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/* $OpenBSD: locking.c,v 1.12 2015/01/16 06:39:50 deraadt Exp $ */
/*
* Copyright (c) 1996-1998 Theo de Raadt <deraadt@theos.com>
* Copyright (c) 1996-1998 David Mazieres <dm@lcs.mit.edu>
* All rights reserved.
*
* 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. The name of the authors may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED ``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 AUTHORS 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.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <pwd.h>
#include <syslog.h>
#include <time.h>
#include <unistd.h>
#include <limits.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include "pathnames.h"
#include "mail.local.h"
static char lpath[PATH_MAX];
void
rellock(void)
{
if (lpath[0])
unlink(lpath);
}
int
getlock(char *name, struct passwd *pw)
{
struct stat sb, fsb;
int lfd=-1;
char buf[8*1024];
int tries = 0;
(void)snprintf(lpath, sizeof lpath, "%s/%s.lock",
_PATH_MAILDIR, name);
if (stat(_PATH_MAILDIR, &sb) != -1 &&
(sb.st_mode & S_IWOTH) == S_IWOTH) {
/*
* We have a writeable spool, deal with it as
* securely as possible.
*/
time_t ctim = -1;
seteuid(pw->pw_uid);
if (lstat(lpath, &sb) != -1)
ctim = sb.st_ctime;
while (1) {
/*
* Deal with existing user.lock files
* or directories or symbolic links that
* should not be here.
*/
if (readlink(lpath, buf, sizeof buf-1) != -1) {
if (lstat(lpath, &sb) != -1 &&
S_ISLNK(sb.st_mode)) {
seteuid(sb.st_uid);
unlink(lpath);
seteuid(pw->pw_uid);
}
goto again;
}
if ((lfd = open(lpath, O_CREAT|O_WRONLY|O_EXCL|O_EXLOCK,
S_IRUSR|S_IWUSR)) != -1)
break;
again:
if (tries > 10) {
merr(NOTFATAL, "%s: %s", lpath,
strerror(errno));
seteuid(0);
return(-1);
}
if (tries > 9 &&
(lfd = open(lpath, O_WRONLY|O_EXLOCK, 0)) != -1) {
if (fstat(lfd, &fsb) != -1 &&
lstat(lpath, &sb) != -1) {
if (fsb.st_dev == sb.st_dev &&
fsb.st_ino == sb.st_ino &&
ctim == fsb.st_ctime ) {
seteuid(fsb.st_uid);
baditem(lpath);
seteuid(pw->pw_uid);
}
}
close(lfd);
}
sleep(1U << tries);
tries++;
continue;
}
seteuid(0);
} else {
/*
* Only root can write the spool directory.
*/
while (1) {
if ((lfd = open(lpath, O_CREAT|O_WRONLY|O_EXCL,
S_IRUSR|S_IWUSR)) != -1)
break;
if (tries > 9) {
merr(NOTFATAL, "%s: %s", lpath, strerror(errno));
return(-1);
}
sleep(1U << tries);
tries++;
}
}
return(lfd);
}
void
baditem(char *path)
{
char npath[PATH_MAX];
int fd;
if (unlink(path) == 0)
return;
snprintf(npath, sizeof npath, "%s/mailXXXXXXXXXX", _PATH_MAILDIR);
if ((fd = mkstemp(npath)) == -1)
return;
close(fd);
if (rename(path, npath) == -1)
unlink(npath);
else
merr(NOTFATAL, "nasty spool item %s renamed to %s",
path, npath);
/* XXX if we fail to rename, another attempt will happen later */
}
void
merr(int isfatal, const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vsyslog(LOG_ERR, fmt, ap);
va_end(ap);
if (isfatal)
exit(1);
}
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