auth-pam.c

OpenSSH 是 SSH （Secure SHell） 协议的免费开源实现。它用安全、加密的网络连接工具代替了 telnet、ftp、 rlogin、rsh 和 rcp 工具。OpenSSH 支持

/*-
 * Copyright (c) 2002 Networks Associates Technology, Inc.
 * All rights reserved.
 *
 * This software was developed for the FreeBSD Project by ThinkSec AS and
 * NAI Labs, the Security Research Division of Network Associates, Inc.
 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
 * DARPA CHATS research program.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 * Copyright (c) 2003,2004 Damien Miller <[e-mail]>
 * Copyright (c) 2003,2004 Darren Tucker <[e-mail]>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/* Based on $FreeBSD: src/crypto/openssh/auth2-pam-freebsd.c,v 1.11 2003/03/31 13:48:18 des Exp $ */
#include "includes.h"
RCSID("$Id: auth-pam.c,v 1.121 2005/01/20 02:29:51 dtucker Exp $");

#ifdef USE_PAM
#if defined(HAVE_SECURITY_PAM_APPL_H)
#include <security/pam_appl.h>
#elif defined (HAVE_PAM_PAM_APPL_H)
#include <pam/pam_appl.h>
#endif

#include "auth.h"
#include "auth-pam.h"
#include "buffer.h"
#include "bufaux.h"
#include "canohost.h"
#include "log.h"
#include "monitor_wrap.h"
#include "msg.h"
#include "packet.h"
#include "misc.h"
#include "servconf.h"
#include "ssh2.h"
#include "xmalloc.h"
#include "auth-options.h"

extern ServerOptions options;
extern Buffer loginmsg;
extern int compat20;
extern u_int utmp_len;

#ifdef USE_POSIX_THREADS
#include <pthread.h>
/*
 * Avoid namespace clash when *not* using pthreads for systems *with*
 * pthreads, which unconditionally define pthread_t via sys/types.h
 * (e.g. Linux)
 */
typedef pthread_t sp_pthread_t;
#else
typedef pid_t sp_pthread_t;
#endif

struct pam_ctxt {
	sp_pthread_t	 pam_thread;
	int		 pam_psock;
	int		 pam_csock;
	int		 pam_done;
};

static void sshpam_free_ctx(void *);
static struct pam_ctxt *cleanup_ctxt;

#ifndef USE_POSIX_THREADS
/*
 * Simulate threads with processes.
 */

static int sshpam_thread_status = -1;
static mysig_t sshpam_oldsig;

static void 
sshpam_sigchld_handler(int sig)
{
	signal(SIGCHLD, SIG_DFL);
	if (cleanup_ctxt == NULL)
		return;	/* handler called after PAM cleanup, shouldn't happen */
	if (waitpid(cleanup_ctxt->pam_thread, &sshpam_thread_status, WNOHANG)
	     <= 0) {
		/* PAM thread has not exitted, privsep slave must have */
		kill(cleanup_ctxt->pam_thread, SIGTERM);
		if (waitpid(cleanup_ctxt->pam_thread, &sshpam_thread_status, 0)
		    <= 0)
			return; /* could not wait */
	}
	if (WIFSIGNALED(sshpam_thread_status) &&
	    WTERMSIG(sshpam_thread_status) == SIGTERM)
		return;	/* terminated by pthread_cancel */
	if (!WIFEXITED(sshpam_thread_status))
		fatal("PAM: authentication thread exited unexpectedly");
	if (WEXITSTATUS(sshpam_thread_status) != 0)
		fatal("PAM: authentication thread exited uncleanly");
}

static void
pthread_exit(void *value __unused)
{
	_exit(0);
}

static int
pthread_create(sp_pthread_t *thread, const void *attr __unused,
    void *(*thread_start)(void *), void *arg)
{
	pid_t pid;

	sshpam_thread_status = -1;
	switch ((pid = fork())) {
	case -1:
		error("fork(): %s", strerror(errno));
		return (-1);
	case 0:
		thread_start(arg);
		_exit(1);
	default:
		*thread = pid;
		sshpam_oldsig = signal(SIGCHLD, sshpam_sigchld_handler);
		return (0);
	}
}

static int
pthread_cancel(sp_pthread_t thread)
{
	signal(SIGCHLD, sshpam_oldsig);
	return (kill(thread, SIGTERM));
}

static int
pthread_join(sp_pthread_t thread, void **value __unused)
{
	int status;

	if (sshpam_thread_status != -1)
		return (sshpam_thread_status);
	signal(SIGCHLD, sshpam_oldsig);
	waitpid(thread, &status, 0);
	return (status);
}
#endif


static pam_handle_t *sshpam_handle = NULL;
static int sshpam_err = 0;
static int sshpam_authenticated = 0;
static int sshpam_session_open = 0;
static int sshpam_cred_established = 0;
static int sshpam_account_status = -1;
static char **sshpam_env = NULL;
static Authctxt *sshpam_authctxt = NULL;
static const char *sshpam_password = NULL;
static char badpw[] = "\b\n\r\177INCORRECT";

/* Some PAM implementations don't implement this */
#ifndef HAVE_PAM_GETENVLIST
static char **
pam_getenvlist(pam_handle_t *pamh)
{
	/*
	 * XXX - If necessary, we can still support envrionment passing
	 * for platforms without pam_getenvlist by searching for known
	 * env vars (e.g. KRB5CCNAME) from the PAM environment.
	 */
	 return NULL;
}
#endif

/*
 * Some platforms, notably Solaris, do not enforce password complexity
 * rules during pam_chauthtok() if the real uid of the calling process
 * is 0, on the assumption that it's being called by "passwd" run by root.
 * This wraps pam_chauthtok and sets/restore the real uid so PAM will do
 * the right thing.
 */
#ifdef SSHPAM_CHAUTHTOK_NEEDS_RUID
static int
sshpam_chauthtok_ruid(pam_handle_t *pamh, int flags)
{
	int result;

	if (sshpam_authctxt == NULL)
		fatal("PAM: sshpam_authctxt not initialized");
	if (setreuid(sshpam_authctxt->pw->pw_uid, -1) == -1)
		fatal("%s: setreuid failed: %s", __func__, strerror(errno));
	result = pam_chauthtok(pamh, flags);
	if (setreuid(0, -1) == -1)
		fatal("%s: setreuid failed: %s", __func__, strerror(errno));
	return result;
}
# define pam_chauthtok(a,b)	(sshpam_chauthtok_ruid((a), (b)))
#endif

void
sshpam_password_change_required(int reqd)
{
	debug3("%s %d", __func__, reqd);
	if (sshpam_authctxt == NULL)
		fatal("%s: PAM authctxt not initialized", __func__);
	sshpam_authctxt->force_pwchange = reqd;
	if (reqd) {
		no_port_forwarding_flag |= 2;
		no_agent_forwarding_flag |= 2;
		no_x11_forwarding_flag |= 2;
	} else {
		no_port_forwarding_flag &= ~2;
		no_agent_forwarding_flag &= ~2;
		no_x11_forwarding_flag &= ~2;
	}
}

/* Import regular and PAM environment from subprocess */
static void
import_environments(Buffer *b)
{
	char *env;
	u_int i, num_env;
	int err;

	debug3("PAM: %s entering", __func__);

#ifndef USE_POSIX_THREADS
	/* Import variables set by do_pam_account */
	sshpam_account_status = buffer_get_int(b);
	sshpam_password_change_required(buffer_get_int(b));

	/* Import environment from subprocess */
	num_env = buffer_get_int(b);
	sshpam_env = xmalloc((num_env + 1) * sizeof(*sshpam_env));
	debug3("PAM: num env strings %d", num_env);
	for(i = 0; i < num_env; i++)
		sshpam_env[i] = buffer_get_string(b, NULL);

	sshpam_env[num_env] = NULL;

	/* Import PAM environment from subprocess */
	num_env = buffer_get_int(b);
	debug("PAM: num PAM env strings %d", num_env);
	for(i = 0; i < num_env; i++) {
		env = buffer_get_string(b, NULL);

#ifdef HAVE_PAM_PUTENV
		/* Errors are not fatal here */
		if ((err = pam_putenv(sshpam_handle, env)) != PAM_SUCCESS) {
			error("PAM: pam_putenv: %s",
			    pam_strerror(sshpam_handle, sshpam_err));
		}
#endif
	}
#endif
}

/*
 * Conversation function for authentication thread.
 */
static int
sshpam_thread_conv(int n, struct pam_message **msg,
    struct pam_response **resp, void *data)
{
	Buffer buffer;
	struct pam_ctxt *ctxt;
	struct pam_response *reply;
	int i;

	debug3("PAM: %s entering, %d messages", __func__, n);
	*resp = NULL;

	if (data == NULL) {
		error("PAM: conversation function passed a null context");
		return (PAM_CONV_ERR);
	}
	ctxt = data;
	if (n <= 0 || n > PAM_MAX_NUM_MSG)
		return (PAM_CONV_ERR);

	if ((reply = malloc(n * sizeof(*reply))) == NULL)
		return (PAM_CONV_ERR);
	memset(reply, 0, n * sizeof(*reply));

	buffer_init(&buffer);
	for (i = 0; i < n; ++i) {
		switch (PAM_MSG_MEMBER(msg, i, msg_style)) {
		case PAM_PROMPT_ECHO_OFF:
			buffer_put_cstring(&buffer,
			    PAM_MSG_MEMBER(msg, i, msg));
			if (ssh_msg_send(ctxt->pam_csock,
			    PAM_MSG_MEMBER(msg, i, msg_style), &buffer) == -1)
				goto fail;
			if (ssh_msg_recv(ctxt->pam_csock, &buffer) == -1)
				goto fail;
			if (buffer_get_char(&buffer) != PAM_AUTHTOK)
				goto fail;
			reply[i].resp = buffer_get_string(&buffer, NULL);
			break;
		case PAM_PROMPT_ECHO_ON:
			buffer_put_cstring(&buffer,
			    PAM_MSG_MEMBER(msg, i, msg));
			if (ssh_msg_send(ctxt->pam_csock,
			    PAM_MSG_MEMBER(msg, i, msg_style), &buffer) == -1)
				goto fail;
			if (ssh_msg_recv(ctxt->pam_csock, &buffer) == -1)
				goto fail;
			if (buffer_get_char(&buffer) != PAM_AUTHTOK)
				goto fail;
			reply[i].resp = buffer_get_string(&buffer, NULL);
			break;
		case PAM_ERROR_MSG:
			buffer_put_cstring(&buffer,
			    PAM_MSG_MEMBER(msg, i, msg));
			if (ssh_msg_send(ctxt->pam_csock,
			    PAM_MSG_MEMBER(msg, i, msg_style), &buffer) == -1)
				goto fail;
			break;
		case PAM_TEXT_INFO:
			buffer_put_cstring(&buffer,
			    PAM_MSG_MEMBER(msg, i, msg));
			if (ssh_msg_send(ctxt->pam_csock,
			    PAM_MSG_MEMBER(msg, i, msg_style), &buffer) == -1)
				goto fail;
			break;
		default:
			goto fail;
		}
		buffer_clear(&buffer);
	}
	buffer_free(&buffer);
	*resp = reply;
	return (PAM_SUCCESS);

 fail:
	for(i = 0; i < n; i++) {
		if (reply[i].resp != NULL)
			xfree(reply[i].resp);
	}
	xfree(reply);
	buffer_free(&buffer);
	return (PAM_CONV_ERR);
}

/*
 * Authentication thread.
 */
static void *
sshpam_thread(void *ctxtp)
{
	struct pam_ctxt *ctxt = ctxtp;
	Buffer buffer;
	struct pam_conv sshpam_conv;
	int flags = (options.permit_empty_passwd == 0 ?
	    PAM_DISALLOW_NULL_AUTHTOK : 0);
#ifndef USE_POSIX_THREADS
	extern char **environ;
	char **env_from_pam;
	u_int i;
	const char *pam_user;

	pam_get_item(sshpam_handle, PAM_USER, (void **)&pam_user);
	environ[0] = NULL;

	if (sshpam_authctxt != NULL) {
		setproctitle("%s [pam]",
		    sshpam_authctxt->valid ? pam_user : "unknown");
	}
#endif

	sshpam_conv.conv = sshpam_thread_conv;
	sshpam_conv.appdata_ptr = ctxt;

	if (sshpam_authctxt == NULL)
		fatal("%s: PAM authctxt not initialized", __func__);

	buffer_init(&buffer);
	sshpam_err = pam_set_item(sshpam_handle, PAM_CONV,
	    (const void *)&sshpam_conv);
	if (sshpam_err != PAM_SUCCESS)
		goto auth_fail;
	sshpam_err = pam_authenticate(sshpam_handle, flags);
	if (sshpam_err != PAM_SUCCESS)
		goto auth_fail;

	if (compat20) {
		if (!do_pam_account())
			goto auth_fail;
		if (sshpam_authctxt->force_pwchange) {
			sshpam_err = pam_chauthtok(sshpam_handle,
			    PAM_CHANGE_EXPIRED_AUTHTOK);
			if (sshpam_err != PAM_SUCCESS)
				goto auth_fail;
			sshpam_password_change_required(0);
		}
	}

	buffer_put_cstring(&buffer, "OK");

#ifndef USE_POSIX_THREADS
	/* Export variables set by do_pam_account */
	buffer_put_int(&buffer, sshpam_account_status);
	buffer_put_int(&buffer, sshpam_authctxt->force_pwchange);

	/* Export any environment strings set in child */
	for(i = 0; environ[i] != NULL; i++)
		; /* Count */
	buffer_put_int(&buffer, i);
	for(i = 0; environ[i] != NULL; i++)
		buffer_put_cstring(&buffer, environ[i]);

	/* Export any environment strings set by PAM in child */
	env_from_pam = pam_getenvlist(sshpam_handle);
	for(i = 0; env_from_pam != NULL && env_from_pam[i] != NULL; i++)
		; /* Count */
	buffer_put_int(&buffer, i);
	for(i = 0; env_from_pam != NULL && env_from_pam[i] != NULL; i++)
		buffer_put_cstring(&buffer, env_from_pam[i]);
#endif /* USE_POSIX_THREADS */

	/* XXX - can't do much about an error here */
	ssh_msg_send(ctxt->pam_csock, sshpam_err, &buffer);
	buffer_free(&buffer);
	pthread_exit(NULL);

 auth_fail:
	buffer_put_cstring(&buffer,
	    pam_strerror(sshpam_handle, sshpam_err));
	/* XXX - can't do much about an error here */
	ssh_msg_send(ctxt->pam_csock, PAM_AUTH_ERR, &buffer);
	buffer_free(&buffer);
	pthread_exit(NULL);

	return (NULL); /* Avoid warning for non-pthread case */
}

void
sshpam_thread_cleanup(void)
{
	struct pam_ctxt *ctxt = cleanup_ctxt;

	debug3("PAM: %s entering", __func__);
	if (ctxt != NULL && ctxt->pam_thread != 0) {
		pthread_cancel(ctxt->pam_thread);
		pthread_join(ctxt->pam_thread, NULL);
		close(ctxt->pam_psock);
		close(ctxt->pam_csock);
		memset(ctxt, 0, sizeof(*ctxt));
		cleanup_ctxt = NULL;
	}
}

static int
sshpam_null_conv(int n, struct pam_message **msg,
    struct pam_response **resp, void *data)
{
	debug3("PAM: %s entering, %d messages", __func__, n);
	return (PAM_CONV_ERR);
}

static struct pam_conv null_conv = { sshpam_null_conv, NULL };

static int
sshpam_store_conv(int n, struct pam_message **msg,
    struct pam_response **resp, void *data)
{
	struct pam_response *reply;
	int i;
	size_t len;

	debug3("PAM: %s called with %d messages", __func__, n);
	*resp = NULL;

	if (n <= 0 || n > PAM_MAX_NUM_MSG)
		return (PAM_CONV_ERR);

	if ((reply = malloc(n * sizeof(*reply))) == NULL)
		return (PAM_CONV_ERR);
	memset(reply, 0, n * sizeof(*reply));

	for (i = 0; i < n; ++i) {
		switch (PAM_MSG_MEMBER(msg, i, msg_style)) {
		case PAM_ERROR_MSG:
		case PAM_TEXT_INFO:
			len = strlen(PAM_MSG_MEMBER(msg, i, msg));
			buffer_append(&loginmsg, PAM_MSG_MEMBER(msg, i, msg), len);
			buffer_append(&loginmsg, "\n", 1 );
			reply[i].resp_retcode = PAM_SUCCESS;
			break;
		default:
			goto fail;
		}
	}
	*resp = reply;
	return (PAM_SUCCESS);

 fail:
	for(i = 0; i < n; i++) {
		if (reply[i].resp != NULL)
			xfree(reply[i].resp);
	}
	xfree(reply);
	return (PAM_CONV_ERR);
}

static struct pam_conv store_conv = { sshpam_store_conv, NULL };

void
sshpam_cleanup(void)
{
	debug("PAM: cleanup");
	if (sshpam_handle == NULL)
		return;
	pam_set_item(sshpam_handle, PAM_CONV, (const void *)&null_conv);
	if (sshpam_cred_established) {
		pam_setcred(sshpam_handle, PAM_DELETE_CRED);
		sshpam_cred_established = 0;
	}
	if (sshpam_session_open) {
		pam_close_session(sshpam_handle, PAM_SILENT);
		sshpam_session_open = 0;
	}
	sshpam_authenticated = 0;
	pam_end(sshpam_handle, sshpam_err);
	sshpam_handle = NULL;
}

static int
sshpam_init(Authctxt *authctxt)
{
	extern char *__progname;
	const char *pam_rhost, *pam_user, *user = authctxt->user;

	if (sshpam_handle != NULL) {
		/* We already have a PAM context; check if the user matches */
		sshpam_err = pam_get_item(sshpam_handle,
		    PAM_USER, (void **)&pam_user);
		if (sshpam_err == PAM_SUCCESS && strcmp(user, pam_user) == 0)
			return (0);
		pam_end(sshpam_handle, sshpam_err);
		sshpam_handle = NULL;
	}