1 /* $OpenBSD: locking.c,v 1.10 2011/01/10 21:00:50 millert Exp $ */ 2 3 /* 4 * Copyright (c) 1996-1998 Theo de Raadt <deraadt@theos.com> 5 * Copyright (c) 1996-1998 David Mazieres <dm@lcs.mit.edu> 6 * All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. The name of the authors may not be used to endorse or promote products 17 * derived from this software without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 20 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY 21 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 22 * THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 23 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 24 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 25 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 26 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 27 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 28 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31 #include <sys/param.h> 32 #include <sys/stat.h> 33 #include <fcntl.h> 34 #include <pwd.h> 35 #include <syslog.h> 36 #include <time.h> 37 #include <unistd.h> 38 #include <errno.h> 39 #include <stdio.h> 40 #include <stdlib.h> 41 #include <string.h> 42 #include <stdarg.h> 43 #include "pathnames.h" 44 #include "mail.local.h" 45 46 static char lpath[MAXPATHLEN]; 47 48 void 49 rellock(void) 50 { 51 52 if (lpath[0]) 53 unlink(lpath); 54 } 55 56 int 57 getlock(char *name, struct passwd *pw) 58 { 59 struct stat sb, fsb; 60 int lfd=-1; 61 char buf[8*1024]; 62 int tries = 0; 63 64 (void)snprintf(lpath, sizeof lpath, "%s/%s.lock", 65 _PATH_MAILDIR, name); 66 67 if (stat(_PATH_MAILDIR, &sb) != -1 && 68 (sb.st_mode & S_IWOTH) == S_IWOTH) { 69 /* 70 * We have a writeable spool, deal with it as 71 * securely as possible. 72 */ 73 time_t ctim = -1; 74 75 seteuid(pw->pw_uid); 76 if (lstat(lpath, &sb) != -1) 77 ctim = sb.st_ctime; 78 while (1) { 79 /* 80 * Deal with existing user.lock files 81 * or directories or symbolic links that 82 * should not be here. 83 */ 84 if (readlink(lpath, buf, sizeof buf-1) != -1) { 85 if (lstat(lpath, &sb) != -1 && 86 S_ISLNK(sb.st_mode)) { 87 seteuid(sb.st_uid); 88 unlink(lpath); 89 seteuid(pw->pw_uid); 90 } 91 goto again; 92 } 93 if ((lfd = open(lpath, O_CREAT|O_WRONLY|O_EXCL|O_EXLOCK, 94 S_IRUSR|S_IWUSR)) != -1) 95 break; 96 again: 97 if (tries > 10) { 98 merr(NOTFATAL, "%s: %s", lpath, 99 strerror(errno)); 100 seteuid(0); 101 return(-1); 102 } 103 if (tries > 9 && 104 (lfd = open(lpath, O_WRONLY|O_EXLOCK, 0)) != -1) { 105 if (fstat(lfd, &fsb) != -1 && 106 lstat(lpath, &sb) != -1) { 107 if (fsb.st_dev == sb.st_dev && 108 fsb.st_ino == sb.st_ino && 109 ctim == fsb.st_ctime ) { 110 seteuid(fsb.st_uid); 111 baditem(lpath); 112 seteuid(pw->pw_uid); 113 } 114 } 115 } 116 sleep(1U << tries); 117 tries++; 118 continue; 119 } 120 seteuid(0); 121 } else { 122 /* 123 * Only root can write the spool directory. 124 */ 125 while (1) { 126 if ((lfd = open(lpath, O_CREAT|O_WRONLY|O_EXCL, 127 S_IRUSR|S_IWUSR)) != -1) 128 break; 129 if (tries > 9) { 130 merr(NOTFATAL, "%s: %s", lpath, strerror(errno)); 131 return(-1); 132 } 133 sleep(1U << tries); 134 tries++; 135 } 136 } 137 return(lfd); 138 } 139 140 void 141 baditem(char *path) 142 { 143 char npath[MAXPATHLEN]; 144 int fd; 145 146 if (unlink(path) == 0) 147 return; 148 snprintf(npath, sizeof npath, "%s/mailXXXXXXXXXX", _PATH_MAILDIR); 149 if ((fd = mkstemp(npath)) == -1) 150 return; 151 close(fd); 152 if (rename(path, npath) == -1) 153 unlink(npath); 154 else 155 merr(NOTFATAL, "nasty spool item %s renamed to %s", 156 path, npath); 157 /* XXX if we fail to rename, another attempt will happen later */ 158 } 159 160 void 161 merr(int isfatal, const char *fmt, ...) 162 { 163 va_list ap; 164 165 va_start(ap, fmt); 166 vsyslog(LOG_ERR, fmt, ap); 167 va_end(ap); 168 if (isfatal) 169 exit(1); 170 } 171