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openssh/auth.c

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/*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
*/
#include "includes.h"
RCSID("$OpenBSD: auth.c,v 1.1 2000/03/28 21:15:45 markus 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 "channels.h"
#include "match.h"
#include "session.h"
#include "dispatch.h"
/* import */
extern ServerOptions options;
extern char *forced_command;
/*
* 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.
* If the user's shell is not executable, false will be returned.
* Otherwise true is returned.
*/
static int
allowed_user(struct passwd * pw)
{
struct stat st;
struct group *grp;
int i;
#ifdef WITH_AIXAUTHENTICATE
char *loginmsg;
#endif /* WITH_AIXAUTHENTICATE */
/* Shouldn't be called if pw is NULL, but better safe than sorry... */
if (!pw)
return 0;
/* deny if shell does not exists or is not executable */
if (stat(pw->pw_shell, &st) != 0)
return 0;
if (!((st.st_mode & S_IFREG) && (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP))))
return 0;
/* 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;
}
}
#ifdef WITH_AIXAUTHENTICATE
if (loginrestrictions(pw->pw_name,S_LOGIN,NULL,&loginmsg) != 0)
return 0;
#endif /* WITH_AIXAUTHENTICATE */
/* We found no reason not to let this user try to log on... */
return 1;
}
/*
* convert ssh auth msg type into description
*/
char *
get_authname(int type)
{
static char buf[1024];
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
}
snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
return buf;
}
#define AUTH_FAIL_MAX 6
#define AUTH_FAIL_LOG (AUTH_FAIL_MAX/2)
#define AUTH_FAIL_MSG "Too many authentication failures for %.100s"
/*
* The user does not exist or access is denied,
* but fake indication that authentication is needed.
*/
void
do_fake_authloop1(char *user)
{
int attempt = 0;
log("Faking authloop for illegal user %.200s from %.200s port %d",
user,
get_remote_ipaddr(),
get_remote_port());
#ifdef WITH_AIXAUTHENTICATE
if (strncmp(get_authname(type),"password",
strlen(get_authname(type))) == 0)
loginfailed(pw->pw_name,get_canonical_hostname(),"ssh");
#endif /* WITH_AIXAUTHENTICATE */
/* 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;
#ifndef SKEY
(void)packet_read(&plen);
#else /* SKEY */
int type = packet_read(&plen);
unsigned int dlen;
char *password, *skeyinfo;
/* Try to send a fake s/key challenge. */
if (options.skey_authentication == 1 &&
(skeyinfo = skey_fake_keyinfo(user)) != NULL) {
password = NULL;
if (type == SSH_CMSG_AUTH_TIS) {
packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
packet_put_string(skeyinfo, strlen(skeyinfo));
packet_send();
packet_write_wait();
continue;
} else if (type == SSH_CMSG_AUTH_PASSWORD &&
options.password_authentication &&
(password = packet_get_string(&dlen)) != NULL &&
dlen == 5 &&
strncasecmp(password, "s/key", 5) == 0 ) {
packet_send_debug(skeyinfo);
}
if (password != NULL)
xfree(password);
}
#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();
}
/*
* 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;
RSA *client_host_key;
BIGNUM *n;
char *client_user = NULL, *password = NULL;
char user[1024];
unsigned int dlen;
int plen, nlen, elen;
unsigned int ulen;
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);
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 = RSA_new();
if (client_host_key == NULL)
fatal("RSA_new failed");
client_host_key->e = BN_new();
client_host_key->n = BN_new();
if (client_host_key->e == NULL || client_host_key->n == NULL)
fatal("BN_new failed");
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);
RSA_free(client_host_key);
snprintf(user, sizeof user, " ruser %s", 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);
#ifdef USE_PAM
/* Do PAM auth with password */
authenticated = auth_pam_password(pw, password);
#else /* USE_PAM */
/* Try authentication with the password. */
authenticated = auth_password(pw, password);
#endif /* USE_PAM */
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;
}
/*
* Check if the user is logging in as root and root logins
* are disallowed.
* Note that root login is allowed for forced commands.
*/
if (authenticated && pw->pw_uid == 0 && !options.permit_root_login) {
if (forced_command) {
log("Root login accepted for forced command.");
} else {
authenticated = 0;
log("ROOT LOGIN REFUSED FROM %.200s",
get_canonical_hostname());
}
}
/* 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);
#ifdef USE_PAM
if (authenticated) {
if (!do_pam_account(pw->pw_name, client_user)) {
if (client_user != NULL) {
xfree(client_user);
client_user = NULL;
}
do_fake_authloop1(pw->pw_name);
}
return;
}
#else /* USE_PAM */
if (authenticated) {
return;
}
#endif /* USE_PAM */
if (client_user != NULL) {
xfree(client_user);
client_user = NULL;
}
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();
}
}
/*
* Performs authentication of an incoming connection. Session key has already
* been exchanged and encryption is enabled.
*/
void
do_authentication()
{
struct passwd *pw, pwcopy;
int plen;
unsigned int ulen;
char *user;
#ifdef WITH_AIXAUTHENTICATE
char *loginmsg;
#endif /* WITH_AIXAUTHENTICATE */
/* Get the name of the user that we wish to log in as. */
packet_read_expect(&plen, SSH_CMSG_USER);
/* Get the user name. */
user = packet_get_string(&ulen);
packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
setproctitle("%s", user);
#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_authloop1(user);
xfree(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;
#ifdef USE_PAM
start_pam(pw);
#endif
/*
* 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.", pw->pw_name);
/* 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 */
#ifdef USE_PAM
auth_pam_password(pw, "")) {
#else /* USE_PAM */
auth_password(pw, "")) {
#endif /* USE_PAM */
/* 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);
}
/* The user has been authenticated and accepted. */
#ifdef WITH_AIXAUTHENTICATE
loginsuccess(user,get_canonical_hostname(),"ssh",&loginmsg);
#endif /* WITH_AIXAUTHENTICATE */
packet_start(SSH_SMSG_SUCCESS);
packet_send();
packet_write_wait();
/* Perform session preparation. */
do_authenticated(pw);
}
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