sshconnect.c

OpenSSH 是 SSH （Secure SHell） 协议的免费开源实现。它用安全、加密的网络连接工具代替了 telnet、ftp、 rlogin、rsh 和 rcp 工具。OpenSSH 支持

/*
 * Author: Tatu Ylonen <[e-mail]>
 * Copyright (c) 1995 Tatu Ylonen <[e-mail]>, Espoo, Finland
 *                    All rights reserved
 * Code to connect to a remote host, and to perform the client side of the
 * login (authentication) dialog.
 *
 * 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"
RCSID("$OpenBSD: sshconnect.c,v 1.161 2005/03/02 01:00:06 djm Exp $");

#include <openssl/bn.h>

#include "ssh.h"
#include "xmalloc.h"
#include "rsa.h"
#include "buffer.h"
#include "packet.h"
#include "uidswap.h"
#include "compat.h"
#include "key.h"
#include "sshconnect.h"
#include "hostfile.h"
#include "log.h"
#include "readconf.h"
#include "atomicio.h"
#include "misc.h"

#include "dns.h"

char *client_version_string = NULL;
char *server_version_string = NULL;

int matching_host_key_dns = 0;

/* import */
extern Options options;
extern char *__progname;
extern uid_t original_real_uid;
extern uid_t original_effective_uid;
extern pid_t proxy_command_pid;

#ifndef INET6_ADDRSTRLEN		/* for non IPv6 machines */
#define INET6_ADDRSTRLEN 46
#endif

static int show_other_keys(const char *, Key *);
static void warn_changed_key(Key *);

/*
 * Connect to the given ssh server using a proxy command.
 */
static int
ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
{
	Buffer command;
	const char *cp;
	char *command_string;
	int pin[2], pout[2];
	pid_t pid;
	char strport[NI_MAXSERV];

	/* Convert the port number into a string. */
	snprintf(strport, sizeof strport, "%hu", port);

	/*
	 * Build the final command string in the buffer by making the
	 * appropriate substitutions to the given proxy command.
	 *
	 * Use "exec" to avoid "sh -c" processes on some platforms
	 * (e.g. Solaris)
	 */
	buffer_init(&command);
	buffer_append(&command, "exec ", 5);

	for (cp = proxy_command; *cp; cp++) {
		if (cp[0] == '%' && cp[1] == '%') {
			buffer_append(&command, "%", 1);
			cp++;
			continue;
		}
		if (cp[0] == '%' && cp[1] == 'h') {
			buffer_append(&command, host, strlen(host));
			cp++;
			continue;
		}
		if (cp[0] == '%' && cp[1] == 'p') {
			buffer_append(&command, strport, strlen(strport));
			cp++;
			continue;
		}
		buffer_append(&command, cp, 1);
	}
	buffer_append(&command, "\0", 1);

	/* Get the final command string. */
	command_string = buffer_ptr(&command);

	/* Create pipes for communicating with the proxy. */
	if (pipe(pin) < 0 || pipe(pout) < 0)
		fatal("Could not create pipes to communicate with the proxy: %.100s",
		    strerror(errno));

	debug("Executing proxy command: %.500s", command_string);

	/* Fork and execute the proxy command. */
	if ((pid = fork()) == 0) {
		char *argv[10];

		/* Child.  Permanently give up superuser privileges. */
		seteuid(original_real_uid);
		setuid(original_real_uid);

		/* Redirect stdin and stdout. */
		close(pin[1]);
		if (pin[0] != 0) {
			if (dup2(pin[0], 0) < 0)
				perror("dup2 stdin");
			close(pin[0]);
		}
		close(pout[0]);
		if (dup2(pout[1], 1) < 0)
			perror("dup2 stdout");
		/* Cannot be 1 because pin allocated two descriptors. */
		close(pout[1]);

		/* Stderr is left as it is so that error messages get
		   printed on the user's terminal. */
		argv[0] = _PATH_BSHELL;
		argv[1] = "-c";
		argv[2] = command_string;
		argv[3] = NULL;

		/* Execute the proxy command.  Note that we gave up any
		   extra privileges above. */
		execv(argv[0], argv);
		perror(argv[0]);
		exit(1);
	}
	/* Parent. */
	if (pid < 0)
		fatal("fork failed: %.100s", strerror(errno));
	else
		proxy_command_pid = pid; /* save pid to clean up later */

	/* Close child side of the descriptors. */
	close(pin[0]);
	close(pout[1]);

	/* Free the command name. */
	buffer_free(&command);

	/* Set the connection file descriptors. */
	packet_set_connection(pout[0], pin[1]);

	/* Indicate OK return */
	return 0;
}

/*
 * Creates a (possibly privileged) socket for use as the ssh connection.
 */
static int
ssh_create_socket(int privileged, struct addrinfo *ai)
{
	int sock, gaierr;
	struct addrinfo hints, *res;

	/*
	 * If we are running as root and want to connect to a privileged
	 * port, bind our own socket to a privileged port.
	 */
	if (privileged) {
		int p = IPPORT_RESERVED - 1;
		PRIV_START;
		sock = rresvport_af(&p, ai->ai_family);
		PRIV_END;
		if (sock < 0)
			error("rresvport: af=%d %.100s", ai->ai_family,
			    strerror(errno));
		else
			debug("Allocated local port %d.", p);
		return sock;
	}
	sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
	if (sock < 0)
		error("socket: %.100s", strerror(errno));

	/* Bind the socket to an alternative local IP address */
	if (options.bind_address == NULL)
		return sock;

	memset(&hints, 0, sizeof(hints));
	hints.ai_family = ai->ai_family;
	hints.ai_socktype = ai->ai_socktype;
	hints.ai_protocol = ai->ai_protocol;
	hints.ai_flags = AI_PASSIVE;
	gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
	if (gaierr) {
		error("getaddrinfo: %s: %s", options.bind_address,
		    gai_strerror(gaierr));
		close(sock);
		return -1;
	}
	if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
		error("bind: %s: %s", options.bind_address, strerror(errno));
		close(sock);
		freeaddrinfo(res);
		return -1;
	}
	freeaddrinfo(res);
	return sock;
}

static int
timeout_connect(int sockfd, const struct sockaddr *serv_addr,
    socklen_t addrlen, int timeout)
{
	fd_set *fdset;
	struct timeval tv;
	socklen_t optlen;
	int fdsetsz, optval, rc, result = -1;

	if (timeout <= 0)
		return (connect(sockfd, serv_addr, addrlen));

	set_nonblock(sockfd);
	rc = connect(sockfd, serv_addr, addrlen);
	if (rc == 0) {
		unset_nonblock(sockfd);
		return (0);
	}
	if (errno != EINPROGRESS)
		return (-1);

	fdsetsz = howmany(sockfd + 1, NFDBITS) * sizeof(fd_mask);
	fdset = (fd_set *)xmalloc(fdsetsz);

	memset(fdset, 0, fdsetsz);
	FD_SET(sockfd, fdset);
	tv.tv_sec = timeout;
	tv.tv_usec = 0;

	for(;;) {
		rc = select(sockfd + 1, NULL, fdset, NULL, &tv);
		if (rc != -1 || errno != EINTR)
			break;
	}

	switch(rc) {
	case 0:
		/* Timed out */
		errno = ETIMEDOUT;
		break;
	case -1:
		/* Select error */
		debug("select: %s", strerror(errno));
		break;
	case 1:
		/* Completed or failed */
		optval = 0;
		optlen = sizeof(optval);
		if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval,
		    &optlen) == -1) {
			debug("getsockopt: %s", strerror(errno));
			break;
		}
		if (optval != 0) {
			errno = optval;
			break;
		}
		result = 0;
		unset_nonblock(sockfd);
		break;
	default:
		/* Should not occur */
		fatal("Bogus return (%d) from select()", rc);
	}

	xfree(fdset);
	return (result);
}

/*
 * Opens a TCP/IP connection to the remote server on the given host.
 * The address of the remote host will be returned in hostaddr.
 * If port is 0, the default port will be used.  If needpriv is true,
 * a privileged port will be allocated to make the connection.
 * This requires super-user privileges if needpriv is true.
 * Connection_attempts specifies the maximum number of tries (one per
 * second).  If proxy_command is non-NULL, it specifies the command (with %h
 * and %p substituted for host and port, respectively) to use to contact
 * the daemon.
 */
int
ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
    u_short port, int family, int connection_attempts,
    int needpriv, const char *proxy_command)
{
	int gaierr;
	int on = 1;
	int sock = -1, attempt;
	char ntop[NI_MAXHOST], strport[NI_MAXSERV];
	struct addrinfo hints, *ai, *aitop;
	struct servent *sp;

	debug2("ssh_connect: needpriv %d", needpriv);

	/* Get default port if port has not been set. */
	if (port == 0) {
		sp = getservbyname(SSH_SERVICE_NAME, "tcp");
		if (sp)
			port = ntohs(sp->s_port);
		else
			port = SSH_DEFAULT_PORT;
	}
	/* If a proxy command is given, connect using it. */
	if (proxy_command != NULL)
		return ssh_proxy_connect(host, port, proxy_command);

	/* No proxy command. */

	memset(&hints, 0, sizeof(hints));
	hints.ai_family = family;
	hints.ai_socktype = SOCK_STREAM;
	snprintf(strport, sizeof strport, "%u", port);
	if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
		fatal("%s: %.100s: %s", __progname, host,
		    gai_strerror(gaierr));

	/*
	 * Try to connect several times.  On some machines, the first time
	 * will sometimes fail.  In general socket code appears to behave
	 * quite magically on many machines.
		 */
	for (attempt = 0; ;) {
		if (attempt > 0)
			debug("Trying again...");

		/* Loop through addresses for this host, and try each one in
		   sequence until the connection succeeds. */
		for (ai = aitop; ai; ai = ai->ai_next) {
			if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
				continue;
			if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
			    ntop, sizeof(ntop), strport, sizeof(strport),
			    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
				error("ssh_connect: getnameinfo failed");
				continue;
			}
			debug("Connecting to %.200s [%.100s] port %s.",
				host, ntop, strport);

			/* Create a socket for connecting. */
			sock = ssh_create_socket(needpriv, ai);
			if (sock < 0)
				/* Any error is already output */
				continue;

			if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen,
			    options.connection_timeout) >= 0) {
				/* Successful connection. */
				memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
				break;
			} else {
				debug("connect to address %s port %s: %s",
				    ntop, strport, strerror(errno));
				/*
				 * Close the failed socket; there appear to
				 * be some problems when reusing a socket for
				 * which connect() has already returned an
				 * error.
				 */
				close(sock);
			}
		}
		if (ai)
			break;	/* Successful connection. */

		attempt++;
		if (attempt >= connection_attempts)
			break;
		/* Sleep a moment before retrying. */
		sleep(1);
	}

	freeaddrinfo(aitop);

	/* Return failure if we didn't get a successful connection. */
	if (attempt >= connection_attempts) {
		error("ssh: connect to host %s port %s: %s",
		    host, strport, strerror(errno));
		return (-1);
	}

	debug("Connection established.");

	/* Set SO_KEEPALIVE if requested. */
	if (options.tcp_keep_alive &&
	    setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
	    sizeof(on)) < 0)
		error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));

	/* Set the connection. */
	packet_set_connection(sock, sock);

	return 0;
}

/*
 * Waits for the server identification string, and sends our own
 * identification string.
 */
static void
ssh_exchange_identification(void)
{
	char buf[256], remote_version[256];	/* must be same size! */
	int remote_major, remote_minor, i, mismatch;
	int connection_in = packet_get_connection_in();
	int connection_out = packet_get_connection_out();
	int minor1 = PROTOCOL_MINOR_1;

	/* Read other side\'s version identification. */
	for (;;) {
		for (i = 0; i < sizeof(buf) - 1; i++) {
			int len = atomicio(read, connection_in, &buf[i], 1);
			if (len < 0)
				fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
			if (len != 1)
				fatal("ssh_exchange_identification: Connection closed by remote host");
			if (buf[i] == '\r') {
				buf[i] = '\n';
				buf[i + 1] = 0;
				continue;		/**XXX wait for \n */
			}
			if (buf[i] == '\n') {
				buf[i + 1] = 0;
				break;
			}
		}
		buf[sizeof(buf) - 1] = 0;
		if (strncmp(buf, "SSH-", 4) == 0)
			break;
		debug("ssh_exchange_identification: %s", buf);
	}
	server_version_string = xstrdup(buf);

	/*
	 * Check that the versions match.  In future this might accept
	 * several versions and set appropriate flags to handle them.
	 */
	if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
	    &remote_major, &remote_minor, remote_version) != 3)
		fatal("Bad remote protocol version identification: '%.100s'", buf);
	debug("Remote protocol version %d.%d, remote software version %.100s",
	    remote_major, remote_minor, remote_version);

	compat_datafellows(remote_version);
	mismatch = 0;

	switch (remote_major) {
	case 1:
		if (remote_minor == 99 &&
		    (options.protocol & SSH_PROTO_2) &&
		    !(options.protocol & SSH_PROTO_1_PREFERRED)) {
			enable_compat20();
			break;
		}
		if (!(options.protocol & SSH_PROTO_1)) {
			mismatch = 1;
			break;
		}
		if (remote_minor < 3) {
			fatal("Remote machine has too old SSH software version.");
		} else if (remote_minor == 3 || remote_minor == 4) {
			/* We speak 1.3, too. */
			enable_compat13();
			minor1 = 3;
			if (options.forward_agent) {
				logit("Agent forwarding disabled for protocol 1.3");
				options.forward_agent = 0;
			}
		}
		break;
	case 2:
		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(vwrite, 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)