view svr-authpam.c @ 1629:258b57b208ae

Fix for issue successfull login of disabled user (#78) This commit introduces fix for scenario: 1. Root login disabled on dropbear 2. PAM authentication model enabled While login as root user, after prompt for password user is being notified about login failrue, but after second attempt of prompt for password within same session, login becames succesfull. Signed-off-by: Pawel Rapkiewicz <[email protected]>
author vincentto13 <33652988+vincentto13@users.noreply.github.com>
date Wed, 20 Mar 2019 15:03:40 +0100
parents 5d2d1021ca00
children
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/*
 * Dropbear SSH
 * 
 * Copyright (c) 2004 Martin Carlsson
 * Portions (c) 2004 Matt Johnston
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

/* Validates a user password using PAM */

#include "includes.h"
#include "session.h"
#include "buffer.h"
#include "dbutil.h"
#include "auth.h"

#if DROPBEAR_SVR_PAM_AUTH

#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

struct UserDataS {
	char* user;
	char* passwd;
};

/* PAM conversation function - for now we only handle one message */
int 
pamConvFunc(int num_msg, 
		const struct pam_message **msg,
		struct pam_response **respp, 
		void *appdata_ptr) {

	int rc = PAM_SUCCESS;
	struct pam_response* resp = NULL;
	struct UserDataS* userDatap = (struct UserDataS*) appdata_ptr;
	unsigned int msg_len = 0;
	unsigned int i = 0;
	char * compare_message = NULL;

	TRACE(("enter pamConvFunc"))

	if (num_msg != 1) {
		/* If you're getting here - Dropbear probably can't support your pam
		 * modules. This whole file is a bit of a hack around lack of
		 * asynchronocity in PAM anyway. */
		dropbear_log(LOG_INFO, "pamConvFunc() called with >1 messages: not supported.");
		return PAM_CONV_ERR;
	}

	/* make a copy we can strip */
	compare_message = m_strdup((*msg)->msg);
	
	/* Make the string lowercase. */
	msg_len = strlen(compare_message);
	for (i = 0; i < msg_len; i++) {
		compare_message[i] = tolower(compare_message[i]);
	}

	/* If the string ends with ": ", remove the space. 
	   ie "login: " vs "login:" */
	if (msg_len > 2 
			&& compare_message[msg_len-2] == ':' 
			&& compare_message[msg_len-1] == ' ') {
		compare_message[msg_len-1] = '\0';
	}

	switch((*msg)->msg_style) {

		case PAM_PROMPT_ECHO_OFF:

			if (!(strcmp(compare_message, "password:") == 0)) {
				/* We don't recognise the prompt as asking for a password,
				   so can't handle it. Add more above as required for
				   different pam modules/implementations. If you need
				   to add an entry here please mail the Dropbear developer */
				dropbear_log(LOG_NOTICE, "PAM unknown prompt '%s' (no echo)",
						compare_message);
				rc = PAM_CONV_ERR;
				break;
			}

			/* You have to read the PAM module-writers' docs (do we look like
			 * module writers? no.) to find out that the module will
			 * free the pam_response and its resp element - ie we _must_ malloc
			 * it here */
			resp = (struct pam_response*) m_malloc(sizeof(struct pam_response));
			memset(resp, 0, sizeof(struct pam_response));

			resp->resp = m_strdup(userDatap->passwd);
			m_burn(userDatap->passwd, strlen(userDatap->passwd));
			(*respp) = resp;
			break;


		case PAM_PROMPT_ECHO_ON:

			if (!(
				(strcmp(compare_message, "login:" ) == 0) 
				|| (strcmp(compare_message, "please enter username:") == 0)
				|| (strcmp(compare_message, "username:") == 0)
				)) {
				/* We don't recognise the prompt as asking for a username,
				   so can't handle it. Add more above as required for
				   different pam modules/implementations. If you need
				   to add an entry here please mail the Dropbear developer */
				dropbear_log(LOG_NOTICE, "PAM unknown prompt '%s' (with echo)",
						compare_message);
				rc = PAM_CONV_ERR;
				break;
			}

			/* You have to read the PAM module-writers' docs (do we look like
			 * module writers? no.) to find out that the module will
			 * free the pam_response and its resp element - ie we _must_ malloc
			 * it here */
			resp = (struct pam_response*) m_malloc(sizeof(struct pam_response));
			memset(resp, 0, sizeof(struct pam_response));

			resp->resp = m_strdup(userDatap->user);
			TRACE(("userDatap->user='%s'", userDatap->user))
			(*respp) = resp;
			break;

		case PAM_ERROR_MSG:
		case PAM_TEXT_INFO:

			if (msg_len > 0) {
				buffer * pam_err = buf_new(msg_len + 4);
				buf_setpos(pam_err, 0);
				buf_putbytes(pam_err, "\r\n", 2);
				buf_putbytes(pam_err, (*msg)->msg, msg_len);
				buf_putbytes(pam_err, "\r\n", 2);
				buf_setpos(pam_err, 0);

				send_msg_userauth_banner(pam_err);
				buf_free(pam_err);
			}
			break;

		default:
			TRACE(("Unknown message type"))
			rc = PAM_CONV_ERR;
			break;      
	}

	m_free(compare_message);
	TRACE(("leave pamConvFunc, rc %d", rc))

	return rc;
}

/* Process a password auth request, sending success or failure messages as
 * appropriate. To the client it looks like it's doing normal password auth (as
 * opposed to keyboard-interactive or something), so the pam module has to be
 * fairly standard (ie just "what's your username, what's your password, OK").
 *
 * Keyboard interactive would be a lot nicer, but since PAM is synchronous, it
 * gets very messy trying to send the interactive challenges, and read the
 * interactive responses, over the network. */
void svr_auth_pam(int valid_user) {

	struct UserDataS userData = {NULL, NULL};
	struct pam_conv pamConv = {
		pamConvFunc,
		&userData /* submitted to pamvConvFunc as appdata_ptr */ 
	};
	const char* printable_user = NULL;

	pam_handle_t* pamHandlep = NULL;

	char * password = NULL;
	unsigned int passwordlen;

	int rc = PAM_SUCCESS;
	unsigned char changepw;

	/* check if client wants to change password */
	changepw = buf_getbool(ses.payload);
	if (changepw) {
		/* not implemented by this server */
		send_msg_userauth_failure(0, 1);
		goto cleanup;
	}

	password = buf_getstring(ses.payload, &passwordlen);

	/* We run the PAM conversation regardless of whether the username is valid
	in case the conversation function has an inherent delay.
	Use ses.authstate.username rather than ses.authstate.pw_name.
	After PAM succeeds we then check the valid_user flag too */

	/* used to pass data to the PAM conversation function - don't bother with
	 * strdup() etc since these are touched only by our own conversation
	 * function (above) which takes care of it */
	userData.user = ses.authstate.username;
	userData.passwd = password;

	if (ses.authstate.pw_name) {
		printable_user = ses.authstate.pw_name;
	} else {
		printable_user = "<invalid username>";
	}

	/* Init pam */
	if ((rc = pam_start("sshd", NULL, &pamConv, &pamHandlep)) != PAM_SUCCESS) {
		dropbear_log(LOG_WARNING, "pam_start() failed, rc=%d, %s", 
				rc, pam_strerror(pamHandlep, rc));
		goto cleanup;
	}

	/* just to set it to something */
	if ((rc = pam_set_item(pamHandlep, PAM_TTY, "ssh")) != PAM_SUCCESS) {
		dropbear_log(LOG_WARNING, "pam_set_item() failed, rc=%d, %s",
				rc, pam_strerror(pamHandlep, rc));
		goto cleanup;
	}

	if ((rc = pam_set_item(pamHandlep, PAM_RHOST, svr_ses.remotehost)) != PAM_SUCCESS) {
		dropbear_log(LOG_WARNING, "pam_set_item() failed, rc=%d, %s",
				rc, pam_strerror(pamHandlep, rc));
		goto cleanup;
	}

#ifdef HAVE_PAM_FAIL_DELAY
	/* We have our own random delay code already, disable PAM's */
	(void) pam_fail_delay(pamHandlep, 0 /* musec_delay */);
#endif

	/* (void) pam_set_item(pamHandlep, PAM_FAIL_DELAY, (void*) pamDelayFunc); */

	if ((rc = pam_authenticate(pamHandlep, 0)) != PAM_SUCCESS) {
		dropbear_log(LOG_WARNING, "pam_authenticate() failed, rc=%d, %s", 
				rc, pam_strerror(pamHandlep, rc));
		dropbear_log(LOG_WARNING,
				"Bad PAM password attempt for '%s' from %s",
				printable_user,
				svr_ses.addrstring);
		send_msg_userauth_failure(0, 1);
		goto cleanup;
	}

	if ((rc = pam_acct_mgmt(pamHandlep, 0)) != PAM_SUCCESS) {
		dropbear_log(LOG_WARNING, "pam_acct_mgmt() failed, rc=%d, %s", 
				rc, pam_strerror(pamHandlep, rc));
		dropbear_log(LOG_WARNING,
				"Bad PAM password attempt for '%s' from %s",
				printable_user,
				svr_ses.addrstring);
		send_msg_userauth_failure(0, 1);
		goto cleanup;
	}

	if (!valid_user) {
		/* PAM auth succeeded but the username isn't allowed in for another reason
		(checkusername() failed) */
		send_msg_userauth_failure(0, 1);
		goto cleanup;
	}

	/* successful authentication */
	dropbear_log(LOG_NOTICE, "PAM password auth succeeded for '%s' from %s",
			ses.authstate.pw_name,
			svr_ses.addrstring);
	send_msg_userauth_success();

cleanup:
	if (password != NULL) {
		m_burn(password, passwordlen);
		m_free(password);
	}
	if (pamHandlep != NULL) {
		TRACE(("pam_end"))
		(void) pam_end(pamHandlep, 0 /* pam_status */);
	}
}

#endif /* DROPBEAR_SVR_PAM_AUTH */