path: root/src/pam-freerdp.c

/*
 * Copyright © 2012 Canonical Ltd.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 3, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranties of
 * MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR
 * PURPOSE.  See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Ted Gould <ted@canonical.com>
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/un.h>
#include <pwd.h>
#include <grp.h>
#include <errno.h>

#include <security/pam_modules.h>
#include <security/pam_modutil.h>
#include <security/pam_appl.h>

#include "pam-freerdp-children.h"
#include "auth-check-path.h"

static int unpriveleged_kill (struct passwd * pwdent);

static char * global_domain = NULL;
/* FIXME? This is a work around to the fact that PAM seems to be clearing
   the auth token between authorize and open_session.  Which then requires
   us to save it.  Seems like we're the wrong people to do it, but we have
   no choice */
static char * global_password = NULL;

/* Either grab a value or prompt for it */
static char *
get_item (pam_handle_t * pamh, int type)
{
	/* Check to see if we just have the value.  If we do, great
	   let's dup it some we're consitently allocating memory */
	if (type != PAM_TYPE_DOMAIN) {
		/* If it's not a domain we can use the PAM functions because the PAM
		   functions don't support the domain */
		char * value = NULL;
		if (pam_get_item(pamh, type, (const void **)&value) == PAM_SUCCESS && value != NULL) {
			return value;
		}
		if (type == PAM_AUTHTOK && global_password != NULL) {
			/* If we're looking for a password, we didn't get one, before
			   prompting see if we've got a global one. */
			return global_password;
		}
	} else {
		/* Here we only have domains, so we can see if the global domain is
		   useful for us, if we have it */
		if (global_domain != NULL) {
			return global_domain;
		}
	}
	/* Now we need to prompt */

	/* Build up the message we're prompting for */
	struct pam_message message;
	const struct pam_message * pmessage = &message;

	message.msg = NULL;
	message.msg_style = PAM_PROMPT_ECHO_ON;

	switch (type) {
	case PAM_USER:
		message.msg = "login:";
		break;
	case PAM_RUSER:
		message.msg = "remote login:";
		break;
	case PAM_RHOST:
		message.msg = "remote host:";
		break;
	case PAM_AUTHTOK:
		message.msg = "password:";
		message.msg_style = PAM_PROMPT_ECHO_OFF;
		break;
	case PAM_TYPE_DOMAIN:
		message.msg = "domain:";
		break;
	default:
		return NULL;
	}

	struct pam_conv * conv = NULL;
	if (pam_get_item(pamh, PAM_CONV, (const void **)&conv) != PAM_SUCCESS || conv == NULL || conv->conv == NULL) {
		return NULL;
	}

	struct pam_response * responses = NULL;
	if (conv->conv(1, &pmessage, &responses, conv->appdata_ptr) != PAM_SUCCESS || responses == NULL) {
		return NULL;
	}

	char * promptval = responses->resp;
	free(responses);

	/* If we didn't get anything, just move on */
	if (promptval == NULL) {
		return NULL;
	}

	if (type == PAM_AUTHTOK) {
		if (mlock(promptval, strlen(promptval) + 1) != 0) {
			free(promptval);
			return NULL;
		}
	}

	/* The way that xfreerdp does parsing means that we can't handle
	   spaces in the username.  Let's block them as early as possible.
	   Though, if the xfreerdp part gets fixed, we want this to disappear
	     http://launchpad.net/bugs/1053102
	*/
	if (type == PAM_RUSER) {
		if (strstr(promptval, " ") != NULL) {
			free(promptval);
			return NULL;
		}
	}

	if (type == PAM_RHOST) {
		char * subloc = strstr(promptval, "://");
		if (subloc != NULL) {
			char * original = promptval;
			char * newish = subloc + strlen("://");
			char * endslash = strstr(newish, "/");

			if (endslash != NULL) {
				endslash[0] = '\0';
			}

			promptval = strdup(newish);
			free(original);
		}
	}

	char * retval = NULL;
	if (promptval != NULL) { /* Can't believe it really would be at this point, but let's be sure */
		if (type != PAM_TYPE_DOMAIN) {
			/* We can only use the PAM functions if it's not the domain */
			pam_set_item(pamh, type, (const void *)promptval);
			/* We're returning the value saved by PAM so we can clear promptval */
			pam_get_item(pamh, type, (const void **)&retval);
		}
		if (type == PAM_TYPE_DOMAIN) {
			/* The domain can be saved globally so we can use it for open */
			if (global_domain != NULL) {
				free(global_domain);
			}
			global_domain = strdup(promptval);
			retval = global_domain;
		}
		if (type == PAM_AUTHTOK) {
			/* We also save the password globally if we've got one */
			if (global_password != NULL) {
				memset(global_password, 0, strlen(global_password));
				munlock(global_password, strlen(global_password) + 1);
				free(global_password);
			}
			global_password = strdup(promptval);
			if (mlock(global_password, strlen(global_password) + 1) != 0) {
				/* Woah, can't lock it.  Can't keep it. */
				free(global_password);
				global_password = NULL;
			} else {
				retval = global_password;
			}
		}

		if (type == PAM_AUTHTOK) {
			memset(promptval, 0, strlen(promptval) + 1);
			munlock(promptval, strlen(promptval) + 1);
		}

		free(promptval);
	}

	return retval;
}

#define GET_ITEM(val, type) \
	if ((val = get_item(pamh, type)) == NULL) { \
		retval = PAM_AUTH_ERR; \
		goto done; \
	}

/* Authenticate.  We need to make sure we have a user account, that
   there are remote accounts and then verify them with FreeRDP */
PAM_EXTERN int
pam_sm_authenticate (pam_handle_t *pamh, int flags, int argc, const char **argv)
{
	char * username = NULL;
	char * password = NULL;
	char * ruser = NULL;
	char * rhost = NULL;
	char * rdomain = NULL;
	int retval = PAM_IGNORE;

	/* Get all the values, or prompt for them, or return with
	   an auth error */
	GET_ITEM(username, PAM_USER);
	GET_ITEM(ruser,    PAM_RUSER);
	GET_ITEM(rhost,    PAM_RHOST);
	GET_ITEM(rdomain,  PAM_TYPE_DOMAIN);
	GET_ITEM(password, PAM_AUTHTOK);

	int stdinpipe[2];
	if (pipe(stdinpipe) != 0) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	/* At this point we should have the values, let's check the auth */
	pid_t pid;
	switch (pid = fork()) {
	case 0: { /* child */
		pam_sm_authenticate_helper (stdinpipe, username, rhost, ruser, rdomain);
		break;
	}
	case -1: { /* fork'n error! */
		retval = PAM_SYSTEM_ERR;
		break;
	}
	default: {
		int forkret = 0;
		int bytesout = 0;

		bytesout += write(stdinpipe[1], password, strlen(password));
		bytesout += write(stdinpipe[1], "\n", 1);

		close(stdinpipe[1]);

		if (waitpid(pid, &forkret, 0) < 0 || bytesout == 0) {
			retval = PAM_SYSTEM_ERR;
		} else if (forkret == 0) {
			retval = PAM_SUCCESS;
		} else {
			retval = PAM_AUTH_ERR;
		}
	}
	}

	/* Return our status */
done:
	return retval;
}



pid_t session_pid = 0;
/* Open Session.  Here we need to fork a little process so that we can
   give the credentials to the session itself so that it can startup the
   xfreerdp viewer for the login */
PAM_EXTERN int
pam_sm_open_session (pam_handle_t *pamh, int flags, int argc, const char ** argv)
{
	char * username = NULL;
	char * password = NULL;
	char * ruser = NULL;
	char * rhost = NULL;
	char * rdomain = NULL;
	int retval = PAM_SUCCESS;

	/* Get all the values, or prompt for them, or return with
	   an auth error */
	GET_ITEM(username, PAM_USER);
	GET_ITEM(ruser,    PAM_RUSER);
	GET_ITEM(rhost,    PAM_RHOST);
	GET_ITEM(rdomain,  PAM_TYPE_DOMAIN);
	GET_ITEM(password, PAM_AUTHTOK);

	struct passwd * pwdent = getpwnam(username);
	if (pwdent == NULL) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	if (session_pid != 0) {
		unpriveleged_kill(pwdent);
	}

	int sessionready[2];
	if (pipe(sessionready) != 0) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	pid_t pid = fork();
	if (pid == 0) {
		
		int ret = session_socket_handler(pwdent, sessionready[1], ruser, rhost, rdomain, password);

		close(sessionready[1]);
		_exit(ret);
	} else if (pid < 0) {
		close(sessionready[0]);
		close(sessionready[1]);

		retval = PAM_SYSTEM_ERR;
	} else {
		char readbuffer[strlen(ALL_GOOD_SIGNAL) + 1];
		int readlen = 0;

		readlen = read(sessionready[0], readbuffer, strlen(ALL_GOOD_SIGNAL) + 1);

		close(sessionready[0]);

		if (readlen == strlen(ALL_GOOD_SIGNAL) + 1) {
			session_pid = pid;
		} else {
			retval = PAM_SYSTEM_ERR;
		}
	}

done:
    return retval;
}

/* Close Session.  Make sure our little guy has died so he doesn't become
   a zombie and eat things. */
PAM_EXTERN int
pam_sm_close_session (pam_handle_t *pamh, int flags, int argc, const char **argv)
{
	if (session_pid == 0) {
		return PAM_IGNORE;
	}

	char * username = NULL;
	int retval = PAM_SUCCESS;

	GET_ITEM(username, PAM_USER);

	struct passwd * pwdent = getpwnam(username);
	if (pwdent == NULL) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	retval = unpriveleged_kill(pwdent);

done:
	return retval;
}

/* Drop privs and try to kill the process with the PID of session_pid.  
   This ensures that we don't kill something important if there is PID wrap
   around.  */
static int
unpriveleged_kill (struct passwd * pwdent)
{
	int retval = PAM_SUCCESS;

	pid_t pid = fork();
	if (pid == 0) {
		/* Setting groups, but allowing EPERM as if we're not 100% root
		   we might not be able to do this */
		if (setgroups(1, &pwdent->pw_gid) != 0 && errno != EPERM) {
			_exit(EXIT_FAILURE);
		}

		if (setgid(pwdent->pw_gid) < 0 || setuid(pwdent->pw_uid) < 0 ||
				setegid(pwdent->pw_gid) < 0 || seteuid(pwdent->pw_uid) < 0) {
			_exit(EXIT_FAILURE);
		}

		if (clearenv() != 0) {
			_exit(EXIT_FAILURE);
		}

		int killval = kill(session_pid, SIGKILL);
		session_pid = 0;

		if (killval != 0) {
			printf("Unable to kill\n");
		}

		/* NOTE: We're ignoring whether we could kill it or not.  It'd be nice to
		   track that but there are a lot of reason that we could fail there and
		   it's not a bad thing.  Really we're attempting a best effort to clean up
		   we won't be able to gaurantee it. */
		_exit(EXIT_SUCCESS);	
	} else if (pid < 0) {
		retval = PAM_SYSTEM_ERR;
	} else {
		int forkret = 0;

		if (waitpid(pid, &forkret, 0) < 0) {
			retval = PAM_SYSTEM_ERR;
		}
	}

	/* We reset this no matter.  If we error'd trying to do it, we don't
	   want to try again.  We'll just return the error for this time. */
	session_pid = 0;

	return retval;
}

/* LightDM likes to have this function around, but we don't need it as we
   don't have a token hanging around. */
PAM_EXTERN int
pam_sm_setcred (pam_handle_t *pamh, int flags, int argc, const char ** argv)
{
	return PAM_SUCCESS;
}

#ifdef PAM_STATIC

struct pam_module _pam_freerdp_modstruct = {
     "pam_freerdp",
     pam_sm_authenticate,
     pam_sm_setcred,
     NULL,
     pam_sm_open_session,
     pam_sm_close_session,
     NULL,
};

#endif