blob: 19925f67f663e1708b82f7a7e39748516f3dd490 [file] [log] [blame]
/**
* \file session_server_ssh.c
* \author Michal Vasko <mvasko@cesnet.cz>
* \brief libnetconf2 SSH server session manipulation functions
*
* Copyright (c) 2015 CESNET, z.s.p.o.
*
* 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.
* 3. Neither the name of the Company nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
*/
#define _GNU_SOURCE
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <shadow.h>
#include <crypt.h>
#include <errno.h>
#include "session_server.h"
#include "session_p.h"
extern struct nc_server_opts server_opts;
static struct nc_ssh_server_opts ssh_opts = {
.auth_methods = NC_SSH_AUTH_PUBLICKEY | NC_SSH_AUTH_PASSWORD | NC_SSH_AUTH_INTERACTIVE,
.auth_attempts = 3,
.auth_timeout = 10
};
API int
nc_ssh_server_set_hostkey(const char *key_path)
{
if (!key_path) {
ERRARG;
return -1;
}
if (!ssh_opts.sshbind) {
ssh_opts.sshbind = ssh_bind_new();
if (!ssh_opts.sshbind) {
ERR("%s: failed to create a new ssh_bind.", __func__);
return -1;
}
}
if (ssh_bind_options_set(ssh_opts.sshbind, SSH_BIND_OPTIONS_HOSTKEY, key_path) != SSH_OK) {
ERR("%s: failed to set host key (%s).", __func__, ssh_get_error(ssh_opts.sshbind));
return -1;
}
return 0;
}
API int
nc_ssh_server_set_banner(const char *banner)
{
if (!banner) {
ERRARG;
return -1;
}
if (!ssh_opts.sshbind) {
ssh_opts.sshbind = ssh_bind_new();
if (!ssh_opts.sshbind) {
ERR("%s: failed to create a new ssh_bind", __func__);
return -1;
}
}
ssh_bind_options_set(ssh_opts.sshbind, SSH_BIND_OPTIONS_BANNER, banner);
return 0;
}
API int
nc_ssh_server_set_auth_methods(int auth_methods)
{
if (!(auth_methods & NC_SSH_AUTH_PUBLICKEY) && !(auth_methods & NC_SSH_AUTH_PASSWORD)
&& !(auth_methods & NC_SSH_AUTH_INTERACTIVE)) {
ERRARG;
return -1;
}
ssh_opts.auth_methods = auth_methods;
return 0;
}
API int
nc_ssh_server_set_auth_attempts(uint16_t auth_attempts)
{
if (!auth_attempts) {
ERRARG;
return -1;
}
ssh_opts.auth_attempts = auth_attempts;
return 0;
}
API int
nc_ssh_server_set_auth_timeout(uint16_t auth_timeout)
{
if (!auth_timeout) {
ERRARG;
return -1;
}
ssh_opts.auth_timeout = auth_timeout;
return 0;
}
API int
nc_ssh_server_add_authkey(const char *keypath, const char *username)
{
if (!keypath || !username) {
ERRARG;
return -1;
}
++ssh_opts.authkey_count;
ssh_opts.authkeys = realloc(ssh_opts.authkeys, ssh_opts.authkey_count * sizeof *ssh_opts.authkeys);
ssh_opts.authkeys[ssh_opts.authkey_count - 1].path = strdup(keypath);
ssh_opts.authkeys[ssh_opts.authkey_count - 1].username = strdup(username);
return 0;
}
API int
nc_ssh_server_del_authkey(const char *keypath, const char *username)
{
uint32_t i;
int ret = -1;
for (i = 0; i < ssh_opts.authkey_count; ++i) {
if ((!keypath || !strcmp(ssh_opts.authkeys[i].path, keypath))
&& (!username || !strcmp(ssh_opts.authkeys[i].username, username))) {
free(ssh_opts.authkeys[i].path);
free(ssh_opts.authkeys[i].username);
--ssh_opts.authkey_count;
memmove(&ssh_opts.authkeys[i], &ssh_opts.authkeys[i + 1], (ssh_opts.authkey_count - i) * sizeof *ssh_opts.authkeys);
ret = 0;
}
}
return ret;
}
API void
nc_ssh_server_free_opts(void)
{
int i;
if (ssh_opts.sshbind) {
ssh_bind_free(ssh_opts.sshbind);
}
if (ssh_opts.authkeys) {
for (i = 0; i < ssh_opts.authkey_count; ++i) {
free(ssh_opts.authkeys[i].path);
free(ssh_opts.authkeys[i].username);
}
free(ssh_opts.authkeys);
}
}
static char *
auth_password_get_pwd_hash(const char *username)
{
struct passwd *pwd, pwd_buf;
struct spwd *spwd, spwd_buf;
char *pass_hash = NULL, buf[256];
getpwnam_r(username, &pwd_buf, buf, 256, &pwd);
if (!pwd) {
VRB("User '%s' not found locally.", username);
return NULL;
}
if (!strcmp(pwd->pw_passwd, "x")) {
getspnam_r(username, &spwd_buf, buf, 256, &spwd);
if (!spwd) {
VRB("Failed to retrieve the shadow entry for \"%s\".", username);
return NULL;
}
pass_hash = spwd->sp_pwdp;
} else {
pass_hash = pwd->pw_passwd;
}
if (!pass_hash) {
ERR("%s: no password could be retrieved for \"%s\".", __func__, username);
return NULL;
}
/* check the hash structure for special meaning */
if (!strcmp(pass_hash, "*") || !strcmp(pass_hash, "!")) {
VRB("User \"%s\" is not allowed to authenticate using a password.", username);
return NULL;
}
if (!strcmp(pass_hash, "*NP*")) {
VRB("Retrieving password for \"%s\" from a NIS+ server not supported.", username);
return NULL;
}
return strdup(pass_hash);
}
static int
auth_password_compare_pwd(const char *pass_hash, const char *pass_clear)
{
char *new_pass_hash;
struct crypt_data cdata;
if (!pass_hash[0]) {
if (!pass_clear[0]) {
WRN("User authentication successful with an empty password!");
return 0;
} else {
/* the user did now know he does not need any password,
* (which should not be used) so deny authentication */
return 1;
}
}
cdata.initialized = 0;
new_pass_hash = crypt_r(pass_clear, pass_hash, &cdata);
return strcmp(new_pass_hash, pass_hash);
}
static void
nc_sshcb_auth_password(struct nc_session *session, ssh_message msg)
{
char *pass_hash;
pass_hash = auth_password_get_pwd_hash(session->username);
if (pass_hash && !auth_password_compare_pwd(pass_hash, ssh_message_auth_password(msg))) {
VRB("User '%s' authenticated.", session->username);
ssh_message_auth_reply_success(msg, 0);
session->flags |= NC_SESSION_SSH_AUTHENTICATED;
free(pass_hash);
return;
}
free(pass_hash);
++session->ssh_auth_attempts;
VRB("Failed user '%s' authentication attempt (#%d).", session->username, session->ssh_auth_attempts);
ssh_message_reply_default(msg);
}
static void
nc_sshcb_auth_kbdint(struct nc_session *session, ssh_message msg)
{
char *pass_hash;
if (!ssh_message_auth_kbdint_is_response(msg)) {
const char *prompts[] = {"Password: "};
char echo[] = {0};
ssh_message_auth_interactive_request(msg, "Interactive SSH Authentication", "Type your password:", 1, prompts, echo);
} else {
if (ssh_userauth_kbdint_getnanswers(session->ti.libssh.session) != 1) {
ssh_message_reply_default(msg);
return;
}
pass_hash = auth_password_get_pwd_hash(session->username);
if (!pass_hash) {
ssh_message_reply_default(msg);
return;
}
if (!auth_password_compare_pwd(pass_hash, ssh_userauth_kbdint_getanswer(session->ti.libssh.session, 0))) {
VRB("User \"%s\" authenticated.", session->username);
session->flags |= NC_SESSION_SSH_AUTHENTICATED;
ssh_message_auth_reply_success(msg, 0);
} else {
++session->ssh_auth_attempts;
VRB("Failed user \"%s\" authentication attempt (#%d).", session->username, session->ssh_auth_attempts);
ssh_message_reply_default(msg);
}
}
}
static const char *
auth_pubkey_compare_key(ssh_key key)
{
uint32_t i;
ssh_key pub_key;
char *username = NULL;
for (i = 0; i < ssh_opts.authkey_count; ++i) {
if (ssh_pki_import_pubkey_file(ssh_opts.authkeys[i].path, &pub_key) != SSH_OK) {
if (eaccess(ssh_opts.authkeys[i].path, R_OK)) {
VRB("%s: failed to import the public key \"%s\" (%s)", __func__, ssh_opts.authkeys[i].path, strerror(errno));
} else {
VRB("%s: failed to import the public key \"%s\" (%s)", __func__, ssh_opts.authkeys[i].path, ssh_get_error(pub_key));
}
continue;
}
if (!ssh_key_cmp(key, pub_key, SSH_KEY_CMP_PUBLIC)) {
ssh_key_free(pub_key);
break;
}
ssh_key_free(pub_key);
}
if (i < ssh_opts.authkey_count) {
username = ssh_opts.authkeys[i].username;
}
return username;
}
static void
nc_sshcb_auth_pubkey(struct nc_session *session, ssh_message msg)
{
const char *username;
int signature_state;
signature_state = ssh_message_auth_publickey_state(msg);
if (signature_state == SSH_PUBLICKEY_STATE_VALID) {
VRB("User \"%s\" authenticated.", session->username);
session->flags |= NC_SESSION_SSH_AUTHENTICATED;
ssh_message_auth_reply_success(msg, 0);
return;
} else if (signature_state == SSH_PUBLICKEY_STATE_NONE) {
if ((username = auth_pubkey_compare_key(ssh_message_auth_pubkey(msg))) == NULL) {
VRB("User \"%s\" tried to use an unknown (unauthorized) public key.", session->username);
} else if (strcmp(session->username, username)) {
VRB("User \"%s\" is not the username identified with the presented public key.", session->username);
} else {
/* accepting only the use of a public key */
ssh_message_auth_reply_pk_ok_simple(msg);
return;
}
}
++session->ssh_auth_attempts;
VRB("Failed user \"%s\" authentication attempt (#%d).", session->username, session->ssh_auth_attempts);
ssh_message_reply_default(msg);
}
static int
nc_sshcb_channel_open(struct nc_session *session, ssh_channel channel)
{
while (session->ti.libssh.next) {
if (session->status == NC_STATUS_STARTING) {
ERRINT;
return -1;
}
session = session->ti.libssh.next;
}
if ((session->status != NC_STATUS_STARTING) || session->ti.libssh.channel) {
ERRINT;
return -1;
}
session->ti.libssh.channel = channel;
return 0;
}
static int
nc_sshcb_channel_subsystem(struct nc_session *session, ssh_channel channel, const char *subsystem)
{
while (session && (session->ti.libssh.channel != channel)) {
session = session->ti.libssh.next;
}
if (!session) {
ERRINT;
return -1;
}
if (!strcmp(subsystem, "netconf")) {
if (session->flags & NC_SESSION_SSH_SUBSYS_NETCONF) {
WRN("Client \"%s\" requested subsystem 'netconf' for the second time.", session->username);
} else {
session->flags |= NC_SESSION_SSH_SUBSYS_NETCONF;
}
} else {
WRN("Client \"%s\" requested an unknown subsystem '%s'.", session->username, subsystem);
return -1;
}
return 0;
}
static int
nc_sshcb_msg(ssh_session sshsession, ssh_message msg, void *data)
{
const char *str_type, *str_subtype = NULL, *username;
int subtype, type;
struct nc_session *session = (struct nc_session *)data;
(void)sshsession;
type = ssh_message_type(msg);
subtype = ssh_message_subtype(msg);
switch (type) {
case SSH_REQUEST_AUTH:
str_type = "request-auth";
switch (subtype) {
case SSH_AUTH_METHOD_NONE:
str_subtype = "none";
break;
case SSH_AUTH_METHOD_PASSWORD:
str_subtype = "password";
break;
case SSH_AUTH_METHOD_PUBLICKEY:
str_subtype = "publickey";
break;
case SSH_AUTH_METHOD_HOSTBASED:
str_subtype = "hostbased";
break;
case SSH_AUTH_METHOD_INTERACTIVE:
str_subtype = "interactive";
break;
case SSH_AUTH_METHOD_GSSAPI_MIC:
str_subtype = "gssapi-mic";
break;
}
break;
case SSH_REQUEST_CHANNEL_OPEN:
str_type = "request-channel-open";
switch (subtype) {
case SSH_CHANNEL_SESSION:
str_subtype = "session";
break;
case SSH_CHANNEL_DIRECT_TCPIP:
str_subtype = "direct-tcpip";
break;
case SSH_CHANNEL_FORWARDED_TCPIP:
str_subtype = "forwarded-tcpip";
break;
case (int)SSH_CHANNEL_X11:
str_subtype = "channel-x11";
break;
case SSH_CHANNEL_UNKNOWN:
/* fallthrough */
default:
str_subtype = "unknown";
break;
}
break;
case SSH_REQUEST_CHANNEL:
str_type = "request-channel";
switch (subtype) {
case SSH_CHANNEL_REQUEST_PTY:
str_subtype = "pty";
break;
case SSH_CHANNEL_REQUEST_EXEC:
str_subtype = "exec";
break;
case SSH_CHANNEL_REQUEST_SHELL:
str_subtype = "shell";
break;
case SSH_CHANNEL_REQUEST_ENV:
str_subtype = "env";
break;
case SSH_CHANNEL_REQUEST_SUBSYSTEM:
str_subtype = "subsystem";
break;
case SSH_CHANNEL_REQUEST_WINDOW_CHANGE:
str_subtype = "window-change";
break;
case SSH_CHANNEL_REQUEST_X11:
str_subtype = "x11";
break;
case SSH_CHANNEL_REQUEST_UNKNOWN:
/* fallthrough */
default:
str_subtype = "unknown";
break;
}
break;
case SSH_REQUEST_SERVICE:
str_type = "request-service";
str_subtype = ssh_message_service_service(msg);
break;
case SSH_REQUEST_GLOBAL:
str_type = "request-global";
switch (subtype) {
case SSH_GLOBAL_REQUEST_TCPIP_FORWARD:
str_subtype = "tcpip-forward";
break;
case SSH_GLOBAL_REQUEST_CANCEL_TCPIP_FORWARD:
str_subtype = "cancel-tcpip-forward";
break;
case SSH_GLOBAL_REQUEST_UNKNOWN:
/* fallthrough */
default:
str_subtype = "unknown";
break;
}
break;
default:
str_type = "unknown";
str_subtype = "unknown";
break;
}
VRB("Received an SSH message \"%s\" of subtype \"%s\".", str_type, str_subtype);
/*
* process known messages
*/
if (type == SSH_REQUEST_AUTH) {
if (session->flags & NC_SESSION_SSH_AUTHENTICATED) {
ERR("User \"%s\" authenticated, but requested another authentication.", session->username);
ssh_message_reply_default(msg);
return 0;
}
if (session->ssh_auth_attempts >= ssh_opts.auth_attempts) {
/* too many failed attempts */
ssh_message_reply_default(msg);
return 0;
}
/* save the username, do not let the client change it */
username = ssh_message_auth_user(msg);
if (!session->username) {
if (!username) {
ERR("Denying an auth request without a username.");
return 1;
}
session->username = lydict_insert(server_opts.ctx, username, 0);
} else if (username) {
if (strcmp(username, session->username)) {
ERR("User \"%s\" changed its username to \"%s\".", session->username, username);
session->status = NC_STATUS_INVALID;
session->term_reason = NC_SESSION_TERM_OTHER;
return 1;
}
}
if (subtype == SSH_AUTH_METHOD_NONE) {
/* libssh will return the supported auth methods */
return 1;
} else if (subtype == SSH_AUTH_METHOD_PASSWORD) {
nc_sshcb_auth_password(session, msg);
return 0;
} else if (subtype == SSH_AUTH_METHOD_PUBLICKEY) {
nc_sshcb_auth_pubkey(session, msg);
return 0;
} else if (subtype == SSH_AUTH_METHOD_INTERACTIVE) {
nc_sshcb_auth_kbdint(session, msg);
return 0;
}
} else if (session->flags & NC_SESSION_SSH_AUTHENTICATED) {
if ((type == SSH_REQUEST_CHANNEL_OPEN) && (subtype == (int)SSH_CHANNEL_SESSION)) {
ssh_channel chan;
if ((chan = ssh_message_channel_request_open_reply_accept(msg)) == NULL) {
ssh_message_reply_default(msg);
return 0;
}
nc_sshcb_channel_open(session, chan);
return 0;
} else if ((type == SSH_REQUEST_CHANNEL) && (subtype == (int)SSH_CHANNEL_REQUEST_SUBSYSTEM)) {
if (!nc_sshcb_channel_subsystem(session, ssh_message_channel_request_channel(msg),
ssh_message_channel_request_subsystem(msg))) {
ssh_message_channel_request_reply_success(msg);
} else {
ssh_message_reply_default(msg);
}
return 0;
}
}
/* we did not process it */
return 1;
}
static int
nc_open_netconf_channel(struct nc_session *session, int timeout)
{
int elapsed = 0;
/* message callback is executed twice to give chance for the channel to be
* created if timeout == 0 (it takes 2 messages, channel-open, subsystem-request) */
do {
if (!nc_session_is_connected(session)) {
ERR("%s: communication channel unexpectedly closed (libssh).", __func__);
return -1;
}
if (ssh_execute_message_callbacks(session->ti.libssh.session) != SSH_OK) {
ERR("%s: failed to receive new messages on the SSH session (%s)",
__func__, ssh_get_error(session->ti.libssh.session));
return -1;
}
if (session->ti.libssh.channel && (session->flags & NC_SESSION_SSH_SUBSYS_NETCONF)) {
return 0;
}
usleep(NC_TIMEOUT_STEP);
elapsed += NC_TIMEOUT_STEP;
if ((timeout > NC_TIMEOUT_STEP) && (elapsed >= timeout)) {
break;
}
if (ssh_execute_message_callbacks(session->ti.libssh.session) != SSH_OK) {
ERR("%s: failed to receive new messages on the SSH session (%s)",
__func__, ssh_get_error(session->ti.libssh.session));
return -1;
}
if (session->ti.libssh.channel && (session->flags & NC_SESSION_SSH_SUBSYS_NETCONF)) {
return 0;
}
usleep(NC_TIMEOUT_STEP);
elapsed += NC_TIMEOUT_STEP;
} while ((timeout == -1) || (timeout && (elapsed < timeout)));
return 1;
}
int
nc_accept_ssh_session(struct nc_session *session, int sock, int timeout)
{
int libssh_auth_methods = 0, elapsed = 0;
/* other transport-specific data */
session->ti_type = NC_TI_LIBSSH;
session->ti.libssh.session = ssh_new();
if (!session->ti.libssh.session) {
ERR("%s: failed to initialize an SSH session.", __func__);
close(sock);
return -1;
}
if (ssh_opts.auth_methods & NC_SSH_AUTH_PUBLICKEY) {
libssh_auth_methods |= SSH_AUTH_METHOD_PUBLICKEY;
}
if (ssh_opts.auth_methods & NC_SSH_AUTH_PASSWORD) {
libssh_auth_methods |= SSH_AUTH_METHOD_PASSWORD;
}
if (ssh_opts.auth_methods & NC_SSH_AUTH_INTERACTIVE) {
libssh_auth_methods |= SSH_AUTH_METHOD_INTERACTIVE;
}
ssh_set_auth_methods(session->ti.libssh.session, libssh_auth_methods);
ssh_set_message_callback(session->ti.libssh.session, nc_sshcb_msg, session);
if (ssh_bind_accept_fd(ssh_opts.sshbind, session->ti.libssh.session, sock) == SSH_ERROR) {
ERR("%s: SSH failed to accept a new connection (%s).", __func__, ssh_get_error(ssh_opts.sshbind));
close(sock);
return -1;
}
if (ssh_handle_key_exchange(session->ti.libssh.session) != SSH_OK) {
ERR("%s: SSH key exchange error (%s).", __func__, ssh_get_error(session->ti.libssh.session));
return -1;
}
/* authenticate */
do {
if (!nc_session_is_connected(session)) {
ERR("%s: communication channel unexpectedly closed (libssh).", __func__);
return -1;
}
if (ssh_execute_message_callbacks(session->ti.libssh.session) != SSH_OK) {
ERR("%s: failed to receive new messages on the SSH session (%s).",
__func__, ssh_get_error(session->ti.libssh.session));
return -1;
}
if (session->flags & NC_SESSION_SSH_AUTHENTICATED) {
break;
}
usleep(NC_TIMEOUT_STEP);
elapsed += NC_TIMEOUT_STEP;
} while ((timeout == -1) || (timeout && (elapsed < timeout)));
if (!(session->flags & NC_SESSION_SSH_AUTHENTICATED)) {
/* timeout */
return -1;
}
if (timeout > 0) {
timeout -= elapsed;
}
/* open channel */
if (nc_open_netconf_channel(session, timeout)) {
return -1;
}
return 0;
}
API struct nc_session *
nc_accept_ssh_channel(struct nc_session *session, int timeout)
{
struct nc_session *new_session;
int ret;
new_session = calloc(1, sizeof *new_session);
new_session->ti.libssh.session = session->ti.libssh.session;
ret = nc_open_netconf_channel(new_session, timeout);
if (ret) {
goto fail;
}
/* new channel was requested and opened, fill in the whole session now */
for (; session->ti.libssh.next; session = session->ti.libssh.next);
session->ti.libssh.next = new_session;
new_session->status = NC_STATUS_STARTING;
new_session->side = NC_SERVER;
new_session->ti_type = NC_TI_LIBSSH;
new_session->ti_lock = session->ti_lock;
new_session->flags = NC_SESSION_SSH_AUTHENTICATED | NC_SESSION_SHAREDCTX;
new_session->ctx = server_opts.ctx;
new_session->username = lydict_insert(server_opts.ctx, session->username, 0);
new_session->host = lydict_insert(server_opts.ctx, session->host, 0);
new_session->port = session->port;
/* NETCONF handshake */
if (nc_handshake(new_session)) {
goto fail;
}
new_session->status = NC_STATUS_RUNNING;
return new_session;
fail:
nc_session_free(new_session);
return NULL;
}