sshconnect.c

OpenSSL Source code for SFTP, SSH, and many others

		if (options.protocol & SSH_PROTO_2) {
			enable_compat20();
			break;
		}
		/* FALLTHROUGH */
	default:
		mismatch = 1;
		break;
	}
	if (mismatch)
		fatal("Protocol major versions differ: %d vs. %d",
		    (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
		    remote_major);
	/* Send our own protocol version identification. */
	snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
	    compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
	    compat20 ? PROTOCOL_MINOR_2 : minor1,
	    SSH_VERSION);
	if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
		fatal("write: %.100s", strerror(errno));
	client_version_string = xstrdup(buf);
	chop(client_version_string);
	chop(server_version_string);
	debug("Local version string %.100s", client_version_string);
}

/* defaults to 'no' */
static int
confirm(const char *prompt)
{
	const char *msg, *again = "Please type 'yes' or 'no': ";
	char *p;
	int ret = -1;

	if (options.batch_mode)
		return 0;
	for (msg = prompt;;msg = again) {
		p = read_passphrase(msg, RP_ECHO);
		if (p == NULL ||
		    (p[0] == '\0') || (p[0] == '\n') ||
		    strncasecmp(p, "no", 2) == 0)
			ret = 0;
		if (strncasecmp(p, "yes", 3) == 0)
			ret = 1;
		if (p)
			xfree(p);
		if (ret != -1)
			return ret;
	}
}

/*
 * check whether the supplied host key is valid, return -1 if the key
 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
 */

static int
check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
    int readonly, const char *user_hostfile, const char *system_hostfile)
{
	Key *file_key;
	char *type = key_type(host_key);
	char *ip = NULL;
	char hostline[1000], *hostp, *fp;
	HostStatus host_status;
	HostStatus ip_status;
	int local = 0, host_ip_differ = 0;
	int salen;
	char ntop[NI_MAXHOST];
	char msg[1024];
	int len, host_line, ip_line;
	const char *host_file = NULL, *ip_file = NULL;

	/*
	 * Force accepting of the host key for loopback/localhost. The
	 * problem is that if the home directory is NFS-mounted to multiple
	 * machines, localhost will refer to a different machine in each of
	 * them, and the user will get bogus HOST_CHANGED warnings.  This
	 * essentially disables host authentication for localhost; however,
	 * this is probably not a real problem.
	 */
	/**  hostaddr == 0! */
	switch (hostaddr->sa_family) {
	case AF_INET:
		local = (ntohl(((struct sockaddr_in *)hostaddr)->
		   sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
		salen = sizeof(struct sockaddr_in);
		break;
	case AF_INET6:
		local = IN6_IS_ADDR_LOOPBACK(
		    &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
		salen = sizeof(struct sockaddr_in6);
		break;
	default:
		local = 0;
		salen = sizeof(struct sockaddr_storage);
		break;
	}
	if (options.no_host_authentication_for_localhost == 1 && local &&
	    options.host_key_alias == NULL) {
		debug("Forcing accepting of host key for "
		    "loopback/localhost.");
		return 0;
	}

	/*
	 * We don't have the remote ip-address for connections
	 * using a proxy command
	 */
	if (options.proxy_command == NULL) {
		if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
		    NULL, 0, NI_NUMERICHOST) != 0)
			fatal("check_host_key: getnameinfo failed");
		ip = xstrdup(ntop);
	} else {
		ip = xstrdup("<no hostip for proxy command>");
	}
	/*
	 * Turn off check_host_ip if the connection is to localhost, via proxy
	 * command or if we don't have a hostname to compare with
	 */
	if (options.check_host_ip &&
	    (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
		options.check_host_ip = 0;

	/*
	 * Allow the user to record the key under a different name. This is
	 * useful for ssh tunneling over forwarded connections or if you run
	 * multiple sshd's on different ports on the same machine.
	 */
	if (options.host_key_alias != NULL) {
		host = options.host_key_alias;
		debug("using hostkeyalias: %s", host);
	}

	/*
	 * Store the host key from the known host file in here so that we can
	 * compare it with the key for the IP address.
	 */
	file_key = key_new(host_key->type);

	/*
	 * Check if the host key is present in the user\'s list of known
	 * hosts or in the systemwide list.
	 */
	host_file = user_hostfile;
	host_status = check_host_in_hostfile(host_file, host, host_key,
	    file_key, &host_line);
	if (host_status == HOST_NEW) {
		host_file = system_hostfile;
		host_status = check_host_in_hostfile(host_file, host, host_key,
		    file_key, &host_line);
	}
	/*
	 * Also perform check for the ip address, skip the check if we are
	 * localhost or the hostname was an ip address to begin with
	 */
	if (options.check_host_ip) {
		Key *ip_key = key_new(host_key->type);

		ip_file = user_hostfile;
		ip_status = check_host_in_hostfile(ip_file, ip, host_key,
		    ip_key, &ip_line);
		if (ip_status == HOST_NEW) {
			ip_file = system_hostfile;
			ip_status = check_host_in_hostfile(ip_file, ip,
			    host_key, ip_key, &ip_line);
		}
		if (host_status == HOST_CHANGED &&
		    (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
			host_ip_differ = 1;

		key_free(ip_key);
	} else
		ip_status = host_status;

	key_free(file_key);

	switch (host_status) {
	case HOST_OK:
		/* The host is known and the key matches. */
		debug("Host '%.200s' is known and matches the %s host key.",
		    host, type);
		debug("Found key in %s:%d", host_file, host_line);
		if (options.check_host_ip && ip_status == HOST_NEW) {
			if (readonly)
				log("%s host key for IP address "
				    "'%.128s' not in list of known hosts.",
				    type, ip);
			else if (!add_host_to_hostfile(user_hostfile, ip,
			    host_key))
				log("Failed to add the %s host key for IP "
				    "address '%.128s' to the list of known "
				    "hosts (%.30s).", type, ip, user_hostfile);
			else
				log("Warning: Permanently added the %s host "
				    "key for IP address '%.128s' to the list "
				    "of known hosts.", type, ip);
		}
		break;
	case HOST_NEW:
		if (readonly)
			goto fail;
		/* The host is new. */
		if (options.strict_host_key_checking == 1) {
			/*
			 * User has requested strict host key checking.  We
			 * will not add the host key automatically.  The only
			 * alternative left is to abort.
			 */
			error("No %s host key is known for %.200s and you "
			    "have requested strict checking.", type, host);
			goto fail;
		} else if (options.strict_host_key_checking == 2) {
			/* The default */
			fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
			snprintf(msg, sizeof(msg),
			    "The authenticity of host '%.200s (%s)' can't be "
			    "established.\n"
			    "%s key fingerprint is %s.\n"
			    "Are you sure you want to continue connecting "
			    "(yes/no)? ", host, ip, type, fp);
			xfree(fp);
			if (!confirm(msg))
				goto fail;
		}
		if (options.check_host_ip && ip_status == HOST_NEW) {
			snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
			hostp = hostline;
		} else
			hostp = host;

		/*
		 * If not in strict mode, add the key automatically to the
		 * local known_hosts file.
		 */
		if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
			log("Failed to add the host to the list of known "
			    "hosts (%.500s).", user_hostfile);
		else
			log("Warning: Permanently added '%.200s' (%s) to the "
			    "list of known hosts.", hostp, type);
		break;
	case HOST_CHANGED:
		if (options.check_host_ip && host_ip_differ) {
			char *msg;
			if (ip_status == HOST_NEW)
				msg = "is unknown";
			else if (ip_status == HOST_OK)
				msg = "is unchanged";
			else
				msg = "has a different value";
			error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
			error("@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @");
			error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
			error("The %s host key for %s has changed,", type, host);
			error("and the key for the according IP address %s", ip);
			error("%s. This could either mean that", msg);
			error("DNS SPOOFING is happening or the IP address for the host");
			error("and its host key have changed at the same time.");
			if (ip_status != HOST_NEW)
				error("Offending key for IP in %s:%d", ip_file, ip_line);
		}
		/* The host key has changed. */
		fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
		error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
		error("@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @");
		error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
		error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
		error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
		error("It is also possible that the %s host key has just been changed.", type);
		error("The fingerprint for the %s key sent by the remote host is\n%s.",
		    type, fp);
		error("Please contact your system administrator.");
		error("Add correct host key in %.100s to get rid of this message.",
		    user_hostfile);
		error("Offending key in %s:%d", host_file, host_line);
		xfree(fp);

		/*
		 * If strict host key checking is in use, the user will have
		 * to edit the key manually and we can only abort.
		 */
		if (options.strict_host_key_checking) {
			error("%s host key for %.200s has changed and you have "
			    "requested strict checking.", type, host);
			goto fail;
		}

		/*
		 * If strict host key checking has not been requested, allow
		 * the connection but without password authentication or
		 * agent forwarding.
		 */
		if (options.password_authentication) {
			error("Password authentication is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.password_authentication = 0;
		}
		if (options.forward_agent) {
			error("Agent forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.forward_agent = 0;
		}
		if (options.forward_x11) {
			error("X11 forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.forward_x11 = 0;
		}
		if (options.num_local_forwards > 0 ||
		    options.num_remote_forwards > 0) {
			error("Port forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.num_local_forwards =
			    options.num_remote_forwards = 0;
		}
		/*
		 * XXX Should permit the user to change to use the new id.
		 * This could be done by converting the host key to an
		 * identifying sentence, tell that the host identifies itself
		 * by that sentence, and ask the user if he/she whishes to
		 * accept the authentication.
		 */
		break;
	}

	if (options.check_host_ip && host_status != HOST_CHANGED &&
	    ip_status == HOST_CHANGED) {
		snprintf(msg, sizeof(msg),
		    "Warning: the %s host key for '%.200s' "
		    "differs from the key for the IP address '%.128s'"
		    "\nOffending key for IP in %s:%d",
		    type, host, ip, ip_file, ip_line);
		if (host_status == HOST_OK) {
			len = strlen(msg);
			snprintf(msg + len, sizeof(msg) - len,
			    "\nMatching host key in %s:%d",
			    host_file, host_line);
		}
		if (options.strict_host_key_checking == 1) {
			log(msg);
			error("Exiting, you have requested strict checking.");
			goto fail;
		} else if (options.strict_host_key_checking == 2) {
			strlcat(msg, "\nAre you sure you want "
			    "to continue connecting (yes/no)? ", sizeof(msg));
			if (!confirm(msg))
				goto fail;
		} else {
			log(msg);
		}
	}

	xfree(ip);
	return 0;

fail:
	xfree(ip);
	return -1;
}

int
verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
{
	struct stat st;

	/* return ok if the key can be found in an old keyfile */
	if (stat(options.system_hostfile2, &st) == 0 ||
	    stat(options.user_hostfile2, &st) == 0) {
		if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
		    options.user_hostfile2, options.system_hostfile2) == 0)
			return 0;
	}
	return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
	    options.user_hostfile, options.system_hostfile);
}

/*
 * Starts a dialog with the server, and authenticates the current user on the
 * server.  This does not need any extra privileges.  The basic connection
 * to the server must already have been established before this is called.
 * If login fails, this function prints an error and never returns.
 * This function does not require super-user privileges.
 */
void
ssh_login(Sensitive *sensitive, const char *orighost,
    struct sockaddr *hostaddr, struct passwd *pw)
{
	char *host, *cp;
	char *server_user, *local_user;

	local_user = xstrdup(pw->pw_name);
	server_user = options.user ? options.user : local_user;

	/* Convert the user-supplied hostname into all lowercase. */
	host = xstrdup(orighost);
	for (cp = host; *cp; cp++)
		if (isupper(*cp))
			*cp = tolower(*cp);

	/* Exchange protocol version identification strings with the server. */
	ssh_exchange_identification();

	/* Put the connection into non-blocking mode. */
	packet_set_nonblocking();

	/* key exchange */
	/* authenticate user */
	if (compat20) {
		ssh_kex2(host, hostaddr);
		ssh_userauth2(local_user, server_user, host, sensitive);
	} else {
		ssh_kex(host, hostaddr);
		ssh_userauth1(local_user, server_user, host, sensitive);
	}
}

void
ssh_put_password(char *password)
{
	int size;
	char *padded;

	if (datafellows & SSH_BUG_PASSWORDPAD) {
		packet_put_cstring(password);
		return;
	}
	size = roundup(strlen(password) + 1, 32);
	padded = xmalloc(size);
	memset(padded, 0, size);
	strlcpy(padded, password, size);
	packet_put_string(padded, size);
	memset(padded, 0, size);
	xfree(padded);
}