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openssh/sshd.c

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/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
* Created: Fri Mar 17 17:09:28 1995 ylo
* This program is the ssh daemon. It listens for connections from clients, and
* performs authentication, executes use commands or shell, and forwards
* information to/from the application to the user client over an encrypted
* connection. This can also handle forwarding of X11, TCP/IP, and authentication
* agent connections.
*
* SSH2 implementation,
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*/
#include "includes.h"
RCSID("$OpenBSD: sshd.c,v 1.107 2000/04/19 07:05:50 deraadt Exp $");
#include "xmalloc.h"
#include "rsa.h"
#include "ssh.h"
#include "pty.h"
#include "packet.h"
#include "cipher.h"
#include "mpaux.h"
#include "servconf.h"
#include "uidswap.h"
#include "compat.h"
#include "buffer.h"
#include "ssh2.h"
#include <openssl/dh.h>
#include <openssl/bn.h>
#include <openssl/hmac.h>
#include "kex.h"
#include <openssl/dsa.h>
#include <openssl/rsa.h>
#include "key.h"
#include "dsa.h"
#include "auth.h"
#include "myproposal.h"
#ifdef LIBWRAP
#include <tcpd.h>
#include <syslog.h>
int allow_severity = LOG_INFO;
int deny_severity = LOG_WARNING;
#endif /* LIBWRAP */
#ifndef O_NOCTTY
#define O_NOCTTY 0
#endif
/* Server configuration options. */
ServerOptions options;
/* Name of the server configuration file. */
char *config_file_name = SERVER_CONFIG_FILE;
/*
* Flag indicating whether IPv4 or IPv6. This can be set on the command line.
* Default value is AF_UNSPEC means both IPv4 and IPv6.
*/
#ifdef IPV4_DEFAULT
int IPv4or6 = AF_INET;
#else
int IPv4or6 = AF_UNSPEC;
#endif
/*
* Debug mode flag. This can be set on the command line. If debug
* mode is enabled, extra debugging output will be sent to the system
* log, the daemon will not go to background, and will exit after processing
* the first connection.
*/
int debug_flag = 0;
/* Flag indicating that the daemon is being started from inetd. */
int inetd_flag = 0;
/* debug goes to stderr unless inetd_flag is set */
int log_stderr = 0;
/* argv[0] without path. */
char *av0;
/* Saved arguments to main(). */
char **saved_argv;
/*
* The sockets that the server is listening; this is used in the SIGHUP
* signal handler.
*/
#define MAX_LISTEN_SOCKS 16
int listen_socks[MAX_LISTEN_SOCKS];
int num_listen_socks = 0;
/*
* the client's version string, passed by sshd2 in compat mode. if != NULL,
* sshd will skip the version-number exchange
*/
char *client_version_string = NULL;
char *server_version_string = NULL;
/*
* Any really sensitive data in the application is contained in this
* structure. The idea is that this structure could be locked into memory so
* that the pages do not get written into swap. However, there are some
* problems. The private key contains BIGNUMs, and we do not (in principle)
* have access to the internals of them, and locking just the structure is
* not very useful. Currently, memory locking is not implemented.
*/
struct {
RSA *private_key; /* Private part of server key. */
RSA *host_key; /* Private part of host key. */
} sensitive_data;
/*
* Flag indicating whether the current session key has been used. This flag
* is set whenever the key is used, and cleared when the key is regenerated.
*/
int key_used = 0;
/* This is set to true when SIGHUP is received. */
int received_sighup = 0;
/* Public side of the server key. This value is regenerated regularly with
the private key. */
RSA *public_key;
/* session identifier, used by RSA-auth */
unsigned char session_id[16];
/* Prototypes for various functions defined later in this file. */
void do_ssh1_kex();
void do_ssh2_kex();
/*
* Close all listening sockets
*/
void
close_listen_socks(void)
{
int i;
for (i = 0; i < num_listen_socks; i++)
close(listen_socks[i]);
num_listen_socks = -1;
}
/*
* Signal handler for SIGHUP. Sshd execs itself when it receives SIGHUP;
* the effect is to reread the configuration file (and to regenerate
* the server key).
*/
void
sighup_handler(int sig)
{
received_sighup = 1;
signal(SIGHUP, sighup_handler);
}
/*
* Called from the main program after receiving SIGHUP.
* Restarts the server.
*/
void
sighup_restart()
{
log("Received SIGHUP; restarting.");
close_listen_socks();
execv(saved_argv[0], saved_argv);
log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno));
exit(1);
}
/*
* Generic signal handler for terminating signals in the master daemon.
* These close the listen socket; not closing it seems to cause "Address
* already in use" problems on some machines, which is inconvenient.
*/
void
sigterm_handler(int sig)
{
log("Received signal %d; terminating.", sig);
close_listen_socks();
exit(255);
}
/*
* SIGCHLD handler. This is called whenever a child dies. This will then
* reap any zombies left by exited c.
*/
void
main_sigchld_handler(int sig)
{
int save_errno = errno;
int status;
while (waitpid(-1, &status, WNOHANG) > 0)
;
signal(SIGCHLD, main_sigchld_handler);
errno = save_errno;
}
/*
* Signal handler for the alarm after the login grace period has expired.
*/
void
grace_alarm_handler(int sig)
{
/* Close the connection. */
packet_close();
/* Log error and exit. */
fatal("Timeout before authentication for %s.", get_remote_ipaddr());
}
/*
* Signal handler for the key regeneration alarm. Note that this
* alarm only occurs in the daemon waiting for connections, and it does not
* do anything with the private key or random state before forking.
* Thus there should be no concurrency control/asynchronous execution
* problems.
*/
void
key_regeneration_alarm(int sig)
{
int save_errno = errno;
/* Check if we should generate a new key. */
if (key_used) {
/* This should really be done in the background. */
log("Generating new %d bit RSA key.", options.server_key_bits);
if (sensitive_data.private_key != NULL)
RSA_free(sensitive_data.private_key);
sensitive_data.private_key = RSA_new();
if (public_key != NULL)
RSA_free(public_key);
public_key = RSA_new();
rsa_generate_key(sensitive_data.private_key, public_key,
options.server_key_bits);
arc4random_stir();
key_used = 0;
log("RSA key generation complete.");
}
/* Reschedule the alarm. */
signal(SIGALRM, key_regeneration_alarm);
alarm(options.key_regeneration_time);
errno = save_errno;
}
char *
chop(char *s)
{
char *t = s;
while (*t) {
if(*t == '\n' || *t == '\r') {
*t = '\0';
return s;
}
t++;
}
return s;
}
void
sshd_exchange_identification(int sock_in, int sock_out)
{
int i, mismatch;
int remote_major, remote_minor;
int major, minor;
char *s;
char buf[256]; /* Must not be larger than remote_version. */
char remote_version[256]; /* Must be at least as big as buf. */
if ((options.protocol & SSH_PROTO_1) &&
(options.protocol & SSH_PROTO_2)) {
major = PROTOCOL_MAJOR_1;
minor = 99;
} else if (options.protocol & SSH_PROTO_2) {
major = PROTOCOL_MAJOR_2;
minor = PROTOCOL_MINOR_2;
} else {
major = PROTOCOL_MAJOR_1;
minor = PROTOCOL_MINOR_1;
}
snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", major, minor, SSH_VERSION);
server_version_string = xstrdup(buf);
if (client_version_string == NULL) {
/* Send our protocol version identification. */
if (atomicio(write, sock_out, server_version_string, strlen(server_version_string))
!= strlen(server_version_string)) {
log("Could not write ident string to %s.", get_remote_ipaddr());
fatal_cleanup();
}
/* Read other side\'s version identification. */
for (i = 0; i < sizeof(buf) - 1; i++) {
if (read(sock_in, &buf[i], 1) != 1) {
log("Did not receive ident string from %s.", get_remote_ipaddr());
fatal_cleanup();
}
if (buf[i] == '\r') {
buf[i] = '\n';
buf[i + 1] = 0;
continue;
}
if (buf[i] == '\n') {
/* buf[i] == '\n' */
buf[i + 1] = 0;
break;
}
}
buf[sizeof(buf) - 1] = 0;
client_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(client_version_string, "SSH-%d.%d-%[^\n]\n",
&remote_major, &remote_minor, remote_version) != 3) {
s = "Protocol mismatch.\n";
(void) atomicio(write, sock_out, s, strlen(s));
close(sock_in);
close(sock_out);
log("Bad protocol version identification '%.100s' from %s",
client_version_string, get_remote_ipaddr());
fatal_cleanup();
}
debug("Client protocol version %d.%d; client software version %.100s",
remote_major, remote_minor, remote_version);
compat_datafellows(remote_version);
mismatch = 0;
switch(remote_major) {
case 1:
if (!(options.protocol & SSH_PROTO_1)) {
mismatch = 1;
break;
}
if (remote_minor < 3) {
packet_disconnect("Your ssh version is too old and"
"is no longer supported. Please install a newer version.");
} else if (remote_minor == 3) {
/* note that this disables agent-forwarding */
enable_compat13();
}
if (remote_minor == 99) {
if (options.protocol & SSH_PROTO_2)
enable_compat20();
else
mismatch = 1;
}
break;
case 2:
if (options.protocol & SSH_PROTO_2) {
enable_compat20();
break;
}
/* FALLTHROUGH */
default:
mismatch = 1;
break;
}
chop(server_version_string);
chop(client_version_string);
debug("Local version string %.200s", server_version_string);
if (mismatch) {
s = "Protocol major versions differ.\n";
(void) atomicio(write, sock_out, s, strlen(s));
close(sock_in);
close(sock_out);
log("Protocol major versions differ for %s: %.200s vs. %.200s",
get_remote_ipaddr(),
server_version_string, client_version_string);
fatal_cleanup();
}
}
/*
* Main program for the daemon.
*/
int
main(int ac, char **av)
{
extern char *optarg;
extern int optind;
int opt, sock_in = 0, sock_out = 0, newsock, i, fdsetsz, on = 1;
pid_t pid;
socklen_t fromlen;
int silentrsa = 0;
fd_set *fdset;
struct sockaddr_storage from;
const char *remote_ip;
int remote_port;
char *comment;
FILE *f;
struct linger linger;
struct addrinfo *ai;
char ntop[NI_MAXHOST], strport[NI_MAXSERV];
int listen_sock, maxfd;
/* Save argv[0]. */
saved_argv = av;
if (strchr(av[0], '/'))
av0 = strrchr(av[0], '/') + 1;
else
av0 = av[0];
/* Initialize configuration options to their default values. */
initialize_server_options(&options);
/* Parse command-line arguments. */
while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:diqQ46")) != EOF) {
switch (opt) {
case '4':
IPv4or6 = AF_INET;
break;
case '6':
IPv4or6 = AF_INET6;
break;
case 'f':
config_file_name = optarg;
break;
case 'd':
debug_flag = 1;
options.log_level = SYSLOG_LEVEL_DEBUG;
break;
case 'i':
inetd_flag = 1;
break;
case 'Q':
silentrsa = 1;
break;
case 'q':
options.log_level = SYSLOG_LEVEL_QUIET;
break;
case 'b':
options.server_key_bits = atoi(optarg);
break;
case 'p':
options.ports_from_cmdline = 1;
if (options.num_ports >= MAX_PORTS)
fatal("too many ports.\n");
options.ports[options.num_ports++] = atoi(optarg);
break;
case 'g':
options.login_grace_time = atoi(optarg);
break;
case 'k':
options.key_regeneration_time = atoi(optarg);
break;
case 'h':
options.host_key_file = optarg;
break;
case 'V':
client_version_string = optarg;
/* only makes sense with inetd_flag, i.e. no listen() */
inetd_flag = 1;
break;
case '?':
default:
fprintf(stderr, "sshd version %s\n", SSH_VERSION);
fprintf(stderr, "Usage: %s [options]\n", av0);
fprintf(stderr, "Options:\n");
fprintf(stderr, " -f file Configuration file (default %s)\n", SERVER_CONFIG_FILE);
fprintf(stderr, " -d Debugging mode\n");
fprintf(stderr, " -i Started from inetd\n");
fprintf(stderr, " -q Quiet (no logging)\n");
fprintf(stderr, " -p port Listen on the specified port (default: 22)\n");
fprintf(stderr, " -k seconds Regenerate server key every this many seconds (default: 3600)\n");
fprintf(stderr, " -g seconds Grace period for authentication (default: 300)\n");
fprintf(stderr, " -b bits Size of server RSA key (default: 768 bits)\n");
fprintf(stderr, " -h file File from which to read host key (default: %s)\n",
HOST_KEY_FILE);
fprintf(stderr, " -4 Use IPv4 only\n");
fprintf(stderr, " -6 Use IPv6 only\n");
exit(1);
}
}
/*
* Force logging to stderr until we have loaded the private host
* key (unless started from inetd)
*/
log_init(av0,
options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
options.log_facility == -1 ? SYSLOG_FACILITY_AUTH : options.log_facility,
!inetd_flag);
/* check if RSA support exists */
if (rsa_alive() == 0) {
if (silentrsa == 0)
printf("sshd: no RSA support in libssl and libcrypto -- exiting. See ssl(8)\n");
log("no RSA support in libssl and libcrypto -- exiting. See ssl(8)");
exit(1);
}
/* Read server configuration options from the configuration file. */
read_server_config(&options, config_file_name);
/* Fill in default values for those options not explicitly set. */
fill_default_server_options(&options);
/* Check certain values for sanity. */
if (options.server_key_bits < 512 ||
options.server_key_bits > 32768) {
fprintf(stderr, "Bad server key size.\n");
exit(1);
}
/* Check that there are no remaining arguments. */
if (optind < ac) {
fprintf(stderr, "Extra argument %s.\n", av[optind]);
exit(1);
}
debug("sshd version %.100s", SSH_VERSION);
sensitive_data.host_key = RSA_new();
errno = 0;
/* Load the host key. It must have empty passphrase. */
if (!load_private_key(options.host_key_file, "",
sensitive_data.host_key, &comment)) {
error("Could not load host key: %.200s: %.100s",
options.host_key_file, strerror(errno));
exit(1);
}
xfree(comment);
/* Initialize the log (it is reinitialized below in case we
forked). */
if (debug_flag && !inetd_flag)
log_stderr = 1;
log_init(av0, options.log_level, options.log_facility, log_stderr);
/* If not in debugging mode, and not started from inetd,
disconnect from the controlling terminal, and fork. The
original process exits. */
if (!debug_flag && !inetd_flag) {
#ifdef TIOCNOTTY
int fd;
#endif /* TIOCNOTTY */
if (daemon(0, 0) < 0)
fatal("daemon() failed: %.200s", strerror(errno));
/* Disconnect from the controlling tty. */
#ifdef TIOCNOTTY
fd = open("/dev/tty", O_RDWR | O_NOCTTY);
if (fd >= 0) {
(void) ioctl(fd, TIOCNOTTY, NULL);
close(fd);
}
#endif /* TIOCNOTTY */
}
/* Reinitialize the log (because of the fork above). */
log_init(av0, options.log_level, options.log_facility, log_stderr);
/* Check that server and host key lengths differ sufficiently.
This is necessary to make double encryption work with rsaref.
Oh, I hate software patents. I dont know if this can go? Niels */
if (options.server_key_bits >
BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED &&
options.server_key_bits <
BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
options.server_key_bits =
BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED;
debug("Forcing server key to %d bits to make it differ from host key.",
options.server_key_bits);
}
/* Do not display messages to stdout in RSA code. */
rsa_set_verbose(0);
/* Initialize the random number generator. */
arc4random_stir();
/* Chdir to the root directory so that the current disk can be
unmounted if desired. */
chdir("/");
/* Start listening for a socket, unless started from inetd. */
if (inetd_flag) {
int s1, s2;
s1 = dup(0); /* Make sure descriptors 0, 1, and 2 are in use. */
s2 = dup(s1);
sock_in = dup(0);
sock_out = dup(1);
/* We intentionally do not close the descriptors 0, 1, and 2
as our code for setting the descriptors won\'t work
if ttyfd happens to be one of those. */
debug("inetd sockets after dupping: %d, %d", sock_in, sock_out);
public_key = RSA_new();
sensitive_data.private_key = RSA_new();
/* XXX check options.protocol */
log("Generating %d bit RSA key.", options.server_key_bits);
rsa_generate_key(sensitive_data.private_key, public_key,
options.server_key_bits);
arc4random_stir();
log("RSA key generation complete.");
} else {
for (ai = options.listen_addrs; ai; ai = ai->ai_next) {
if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
continue;
if (num_listen_socks >= MAX_LISTEN_SOCKS)
fatal("Too many listen sockets. "
"Enlarge MAX_LISTEN_SOCKS");
if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
ntop, sizeof(ntop), strport, sizeof(strport),
NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
error("getnameinfo failed");
continue;
}
/* Create socket for listening. */
listen_sock = socket(ai->ai_family, SOCK_STREAM, 0);
if (listen_sock < 0) {
/* kernel may not support ipv6 */
verbose("socket: %.100s", strerror(errno));
continue;
}
if (fcntl(listen_sock, F_SETFL, O_NONBLOCK) < 0) {
error("listen_sock O_NONBLOCK: %s", strerror(errno));
close(listen_sock);
continue;
}
/*
* Set socket options. We try to make the port
* reusable and have it close as fast as possible
* without waiting in unnecessary wait states on
* close.
*/
setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR,
(void *) &on, sizeof(on));
linger.l_onoff = 1;
linger.l_linger = 5;
setsockopt(listen_sock, SOL_SOCKET, SO_LINGER,
(void *) &linger, sizeof(linger));
debug("Bind to port %s on %s.", strport, ntop);
/* Bind the socket to the desired port. */
if ((bind(listen_sock, ai->ai_addr, ai->ai_addrlen) < 0) &&
(!ai->ai_next)) {
error("Bind to port %s on %s failed: %.200s.",
strport, ntop, strerror(errno));
close(listen_sock);
continue;
}
listen_socks[num_listen_socks] = listen_sock;
num_listen_socks++;
/* Start listening on the port. */
log("Server listening on %s port %s.", ntop, strport);
if (listen(listen_sock, 5) < 0)
fatal("listen: %.100s", strerror(errno));
}
freeaddrinfo(options.listen_addrs);
if (!num_listen_socks)
fatal("Cannot bind any address.");
if (!debug_flag) {
/*
* Record our pid in /etc/sshd_pid to make it easier
* to kill the correct sshd. We don\'t want to do
* this before the bind above because the bind will
* fail if there already is a daemon, and this will
* overwrite any old pid in the file.
*/
f = fopen(SSH_DAEMON_PID_FILE, "w");
if (f) {
fprintf(f, "%u\n", (unsigned int) getpid());
fclose(f);
}
}
public_key = RSA_new();
sensitive_data.private_key = RSA_new();
log("Generating %d bit RSA key.", options.server_key_bits);
rsa_generate_key(sensitive_data.private_key, public_key,
options.server_key_bits);
arc4random_stir();
log("RSA key generation complete.");
/* Schedule server key regeneration alarm. */
signal(SIGALRM, key_regeneration_alarm);
alarm(options.key_regeneration_time);
/* Arrange to restart on SIGHUP. The handler needs listen_sock. */
signal(SIGHUP, sighup_handler);
signal(SIGTERM, sigterm_handler);
signal(SIGQUIT, sigterm_handler);
/* Arrange SIGCHLD to be caught. */
signal(SIGCHLD, main_sigchld_handler);
/* setup fd set for listen */
maxfd = 0;
for (i = 0; i < num_listen_socks; i++)
if (listen_socks[i] > maxfd)
maxfd = listen_socks[i];
fdsetsz = howmany(maxfd, NFDBITS) * sizeof(fd_mask);
fdset = (fd_set *)xmalloc(fdsetsz);
/*
* Stay listening for connections until the system crashes or
* the daemon is killed with a signal.
*/
for (;;) {
if (received_sighup)
sighup_restart();
/* Wait in select until there is a connection. */
memset(fdset, 0, fdsetsz);
for (i = 0; i < num_listen_socks; i++)
FD_SET(listen_socks[i], fdset);
if (select(maxfd + 1, fdset, NULL, NULL, NULL) < 0) {
if (errno != EINTR)
error("select: %.100s", strerror(errno));
continue;
}
for (i = 0; i < num_listen_socks; i++) {
if (!FD_ISSET(listen_socks[i], fdset))
continue;
fromlen = sizeof(from);
newsock = accept(listen_socks[i], (struct sockaddr *)&from,
&fromlen);
if (newsock < 0) {
if (errno != EINTR && errno != EWOULDBLOCK)
error("accept: %.100s", strerror(errno));
continue;
}
if (fcntl(newsock, F_SETFL, 0) < 0) {
error("newsock del O_NONBLOCK: %s", strerror(errno));
continue;
}
/*
* Got connection. Fork a child to handle it, unless
* we are in debugging mode.
*/
if (debug_flag) {
/*
* In debugging mode. Close the listening
* socket, and start processing the
* connection without forking.
*/
debug("Server will not fork when running in debugging mode.");
close_listen_socks();
sock_in = newsock;
sock_out = newsock;
pid = getpid();
break;
} else {
/*
* Normal production daemon. Fork, and have
* the child process the connection. The
* parent continues listening.
*/
if ((pid = fork()) == 0) {
/*
* Child. Close the listening socket, and start using the
* accepted socket. Reinitialize logging (since our pid has
* changed). We break out of the loop to handle the connection.
*/
close_listen_socks();
sock_in = newsock;
sock_out = newsock;
log_init(av0, options.log_level, options.log_facility, log_stderr);
break;
}
}
/* Parent. Stay in the loop. */
if (pid < 0)
error("fork: %.100s", strerror(errno));
else
debug("Forked child %d.", pid);
/* Mark that the key has been used (it was "given" to the child). */
key_used = 1;
arc4random_stir();
/* Close the new socket (the child is now taking care of it). */
close(newsock);
} /* for (i = 0; i < num_listen_socks; i++) */
/* child process check (or debug mode) */
if (num_listen_socks < 0)
break;
}
}
/* This is the child processing a new connection. */
/*
* Disable the key regeneration alarm. We will not regenerate the
* key since we are no longer in a position to give it to anyone. We
* will not restart on SIGHUP since it no longer makes sense.
*/
alarm(0);
signal(SIGALRM, SIG_DFL);
signal(SIGHUP, SIG_DFL);
signal(SIGTERM, SIG_DFL);
signal(SIGQUIT, SIG_DFL);
signal(SIGCHLD, SIG_DFL);
/*
* Set socket options for the connection. We want the socket to
* close as fast as possible without waiting for anything. If the
* connection is not a socket, these will do nothing.
*/
/* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
linger.l_onoff = 1;
linger.l_linger = 5;
setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
/*
* Register our connection. This turns encryption off because we do
* not have a key.
*/
packet_set_connection(sock_in, sock_out);
remote_port = get_remote_port();
remote_ip = get_remote_ipaddr();
/* Check whether logins are denied from this host. */
#ifdef LIBWRAP
/* XXX LIBWRAP noes not know about IPv6 */
{
struct request_info req;
request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL);
fromhost(&req);
if (!hosts_access(&req)) {
close(sock_in);
close(sock_out);
refuse(&req);
}
/*XXX IPv6 verbose("Connection from %.500s port %d", eval_client(&req), remote_port); */
}
#endif /* LIBWRAP */
/* Log the connection. */
verbose("Connection from %.500s port %d", remote_ip, remote_port);
/*
* We don\'t want to listen forever unless the other side
* successfully authenticates itself. So we set up an alarm which is
* cleared after successful authentication. A limit of zero
* indicates no limit. Note that we don\'t set the alarm in debugging
* mode; it is just annoying to have the server exit just when you
* are about to discover the bug.
*/
signal(SIGALRM, grace_alarm_handler);
if (!debug_flag)
alarm(options.login_grace_time);
sshd_exchange_identification(sock_in, sock_out);
/*
* Check that the connection comes from a privileged port. Rhosts-
* and Rhosts-RSA-Authentication only make sense from priviledged
* programs. Of course, if the intruder has root access on his local
* machine, he can connect from any port. So do not use these
* authentication methods from machines that you do not trust.
*/
if (remote_port >= IPPORT_RESERVED ||
remote_port < IPPORT_RESERVED / 2) {
options.rhosts_authentication = 0;
options.rhosts_rsa_authentication = 0;
}
#ifdef KRB4
if (!packet_connection_is_ipv4() &&
options.kerberos_authentication) {
debug("Kerberos Authentication disabled, only available for IPv4.");
options.kerberos_authentication = 0;
}
#endif /* KRB4 */
packet_set_nonblocking();
/* perform the key exchange */
/* authenticate user and start session */
if (compat20) {
do_ssh2_kex();
do_authentication2();
} else {
do_ssh1_kex();
do_authentication();
}
#ifdef KRB4
/* Cleanup user's ticket cache file. */
if (options.kerberos_ticket_cleanup)
(void) dest_tkt();
#endif /* KRB4 */
/* The connection has been terminated. */
verbose("Closing connection to %.100s", remote_ip);
#ifdef USE_PAM
finish_pam();
#endif /* USE_PAM */
packet_close();
exit(0);
}
/*
* SSH1 key exchange
*/
void
do_ssh1_kex()
{
int i, len;
int plen, slen;
BIGNUM *session_key_int;
unsigned char session_key[SSH_SESSION_KEY_LENGTH];
unsigned char cookie[8];
unsigned int cipher_type, auth_mask, protocol_flags;
u_int32_t rand = 0;
/*
* Generate check bytes that the client must send back in the user
* packet in order for it to be accepted; this is used to defy ip
* spoofing attacks. Note that this only works against somebody
* doing IP spoofing from a remote machine; any machine on the local
* network can still see outgoing packets and catch the random
* cookie. This only affects rhosts authentication, and this is one
* of the reasons why it is inherently insecure.
*/
for (i = 0; i < 8; i++) {
if (i % 4 == 0)
rand = arc4random();
cookie[i] = rand & 0xff;
rand >>= 8;
}
/*
* Send our public key. We include in the packet 64 bits of random
* data that must be matched in the reply in order to prevent IP
* spoofing.
*/
packet_start(SSH_SMSG_PUBLIC_KEY);
for (i = 0; i < 8; i++)
packet_put_char(cookie[i]);
/* Store our public server RSA key. */
packet_put_int(BN_num_bits(public_key->n));
packet_put_bignum(public_key->e);
packet_put_bignum(public_key->n);
/* Store our public host RSA key. */
packet_put_int(BN_num_bits(sensitive_data.host_key->n));
packet_put_bignum(sensitive_data.host_key->e);
packet_put_bignum(sensitive_data.host_key->n);
/* Put protocol flags. */
packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN);
/* Declare which ciphers we support. */
packet_put_int(cipher_mask1());
/* Declare supported authentication types. */
auth_mask = 0;
if (options.rhosts_authentication)
auth_mask |= 1 << SSH_AUTH_RHOSTS;
if (options.rhosts_rsa_authentication)
auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA;
if (options.rsa_authentication)
auth_mask |= 1 << SSH_AUTH_RSA;
#ifdef KRB4
if (options.kerberos_authentication)
auth_mask |= 1 << SSH_AUTH_KERBEROS;
#endif
#ifdef AFS
if (options.kerberos_tgt_passing)
auth_mask |= 1 << SSH_PASS_KERBEROS_TGT;
if (options.afs_token_passing)
auth_mask |= 1 << SSH_PASS_AFS_TOKEN;
#endif
#ifdef SKEY
if (options.skey_authentication == 1)
auth_mask |= 1 << SSH_AUTH_TIS;
#endif
if (options.password_authentication)
auth_mask |= 1 << SSH_AUTH_PASSWORD;
packet_put_int(auth_mask);
/* Send the packet and wait for it to be sent. */
packet_send();
packet_write_wait();
debug("Sent %d bit public key and %d bit host key.",
BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n));
/* Read clients reply (cipher type and session key). */
packet_read_expect(&plen, SSH_CMSG_SESSION_KEY);
/* Get cipher type and check whether we accept this. */
cipher_type = packet_get_char();
if (!(cipher_mask() & (1 << cipher_type)))
packet_disconnect("Warning: client selects unsupported cipher.");
/* Get check bytes from the packet. These must match those we
sent earlier with the public key packet. */
for (i = 0; i < 8; i++)
if (cookie[i] != packet_get_char())
packet_disconnect("IP Spoofing check bytes do not match.");
debug("Encryption type: %.200s", cipher_name(cipher_type));
/* Get the encrypted integer. */
session_key_int = BN_new();
packet_get_bignum(session_key_int, &slen);
protocol_flags = packet_get_int();
packet_set_protocol_flags(protocol_flags);
packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY);
/*
* Decrypt it using our private server key and private host key (key
* with larger modulus first).
*/
if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) {
/* Private key has bigger modulus. */
if (BN_num_bits(sensitive_data.private_key->n) <
BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
get_remote_ipaddr(),
BN_num_bits(sensitive_data.private_key->n),
BN_num_bits(sensitive_data.host_key->n),
SSH_KEY_BITS_RESERVED);
}
rsa_private_decrypt(session_key_int, session_key_int,
sensitive_data.private_key);
rsa_private_decrypt(session_key_int, session_key_int,
sensitive_data.host_key);
} else {
/* Host key has bigger modulus (or they are equal). */
if (BN_num_bits(sensitive_data.host_key->n) <
BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) {
fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d",
get_remote_ipaddr(),
BN_num_bits(sensitive_data.host_key->n),
BN_num_bits(sensitive_data.private_key->n),
SSH_KEY_BITS_RESERVED);
}
rsa_private_decrypt(session_key_int, session_key_int,
sensitive_data.host_key);
rsa_private_decrypt(session_key_int, session_key_int,
sensitive_data.private_key);
}
compute_session_id(session_id, cookie,
sensitive_data.host_key->n,
sensitive_data.private_key->n);
/* Destroy the private and public keys. They will no longer be needed. */
RSA_free(public_key);
RSA_free(sensitive_data.private_key);
RSA_free(sensitive_data.host_key);
/*
* Extract session key from the decrypted integer. The key is in the
* least significant 256 bits of the integer; the first byte of the
* key is in the highest bits.
*/
BN_mask_bits(session_key_int, sizeof(session_key) * 8);
len = BN_num_bytes(session_key_int);
if (len < 0 || len > sizeof(session_key))
fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
get_remote_ipaddr(),
len, sizeof(session_key));
memset(session_key, 0, sizeof(session_key));
BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
/* Destroy the decrypted integer. It is no longer needed. */
BN_clear_free(session_key_int);
/* Xor the first 16 bytes of the session key with the session id. */
for (i = 0; i < 16; i++)
session_key[i] ^= session_id[i];
/* Set the session key. From this on all communications will be encrypted. */
packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);
/* Destroy our copy of the session key. It is no longer needed. */
memset(session_key, 0, sizeof(session_key));
debug("Received session key; encryption turned on.");
/* Send an acknowledgement packet. Note that this packet is sent encrypted. */
packet_start(SSH_SMSG_SUCCESS);
packet_send();
packet_write_wait();
}
/*
* SSH2 key exchange: diffie-hellman-group1-sha1
*/
void
do_ssh2_kex()
{
Buffer *server_kexinit;
Buffer *client_kexinit;
int payload_len, dlen;
int slen;
unsigned int klen, kout;
char *ptr;
unsigned char *signature = NULL;
unsigned char *server_host_key_blob = NULL;
unsigned int sbloblen;
DH *dh;
BIGNUM *dh_client_pub = 0;
BIGNUM *shared_secret = 0;
int i;
unsigned char *kbuf;
unsigned char *hash;
Kex *kex;
Key *server_host_key;
char *cprop[PROPOSAL_MAX];
char *sprop[PROPOSAL_MAX];
/* KEXINIT */
if (options.ciphers != NULL) {
myproposal[PROPOSAL_ENC_ALGS_CTOS] =
myproposal[PROPOSAL_ENC_ALGS_STOC] = options.ciphers;
}
debug("Sending KEX init.");
for (i = 0; i < PROPOSAL_MAX; i++)
sprop[i] = xstrdup(myproposal[i]);
server_kexinit = kex_init(sprop);
packet_start(SSH2_MSG_KEXINIT);
packet_put_raw(buffer_ptr(server_kexinit), buffer_len(server_kexinit));
packet_send();
packet_write_wait();
debug("done");
packet_read_expect(&payload_len, SSH2_MSG_KEXINIT);
/*
* save raw KEXINIT payload in buffer. this is used during
* computation of the session_id and the session keys.
*/
client_kexinit = xmalloc(sizeof(*client_kexinit));
buffer_init(client_kexinit);
ptr = packet_get_raw(&payload_len);
buffer_append(client_kexinit, ptr, payload_len);
/* skip cookie */
for (i = 0; i < 16; i++)
(void) packet_get_char();
/* save kex init proposal strings */
for (i = 0; i < PROPOSAL_MAX; i++) {
cprop[i] = packet_get_string(NULL);
debug("got kexinit string: %s", cprop[i]);
}
i = (int) packet_get_char();
debug("first kex follow == %d", i);
i = packet_get_int();
debug("reserved == %d", i);
debug("done read kexinit");
kex = kex_choose_conf(cprop, sprop, 1);
/* KEXDH */
debug("Wait SSH2_MSG_KEXDH_INIT.");
packet_read_expect(&payload_len, SSH2_MSG_KEXDH_INIT);
/* key, cert */
dh_client_pub = BN_new();
if (dh_client_pub == NULL)
fatal("dh_client_pub == NULL");
packet_get_bignum2(dh_client_pub, &dlen);
#ifdef DEBUG_KEXDH
fprintf(stderr, "\ndh_client_pub= ");
bignum_print(dh_client_pub);
fprintf(stderr, "\n");
debug("bits %d", BN_num_bits(dh_client_pub));
#endif
/* generate DH key */
dh = dh_new_group1(); /* XXX depends on 'kex' */
#ifdef DEBUG_KEXDH
fprintf(stderr, "\np= ");
bignum_print(dh->p);
fprintf(stderr, "\ng= ");
bignum_print(dh->g);
fprintf(stderr, "\npub= ");
bignum_print(dh->pub_key);
fprintf(stderr, "\n");
#endif
if (!dh_pub_is_valid(dh, dh_client_pub))
packet_disconnect("bad client public DH value");
klen = DH_size(dh);
kbuf = xmalloc(klen);
kout = DH_compute_key(kbuf, dh_client_pub, dh);
#ifdef DEBUG_KEXDH
debug("shared secret: len %d/%d", klen, kout);
fprintf(stderr, "shared secret == ");
for (i = 0; i< kout; i++)
fprintf(stderr, "%02x", (kbuf[i])&0xff);
fprintf(stderr, "\n");
#endif
shared_secret = BN_new();
BN_bin2bn(kbuf, kout, shared_secret);
memset(kbuf, 0, klen);
xfree(kbuf);
server_host_key = dsa_get_serverkey(options.dsa_key_file);
dsa_make_serverkey_blob(server_host_key, &server_host_key_blob, &sbloblen);
/* calc H */ /* XXX depends on 'kex' */
hash = kex_hash(
client_version_string,
server_version_string,
buffer_ptr(client_kexinit), buffer_len(client_kexinit),
buffer_ptr(server_kexinit), buffer_len(server_kexinit),
(char *)server_host_key_blob, sbloblen,
dh_client_pub,
dh->pub_key,
shared_secret
);
buffer_free(client_kexinit);
buffer_free(server_kexinit);
xfree(client_kexinit);
xfree(server_kexinit);
#ifdef DEBUG_KEXDH
fprintf(stderr, "hash == ");
for (i = 0; i< 20; i++)
fprintf(stderr, "%02x", (hash[i])&0xff);
fprintf(stderr, "\n");
#endif
/* sign H */
dsa_sign(server_host_key, &signature, &slen, hash, 20);
/* hashlen depends on KEX */
key_free(server_host_key);
/* send server hostkey, DH pubkey 'f' and singed H */
packet_start(SSH2_MSG_KEXDH_REPLY);
packet_put_string((char *)server_host_key_blob, sbloblen);
packet_put_bignum2(dh->pub_key); // f
packet_put_string((char *)signature, slen);
packet_send();
xfree(signature);
packet_write_wait();
kex_derive_keys(kex, hash, shared_secret);
packet_set_kex(kex);
/* have keys, free DH */
DH_free(dh);
debug("send SSH2_MSG_NEWKEYS.");
packet_start(SSH2_MSG_NEWKEYS);
packet_send();
packet_write_wait();
debug("done: send SSH2_MSG_NEWKEYS.");
debug("Wait SSH2_MSG_NEWKEYS.");
packet_read_expect(&payload_len, SSH2_MSG_NEWKEYS);
debug("GOT SSH2_MSG_NEWKEYS.");
#ifdef DEBUG_KEXDH
/* send 1st encrypted/maced/compressed message */
packet_start(SSH2_MSG_IGNORE);
packet_put_cstring("markus");
packet_send();
packet_write_wait();
#endif
debug("done: KEX2.");
}
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