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openssh/auth1.c

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/*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
*
* As far as I am concerned, the code I have written for this software
* can be used freely for any purpose. Any derived versions of this
* software must be clearly marked as such, and if the derived work is
* incompatible with the protocol description in the RFC file, it must be
* called by a name other than "ssh" or "Secure Shell".
*/
#include "includes.h"
RCSID("$OpenBSD: auth1.c,v 1.27 2001/12/19 07:18:56 deraadt Exp $");
#include "xmalloc.h"
#include "rsa.h"
#include "ssh1.h"
#include "packet.h"
#include "buffer.h"
#include "mpaux.h"
#include "log.h"
#include "servconf.h"
#include "compat.h"
#include "auth.h"
#include "session.h"
#include "misc.h"
#include "uidswap.h"
/* import */
extern ServerOptions options;
/*
* convert ssh auth msg type into description
*/
static 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";
case SSH_CMSG_AUTH_TIS:
case SSH_CMSG_AUTH_TIS_RESPONSE:
return "challenge-response";
#if defined(KRB4) || defined(KRB5)
case SSH_CMSG_AUTH_KERBEROS:
return "kerberos";
#endif
}
snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
return buf;
}
/*
* read packets, try to authenticate the user and
* return only if authentication is successful
*/
static void
do_authloop(Authctxt *authctxt)
{
int authenticated = 0;
u_int bits;
RSA *client_host_key;
BIGNUM *n;
char *client_user, *password;
char info[1024];
u_int dlen;
int plen, nlen, elen;
u_int ulen;
int type = 0;
struct passwd *pw = authctxt->pw;
debug("Attempting authentication for %s%.100s.",
authctxt->valid ? "" : "illegal user ", authctxt->user);
/* If the user has no password, accept authentication immediately. */
if (options.password_authentication &&
#if defined(KRB4) || defined(KRB5)
(!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
#endif
#ifdef USE_PAM
auth_pam_password(pw, "")) {
#elif defined(HAVE_OSF_SIA)
0) {
#else
auth_password(authctxt, "")) {
#endif
auth_log(authctxt, 1, "without authentication", "");
return;
}
/* Indicate that authentication is needed. */
packet_start(SSH_SMSG_FAILURE);
packet_send();
packet_write_wait();
client_user = NULL;
for (;;) {
/* default to fail */
authenticated = 0;
info[0] = '\0';
/* Get a packet from the client. */
type = packet_read(&plen);
/* Process the packet. */
switch (type) {
#if defined(KRB4) || defined(KRB5)
case SSH_CMSG_AUTH_KERBEROS:
if (!options.kerberos_authentication) {
verbose("Kerberos authentication disabled.");
} else {
char *kdata = packet_get_string(&dlen);
packet_integrity_check(plen, 4 + dlen, type);
if (kdata[0] == 4) { /* KRB_PROT_VERSION */
#ifdef KRB4
KTEXT_ST tkt;
tkt.length = dlen;
if (tkt.length < MAX_KTXT_LEN)
memcpy(tkt.dat, kdata, tkt.length);
if (auth_krb4(authctxt, &tkt, &client_user)) {
authenticated = 1;
snprintf(info, sizeof(info),
" tktuser %.100s",
client_user);
}
#endif /* KRB4 */
} else {
#ifdef KRB5
krb5_data tkt;
tkt.length = dlen;
tkt.data = kdata;
if (auth_krb5(authctxt, &tkt, &client_user)) {
authenticated = 1;
snprintf(info, sizeof(info),
" tktuser %.100s",
client_user);
}
#endif /* KRB5 */
}
xfree(kdata);
}
break;
#endif /* KRB4 || KRB5 */
#if defined(AFS) || defined(KRB5)
/* XXX - punt on backward compatibility here. */
case SSH_CMSG_HAVE_KERBEROS_TGT:
packet_send_debug("Kerberos TGT passing disabled before authentication.");
break;
#ifdef AFS
case SSH_CMSG_HAVE_AFS_TOKEN:
packet_send_debug("AFS token passing disabled before authentication.");
break;
#endif /* AFS */
#endif /* AFS || KRB5 */
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(info, sizeof info, " ruser %.100s", 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))
verbose("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(info, sizeof info, " ruser %.100s", 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);
#elif defined(HAVE_OSF_SIA)
/* Do SIA auth with password */
authenticated = auth_sia_password(authctxt->user,
password);
#else /* !USE_PAM && !HAVE_OSF_SIA */
/* Try authentication with the password. */
authenticated = auth_password(authctxt, password);
#endif /* USE_PAM */
memset(password, 0, strlen(password));
xfree(password);
break;
case SSH_CMSG_AUTH_TIS:
debug("rcvd SSH_CMSG_AUTH_TIS");
if (options.challenge_response_authentication == 1) {
char *challenge = get_challenge(authctxt);
if (challenge != NULL) {
debug("sending challenge '%s'", challenge);
packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
packet_put_cstring(challenge);
xfree(challenge);
packet_send();
packet_write_wait();
continue;
}
}
break;
case SSH_CMSG_AUTH_TIS_RESPONSE:
debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
if (options.challenge_response_authentication == 1) {
char *response = packet_get_string(&dlen);
debug("got response '%s'", response);
packet_integrity_check(plen, 4 + dlen, type);
authenticated = verify_response(authctxt, response);
memset(response, 'r', dlen);
xfree(response);
}
break;
default:
/*
* Any unknown messages will be ignored (and failure
* returned) during authentication.
*/
log("Unknown message during authentication: type %d", type);
break;
}
#ifdef BSD_AUTH
if (authctxt->as) {
auth_close(authctxt->as);
authctxt->as = NULL;
}
#endif
if (!authctxt->valid && authenticated)
fatal("INTERNAL ERROR: authenticated invalid user %s",
authctxt->user);
#ifdef HAVE_CYGWIN
if (authenticated &&
!check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,pw->pw_uid)) {
packet_disconnect("Authentication rejected for uid %d.",
(int)pw->pw_uid);
authenticated = 0;
}
#else
/* Special handling for root */
if (authenticated && authctxt->pw->pw_uid == 0 &&
!auth_root_allowed(get_authname(type)))
authenticated = 0;
#endif
#ifdef USE_PAM
if (authenticated && !do_pam_account(pw->pw_name, client_user))
authenticated = 0;
#endif
/* Log before sending the reply */
auth_log(authctxt, authenticated, get_authname(type), info);
if (client_user != NULL) {
xfree(client_user);
client_user = NULL;
}
if (authenticated)
return;
if (authctxt->failures++ > AUTH_FAIL_MAX) {
#ifdef WITH_AIXAUTHENTICATE
loginfailed(authctxt->user,
get_canonical_hostname(options.reverse_mapping_check),
"ssh");
#endif /* WITH_AIXAUTHENTICATE */
packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
}
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(void)
{
Authctxt *authctxt;
struct passwd *pw;
int plen;
u_int ulen;
char *p, *user, *style = NULL;
/* 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);
if ((style = strchr(user, ':')) != NULL)
*style++ = '\0';
/* XXX - SSH.com Kerberos v5 braindeath. */
if ((p = strchr(user, '@')) != NULL)
*p = '\0';
authctxt = authctxt_new();
authctxt->user = user;
authctxt->style = style;
/* Verify that the user is a valid user. */
pw = getpwnam(user);
if (pw && allowed_user(pw)) {
authctxt->valid = 1;
pw = pwcopy(pw);
} else {
debug("do_authentication: illegal user %s", user);
pw = NULL;
}
authctxt->pw = pw;
setproctitle("%s", pw ? user : "unknown");
#ifdef USE_PAM
if (pw)
start_pam(user);
#endif
/*
* If we are not running as root, the user must have the same uid as
* the server. (Unless you are running Windows)
*/
#ifndef HAVE_CYGWIN
if (getuid() != 0 && pw && pw->pw_uid != getuid())
packet_disconnect("Cannot change user when server not running as root.");
#endif
/*
* Loop until the user has been authenticated or the connection is
* closed, do_authloop() returns only if authentication is successful
*/
do_authloop(authctxt);
/* The user has been authenticated and accepted. */
packet_start(SSH_SMSG_SUCCESS);
packet_send();
packet_write_wait();
/* Perform session preparation. */
do_authenticated(authctxt);
}
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