File: [local] / src / usr.bin / ssh / sshconnect.c (download)
Revision 1.302, Thu Jul 19 10:28:47 2018 UTC (5 years, 10 months ago) by dtucker
Branch: MAIN
Changes since 1.301: +10 -14 lines
Deprecate UsePrivilegedPort now that support for running ssh(1)
setuid has been removed, remove supporting code and clean up
references to it in the man pages
We have not shipped ssh(1) the setuid bit since 2002. If ayone
really needs to make connections from a low port number this can
be implemented via a small setuid ProxyCommand.
ok markus@ jmc@ djm@
|
/* $OpenBSD: sshconnect.c,v 1.302 2018/07/19 10:28:47 dtucker 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 <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <net/if.h>
#include <netinet/in.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <paths.h>
#include <poll.h>
#include <signal.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ifaddrs.h>
#include "xmalloc.h"
#include "ssh.h"
#include "sshbuf.h"
#include "packet.h"
#include "compat.h"
#include "sshkey.h"
#include "sshconnect.h"
#include "hostfile.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"
char *client_version_string = NULL;
char *server_version_string = NULL;
struct sshkey *previous_host_key = NULL;
static int matching_host_key_dns = 0;
static pid_t proxy_command_pid = 0;
/* import */
extern Options options;
extern char *__progname;
extern uid_t original_real_uid;
extern uid_t original_effective_uid;
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, 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, "p", strport,
"r", options.user, (char *)NULL);
free(tmp);
return ret;
}
/*
* 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, 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) < 0)
fatal("Could not create socketpair to communicate with "
"proxy dialer: %.100s", strerror(errno));
command_string = expand_proxy_command(proxy_command, options.user,
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) < 0)
perror("dup2 stdin");
}
if (sp[0] != 1) {
if (dup2(sp[0], 1) < 0)
perror("dup2 stdout");
}
if (sp[0] >= 2)
close(sp[0]);
/*
* Stderr is left as it is so that error messages get
* printed on the user's terminal.
*/
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 < 0)
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, 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) < 0 || pipe(pout) < 0)
fatal("Could not create pipes to communicate with the proxy: %.100s",
strerror(errno));
command_string = expand_proxy_command(proxy_command, options.user,
host, port);
debug("Executing proxy command: %.500s", command_string);
/* 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) < 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] = 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);
}
/* 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. */
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);
}
/*
* 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;
}
/*
* Creates a ocket 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;
struct ifaddrs *ifaddrs = NULL;
char ntop[NI_MAXHOST];
sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
if (sock < 0) {
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;
}
if (res->ai_addrlen > sizeof(bindaddr)) {
error("%s: addr doesn't fit", __func__);
goto fail;
}
memcpy(&bindaddr, res->ai_addr, res->ai_addrlen);
bindaddrlen = res->ai_addrlen;
} else if (options.bind_interface != NULL) {
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;
}
}
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);
if (ifaddrs != NULL)
freeifaddrs(ifaddrs);
return sock;
}
/*
* Wait up to *timeoutp milliseconds for fd to be readable. Updates
* *timeoutp with time remaining.
* Returns 0 if fd ready or -1 on timeout or error (see errno).
*/
static int
waitrfd(int fd, int *timeoutp)
{
struct pollfd pfd;
struct timeval t_start;
int oerrno, r;
monotime_tv(&t_start);
pfd.fd = fd;
pfd.events = POLLIN;
for (; *timeoutp >= 0;) {
r = poll(&pfd, 1, *timeoutp);
oerrno = errno;
ms_subtract_diff(&t_start, timeoutp);
errno = oerrno;
if (r > 0)
return 0;
else if (r == -1 && errno != EAGAIN)
return -1;
else if (r == 0)
break;
}
/* timeout */
errno = ETIMEDOUT;
return -1;
}
static int
timeout_connect(int sockfd, const struct sockaddr *serv_addr,
socklen_t addrlen, int *timeoutp)
{
int optval = 0;
socklen_t optlen = sizeof(optval);
/* No timeout: just do a blocking connect() */
if (*timeoutp <= 0)
return connect(sockfd, serv_addr, addrlen);
set_nonblock(sockfd);
if (connect(sockfd, serv_addr, addrlen) == 0) {
/* Succeeded already? */
unset_nonblock(sockfd);
return 0;
} else if (errno != EINPROGRESS)
return -1;
if (waitrfd(sockfd, timeoutp) == -1)
return -1;
/* Completed or failed */
if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval, &optlen) == -1) {
debug("getsockopt: %s", strerror(errno));
return -1;
}
if (optval != 0) {
errno = optval;
return -1;
}
unset_nonblock(sockfd);
return 0;
}
/*
* 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;
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;
}
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)) < 0)
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, struct addrinfo *addrs,
struct sockaddr_storage *hostaddr, u_short port, int family,
int connection_attempts, int *timeout_ms, int want_keepalive)
{
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 ((ssh_packet_set_connection(ssh,
STDIN_FILENO, STDOUT_FILENO)) == NULL)
return -1; /* ssh_packet_set_connection logs error */
return 0;
} else if (options.proxy_use_fdpass) {
return ssh_proxy_fdpass_connect(ssh, host, port,
options.proxy_command);
}
return ssh_proxy_connect(ssh, host, port, options.proxy_command);
}
static void
send_client_banner(int connection_out, int minor1)
{
/* Send our own protocol version identification. */
xasprintf(&client_version_string, "SSH-%d.%d-%.100s\r\n",
PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION);
if (atomicio(vwrite, connection_out, client_version_string,
strlen(client_version_string)) != strlen(client_version_string))
fatal("write: %.100s", strerror(errno));
chop(client_version_string);
debug("Local version string %.100s", client_version_string);
}
/*
* Waits for the server identification string, and sends our own
* identification string.
*/
void
ssh_exchange_identification(int timeout_ms)
{
char buf[256], remote_version[256]; /* must be same size! */
int remote_major, remote_minor, mismatch;
int connection_in = packet_get_connection_in();
int connection_out = packet_get_connection_out();
u_int i, n;
size_t len;
int rc;
send_client_banner(connection_out, 0);
/* Read other side's version identification. */
for (n = 0;;) {
for (i = 0; i < sizeof(buf) - 1; i++) {
if (timeout_ms > 0) {
rc = waitrfd(connection_in, &timeout_ms);
if (rc == -1 && errno == ETIMEDOUT) {
fatal("Connection timed out during "
"banner exchange");
} else if (rc == -1) {
fatal("%s: %s",
__func__, strerror(errno));
}
}
len = atomicio(read, connection_in, &buf[i], 1);
if (len != 1 && errno == EPIPE)
fatal("ssh_exchange_identification: "
"Connection closed by remote host");
else if (len != 1)
fatal("ssh_exchange_identification: "
"read: %.100s", strerror(errno));
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;
}
if (++n > 65536)
fatal("ssh_exchange_identification: "
"No banner received");
}
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);
active_state->compat = compat_datafellows(remote_version);
mismatch = 0;
switch (remote_major) {
case 2:
break;
case 1:
if (remote_minor != 99)
mismatch = 1;
break;
default:
mismatch = 1;
break;
}
if (mismatch)
fatal("Protocol major versions differ: %d vs. %d",
PROTOCOL_MAJOR_2, remote_major);
if ((datafellows & SSH_BUG_RSASIGMD5) != 0)
logit("Server version \"%.100s\" uses unsafe RSA signature "
"scheme; disabling use of RSA keys", remote_version);
chop(server_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)
return 0;
p[strcspn(p, "\n")] = '\0';
if (p[0] == '\0' || strcasecmp(p, "no") == 0)
ret = 0;
else if (strcasecmp(p, "yes") == 0)
ret = 1;
free(p);
if (ret != -1)
return ret;
}
}
static int
check_host_cert(const char *host, const struct sshkey *host_key)
{
const char *reason;
if (sshkey_cert_check_authority(host_key, 1, 0, host, &reason) != 0) {
error("%s", reason);
return 0;
}
if (sshbuf_len(host_key->cert->critical) != 0) {
error("Certificate for %s contains unsupported "
"critical options(s)", host);
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];
/*
* 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, hostaddr->sa_len,
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;
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)? ",
host, ip, msg1, type, fp,
options.visual_host_key ? "\n" : "",
options.visual_host_key ? ra : "",
msg2);
free(ra);
free(fp);
if (!confirm(msg))
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))
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(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. */
ssh_exchange_identification(timeout_ms);
/* Put the connection into non-blocking mode. */
packet_set_nonblocking();
/* key exchange */
/* authenticate user */
debug("Authenticating to %s:%d as '%s'", host, port, server_user);
ssh_kex2(host, hostaddr, port);
ssh_userauth2(local_user, server_user, host, sensitive);
free(local_user);
}
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 = xcalloc(1, size);
strlcpy(padded, password, size);
packet_put_string(padded, size);
explicit_bzero(padded, size);
free(padded);
}
/* 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);
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, const 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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