/* $OpenBSD: auth2.c,v 1.136 2016/05/02 08:49:03 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"
__RCSID("$FreeBSD$");
#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 "misc.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"
#include "blacklist_client.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
Authmethod *authmethods[] = {
&method_none,
&method_pubkey,
#ifdef GSSAPI
&method_gssapi,
#endif
&method_passwd,
&method_kbdint,
&method_hostbased,
NULL
};
/* protocol */
static int input_service_request(int, u_int32_t, void *);
static int 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 || (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 int
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);
return 0;
}
/*ARGSUSED*/
static int
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;
#ifdef HAVE_LOGIN_CAP
struct ssh *ssh = active_state; /* XXX */
login_cap_t *lc;
const char *from_host, *from_ip;
#endif
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();
BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL);
#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);
}
#ifdef HAVE_LOGIN_CAP
if (authctxt->pw != NULL &&
(lc = login_getpwclass(authctxt->pw)) != NULL) {
logit("user %s login class %s", authctxt->pw->pw_name,
authctxt->pw->pw_class);
from_host = auth_get_canonical_hostname(ssh, options.use_dns);
from_ip = ssh_remote_ipaddr(ssh);
if (!auth_hostok(lc, from_host, from_ip)) {
logit("Denied connection for %.200s from %.200s [%.200s].",
authctxt->pw->pw_name, from_host, from_ip);
packet_disconnect("Sorry, you are not allowed to connect.");
}
if (!auth_timeok(lc, time(NULL))) {
logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
authctxt->pw->pw_name, from_host);
packet_disconnect("Logins not available right now.");
}
login_close(lc);
}
#endif /* HAVE_LOGIN_CAP */
/* reset state */
auth2_challenge_stop(authctxt);
#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);
return 0;
}
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);
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 (!partial && !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
auth_maxtries_exceeded(authctxt);
}
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));
}
if ((list = sshbuf_dup_string(&b)) == NULL)
fatal("%s: sshbuf_dup_string failed", __func__);
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;
}
