dma-mbox-create.c

/*
 * Copyright (c) 2010-2014, Simon Schubert <[email protected]>.
 * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Simon Schubert <[email protected]>.
 *
 * 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.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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.
 */

/*
 * This binary is setuid root.  Use extreme caution when touching
 * user-supplied information.  Keep the root window as small as possible.
 */

#ifdef __FreeBSD__
#define	USE_CAPSICUM	1
#endif

#include <sys/param.h>
#if USE_CAPSICUM
#include <sys/capsicum.h>
#endif
#include <sys/stat.h>

#include <capsicum_helpers.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <paths.h>
#include <pwd.h>
#include <stdio.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

#include "dma.h"


static void
logfail(int exitcode, const char *fmt, ...)
{
	int oerrno = errno;
	va_list ap;
	char outs[1024];

	outs[0] = 0;
	if (fmt != NULL) {
		va_start(ap, fmt);
		vsnprintf(outs, sizeof(outs), fmt, ap);
		va_end(ap);
	}

	errno = oerrno;
	if (*outs != 0)
		syslog(LOG_ERR, errno ? "%s: %m" : "%s", outs);
	else
		syslog(LOG_ERR, errno ? "%m" : "unknown error");

	exit(exitcode);
}

/*
 * Create a mbox in /var/mail for a given user, or make sure
 * the permissions are correct for dma.
 */

int
main(int argc, char **argv)
{
#if USE_CAPSICUM
	cap_rights_t rights;
#endif
	const char *user;
	struct passwd *pw;
	struct group *gr;
	uid_t user_uid;
	gid_t mail_gid;
	int f, maildirfd;

	/*
	 * Open log fd now for capability sandbox.
	 */
	openlog("dma-mbox-create", LOG_NDELAY, LOG_MAIL);

	errno = 0;
	gr = getgrnam(DMA_GROUP);
	if (!gr)
		logfail(EX_CONFIG, "cannot find dma group `%s'", DMA_GROUP);

	mail_gid = gr->gr_gid;

	if (setgid(mail_gid) != 0)
		logfail(EX_NOPERM, "cannot set gid to %d (%s)", mail_gid, DMA_GROUP);
	if (getegid() != mail_gid)
		logfail(EX_NOPERM, "cannot set gid to %d (%s), still at %d", mail_gid, DMA_GROUP, getegid());

	/*
	 * We take exactly one argument: the username.
	 */
	if (argc != 2) {
		errno = 0;
		logfail(EX_USAGE, "no arguments");
	}
	user = argv[1];

	syslog(LOG_NOTICE, "creating mbox for `%s'", user);

	/* the username may not contain a pathname separator */
	if (strchr(user, '/')) {
		errno = 0;
		logfail(EX_DATAERR, "path separator in username `%s'", user);
		exit(1);
	}

	/* verify the user exists */
	errno = 0;
	pw = getpwnam(user);
	if (!pw)
		logfail(EX_NOUSER, "cannot find user `%s'", user);

	maildirfd = open(_PATH_MAILDIR, O_RDONLY);
	if (maildirfd < 0)
		logfail(EX_NOINPUT, "cannot open maildir %s", _PATH_MAILDIR);

	/*
	 * Cache NLS data, for strerror, for err(3), before entering capability
	 * mode.
	 */
	caph_cache_catpages();

	/*
	 * Cache local time before entering Capsicum capability sandbox.
	 */
	caph_cache_tzdata();

#if USE_CAPSICUM
	cap_rights_init(&rights, CAP_CREATE, CAP_FCHMOD, CAP_FCHOWN,
	    CAP_LOOKUP, CAP_READ);
	if (cap_rights_limit(maildirfd, &rights) < 0 && errno != ENOSYS)
		err(EX_OSERR, "can't limit maildirfd rights");

	/* Enter Capsicum capability sandbox */
	if (caph_enter() < 0)
		err(EX_OSERR, "cap_enter");
#endif

	user_uid = pw->pw_uid;

	f = openat(maildirfd, user, O_RDONLY|O_CREAT|O_NOFOLLOW, 0600);
	if (f < 0)
		logfail(EX_NOINPUT, "cannot open mbox `%s'", user);

	if (fchown(f, user_uid, mail_gid))
		logfail(EX_OSERR, "cannot change owner of mbox `%s'", user);

	if (fchmod(f, 0620))
		logfail(EX_OSERR, "cannot change permissions of mbox `%s'",
		    user);

	/* file should be present with the right owner and permissions */

	syslog(LOG_NOTICE, "successfully created mbox for `%s'", user);

	return (0);
}