File: [local] / src / usr.bin / ssh / sshd.c (download)
Revision 1.65, Wed Nov 24 00:26:03 1999 UTC (24 years, 6 months ago) by deraadt
Branch: MAIN
Changes since 1.64: +116 -94 lines
much more KNF
|
/*
* 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.
*/
#include "includes.h"
RCSID("$Id: sshd.c,v 1.65 1999/11/24 00:26:03 deraadt Exp $");
#include "xmalloc.h"
#include "rsa.h"
#include "ssh.h"
#include "pty.h"
#include "packet.h"
#include "buffer.h"
#include "cipher.h"
#include "mpaux.h"
#include "servconf.h"
#include "uidswap.h"
#include "compat.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
/* Local Xauthority file. */
static char *xauthfile = NULL;
/* Server configuration options. */
ServerOptions options;
/* Name of the server configuration file. */
char *config_file_name = SERVER_CONFIG_FILE;
/*
* 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;
/* This is set to the socket that the server is listening; this is used in
the SIGHUP signal handler. */
int listen_sock;
/* 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;
/* Flags set in auth-rsa from authorized_keys flags. These are set in auth-rsa.c. */
int no_port_forwarding_flag = 0;
int no_agent_forwarding_flag = 0;
int no_x11_forwarding_flag = 0;
int no_pty_flag = 0;
/* RSA authentication "command=" option. */
char *forced_command = NULL;
/* RSA authentication "environment=" options. */
struct envstring *custom_environment = NULL;
/* Session id for the current session. */
unsigned char session_id[16];
/* 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;
/* Prototypes for various functions defined later in this file. */
void do_connection();
void do_authentication(char *user);
void do_authloop(struct passwd * pw);
void do_fake_authloop(char *user);
void do_authenticated(struct passwd * pw);
void do_exec_pty(const char *command, int ptyfd, int ttyfd,
const char *ttyname, struct passwd * pw, const char *term,
const char *display, const char *auth_proto,
const char *auth_data);
void do_exec_no_pty(const char *command, struct passwd * pw,
const char *display, const char *auth_proto,
const char *auth_data);
void do_child(const char *command, struct passwd * pw, const char *term,
const char *display, const char *auth_proto,
const char *auth_data, const char *ttyname);
/*
* 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_sock);
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_sock);
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());
}
/*
* convert ssh auth msg type into description
*/
char *
get_authname(int type)
{
switch (type) {
case SSH_CMSG_AUTH_PASSWORD:
return "password";
case SSH_CMSG_AUTH_RSA:
return "rsa";
case SSH_CMSG_AUTH_RHOSTS_RSA:
return "rhosts-rsa";
case SSH_CMSG_AUTH_RHOSTS:
return "rhosts";
#ifdef KRB4
case SSH_CMSG_AUTH_KERBEROS:
return "kerberos";
#endif
#ifdef SKEY
case SSH_CMSG_AUTH_TIS_RESPONSE:
return "s/key";
#endif
}
fatal("get_authname: unknown auth %d: internal error", type);
return NULL;
}
/*
* 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;
}
/*
* Main program for the daemon.
*/
int
main(int ac, char **av)
{
extern char *optarg;
extern int optind;
int opt, aux, sock_in, sock_out, newsock, i, pid, on = 1;
int remote_major, remote_minor;
int silentrsa = 0;
struct sockaddr_in sin;
char buf[100]; /* Must not be larger than remote_version. */
char remote_version[100]; /* Must be at least as big as buf. */
const char *remote_ip;
int remote_port;
char *comment;
FILE *f;
struct linger linger;
/* 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:diqQ")) != EOF) {
switch (opt) {
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.port = 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/sshd_config)\n", ETCDIR);
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);
exit(1);
}
}
/* 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);
}
if (options.port < 1 || options.port > 65535) {
fprintf(stderr, "Bad port number.\n");
exit(1);
}
/* Check that there are no remaining arguments. */
if (optind < ac) {
fprintf(stderr, "Extra argument %s.\n", av[optind]);
exit(1);
}
/* Force logging to stderr while loading the private host key
unless started from inetd */
log_init(av0, options.log_level, options.log_facility, !inetd_flag);
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("/");
/* Close connection cleanly after attack. */
cipher_attack_detected = packet_disconnect;
/* 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();
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 {
/* Create socket for listening. */
listen_sock = socket(AF_INET, SOCK_STREAM, 0);
if (listen_sock < 0)
fatal("socket: %.100s", strerror(errno));
/* 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));
/* Initialize the socket address. */
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr = options.listen_addr;
sin.sin_port = htons(options.port);
/* Bind the socket to the desired port. */
if (bind(listen_sock, (struct sockaddr *) & sin, sizeof(sin)) < 0) {
error("bind: %.100s", strerror(errno));
shutdown(listen_sock, SHUT_RDWR);
close(listen_sock);
fatal("Bind to port %d failed.", options.port);
}
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);
}
}
log("Server listening on port %d.", options.port);
if (listen(listen_sock, 5) < 0)
fatal("listen: %.100s", strerror(errno));
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);
/* Stay listening for connections until the system crashes
or the daemon is killed with a signal. */
for (;;) {
if (received_sighup)
sighup_restart();
/* Wait in accept until there is a connection. */
aux = sizeof(sin);
newsock = accept(listen_sock, (struct sockaddr *) & sin, &aux);
if (received_sighup)
sighup_restart();
if (newsock < 0) {
if (errno == EINTR)
continue;
error("accept: %.100s", 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_sock);
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_sock);
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);
}
}
/* 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
{
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);
}
verbose("Connection from %.500s port %d", eval_client(&req), remote_port);
}
#else
/* Log the connection. */
verbose("Connection from %.500s port %d", remote_ip, remote_port);
#endif /* LIBWRAP */
/* 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);
if (client_version_string != NULL) {
/* we are exec'ed by sshd2, so skip exchange of protocol version */
strlcpy(buf, client_version_string, sizeof(buf));
} else {
/* Send our protocol version identification. */
snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
PROTOCOL_MAJOR, PROTOCOL_MINOR, SSH_VERSION);
if (write(sock_out, buf, strlen(buf)) != strlen(buf))
fatal("Could not write ident string to %s.", get_remote_ipaddr());
/* Read other side\'s version identification. */
for (i = 0; i < sizeof(buf) - 1; i++) {
if (read(sock_in, &buf[i], 1) != 1)
fatal("Did not receive ident string from %s.", get_remote_ipaddr());
if (buf[i] == '\r') {
buf[i] = '\n';
buf[i + 1] = 0;
break;
}
if (buf[i] == '\n') {
/* buf[i] == '\n' */
buf[i + 1] = 0;
break;
}
}
buf[sizeof(buf) - 1] = 0;
}
/* Check that the versions match. In future this might accept
several versions and set appropriate flags to handle them. */
if (sscanf(buf, "SSH-%d.%d-%[^\n]\n", &remote_major, &remote_minor,
remote_version) != 3) {
const char *s = "Protocol mismatch.\n";
(void) write(sock_out, s, strlen(s));
close(sock_in);
close(sock_out);
fatal("Bad protocol version identification '%.100s' from %s",
buf, get_remote_ipaddr());
}
debug("Client protocol version %d.%d; client software version %.100s",
remote_major, remote_minor, remote_version);
if (remote_major != PROTOCOL_MAJOR) {
const char *s = "Protocol major versions differ.\n";
(void) write(sock_out, s, strlen(s));
close(sock_in);
close(sock_out);
fatal("Protocol major versions differ for %s: %d vs. %d",
get_remote_ipaddr(),
PROTOCOL_MAJOR, remote_major);
}
/* Check that the client has sufficiently high software version. */
if (remote_major == 1 && remote_minor < 3)
packet_disconnect("Your ssh version is too old and is no longer supported. Please install a newer version.");
if (remote_major == 1 && remote_minor == 3) {
enable_compat13();
if (strcmp(remote_version, "OpenSSH-1.1") != 0) {
debug("Agent forwarding disabled, remote version is not compatible.");
no_agent_forwarding_flag = 1;
}
}
/* 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;
}
packet_set_nonblocking();
/* Handle the connection. */
do_connection();
#ifdef KRB4
/* Cleanup user's ticket cache file. */
if (options.kerberos_ticket_cleanup)
(void) dest_tkt();
#endif /* KRB4 */
/* Cleanup user's local Xauthority file. */
if (xauthfile)
unlink(xauthfile);
/* The connection has been terminated. */
verbose("Closing connection to %.100s", remote_ip);
packet_close();
exit(0);
}
/*
* Process an incoming connection. Protocol version identifiers have already
* been exchanged. This sends server key and performs the key exchange.
* Server and host keys will no longer be needed after this functions.
*/
void
do_connection()
{
int i, len;
BIGNUM *session_key_int;
unsigned char session_key[SSH_SESSION_KEY_LENGTH];
unsigned char check_bytes[8];
char *user;
unsigned int cipher_type, auth_mask, protocol_flags;
int plen, slen;
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();
check_bytes[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(check_bytes[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_mask());
/* 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. */
cipher_type = packet_get_char();
/* 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 (check_bytes[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);
/* Get protocol flags. */
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 for this session. */
compute_session_id(session_id, check_bytes,
sensitive_data.host_key->n,
sensitive_data.private_key->n);
/* 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);
/* 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];
/* Destroy the decrypted integer. It is no longer needed. */
BN_clear_free(session_key_int);
/* 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();
/* Get the name of the user that we wish to log in as. */
packet_read_expect(&plen, SSH_CMSG_USER);
/* Get the user name. */
{
int ulen;
user = packet_get_string(&ulen);
packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
}
/* 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);
setproctitle("%s", user);
/* Do the authentication. */
do_authentication(user);
}
/*
* Check if the user is allowed to log in via ssh. If user is listed in
* DenyUsers or user's primary group is listed in DenyGroups, false will
* be returned. If AllowUsers isn't empty and user isn't listed there, or
* if AllowGroups isn't empty and user isn't listed there, false will be
* returned. Otherwise true is returned.
* XXX This function should also check if user has a valid shell
*/
static int
allowed_user(struct passwd * pw)
{
struct group *grp;
int i;
/* Shouldn't be called if pw is NULL, but better safe than sorry... */
if (!pw)
return 0;
/* XXX Should check for valid login shell */
/* Return false if user is listed in DenyUsers */
if (options.num_deny_users > 0) {
if (!pw->pw_name)
return 0;
for (i = 0; i < options.num_deny_users; i++)
if (match_pattern(pw->pw_name, options.deny_users[i]))
return 0;
}
/* Return false if AllowUsers isn't empty and user isn't listed
there */
if (options.num_allow_users > 0) {
if (!pw->pw_name)
return 0;
for (i = 0; i < options.num_allow_users; i++)
if (match_pattern(pw->pw_name, options.allow_users[i]))
break;
/* i < options.num_allow_users iff we break for loop */
if (i >= options.num_allow_users)
return 0;
}
/* Get the primary group name if we need it. Return false if it fails */
if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
grp = getgrgid(pw->pw_gid);
if (!grp)
return 0;
/* Return false if user's group is listed in DenyGroups */
if (options.num_deny_groups > 0) {
if (!grp->gr_name)
return 0;
for (i = 0; i < options.num_deny_groups; i++)
if (match_pattern(grp->gr_name, options.deny_groups[i]))
return 0;
}
/* Return false if AllowGroups isn't empty and user's
group isn't listed there */
if (options.num_allow_groups > 0) {
if (!grp->gr_name)
return 0;
for (i = 0; i < options.num_allow_groups; i++)
if (match_pattern(grp->gr_name, options.allow_groups[i]))
break;
/* i < options.num_allow_groups iff we break for
loop */
if (i >= options.num_allow_groups)
return 0;
}
}
/* We found no reason not to let this user try to log on... */
return 1;
}
/*
* Performs authentication of an incoming connection. Session key has already
* been exchanged and encryption is enabled. User is the user name to log
* in as (received from the client).
*/
void
do_authentication(char *user)
{
struct passwd *pw, pwcopy;
#ifdef AFS
/* If machine has AFS, set process authentication group. */
if (k_hasafs()) {
k_setpag();
k_unlog();
}
#endif /* AFS */
/* Verify that the user is a valid user. */
pw = getpwnam(user);
if (!pw || !allowed_user(pw))
do_fake_authloop(user);
/* Take a copy of the returned structure. */
memset(&pwcopy, 0, sizeof(pwcopy));
pwcopy.pw_name = xstrdup(pw->pw_name);
pwcopy.pw_passwd = xstrdup(pw->pw_passwd);
pwcopy.pw_uid = pw->pw_uid;
pwcopy.pw_gid = pw->pw_gid;
pwcopy.pw_dir = xstrdup(pw->pw_dir);
pwcopy.pw_shell = xstrdup(pw->pw_shell);
pw = &pwcopy;
/* If we are not running as root, the user must have the same uid
as the server. */
if (getuid() != 0 && pw->pw_uid != getuid())
packet_disconnect("Cannot change user when server not running as root.");
debug("Attempting authentication for %.100s.", user);
/* If the user has no password, accept authentication immediately. */
if (options.password_authentication &&
#ifdef KRB4
(!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
#endif /* KRB4 */
auth_password(pw, "")) {
/* Authentication with empty password succeeded. */
log("Login for user %s from %.100s, accepted without authentication.",
pw->pw_name, get_remote_ipaddr());
} else {
/* Loop until the user has been authenticated or the
connection is closed, do_authloop() returns only if
authentication is successfull */
do_authloop(pw);
}
/* Check if the user is logging in as root and root logins are disallowed. */
if (pw->pw_uid == 0 && !options.permit_root_login) {
if (forced_command)
log("Root login accepted for forced command.");
else
packet_disconnect("ROOT LOGIN REFUSED FROM %.200s",
get_canonical_hostname());
}
/* The user has been authenticated and accepted. */
packet_start(SSH_SMSG_SUCCESS);
packet_send();
packet_write_wait();
/* Perform session preparation. */
do_authenticated(pw);
}
#define AUTH_FAIL_MAX 6
#define AUTH_FAIL_LOG (AUTH_FAIL_MAX/2)
#define AUTH_FAIL_MSG "Too many authentication failures for %.100s"
/*
* read packets and try to authenticate local user *pw.
* return if authentication is successfull
*/
void
do_authloop(struct passwd * pw)
{
int attempt = 0;
unsigned int bits;
BIGNUM *client_host_key_e, *client_host_key_n;
BIGNUM *n;
char *client_user, *password;
char user[1024];
int plen, dlen, nlen, ulen, elen;
int type = 0;
void (*authlog) (const char *fmt,...) = verbose;
/* Indicate that authentication is needed. */
packet_start(SSH_SMSG_FAILURE);
packet_send();
packet_write_wait();
for (attempt = 1;; attempt++) {
int authenticated = 0;
strlcpy(user, "", sizeof user);
/* Get a packet from the client. */
type = packet_read(&plen);
/* Process the packet. */
switch (type) {
#ifdef AFS
case SSH_CMSG_HAVE_KERBEROS_TGT:
if (!options.kerberos_tgt_passing) {
/* packet_get_all(); */
verbose("Kerberos tgt passing disabled.");
break;
} else {
/* Accept Kerberos tgt. */
char *tgt = packet_get_string(&dlen);
packet_integrity_check(plen, 4 + dlen, type);
if (!auth_kerberos_tgt(pw, tgt))
verbose("Kerberos tgt REFUSED for %s", pw->pw_name);
xfree(tgt);
}
continue;
case SSH_CMSG_HAVE_AFS_TOKEN:
if (!options.afs_token_passing || !k_hasafs()) {
/* packet_get_all(); */
verbose("AFS token passing disabled.");
break;
} else {
/* Accept AFS token. */
char *token_string = packet_get_string(&dlen);
packet_integrity_check(plen, 4 + dlen, type);
if (!auth_afs_token(pw, token_string))
verbose("AFS token REFUSED for %s", pw->pw_name);
xfree(token_string);
}
continue;
#endif /* AFS */
#ifdef KRB4
case SSH_CMSG_AUTH_KERBEROS:
if (!options.kerberos_authentication) {
/* packet_get_all(); */
verbose("Kerberos authentication disabled.");
break;
} else {
/* Try Kerberos v4 authentication. */
KTEXT_ST auth;
char *tkt_user = NULL;
char *kdata = packet_get_string((unsigned int *) &auth.length);
packet_integrity_check(plen, 4 + auth.length, type);
if (auth.length < MAX_KTXT_LEN)
memcpy(auth.dat, kdata, auth.length);
xfree(kdata);
authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user);
if (authenticated) {
snprintf(user, sizeof user, " tktuser %s", tkt_user);
xfree(tkt_user);
}
}
break;
#endif /* KRB4 */
case SSH_CMSG_AUTH_RHOSTS:
if (!options.rhosts_authentication) {
verbose("Rhosts authentication disabled.");
break;
}
/* Get client user name. Note that we just have
to trust the client; this is one reason why
rhosts authentication is insecure. (Another is
IP-spoofing on a local network.) */
client_user = packet_get_string(&ulen);
packet_integrity_check(plen, 4 + ulen, type);
/* Try to authenticate using /etc/hosts.equiv and
.rhosts. */
authenticated = auth_rhosts(pw, client_user);
snprintf(user, sizeof user, " ruser %s", client_user);
xfree(client_user);
break;
case SSH_CMSG_AUTH_RHOSTS_RSA:
if (!options.rhosts_rsa_authentication) {
verbose("Rhosts with RSA authentication disabled.");
break;
}
/* Get client user name. Note that we just have
to trust the client; root on the client machine
can claim to be any user. */
client_user = packet_get_string(&ulen);
/* Get the client host key. */
client_host_key_e = BN_new();
client_host_key_n = BN_new();
bits = packet_get_int();
packet_get_bignum(client_host_key_e, &elen);
packet_get_bignum(client_host_key_n, &nlen);
if (bits != BN_num_bits(client_host_key_n))
error("Warning: keysize mismatch for client_host_key: "
"actual %d, announced %d", BN_num_bits(client_host_key_n), bits);
packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);
authenticated = auth_rhosts_rsa(pw, client_user,
client_host_key_e, client_host_key_n);
BN_clear_free(client_host_key_e);
BN_clear_free(client_host_key_n);
snprintf(user, sizeof user, " ruser %s", client_user);
xfree(client_user);
break;
case SSH_CMSG_AUTH_RSA:
if (!options.rsa_authentication) {
verbose("RSA authentication disabled.");
break;
}
/* RSA authentication requested. */
n = BN_new();
packet_get_bignum(n, &nlen);
packet_integrity_check(plen, nlen, type);
authenticated = auth_rsa(pw, n);
BN_clear_free(n);
break;
case SSH_CMSG_AUTH_PASSWORD:
if (!options.password_authentication) {
verbose("Password authentication disabled.");
break;
}
/* Read user password. It is in plain text, but
was transmitted over the encrypted channel so
it is not visible to an outside observer. */
password = packet_get_string(&dlen);
packet_integrity_check(plen, 4 + dlen, type);
/* Try authentication with the password. */
authenticated = auth_password(pw, password);
memset(password, 0, strlen(password));
xfree(password);
break;
#ifdef SKEY
case SSH_CMSG_AUTH_TIS:
debug("rcvd SSH_CMSG_AUTH_TIS");
if (options.skey_authentication == 1) {
char *skeyinfo = skey_keyinfo(pw->pw_name);
if (skeyinfo == NULL) {
debug("generating fake skeyinfo for %.100s.", pw->pw_name);
skeyinfo = skey_fake_keyinfo(pw->pw_name);
}
if (skeyinfo != NULL) {
/* we send our s/key- in
tis-challenge messages */
debug("sending challenge '%s'", skeyinfo);
packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
packet_put_string(skeyinfo, strlen(skeyinfo));
packet_send();
packet_write_wait();
continue;
}
}
break;
case SSH_CMSG_AUTH_TIS_RESPONSE:
debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
if (options.skey_authentication == 1) {
char *response = packet_get_string(&dlen);
debug("skey response == '%s'", response);
packet_integrity_check(plen, 4 + dlen, type);
authenticated = (skey_haskey(pw->pw_name) == 0 &&
skey_passcheck(pw->pw_name, response) != -1);
xfree(response);
}
break;
#else
case SSH_CMSG_AUTH_TIS:
/* TIS Authentication is unsupported */
log("TIS authentication unsupported.");
break;
#endif
default:
/* Any unknown messages will be ignored (and
failure returned) during authentication. */
log("Unknown message during authentication: type %d", type);
break;
}
/* Raise logging level */
if (authenticated ||
attempt == AUTH_FAIL_LOG ||
type == SSH_CMSG_AUTH_PASSWORD)
authlog = log;
authlog("%s %s for %.200s from %.200s port %d%s",
authenticated ? "Accepted" : "Failed",
get_authname(type),
pw->pw_uid == 0 ? "ROOT" : pw->pw_name,
get_remote_ipaddr(),
get_remote_port(),
user);
if (authenticated)
return;
if (attempt > AUTH_FAIL_MAX)
packet_disconnect(AUTH_FAIL_MSG, pw->pw_name);
/* Send a message indicating that the authentication attempt failed. */
packet_start(SSH_SMSG_FAILURE);
packet_send();
packet_write_wait();
}
}
/*
* The user does not exist or access is denied,
* but fake indication that authentication is needed.
*/
void
do_fake_authloop(char *user)
{
int attempt = 0;
log("Faking authloop for illegal user %.200s from %.200s port %d",
user,
get_remote_ipaddr(),
get_remote_port());
/* Indicate that authentication is needed. */
packet_start(SSH_SMSG_FAILURE);
packet_send();
packet_write_wait();
/* Keep reading packets, and always respond with a failure. This
is to avoid disclosing whether such a user really exists. */
for (attempt = 1;; attempt++) {
/* Read a packet. This will not return if the client
disconnects. */
int plen;
int type = packet_read(&plen);
#ifdef SKEY
int dlen;
char *password, *skeyinfo;
if (options.password_authentication &&
options.skey_authentication == 1 &&
type == SSH_CMSG_AUTH_PASSWORD &&
(password = packet_get_string(&dlen)) != NULL &&
dlen == 5 &&
strncasecmp(password, "s/key", 5) == 0 &&
(skeyinfo = skey_fake_keyinfo(user)) != NULL) {
/* Send a fake s/key challenge. */
packet_send_debug(skeyinfo);
}
#endif
if (attempt > AUTH_FAIL_MAX)
packet_disconnect(AUTH_FAIL_MSG, user);
/* Send failure. This should be indistinguishable from a
failed authentication. */
packet_start(SSH_SMSG_FAILURE);
packet_send();
packet_write_wait();
}
/* NOTREACHED */
abort();
}
/*
* Remove local Xauthority file.
*/
static void
xauthfile_cleanup_proc(void *ignore)
{
debug("xauthfile_cleanup_proc called");
if (xauthfile != NULL) {
unlink(xauthfile);
xfree(xauthfile);
xauthfile = NULL;
}
}
/*
* Prepares for an interactive session. This is called after the user has
* been successfully authenticated. During this message exchange, pseudo
* terminals are allocated, X11, TCP/IP, and authentication agent forwardings
* are requested, etc.
*/
void
do_authenticated(struct passwd * pw)
{
int type;
int compression_level = 0, enable_compression_after_reply = 0;
int have_pty = 0, ptyfd = -1, ttyfd = -1, xauthfd = -1;
int row, col, xpixel, ypixel, screen;
char ttyname[64];
char *command, *term = NULL, *display = NULL, *proto = NULL,
*data = NULL;
struct group *grp;
gid_t tty_gid;
mode_t tty_mode;
int n_bytes;
/* Cancel the alarm we set to limit the time taken for
authentication. */
alarm(0);
/* Inform the channel mechanism that we are the server side and
that the client may request to connect to any port at all.
(The user could do it anyway, and we wouldn\'t know what is
permitted except by the client telling us, so we can equally
well trust the client not to request anything bogus.) */
channel_permit_all_opens();
/* We stay in this loop until the client requests to execute a
shell or a command. */
while (1) {
int plen, dlen;
/* Get a packet from the client. */
type = packet_read(&plen);
/* Process the packet. */
switch (type) {
case SSH_CMSG_REQUEST_COMPRESSION:
packet_integrity_check(plen, 4, type);
compression_level = packet_get_int();
if (compression_level < 1 || compression_level > 9) {
packet_send_debug("Received illegal compression level %d.",
compression_level);
goto fail;
}
/* Enable compression after we have responded with SUCCESS. */
enable_compression_after_reply = 1;
break;
case SSH_CMSG_REQUEST_PTY:
if (no_pty_flag) {
debug("Allocating a pty not permitted for this authentication.");
goto fail;
}
if (have_pty)
packet_disconnect("Protocol error: you already have a pty.");
debug("Allocating pty.");
/* Allocate a pty and open it. */
if (!pty_allocate(&ptyfd, &ttyfd, ttyname)) {
error("Failed to allocate pty.");
goto fail;
}
/* Determine the group to make the owner of the tty. */
grp = getgrnam("tty");
if (grp) {
tty_gid = grp->gr_gid;
tty_mode = S_IRUSR | S_IWUSR | S_IWGRP;
} else {
tty_gid = pw->pw_gid;
tty_mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
}
/* Change ownership of the tty. */
if (chown(ttyname, pw->pw_uid, tty_gid) < 0)
fatal("chown(%.100s, %d, %d) failed: %.100s",
ttyname, pw->pw_uid, tty_gid, strerror(errno));
if (chmod(ttyname, tty_mode) < 0)
fatal("chmod(%.100s, 0%o) failed: %.100s",
ttyname, tty_mode, strerror(errno));
/* Get TERM from the packet. Note that the value may be of arbitrary length. */
term = packet_get_string(&dlen);
packet_integrity_check(dlen, strlen(term), type);
/* packet_integrity_check(plen, 4 + dlen + 4*4 + n_bytes, type); */
/* Remaining bytes */
n_bytes = plen - (4 + dlen + 4 * 4);
if (strcmp(term, "") == 0)
term = NULL;
/* Get window size from the packet. */
row = packet_get_int();
col = packet_get_int();
xpixel = packet_get_int();
ypixel = packet_get_int();
pty_change_window_size(ptyfd, row, col, xpixel, ypixel);
/* Get tty modes from the packet. */
tty_parse_modes(ttyfd, &n_bytes);
packet_integrity_check(plen, 4 + dlen + 4 * 4 + n_bytes, type);
/* Indicate that we now have a pty. */
have_pty = 1;
break;
case SSH_CMSG_X11_REQUEST_FORWARDING:
if (!options.x11_forwarding) {
packet_send_debug("X11 forwarding disabled in server configuration file.");
goto fail;
}
#ifdef XAUTH_PATH
if (no_x11_forwarding_flag) {
packet_send_debug("X11 forwarding not permitted for this authentication.");
goto fail;
}
debug("Received request for X11 forwarding with auth spoofing.");
if (display)
packet_disconnect("Protocol error: X11 display already set.");
{
int proto_len, data_len;
proto = packet_get_string(&proto_len);
data = packet_get_string(&data_len);
packet_integrity_check(plen, 4 + proto_len + 4 + data_len + 4, type);
}
if (packet_get_protocol_flags() & SSH_PROTOFLAG_SCREEN_NUMBER)
screen = packet_get_int();
else
screen = 0;
display = x11_create_display_inet(screen);
if (!display)
goto fail;
/* Setup to always have a local .Xauthority. */
xauthfile = xmalloc(MAXPATHLEN);
snprintf(xauthfile, MAXPATHLEN, "/tmp/XauthXXXXXX");
if ((xauthfd = mkstemp(xauthfile)) != -1) {
fchown(xauthfd, pw->pw_uid, pw->pw_gid);
close(xauthfd);
fatal_add_cleanup(xauthfile_cleanup_proc, NULL);
} else {
xfree(xauthfile);
xauthfile = NULL;
}
break;
#else /* XAUTH_PATH */
packet_send_debug("No xauth program; cannot forward with spoofing.");
goto fail;
#endif /* XAUTH_PATH */
case SSH_CMSG_AGENT_REQUEST_FORWARDING:
if (no_agent_forwarding_flag) {
debug("Authentication agent forwarding not permitted for this authentication.");
goto fail;
}
debug("Received authentication agent forwarding request.");
auth_input_request_forwarding(pw);
break;
case SSH_CMSG_PORT_FORWARD_REQUEST:
if (no_port_forwarding_flag) {
debug("Port forwarding not permitted for this authentication.");
goto fail;
}
debug("Received TCP/IP port forwarding request.");
channel_input_port_forward_request(pw->pw_uid == 0);
break;
case SSH_CMSG_MAX_PACKET_SIZE:
if (packet_set_maxsize(packet_get_int()) < 0)
goto fail;
break;
case SSH_CMSG_EXEC_SHELL:
/* Set interactive/non-interactive mode. */
packet_set_interactive(have_pty || display != NULL,
options.keepalives);
if (forced_command != NULL)
goto do_forced_command;
debug("Forking shell.");
packet_integrity_check(plen, 0, type);
if (have_pty)
do_exec_pty(NULL, ptyfd, ttyfd, ttyname, pw, term, display, proto, data);
else
do_exec_no_pty(NULL, pw, display, proto, data);
return;
case SSH_CMSG_EXEC_CMD:
/* Set interactive/non-interactive mode. */
packet_set_interactive(have_pty || display != NULL,
options.keepalives);
if (forced_command != NULL)
goto do_forced_command;
/* Get command from the packet. */
{
int dlen;
command = packet_get_string(&dlen);
debug("Executing command '%.500s'", command);
packet_integrity_check(plen, 4 + dlen, type);
}
if (have_pty)
do_exec_pty(command, ptyfd, ttyfd, ttyname, pw, term, display, proto, data);
else
do_exec_no_pty(command, pw, display, proto, data);
xfree(command);
return;
default:
/* Any unknown messages in this phase are ignored,
and a failure message is returned. */
log("Unknown packet type received after authentication: %d", type);
goto fail;
}
/* The request was successfully processed. */
packet_start(SSH_SMSG_SUCCESS);
packet_send();
packet_write_wait();
/* Enable compression now that we have replied if appropriate. */
if (enable_compression_after_reply) {
enable_compression_after_reply = 0;
packet_start_compression(compression_level);
}
continue;
fail:
/* The request failed. */
packet_start(SSH_SMSG_FAILURE);
packet_send();
packet_write_wait();
continue;
do_forced_command:
/* There is a forced command specified for this login.
Execute it. */
debug("Executing forced command: %.900s", forced_command);
if (have_pty)
do_exec_pty(forced_command, ptyfd, ttyfd, ttyname, pw, term, display, proto, data);
else
do_exec_no_pty(forced_command, pw, display, proto, data);
return;
}
}
/*
* This is called to fork and execute a command when we have no tty. This
* will call do_child from the child, and server_loop from the parent after
* setting up file descriptors and such.
*/
void
do_exec_no_pty(const char *command, struct passwd * pw,
const char *display, const char *auth_proto,
const char *auth_data)
{
int pid;
#ifdef USE_PIPES
int pin[2], pout[2], perr[2];
/* Allocate pipes for communicating with the program. */
if (pipe(pin) < 0 || pipe(pout) < 0 || pipe(perr) < 0)
packet_disconnect("Could not create pipes: %.100s",
strerror(errno));
#else /* USE_PIPES */
int inout[2], err[2];
/* Uses socket pairs to communicate with the program. */
if (socketpair(AF_UNIX, SOCK_STREAM, 0, inout) < 0 ||
socketpair(AF_UNIX, SOCK_STREAM, 0, err) < 0)
packet_disconnect("Could not create socket pairs: %.100s",
strerror(errno));
#endif /* USE_PIPES */
setproctitle("%s@notty", pw->pw_name);
/* Fork the child. */
if ((pid = fork()) == 0) {
/* Child. Reinitialize the log since the pid has changed. */
log_init(av0, options.log_level, options.log_facility, log_stderr);
/* Create a new session and process group since the 4.4BSD
setlogin() affects the entire process group. */
if (setsid() < 0)
error("setsid failed: %.100s", strerror(errno));
#ifdef USE_PIPES
/* Redirect stdin. We close the parent side of the socket
pair, and make the child side the standard input. */
close(pin[1]);
if (dup2(pin[0], 0) < 0)
perror("dup2 stdin");
close(pin[0]);
/* Redirect stdout. */
close(pout[0]);
if (dup2(pout[1], 1) < 0)
perror("dup2 stdout");
close(pout[1]);
/* Redirect stderr. */
close(perr[0]);
if (dup2(perr[1], 2) < 0)
perror("dup2 stderr");
close(perr[1]);
#else /* USE_PIPES */
/* Redirect stdin, stdout, and stderr. Stdin and stdout
will use the same socket, as some programs
(particularly rdist) seem to depend on it. */
close(inout[1]);
close(err[1]);
if (dup2(inout[0], 0) < 0) /* stdin */
perror("dup2 stdin");
if (dup2(inout[0], 1) < 0) /* stdout. Note: same socket as stdin. */
perror("dup2 stdout");
if (dup2(err[0], 2) < 0) /* stderr */
perror("dup2 stderr");
#endif /* USE_PIPES */
/* Do processing for the child (exec command etc). */
do_child(command, pw, NULL, display, auth_proto, auth_data, NULL);
/* NOTREACHED */
}
if (pid < 0)
packet_disconnect("fork failed: %.100s", strerror(errno));
#ifdef USE_PIPES
/* We are the parent. Close the child sides of the pipes. */
close(pin[0]);
close(pout[1]);
close(perr[1]);
/* Enter the interactive session. */
server_loop(pid, pin[1], pout[0], perr[0]);
/* server_loop has closed pin[1], pout[1], and perr[1]. */
#else /* USE_PIPES */
/* We are the parent. Close the child sides of the socket pairs. */
close(inout[0]);
close(err[0]);
/* Enter the interactive session. Note: server_loop must be able
to handle the case that fdin and fdout are the same. */
server_loop(pid, inout[1], inout[1], err[1]);
/* server_loop has closed inout[1] and err[1]. */
#endif /* USE_PIPES */
}
struct pty_cleanup_context {
const char *ttyname;
int pid;
};
/*
* Function to perform cleanup if we get aborted abnormally (e.g., due to a
* dropped connection).
*/
void
pty_cleanup_proc(void *context)
{
struct pty_cleanup_context *cu = context;
debug("pty_cleanup_proc called");
/* Record that the user has logged out. */
record_logout(cu->pid, cu->ttyname);
/* Release the pseudo-tty. */
pty_release(cu->ttyname);
}
/*
* This is called to fork and execute a command when we have a tty. This
* will call do_child from the child, and server_loop from the parent after
* setting up file descriptors, controlling tty, updating wtmp, utmp,
* lastlog, and other such operations.
*/
void
do_exec_pty(const char *command, int ptyfd, int ttyfd,
const char *ttyname, struct passwd * pw, const char *term,
const char *display, const char *auth_proto,
const char *auth_data)
{
int pid, fdout;
const char *hostname;
time_t last_login_time;
char buf[100], *time_string;
FILE *f;
char line[256];
struct stat st;
int quiet_login;
struct sockaddr_in from;
int fromlen;
struct pty_cleanup_context cleanup_context;
/* Get remote host name. */
hostname = get_canonical_hostname();
/* Get the time when the user last logged in. Buf will be set to
contain the hostname the last login was from. */
if (!options.use_login) {
last_login_time = get_last_login_time(pw->pw_uid, pw->pw_name,
buf, sizeof(buf));
}
setproctitle("%s@%s", pw->pw_name, strrchr(ttyname, '/') + 1);
/* Fork the child. */
if ((pid = fork()) == 0) {
pid = getpid();
/* Child. Reinitialize the log because the pid has
changed. */
log_init(av0, options.log_level, options.log_facility, log_stderr);
/* Close the master side of the pseudo tty. */
close(ptyfd);
/* Make the pseudo tty our controlling tty. */
pty_make_controlling_tty(&ttyfd, ttyname);
/* Redirect stdin from the pseudo tty. */
if (dup2(ttyfd, fileno(stdin)) < 0)
error("dup2 stdin failed: %.100s", strerror(errno));
/* Redirect stdout to the pseudo tty. */
if (dup2(ttyfd, fileno(stdout)) < 0)
error("dup2 stdin failed: %.100s", strerror(errno));
/* Redirect stderr to the pseudo tty. */
if (dup2(ttyfd, fileno(stderr)) < 0)
error("dup2 stdin failed: %.100s", strerror(errno));
/* Close the extra descriptor for the pseudo tty. */
close(ttyfd);
/* Get IP address of client. This is needed because we
want to record where the user logged in from. If the
connection is not a socket, let the ip address be 0.0.0.0. */
memset(&from, 0, sizeof(from));
if (packet_get_connection_in() == packet_get_connection_out()) {
fromlen = sizeof(from);
if (getpeername(packet_get_connection_in(),
(struct sockaddr *) & from, &fromlen) < 0) {
debug("getpeername: %.100s", strerror(errno));
fatal_cleanup();
}
}
/* Record that there was a login on that terminal. */
record_login(pid, ttyname, pw->pw_name, pw->pw_uid, hostname,
&from);
/* Check if .hushlogin exists. */
snprintf(line, sizeof line, "%.200s/.hushlogin", pw->pw_dir);
quiet_login = stat(line, &st) >= 0;
/* If the user has logged in before, display the time of
last login. However, don't display anything extra if a
command has been specified (so that ssh can be used to
execute commands on a remote machine without users
knowing they are going to another machine). Login(1)
will do this for us as well, so check if login(1) is used */
if (command == NULL && last_login_time != 0 && !quiet_login &&
!options.use_login) {
/* Convert the date to a string. */
time_string = ctime(&last_login_time);
/* Remove the trailing newline. */
if (strchr(time_string, '\n'))
*strchr(time_string, '\n') = 0;
/* Display the last login time. Host if displayed
if known. */
if (strcmp(buf, "") == 0)
printf("Last login: %s\r\n", time_string);
else
printf("Last login: %s from %s\r\n", time_string, buf);
}
/* Print /etc/motd unless a command was specified or
printing it was disabled in server options or login(1)
will be used. Note that some machines appear to print
it in /etc/profile or similar. */
if (command == NULL && options.print_motd && !quiet_login &&
!options.use_login) {
/* Print /etc/motd if it exists. */
f = fopen("/etc/motd", "r");
if (f) {
while (fgets(line, sizeof(line), f))
fputs(line, stdout);
fclose(f);
}
}
/* Do common processing for the child, such as execing the command. */
do_child(command, pw, term, display, auth_proto, auth_data, ttyname);
/* NOTREACHED */
}
if (pid < 0)
packet_disconnect("fork failed: %.100s", strerror(errno));
/* Parent. Close the slave side of the pseudo tty. */
close(ttyfd);
/* Create another descriptor of the pty master side for use as the
standard input. We could use the original descriptor, but this
simplifies code in server_loop. The descriptor is bidirectional. */
fdout = dup(ptyfd);
if (fdout < 0)
packet_disconnect("dup failed: %.100s", strerror(errno));
/* Add a cleanup function to clear the utmp entry and record logout
time in case we call fatal() (e.g., the connection gets closed). */
cleanup_context.pid = pid;
cleanup_context.ttyname = ttyname;
fatal_add_cleanup(pty_cleanup_proc, (void *) &cleanup_context);
/* Enter interactive session. */
server_loop(pid, ptyfd, fdout, -1);
/* server_loop has not closed ptyfd and fdout. */
/* Cancel the cleanup function. */
fatal_remove_cleanup(pty_cleanup_proc, (void *) &cleanup_context);
/* Record that the user has logged out. */
record_logout(pid, ttyname);
/* Release the pseudo-tty. */
pty_release(ttyname);
/* Close the server side of the socket pairs. We must do this
after the pty cleanup, so that another process doesn't get this
pty while we're still cleaning up. */
close(ptyfd);
close(fdout);
}
/*
* Sets the value of the given variable in the environment. If the variable
* already exists, its value is overriden.
*/
void
child_set_env(char ***envp, unsigned int *envsizep, const char *name,
const char *value)
{
unsigned int i, namelen;
char **env;
/* Find the slot where the value should be stored. If the
variable already exists, we reuse the slot; otherwise we append
a new slot at the end of the array, expanding if necessary. */
env = *envp;
namelen = strlen(name);
for (i = 0; env[i]; i++)
if (strncmp(env[i], name, namelen) == 0 && env[i][namelen] == '=')
break;
if (env[i]) {
/* Name already exists. Reuse the slot. */
xfree(env[i]);
} else {
/* New variable. Expand the array if necessary. */
if (i >= (*envsizep) - 1) {
(*envsizep) += 50;
env = (*envp) = xrealloc(env, (*envsizep) * sizeof(char *));
}
/* Need to set the NULL pointer at end of array beyond the new slot. */
env[i + 1] = NULL;
}
/* Allocate space and format the variable in the appropriate slot. */
env[i] = xmalloc(strlen(name) + 1 + strlen(value) + 1);
snprintf(env[i], strlen(name) + 1 + strlen(value) + 1, "%s=%s", name, value);
}
/*
* Reads environment variables from the given file and adds/overrides them
* into the environment. If the file does not exist, this does nothing.
* Otherwise, it must consist of empty lines, comments (line starts with '#')
* and assignments of the form name=value. No other forms are allowed.
*/
void
read_environment_file(char ***env, unsigned int *envsize,
const char *filename)
{
FILE *f;
char buf[4096];
char *cp, *value;
/* Open the environment file. */
f = fopen(filename, "r");
if (!f)
return;
/* Process each line. */
while (fgets(buf, sizeof(buf), f)) {
/* Skip leading whitespace. */
for (cp = buf; *cp == ' ' || *cp == '\t'; cp++);
/* Ignore empty and comment lines. */
if (!*cp || *cp == '#' || *cp == '\n')
continue;
/* Remove newline. */
if (strchr(cp, '\n'))
*strchr(cp, '\n') = '\0';
/* Find the equals sign. Its lack indicates badly
formatted line. */
value = strchr(cp, '=');
if (value == NULL) {
fprintf(stderr, "Bad line in %.100s: %.200s\n", filename, buf);
continue;
}
/* Replace the equals sign by nul, and advance value to
the value string. */
*value = '\0';
value++;
/* Set the value in environment. */
child_set_env(env, envsize, cp, value);
}
fclose(f);
}
/*
* Performs common processing for the child, such as setting up the
* environment, closing extra file descriptors, setting the user and group
* ids, and executing the command or shell.
*/
void
do_child(const char *command, struct passwd * pw, const char *term,
const char *display, const char *auth_proto,
const char *auth_data, const char *ttyname)
{
const char *shell, *cp = NULL;
char buf[256];
FILE *f;
unsigned int envsize, i;
char **env;
extern char **environ;
struct stat st;
char *argv[10];
/* Check /etc/nologin. */
f = fopen("/etc/nologin", "r");
if (f) {
/* /etc/nologin exists. Print its contents and exit. */
while (fgets(buf, sizeof(buf), f))
fputs(buf, stderr);
fclose(f);
if (pw->pw_uid != 0)
exit(254);
}
/* Set login name in the kernel. */
if (setlogin(pw->pw_name) < 0)
error("setlogin failed: %s", strerror(errno));
/* Set uid, gid, and groups. */
/* Login(1) does this as well, and it needs uid 0 for the "-h"
switch, so we let login(1) to this for us. */
if (!options.use_login) {
if (getuid() == 0 || geteuid() == 0) {
if (setgid(pw->pw_gid) < 0) {
perror("setgid");
exit(1);
}
/* Initialize the group list. */
if (initgroups(pw->pw_name, pw->pw_gid) < 0) {
perror("initgroups");
exit(1);
}
endgrent();
/* Permanently switch to the desired uid. */
permanently_set_uid(pw->pw_uid);
}
if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid)
fatal("Failed to set uids to %d.", (int) pw->pw_uid);
}
/* Get the shell from the password data. An empty shell field is
legal, and means /bin/sh. */
shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
#ifdef AFS
/* Try to get AFS tokens for the local cell. */
if (k_hasafs()) {
char cell[64];
if (k_afs_cell_of_file(pw->pw_dir, cell, sizeof(cell)) == 0)
krb_afslog(cell, 0);
krb_afslog(0, 0);
}
#endif /* AFS */
/* Initialize the environment. In the first part we allocate
space for all environment variables. */
envsize = 100;
env = xmalloc(envsize * sizeof(char *));
env[0] = NULL;
if (!options.use_login) {
/* Set basic environment. */
child_set_env(&env, &envsize, "USER", pw->pw_name);
child_set_env(&env, &envsize, "LOGNAME", pw->pw_name);
child_set_env(&env, &envsize, "HOME", pw->pw_dir);
child_set_env(&env, &envsize, "PATH", _PATH_STDPATH);
snprintf(buf, sizeof buf, "%.200s/%.50s",
_PATH_MAILDIR, pw->pw_name);
child_set_env(&env, &envsize, "MAIL", buf);
/* Normal systems set SHELL by default. */
child_set_env(&env, &envsize, "SHELL", shell);
}
/* Let it inherit timezone if we have one. */
if (getenv("TZ"))
child_set_env(&env, &envsize, "TZ", getenv("TZ"));
/* Set custom environment options from RSA authentication. */
while (custom_environment) {
struct envstring *ce = custom_environment;
char *s = ce->s;
int i;
for (i = 0; s[i] != '=' && s[i]; i++);
if (s[i] == '=') {
s[i] = 0;
child_set_env(&env, &envsize, s, s + i + 1);
}
custom_environment = ce->next;
xfree(ce->s);
xfree(ce);
}
/* Set SSH_CLIENT. */
snprintf(buf, sizeof buf, "%.50s %d %d",
get_remote_ipaddr(), get_remote_port(), options.port);
child_set_env(&env, &envsize, "SSH_CLIENT", buf);
/* Set SSH_TTY if we have a pty. */
if (ttyname)
child_set_env(&env, &envsize, "SSH_TTY", ttyname);
/* Set TERM if we have a pty. */
if (term)
child_set_env(&env, &envsize, "TERM", term);
/* Set DISPLAY if we have one. */
if (display)
child_set_env(&env, &envsize, "DISPLAY", display);
#ifdef KRB4
{
extern char *ticket;
if (ticket)
child_set_env(&env, &envsize, "KRBTKFILE", ticket);
}
#endif /* KRB4 */
/* Set XAUTHORITY to always be a local file. */
if (xauthfile)
child_set_env(&env, &envsize, "XAUTHORITY", xauthfile);
/* Set variable for forwarded authentication connection, if we
have one. */
if (auth_get_socket_name() != NULL)
child_set_env(&env, &envsize, SSH_AUTHSOCKET_ENV_NAME,
auth_get_socket_name());
/* Read $HOME/.ssh/environment. */
if (!options.use_login) {
snprintf(buf, sizeof buf, "%.200s/.ssh/environment", pw->pw_dir);
read_environment_file(&env, &envsize, buf);
}
/* If debugging, dump the environment to stderr. */
if (debug_flag) {
fprintf(stderr, "Environment:\n");
for (i = 0; env[i]; i++)
fprintf(stderr, " %.200s\n", env[i]);
}
/* Close the connection descriptors; note that this is the child,
and the server will still have the socket open, and it is
important that we do not shutdown it. Note that the
descriptors cannot be closed before building the environment,
as we call get_remote_ipaddr there. */
if (packet_get_connection_in() == packet_get_connection_out())
close(packet_get_connection_in());
else {
close(packet_get_connection_in());
close(packet_get_connection_out());
}
/* Close all descriptors related to channels. They will still
remain open in the parent. */
channel_close_all();
/* Close any extra file descriptors. Note that there may still be
descriptors left by system functions. They will be closed
later. */
endpwent();
endhostent();
/* Close any extra open file descriptors so that we don\'t have
them hanging around in clients. Note that we want to do this
after initgroups, because at least on Solaris 2.3 it leaves
file descriptors open. */
for (i = 3; i < 64; i++)
close(i);
/* Change current directory to the user\'s home directory. */
if (chdir(pw->pw_dir) < 0)
fprintf(stderr, "Could not chdir to home directory %s: %s\n",
pw->pw_dir, strerror(errno));
/* Must take new environment into use so that .ssh/rc, /etc/sshrc
and xauth are run in the proper environment. */
environ = env;
/* Run $HOME/.ssh/rc, /etc/sshrc, or xauth (whichever is found
first in this order). */
if (!options.use_login) {
if (stat(SSH_USER_RC, &st) >= 0) {
if (debug_flag)
fprintf(stderr, "Running /bin/sh %s\n", SSH_USER_RC);
f = popen("/bin/sh " SSH_USER_RC, "w");
if (f) {
if (auth_proto != NULL && auth_data != NULL)
fprintf(f, "%s %s\n", auth_proto, auth_data);
pclose(f);
} else
fprintf(stderr, "Could not run %s\n", SSH_USER_RC);
} else if (stat(SSH_SYSTEM_RC, &st) >= 0) {
if (debug_flag)
fprintf(stderr, "Running /bin/sh %s\n", SSH_SYSTEM_RC);
f = popen("/bin/sh " SSH_SYSTEM_RC, "w");
if (f) {
if (auth_proto != NULL && auth_data != NULL)
fprintf(f, "%s %s\n", auth_proto, auth_data);
pclose(f);
} else
fprintf(stderr, "Could not run %s\n", SSH_SYSTEM_RC);
}
#ifdef XAUTH_PATH
else {
/* Add authority data to .Xauthority if
appropriate. */
if (auth_proto != NULL && auth_data != NULL) {
if (debug_flag)
fprintf(stderr, "Running %.100s add %.100s %.100s %.100s\n",
XAUTH_PATH, display, auth_proto, auth_data);
f = popen(XAUTH_PATH " -q -", "w");
if (f) {
fprintf(f, "add %s %s %s\n", display, auth_proto, auth_data);
fclose(f);
} else
fprintf(stderr, "Could not run %s -q -\n", XAUTH_PATH);
}
}
#endif /* XAUTH_PATH */
/* Get the last component of the shell name. */
cp = strrchr(shell, '/');
if (cp)
cp++;
else
cp = shell;
}
/* If we have no command, execute the shell. In this case, the
shell name to be passed in argv[0] is preceded by '-' to
indicate that this is a login shell. */
if (!command) {
if (!options.use_login) {
char buf[256];
/* Check for mail if we have a tty and it was
enabled in server options. */
if (ttyname && options.check_mail) {
char *mailbox;
struct stat mailstat;
mailbox = getenv("MAIL");
if (mailbox != NULL) {
if (stat(mailbox, &mailstat) != 0 || mailstat.st_size == 0)
printf("No mail.\n");
else if (mailstat.st_mtime < mailstat.st_atime)
printf("You have mail.\n");
else
printf("You have new mail.\n");
}
}
/* Start the shell. Set initial character to '-'. */
buf[0] = '-';
strncpy(buf + 1, cp, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = 0;
/* Execute the shell. */
argv[0] = buf;
argv[1] = NULL;
execve(shell, argv, env);
/* Executing the shell failed. */
perror(shell);
exit(1);
} else {
/* Launch login(1). */
execl("/usr/bin/login", "login", "-h", get_remote_ipaddr(),
"-p", "-f", "--", pw->pw_name, NULL);
/* Login couldn't be executed, die. */
perror("login");
exit(1);
}
}
/* Execute the command using the user's shell. This uses the -c
option to execute the command. */
argv[0] = (char *) cp;
argv[1] = "-c";
argv[2] = (char *) command;
argv[3] = NULL;
execve(shell, argv, env);
perror(shell);
exit(1);
}
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