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openssh-portable/sshconnect.c

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/* $OpenBSD: sshconnect.c,v 1.319 2019/09/13 04:31:19 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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"
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif
#include <net/if.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#ifdef HAVE_PATHS_H
#include <paths.h>
#endif
#include <pwd.h>
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#ifdef HAVE_IFADDRS_H
# include <ifaddrs.h>
#endif
#include "xmalloc.h"
#include "hostfile.h"
#include "ssh.h"
#include "sshbuf.h"
#include "packet.h"
#include "compat.h"
#include "sshkey.h"
#include "sshconnect.h"
#include "log.h"
#include "misc.h"
#include "readconf.h"
#include "atomicio.h"
#include "dns.h"
#include "monitor_fdpass.h"
#include "ssh2.h"
#include "version.h"
#include "authfile.h"
#include "ssherr.h"
#include "authfd.h"
#include "kex.h"
struct sshkey *previous_host_key = NULL;
static int matching_host_key_dns = 0;
static pid_t proxy_command_pid = 0;
/* import */
extern int debug_flag;
extern Options options;
extern char *__progname;
static int show_other_keys(struct hostkeys *, struct sshkey *);
static void warn_changed_key(struct sshkey *);
/* Expand a proxy command */
static char *
expand_proxy_command(const char *proxy_command, const char *user,
const char *host, const char *host_arg, int port)
{
char *tmp, *ret, strport[NI_MAXSERV];
snprintf(strport, sizeof strport, "%d", port);
xasprintf(&tmp, "exec %s", proxy_command);
ret = percent_expand(tmp,
"h", host,
"n", host_arg,
"p", strport,
"r", options.user,
(char *)NULL);
free(tmp);
return ret;
}
static void
stderr_null(void)
{
int devnull;
if ((devnull = open(_PATH_DEVNULL, O_WRONLY)) == -1) {
error("Can't open %s for stderr redirection: %s",
_PATH_DEVNULL, strerror(errno));
return;
}
if (devnull == STDERR_FILENO)
return;
if (dup2(devnull, STDERR_FILENO) == -1)
error("Cannot redirect stderr to %s", _PATH_DEVNULL);
if (devnull > STDERR_FILENO)
close(devnull);
}
/*
* Connect to the given ssh server using a proxy command that passes a
* a connected fd back to us.
*/
static int
ssh_proxy_fdpass_connect(struct ssh *ssh, const char *host,
const char *host_arg, u_short port, const char *proxy_command)
{
char *command_string;
int sp[2], sock;
pid_t pid;
char *shell;
if ((shell = getenv("SHELL")) == NULL)
shell = _PATH_BSHELL;
if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) == -1)
fatal("Could not create socketpair to communicate with "
"proxy dialer: %.100s", strerror(errno));
command_string = expand_proxy_command(proxy_command, options.user,
host_arg, host, port);
debug("Executing proxy dialer command: %.500s", command_string);
/* Fork and execute the proxy command. */
if ((pid = fork()) == 0) {
char *argv[10];
close(sp[1]);
/* Redirect stdin and stdout. */
if (sp[0] != 0) {
if (dup2(sp[0], 0) == -1)
perror("dup2 stdin");
}
if (sp[0] != 1) {
if (dup2(sp[0], 1) == -1)
perror("dup2 stdout");
}
if (sp[0] >= 2)
close(sp[0]);
/*
* Stderr is left for non-ControlPersist connections is so
* error messages may be printed on the user's terminal.
*/
if (!debug_flag && options.control_path != NULL &&
options.control_persist)
stderr_null();
argv[0] = shell;
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 == -1)
fatal("fork failed: %.100s", strerror(errno));
close(sp[0]);
free(command_string);
if ((sock = mm_receive_fd(sp[1])) == -1)
fatal("proxy dialer did not pass back a connection");
close(sp[1]);
while (waitpid(pid, NULL, 0) == -1)
if (errno != EINTR)
fatal("Couldn't wait for child: %s", strerror(errno));
/* Set the connection file descriptors. */
if (ssh_packet_set_connection(ssh, sock, sock) == NULL)
return -1; /* ssh_packet_set_connection logs error */
return 0;
}
/*
* Connect to the given ssh server using a proxy command.
*/
static int
ssh_proxy_connect(struct ssh *ssh, const char *host, const char *host_arg,
u_short port, const char *proxy_command)
{
char *command_string;
int pin[2], pout[2];
pid_t pid;
char *shell;
if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
shell = _PATH_BSHELL;
/* Create pipes for communicating with the proxy. */
if (pipe(pin) == -1 || pipe(pout) == -1)
fatal("Could not create pipes to communicate with the proxy: %.100s",
strerror(errno));
command_string = expand_proxy_command(proxy_command, options.user,
host_arg, host, port);
debug("Executing proxy command: %.500s", command_string);
#ifdef FORK_NOT_SUPPORTED
{
posix_spawn_file_actions_t actions;
char* spawn_argv[2];
/*
* expand_proxy_command prefixes cmdline with "exec "
*/
spawn_argv[0] = command_string + 5;
spawn_argv[1] = NULL;
pid = -1;
/* disable inheritance */
fcntl(pin[1], F_SETFD, FD_CLOEXEC);
fcntl(pout[0], F_SETFD, FD_CLOEXEC);
if (posix_spawn_file_actions_init(&actions) != 0 ||
posix_spawn_file_actions_adddup2(&actions, pin[0], STDIN_FILENO) != 0 ||
posix_spawn_file_actions_adddup2(&actions, pout[1], STDOUT_FILENO) != 0)
fatal("posix_spawn initialization failed");
else if (posix_spawnp(&pid, spawn_argv[0], &actions, NULL, spawn_argv, NULL) != 0)
fatal("posix_spawnp: %s", strerror(errno));
posix_spawn_file_actions_destroy(&actions);
}
#else
/* Fork and execute the proxy command. */
if ((pid = fork()) == 0) {
char *argv[10];
/* Redirect stdin and stdout. */
close(pin[1]);
if (pin[0] != 0) {
if (dup2(pin[0], 0) == -1)
perror("dup2 stdin");
close(pin[0]);
}
close(pout[0]);
if (dup2(pout[1], 1) == -1)
perror("dup2 stdout");
/* Cannot be 1 because pin allocated two descriptors. */
close(pout[1]);
/*
* Stderr is left for non-ControlPersist connections is so
* error messages may be printed on the user's terminal.
*/
if (!debug_flag && options.control_path != NULL &&
options.control_persist)
stderr_null();
argv[0] = shell;
argv[1] = "-c";
argv[2] = command_string;
argv[3] = NULL;
/* Execute the proxy command. Note that we gave up any
extra privileges above. */
signal(SIGPIPE, SIG_DFL);
execv(argv[0], argv);
perror(argv[0]);
exit(1);
}
#endif
/* Parent. */
if (pid == -1)
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. */
free(command_string);
/* Set the connection file descriptors. */
if (ssh_packet_set_connection(ssh, pout[0], pin[1]) == NULL)
return -1; /* ssh_packet_set_connection logs error */
return 0;
}
void
ssh_kill_proxy_command(void)
{
/*
* Send SIGHUP to proxy command if used. We don't wait() in
* case it hangs and instead rely on init to reap the child
*/
if (proxy_command_pid > 1)
kill(proxy_command_pid, SIGHUP);
}
#ifdef HAVE_IFADDRS_H
/*
* Search a interface address list (returned from getifaddrs(3)) for an
* address that matches the desired address family on the specified interface.
* Returns 0 and fills in *resultp and *rlenp on success. Returns -1 on failure.
*/
static int
check_ifaddrs(const char *ifname, int af, const struct ifaddrs *ifaddrs,
struct sockaddr_storage *resultp, socklen_t *rlenp)
{
struct sockaddr_in6 *sa6;
struct sockaddr_in *sa;
struct in6_addr *v6addr;
const struct ifaddrs *ifa;
int allow_local;
/*
* Prefer addresses that are not loopback or linklocal, but use them
* if nothing else matches.
*/
for (allow_local = 0; allow_local < 2; allow_local++) {
for (ifa = ifaddrs; ifa != NULL; ifa = ifa->ifa_next) {
if (ifa->ifa_addr == NULL || ifa->ifa_name == NULL ||
(ifa->ifa_flags & IFF_UP) == 0 ||
ifa->ifa_addr->sa_family != af ||
strcmp(ifa->ifa_name, options.bind_interface) != 0)
continue;
switch (ifa->ifa_addr->sa_family) {
case AF_INET:
sa = (struct sockaddr_in *)ifa->ifa_addr;
if (!allow_local && sa->sin_addr.s_addr ==
htonl(INADDR_LOOPBACK))
continue;
if (*rlenp < sizeof(struct sockaddr_in)) {
error("%s: v4 addr doesn't fit",
__func__);
return -1;
}
*rlenp = sizeof(struct sockaddr_in);
memcpy(resultp, sa, *rlenp);
return 0;
case AF_INET6:
sa6 = (struct sockaddr_in6 *)ifa->ifa_addr;
v6addr = &sa6->sin6_addr;
if (!allow_local &&
(IN6_IS_ADDR_LINKLOCAL(v6addr) ||
IN6_IS_ADDR_LOOPBACK(v6addr)))
continue;
if (*rlenp < sizeof(struct sockaddr_in6)) {
error("%s: v6 addr doesn't fit",
__func__);
return -1;
}
*rlenp = sizeof(struct sockaddr_in6);
memcpy(resultp, sa6, *rlenp);
return 0;
}
}
}
return -1;
}
#endif
/*
* Creates a socket for use as the ssh connection.
*/
static int
ssh_create_socket(struct addrinfo *ai)
{
int sock, r;
struct sockaddr_storage bindaddr;
socklen_t bindaddrlen = 0;
struct addrinfo hints, *res = NULL;
#ifdef HAVE_IFADDRS_H
struct ifaddrs *ifaddrs = NULL;
#endif
char ntop[NI_MAXHOST];
sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
if (sock == -1) {
error("socket: %s", strerror(errno));
return -1;
}
fcntl(sock, F_SETFD, FD_CLOEXEC);
/* Bind the socket to an alternative local IP address */
if (options.bind_address == NULL && options.bind_interface == NULL)
return sock;
if (options.bind_address != NULL) {
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;
if ((r = getaddrinfo(options.bind_address, NULL,
&hints, &res)) != 0) {
error("getaddrinfo: %s: %s", options.bind_address,
ssh_gai_strerror(r));
goto fail;
}
if (res == NULL) {
error("getaddrinfo: no addrs");
goto fail;
}
memcpy(&bindaddr, res->ai_addr, res->ai_addrlen);
bindaddrlen = res->ai_addrlen;
} else if (options.bind_interface != NULL) {
#ifdef HAVE_IFADDRS_H
if ((r = getifaddrs(&ifaddrs)) != 0) {
error("getifaddrs: %s: %s", options.bind_interface,
strerror(errno));
goto fail;
}
bindaddrlen = sizeof(bindaddr);
if (check_ifaddrs(options.bind_interface, ai->ai_family,
ifaddrs, &bindaddr, &bindaddrlen) != 0) {
logit("getifaddrs: %s: no suitable addresses",
options.bind_interface);
goto fail;
}
#else
error("BindInterface not supported on this platform.");
#endif
}
if ((r = getnameinfo((struct sockaddr *)&bindaddr, bindaddrlen,
ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST)) != 0) {
error("%s: getnameinfo failed: %s", __func__,
ssh_gai_strerror(r));
goto fail;
}
if (bind(sock, (struct sockaddr *)&bindaddr, bindaddrlen) != 0) {
error("bind %s: %s", ntop, strerror(errno));
goto fail;
}
debug("%s: bound to %s", __func__, ntop);
/* success */
goto out;
fail:
close(sock);
sock = -1;
out:
if (res != NULL)
freeaddrinfo(res);
#ifdef HAVE_IFADDRS_H
if (ifaddrs != NULL)
freeifaddrs(ifaddrs);
#endif
return sock;
}
/*
* 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.
* 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.
*/
static int
ssh_connect_direct(struct ssh *ssh, const char *host, struct addrinfo *aitop,
struct sockaddr_storage *hostaddr, u_short port, int family,
int connection_attempts, int *timeout_ms, int want_keepalive)
{
int on = 1, saved_timeout_ms = *timeout_ms;
int oerrno, sock = -1, attempt;
char ntop[NI_MAXHOST], strport[NI_MAXSERV];
struct addrinfo *ai;
debug2("%s", __func__);
memset(ntop, 0, sizeof(ntop));
memset(strport, 0, sizeof(strport));
for (attempt = 0; attempt < connection_attempts; attempt++) {
if (attempt > 0) {
/* Sleep a moment before retrying. */
sleep(1);
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) {
errno = EAFNOSUPPORT;
continue;
}
if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
ntop, sizeof(ntop), strport, sizeof(strport),
NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
oerrno = errno;
error("%s: getnameinfo failed", __func__);
errno = oerrno;
continue;
}
debug("Connecting to %.200s [%.100s] port %s.",
host, ntop, strport);
/* Create a socket for connecting. */
sock = ssh_create_socket(ai);
if (sock < 0) {
/* Any error is already output */
errno = 0;
continue;
}
*timeout_ms = saved_timeout_ms;
if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen,
timeout_ms) >= 0) {
/* Successful connection. */
memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
break;
} else {
oerrno = errno;
debug("connect to address %s port %s: %s",
ntop, strport, strerror(errno));
close(sock);
sock = -1;
errno = oerrno;
}
}
if (sock != -1)
break; /* Successful connection. */
}
/* Return failure if we didn't get a successful connection. */
if (sock == -1) {
error("ssh: connect to host %s port %s: %s",
host, strport, errno == 0 ? "failure" : strerror(errno));
return -1;
}
debug("Connection established.");
/* Set SO_KEEPALIVE if requested. */
if (want_keepalive &&
setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
sizeof(on)) == -1)
error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
/* Set the connection. */
if (ssh_packet_set_connection(ssh, sock, sock) == NULL)
return -1; /* ssh_packet_set_connection logs error */
return 0;
}
int
ssh_connect(struct ssh *ssh, const char *host, const char *host_arg,
struct addrinfo *addrs, struct sockaddr_storage *hostaddr, u_short port,
int family, int connection_attempts, int *timeout_ms, int want_keepalive)
{
int in, out;
if (options.proxy_command == NULL) {
return ssh_connect_direct(ssh, host, addrs, hostaddr, port,
family, connection_attempts, timeout_ms, want_keepalive);
} else if (strcmp(options.proxy_command, "-") == 0) {
if ((in = dup(STDIN_FILENO)) == -1 ||
(out = dup(STDOUT_FILENO)) == -1) {
if (in >= 0)
close(in);
error("%s: dup() in/out failed", __func__);
return -1; /* ssh_packet_set_connection logs error */
}
if ((ssh_packet_set_connection(ssh, in, out)) == NULL)
return -1; /* ssh_packet_set_connection logs error */
return 0;
} else if (options.proxy_use_fdpass) {
return ssh_proxy_fdpass_connect(ssh, host, host_arg, port,
options.proxy_command);
}
return ssh_proxy_connect(ssh, host, host_arg, port,
options.proxy_command);
}
/* defaults to 'no' */
static int
confirm(const char *prompt, const char *fingerprint)
{
const char *msg, *again = "Please type 'yes' or 'no': ";
const char *again_fp = "Please type 'yes', 'no' or the fingerprint: ";
char *p;
int ret = -1;
if (options.batch_mode)
return 0;
for (msg = prompt;;msg = fingerprint ? again_fp : again) {
p = read_passphrase(msg, RP_ECHO);
if (p == NULL)
return 0;
p[strcspn(p, "\n")] = '\0';
if (p[0] == '\0' || strcasecmp(p, "no") == 0)
ret = 0;
else if (strcasecmp(p, "yes") == 0 || (fingerprint != NULL &&
strcasecmp(p, fingerprint) == 0))
ret = 1;
free(p);
if (ret != -1)
return ret;
}
}
static int
check_host_cert(const char *host, const struct sshkey *key)
{
const char *reason;
int r;
if (sshkey_cert_check_authority(key, 1, 0, host, &reason) != 0) {
error("%s", reason);
return 0;
}
if (sshbuf_len(key->cert->critical) != 0) {
error("Certificate for %s contains unsupported "
"critical options(s)", host);
return 0;
}
if ((r = sshkey_check_cert_sigtype(key,
options.ca_sign_algorithms)) != 0) {
logit("%s: certificate signature algorithm %s: %s", __func__,
(key->cert == NULL || key->cert->signature_type == NULL) ?
"(null)" : key->cert->signature_type, ssh_err(r));
return 0;
}
return 1;
}
static int
sockaddr_is_local(struct sockaddr *hostaddr)
{
switch (hostaddr->sa_family) {
case AF_INET:
return (ntohl(((struct sockaddr_in *)hostaddr)->
sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
case AF_INET6:
return IN6_IS_ADDR_LOOPBACK(
&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
default:
return 0;
}
}
/*
* Prepare the hostname and ip address strings that are used to lookup
* host keys in known_hosts files. These may have a port number appended.
*/
void
get_hostfile_hostname_ipaddr(char *hostname, struct sockaddr *hostaddr,
u_short port, char **hostfile_hostname, char **hostfile_ipaddr)
{
char ntop[NI_MAXHOST];
socklen_t addrlen;
switch (hostaddr == NULL ? -1 : hostaddr->sa_family) {
case -1:
addrlen = 0;
break;
case AF_INET:
addrlen = sizeof(struct sockaddr_in);
break;
case AF_INET6:
addrlen = sizeof(struct sockaddr_in6);
break;
default:
addrlen = sizeof(struct sockaddr);
break;
}
/*
* We don't have the remote ip-address for connections
* using a proxy command
*/
if (hostfile_ipaddr != NULL) {
if (options.proxy_command == NULL) {
if (getnameinfo(hostaddr, addrlen,
ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST) != 0)
fatal("%s: getnameinfo failed", __func__);
*hostfile_ipaddr = put_host_port(ntop, port);
} else {
*hostfile_ipaddr = xstrdup("<no hostip for proxy "
"command>");
}
}
/*
* Allow the user to record the key under a different name or
* differentiate a non-standard port. This is useful for ssh
* tunneling over forwarded connections or if you run multiple
* sshd's on different ports on the same machine.
*/
if (hostfile_hostname != NULL) {
if (options.host_key_alias != NULL) {
*hostfile_hostname = xstrdup(options.host_key_alias);
debug("using hostkeyalias: %s", *hostfile_hostname);
} else {
*hostfile_hostname = put_host_port(hostname, port);
}
}
}
/*
* check whether the supplied host key is valid, return -1 if the key
* is not valid. user_hostfile[0] will not be updated if 'readonly' is true.
*/
#define RDRW 0
#define RDONLY 1
#define ROQUIET 2
static int
check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
struct sshkey *host_key, int readonly,
char **user_hostfiles, u_int num_user_hostfiles,
char **system_hostfiles, u_int num_system_hostfiles)
{
HostStatus host_status;
HostStatus ip_status;
struct sshkey *raw_key = NULL;
char *ip = NULL, *host = NULL;
char hostline[1000], *hostp, *fp, *ra;
char msg[1024];
const char *type;
const struct hostkey_entry *host_found, *ip_found;
int len, cancelled_forwarding = 0, confirmed;
int local = sockaddr_is_local(hostaddr);
int r, want_cert = sshkey_is_cert(host_key), host_ip_differ = 0;
int hostkey_trusted = 0; /* Known or explicitly accepted by user */
struct hostkeys *host_hostkeys, *ip_hostkeys;
u_int i;
/*
* 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.
*/
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;
}
/*
* Prepare the hostname and address strings used for hostkey lookup.
* In some cases, these will have a port number appended.
*/
get_hostfile_hostname_ipaddr(hostname, hostaddr, port, &host, &ip);
/*
* 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(hostname, ip) == 0 || options.proxy_command != NULL))
options.check_host_ip = 0;
host_hostkeys = init_hostkeys();
for (i = 0; i < num_user_hostfiles; i++)
load_hostkeys(host_hostkeys, host, user_hostfiles[i]);
for (i = 0; i < num_system_hostfiles; i++)
load_hostkeys(host_hostkeys, host, system_hostfiles[i]);
ip_hostkeys = NULL;
if (!want_cert && options.check_host_ip) {
ip_hostkeys = init_hostkeys();
for (i = 0; i < num_user_hostfiles; i++)
load_hostkeys(ip_hostkeys, ip, user_hostfiles[i]);
for (i = 0; i < num_system_hostfiles; i++)
load_hostkeys(ip_hostkeys, ip, system_hostfiles[i]);
}
retry:
/* Reload these as they may have changed on cert->key downgrade */
want_cert = sshkey_is_cert(host_key);
type = sshkey_type(host_key);
/*
* Check if the host key is present in the user's list of known
* hosts or in the systemwide list.
*/
host_status = check_key_in_hostkeys(host_hostkeys, host_key,
&host_found);
/*
* Also perform check for the ip address, skip the check if we are
* localhost, looking for a certificate, or the hostname was an ip
* address to begin with.
*/
if (!want_cert && ip_hostkeys != NULL) {
ip_status = check_key_in_hostkeys(ip_hostkeys, host_key,
&ip_found);
if (host_status == HOST_CHANGED &&
(ip_status != HOST_CHANGED ||
(ip_found != NULL &&
!sshkey_equal(ip_found->key, host_found->key))))
host_ip_differ = 1;
} else
ip_status = host_status;
switch (host_status) {
case HOST_OK:
/* The host is known and the key matches. */
debug("Host '%.200s' is known and matches the %s host %s.",
host, type, want_cert ? "certificate" : "key");
debug("Found %s in %s:%lu", want_cert ? "CA key" : "key",
host_found->file, host_found->line);
if (want_cert &&
!check_host_cert(options.host_key_alias == NULL ?
hostname : options.host_key_alias, host_key))
goto fail;
if (options.check_host_ip && ip_status == HOST_NEW) {
if (readonly || want_cert)
logit("%s host key for IP address "
"'%.128s' not in list of known hosts.",
type, ip);
else if (!add_host_to_hostfile(user_hostfiles[0], ip,
host_key, options.hash_known_hosts))
logit("Failed to add the %s host key for IP "
"address '%.128s' to the list of known "
"hosts (%.500s).", type, ip,
user_hostfiles[0]);
else
logit("Warning: Permanently added the %s host "
"key for IP address '%.128s' to the list "
"of known hosts.", type, ip);
} else if (options.visual_host_key) {
fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
ra = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_RANDOMART);
if (fp == NULL || ra == NULL)
fatal("%s: sshkey_fingerprint fail", __func__);
logit("Host key fingerprint is %s\n%s", fp, ra);
free(ra);
free(fp);
}
hostkey_trusted = 1;
break;
case HOST_NEW:
if (options.host_key_alias == NULL && port != 0 &&
port != SSH_DEFAULT_PORT) {
debug("checking without port identifier");
if (check_host_key(hostname, hostaddr, 0, host_key,
ROQUIET, user_hostfiles, num_user_hostfiles,
system_hostfiles, num_system_hostfiles) == 0) {
debug("found matching key w/out port");
break;
}
}
if (readonly || want_cert)
goto fail;
/* The host is new. */
if (options.strict_host_key_checking ==
SSH_STRICT_HOSTKEY_YES) {
/*
* 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 ==
SSH_STRICT_HOSTKEY_ASK) {
char msg1[1024], msg2[1024];
if (show_other_keys(host_hostkeys, host_key))
snprintf(msg1, sizeof(msg1),
"\nbut keys of different type are already"
" known for this host.");
else
snprintf(msg1, sizeof(msg1), ".");
/* The default */
fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
ra = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_RANDOMART);
if (fp == NULL || ra == NULL)
fatal("%s: sshkey_fingerprint fail", __func__);
msg2[0] = '\0';
if (options.verify_host_key_dns) {
if (matching_host_key_dns)
snprintf(msg2, sizeof(msg2),
"Matching host key fingerprint"
" found in DNS.\n");
else
snprintf(msg2, sizeof(msg2),
"No matching host key fingerprint"
" found in DNS.\n");
}
snprintf(msg, sizeof(msg),
"The authenticity of host '%.200s (%s)' can't be "
"established%s\n"
"%s key fingerprint is %s.%s%s\n%s"
"Are you sure you want to continue connecting "
"(yes/no/[fingerprint])? ",
host, ip, msg1, type, fp,
options.visual_host_key ? "\n" : "",
options.visual_host_key ? ra : "",
msg2);
free(ra);
confirmed = confirm(msg, fp);
free(fp);
if (!confirmed)
goto fail;
hostkey_trusted = 1; /* user explicitly confirmed */
}
/*
* If in "new" or "off" strict mode, add the key automatically
* to the local known_hosts file.
*/
if (options.check_host_ip && ip_status == HOST_NEW) {
snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
hostp = hostline;
if (options.hash_known_hosts) {
/* Add hash of host and IP separately */
r = add_host_to_hostfile(user_hostfiles[0],
host, host_key, options.hash_known_hosts) &&
add_host_to_hostfile(user_hostfiles[0], ip,
host_key, options.hash_known_hosts);
} else {
/* Add unhashed "host,ip" */
r = add_host_to_hostfile(user_hostfiles[0],
hostline, host_key,
options.hash_known_hosts);
}
} else {
r = add_host_to_hostfile(user_hostfiles[0], host,
host_key, options.hash_known_hosts);
hostp = host;
}
if (!r)
logit("Failed to add the host to the list of known "
"hosts (%.500s).", user_hostfiles[0]);
else
logit("Warning: Permanently added '%.200s' (%s) to the "
"list of known hosts.", hostp, type);
break;
case HOST_REVOKED:
error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
error("@ WARNING: REVOKED HOST KEY DETECTED! @");
error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
error("The %s host key for %s is marked as revoked.", type, host);
error("This could mean that a stolen key is being used to");
error("impersonate this host.");
/*
* 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 !=
SSH_STRICT_HOSTKEY_OFF) {
error("%s host key for %.200s was revoked and you have "
"requested strict checking.", type, host);
goto fail;
}
goto continue_unsafe;
case HOST_CHANGED:
if (want_cert) {
/*
* This is only a debug() since it is valid to have
* CAs with wildcard DNS matches that don't match
* all hosts that one might visit.
*/
debug("Host certificate authority does not "
"match %s in %s:%lu", CA_MARKER,
host_found->file, host_found->line);
goto fail;
}
if (readonly == ROQUIET)
goto fail;
if (options.check_host_ip && host_ip_differ) {
char *key_msg;
if (ip_status == HOST_NEW)
key_msg = "is unknown";
else if (ip_status == HOST_OK)
key_msg = "is unchanged";
else
key_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 corresponding IP address %s", ip);
error("%s. This could either mean that", key_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:%lu",
ip_found->file, ip_found->line);
}
/* The host key has changed. */
warn_changed_key(host_key);
error("Add correct host key in %.100s to get rid of this message.",
user_hostfiles[0]);
error("Offending %s key in %s:%lu",
sshkey_type(host_found->key),
host_found->file, host_found->line);
/*
* 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 !=
SSH_STRICT_HOSTKEY_OFF) {
error("%s host key for %.200s has changed and you have "
"requested strict checking.", type, host);
goto fail;
}
continue_unsafe:
/*
* If strict host key checking has not been requested, allow
* the connection but without MITM-able authentication or
* forwarding.
*/
if (options.password_authentication) {
error("Password authentication is disabled to avoid "
"man-in-the-middle attacks.");
options.password_authentication = 0;
cancelled_forwarding = 1;
}
if (options.kbd_interactive_authentication) {
error("Keyboard-interactive authentication is disabled"
" to avoid man-in-the-middle attacks.");
options.kbd_interactive_authentication = 0;
options.challenge_response_authentication = 0;
cancelled_forwarding = 1;
}
if (options.challenge_response_authentication) {
error("Challenge/response authentication is disabled"
" to avoid man-in-the-middle attacks.");
options.challenge_response_authentication = 0;
cancelled_forwarding = 1;
}
if (options.forward_agent) {
error("Agent forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.forward_agent = 0;
cancelled_forwarding = 1;
}
if (options.forward_x11) {
error("X11 forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.forward_x11 = 0;
cancelled_forwarding = 1;
}
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;
cancelled_forwarding = 1;
}
if (options.tun_open != SSH_TUNMODE_NO) {
error("Tunnel forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.tun_open = SSH_TUNMODE_NO;
cancelled_forwarding = 1;
}
if (options.exit_on_forward_failure && cancelled_forwarding)
fatal("Error: forwarding disabled due to host key "
"check failure");
/*
* 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 wishes to
* accept the authentication.
*/
break;
case HOST_FOUND:
fatal("internal error");
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:%lu",
type, host, ip, ip_found->file, ip_found->line);
if (host_status == HOST_OK) {
len = strlen(msg);
snprintf(msg + len, sizeof(msg) - len,
"\nMatching host key in %s:%lu",
host_found->file, host_found->line);
}
if (options.strict_host_key_checking ==
SSH_STRICT_HOSTKEY_ASK) {
strlcat(msg, "\nAre you sure you want "
"to continue connecting (yes/no)? ", sizeof(msg));
if (!confirm(msg, NULL))
goto fail;
} else if (options.strict_host_key_checking !=
SSH_STRICT_HOSTKEY_OFF) {
logit("%s", msg);
error("Exiting, you have requested strict checking.");
goto fail;
} else {
logit("%s", msg);
}
}
if (!hostkey_trusted && options.update_hostkeys) {
debug("%s: hostkey not known or explicitly trusted: "
"disabling UpdateHostkeys", __func__);
options.update_hostkeys = 0;
}
free(ip);
free(host);
if (host_hostkeys != NULL)
free_hostkeys(host_hostkeys);
if (ip_hostkeys != NULL)
free_hostkeys(ip_hostkeys);
return 0;
fail:
if (want_cert && host_status != HOST_REVOKED) {
/*
* No matching certificate. Downgrade cert to raw key and
* search normally.
*/
debug("No matching CA found. Retry with plain key");
if ((r = sshkey_from_private(host_key, &raw_key)) != 0)
fatal("%s: sshkey_from_private: %s",
__func__, ssh_err(r));
if ((r = sshkey_drop_cert(raw_key)) != 0)
fatal("Couldn't drop certificate: %s", ssh_err(r));
host_key = raw_key;
goto retry;
}
sshkey_free(raw_key);
free(ip);
free(host);
if (host_hostkeys != NULL)
free_hostkeys(host_hostkeys);
if (ip_hostkeys != NULL)
free_hostkeys(ip_hostkeys);
return -1;
}
/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, struct sshkey *host_key)
{
u_int i;
int r = -1, flags = 0;
char valid[64], *fp = NULL, *cafp = NULL;
struct sshkey *plain = NULL;
if ((fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: fingerprint host key: %s", __func__, ssh_err(r));
r = -1;
goto out;
}
if (sshkey_is_cert(host_key)) {
if ((cafp = sshkey_fingerprint(host_key->cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: fingerprint CA key: %s",
__func__, ssh_err(r));
r = -1;
goto out;
}
sshkey_format_cert_validity(host_key->cert,
valid, sizeof(valid));
debug("Server host certificate: %s %s, serial %llu "
"ID \"%s\" CA %s %s valid %s",
sshkey_ssh_name(host_key), fp,
(unsigned long long)host_key->cert->serial,
host_key->cert->key_id,
sshkey_ssh_name(host_key->cert->signature_key), cafp,
valid);
for (i = 0; i < host_key->cert->nprincipals; i++) {
debug2("Server host certificate hostname: %s",
host_key->cert->principals[i]);
}
} else {
debug("Server host key: %s %s", sshkey_ssh_name(host_key), fp);
}
if (sshkey_equal(previous_host_key, host_key)) {
debug2("%s: server host key %s %s matches cached key",
__func__, sshkey_type(host_key), fp);
r = 0;
goto out;
}
/* Check in RevokedHostKeys file if specified */
if (options.revoked_host_keys != NULL) {
r = sshkey_check_revoked(host_key, options.revoked_host_keys);
switch (r) {
case 0:
break; /* not revoked */
case SSH_ERR_KEY_REVOKED:
error("Host key %s %s revoked by file %s",
sshkey_type(host_key), fp,
options.revoked_host_keys);
r = -1;
goto out;
default:
error("Error checking host key %s %s in "
"revoked keys file %s: %s", sshkey_type(host_key),
fp, options.revoked_host_keys, ssh_err(r));
r = -1;
goto out;
}
}
if (options.verify_host_key_dns) {
/*
* XXX certs are not yet supported for DNS, so downgrade
* them and try the plain key.
*/
if ((r = sshkey_from_private(host_key, &plain)) != 0)
goto out;
if (sshkey_is_cert(plain))
sshkey_drop_cert(plain);
if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
if (flags & DNS_VERIFY_FOUND) {
if (options.verify_host_key_dns == 1 &&
flags & DNS_VERIFY_MATCH &&
flags & DNS_VERIFY_SECURE) {
r = 0;
goto out;
}
if (flags & DNS_VERIFY_MATCH) {
matching_host_key_dns = 1;
} else {
warn_changed_key(plain);
error("Update the SSHFP RR in DNS "
"with the new host key to get rid "
"of this message.");
}
}
}
}
r = check_host_key(host, hostaddr, options.port, host_key, RDRW,
options.user_hostfiles, options.num_user_hostfiles,
options.system_hostfiles, options.num_system_hostfiles);
out:
sshkey_free(plain);
free(fp);
free(cafp);
if (r == 0 && host_key != NULL) {
sshkey_free(previous_host_key);
r = sshkey_from_private(host_key, &previous_host_key);
}
return r;
}
/*
* 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(struct ssh *ssh, Sensitive *sensitive, const char *orighost,
struct sockaddr *hostaddr, u_short port, struct passwd *pw, int timeout_ms)
{
char *host;
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);
lowercase(host);
/* Exchange protocol version identification strings with the server. */
if (kex_exchange_identification(ssh, timeout_ms, NULL) != 0)
cleanup_exit(255); /* error already logged */
/* Put the connection into non-blocking mode. */
ssh_packet_set_nonblocking(ssh);
/* key exchange */
/* authenticate user */
debug("Authenticating to %s:%d as '%s'", host, port, server_user);
ssh_kex2(ssh, host, hostaddr, port);
ssh_userauth2(ssh, local_user, server_user, host, sensitive);
free(local_user);
free(host);
}
/* print all known host keys for a given host, but skip keys of given type */
static int
show_other_keys(struct hostkeys *hostkeys, struct sshkey *key)
{
int type[] = {
KEY_RSA,
KEY_DSA,
KEY_ECDSA,
KEY_ED25519,
KEY_XMSS,
-1
};
int i, ret = 0;
char *fp, *ra;
const struct hostkey_entry *found;
for (i = 0; type[i] != -1; i++) {
if (type[i] == key->type)
continue;
if (!lookup_key_in_hostkeys_by_type(hostkeys, type[i], &found))
continue;
fp = sshkey_fingerprint(found->key,
options.fingerprint_hash, SSH_FP_DEFAULT);
ra = sshkey_fingerprint(found->key,
options.fingerprint_hash, SSH_FP_RANDOMART);
if (fp == NULL || ra == NULL)
fatal("%s: sshkey_fingerprint fail", __func__);
logit("WARNING: %s key found for host %s\n"
"in %s:%lu\n"
"%s key fingerprint %s.",
sshkey_type(found->key),
found->host, found->file, found->line,
sshkey_type(found->key), fp);
if (options.visual_host_key)
logit("%s", ra);
free(ra);
free(fp);
ret = 1;
}
return ret;
}
static void
warn_changed_key(struct sshkey *host_key)
{
char *fp;
fp = sshkey_fingerprint(host_key, options.fingerprint_hash,
SSH_FP_DEFAULT);
if (fp == NULL)
fatal("%s: sshkey_fingerprint fail", __func__);
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 a host key has just been changed.");
error("The fingerprint for the %s key sent by the remote host is\n%s.",
sshkey_type(host_key), fp);
error("Please contact your system administrator.");
free(fp);
}
/*
* Execute a local command
*/
int
ssh_local_cmd(const char *args)
{
char *shell;
pid_t pid;
int status;
void (*osighand)(int);
if (!options.permit_local_command ||
args == NULL || !*args)
return (1);
#ifdef WINDOWS
return system(args);
#endif
if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
shell = _PATH_BSHELL;
osighand = signal(SIGCHLD, SIG_DFL);
pid = fork();
if (pid == 0) {
signal(SIGPIPE, SIG_DFL);
debug3("Executing %s -c \"%s\"", shell, args);
execl(shell, shell, "-c", args, (char *)NULL);
error("Couldn't execute %s -c \"%s\": %s",
shell, args, strerror(errno));
_exit(1);
} else if (pid == -1)
fatal("fork failed: %.100s", strerror(errno));
while (waitpid(pid, &status, 0) == -1)
if (errno != EINTR)
fatal("Couldn't wait for child: %s", strerror(errno));
signal(SIGCHLD, osighand);
if (!WIFEXITED(status))
return (1);
return (WEXITSTATUS(status));
}
void
maybe_add_key_to_agent(char *authfile, struct sshkey *private,
char *comment, char *passphrase)
{
int auth_sock = -1, r;
if (options.add_keys_to_agent == 0)
return;
if ((r = ssh_get_authentication_socket(&auth_sock)) != 0) {
debug3("no authentication agent, not adding key");
return;
}
if (options.add_keys_to_agent == 2 &&
!ask_permission("Add key %s (%s) to agent?", authfile, comment)) {
debug3("user denied adding this key");
close(auth_sock);
return;
}
if ((r = ssh_add_identity_constrained(auth_sock, private, comment, 0,
(options.add_keys_to_agent == 3), 0)) == 0)
debug("identity added to agent: %s", authfile);
else
debug("could not add identity to agent: %s (%d)", authfile, r);
close(auth_sock);
}
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