* any methods lists that include disabled methods. Note that this might
	* leave authctxt->num_auth_methods == 0, even when multiple required auth
	* has been requested. For this reason, all tests for whether multiple is
	* enabled should consult options.num_auth_methods directly.
	*/
	int
	auth2_setup_methods_lists(Authctxt *authctxt)
	{
	u_int i;

	if (options.num_auth_methods == 0)
	return 0;
	debug3("%s: checking methods", __func__);
	authctxt->auth_methods = xcalloc(options.num_auth_methods,
	sizeof(*authctxt->auth_methods));
	authctxt->num_auth_methods = 0;
	for (i = 0; i < options.num_auth_methods; i++) {
	if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
	logit("Authentication methods list \"%s\" contains "
	"disabled method, skipping",
	options.auth_methods[i]);
	continue;
	}
	debug("authentication methods list %d: %s",
	authctxt->num_auth_methods, options.auth_methods[i]);
	authctxt->auth_methods[authctxt->num_auth_methods++] =
	xstrdup(options.auth_methods[i]);
	}
	if (authctxt->num_auth_methods == 0) {
	error("No AuthenticationMethods left after eliminating "
	"disabled methods");
	return -1;
	}
	return 0;
	}

	static int
	list_starts_with(const char methods, const char method,
	const char *submethod)
	{
	size_t l = strlen(method);
	int match;
	const char *p;

	if (strncmp(methods, method, l) != 0)
	return MATCH_NONE;
	p = methods + l;
	match = MATCH_METHOD;
	if (*p == ':') {
	if (!submethod)
	return MATCH_PARTIAL;
	l = strlen(submethod);
	p += 1;
	if (strncmp(submethod, p, l))
	return MATCH_NONE;
	p += l;
	match = MATCH_BOTH;
	}
	if (p != ',' && p != '\0')
	return MATCH_NONE;
	return match;
	}

	/*
	* Remove method from the start of a comma-separated list of methods.
	* Returns 0 if the list of methods did not start with that method or 1
	* if it did.
	*/
	static int
	remove_method(char *methods, const char method, const char *submethod)
	{
	char omethods = methods, *p;
	size_t l = strlen(method);
	int match;

	match = list_starts_with(omethods, method, submethod);
	if (match != MATCH_METHOD && match != MATCH_BOTH)
	return 0;
	p = omethods + l;
	if (submethod && match == MATCH_BOTH)
	p += 1 + strlen(submethod); /* include colon */
	if (*p == ',')
	p++;
	*methods = xstrdup(p);
	free(omethods);
	return 1;
	}

	/*
	* Called after successful authentication. Will remove the successful method
	* from the start of each list in which it occurs. If it was the last method
	* in any list, then authentication is deemed successful.
	* Returns 1 if the method completed any authentication list or 0 otherwise.
	*/
	int
	auth2_update_methods_lists(Authctxt authctxt, const char method,
	const char *submethod)
	{
	u_int i, found = 0;

	debug3("%s: updating methods list after \"%s\"", __func__, method);
	for (i = 0; i < authctxt->num_auth_methods; i++) {
	if (!remove_method(&(authctxt->auth_methods[i]), method,
	submethod))
	continue;
	found = 1;
	if (*authctxt->auth_methods[i] == '\0') {
	debug2("authentication methods list %d complete", i);
	return 1;
	}
	debug3("authentication methods list %d remaining: \"%s\"",
	i, authctxt->auth_methods[i]);
	}
	/* This should not happen, but would be bad if it did */
	if (!found)
	fatal("%s: method not in AuthenticationMethods", __func__);
	return 0;
	}