darwin/_dirhelper.c

   1 /*
   2  * Copyright (c) 2006, 2007 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #include <mach/mach.h>
  25 #include <mach/mach_error.h>
  26 #include <servers/bootstrap.h>
  27 #include <unistd.h>
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <stdbool.h>
  31 #include <membership.h>
  32 #include <pthread.h>
  33 #include <errno.h>
  34 #include <sys/types.h>
  35 #include <sys/stat.h>
  36 #include <sys/param.h>
  37 #include <uuid/uuid.h>
  38 #include <string.h>
  39 #include <libkern/OSByteOrder.h>
  40
  41 #include "dirhelper.h"
  42 #include "dirhelper_priv.h"
  43
  44 #define BUCKETLEN       2
  45
  46 #define MUTEX_LOCK(x)   if(__is_threaded) pthread_mutex_lock(x)
  47 #define MUTEX_UNLOCK(x) if(__is_threaded) pthread_mutex_unlock(x)
  48
  49 #define ENCODEBITS      6
  50 #define ENCODEDSIZE     ((8 * UUID_UID_SIZE + ENCODEBITS - 1) / ENCODEBITS)
  51 #define UUID_UID_SIZE   (sizeof(uuid_t) + sizeof(uid_t))
  52
  53 extern int __is_threaded;
  54
  55 static const mode_t modes[] = {
  56     0,          /* unused */
  57     0700,       /* temp */
  58     0700,       /* cache */
  59 };
  60
  61 static const char *subdirs[] = {
  62     DIRHELPER_TOP_STR,
  63     DIRHELPER_TEMP_STR,
  64     DIRHELPER_CACHE_STR,
  65 };
  66
  67 static const char encode[] = "+-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
  68
  69 static void
  70 encode_uuid_uid(uuid_t uuid, uid_t uid, char *str)
  71 {
  72     unsigned char buf[UUID_UID_SIZE + 1];
  73     unsigned char *bp = buf;
  74     int i = 0;
  75     unsigned int n;
  76
  77     memcpy(bp, uuid, sizeof(uuid_t));
  78     uid = OSSwapHostToBigInt32(uid);
  79     memcpy(bp + sizeof(uuid_t), &uid, sizeof(uid_t));
  80     bp[UUID_UID_SIZE] = 0; // this ensures the last encoded byte will have trailing zeros
  81     while(i < ENCODEDSIZE) {
  82         switch(i % 4) {
  83         case 0:
  84             n = *bp++;
  85             *str++ = encode[n >> 2];
  86             break;
  87         case 1:
  88             n = ((n & 0x3) << 8) | *bp++;
  89             *str++ = encode[n >> 4];
  90             break;
  91         case 2:
  92             n = ((n & 0xf) << 8) | *bp++;
  93             *str++ = encode[n >> 6];
  94             break;
  95         case 3:
  96             *str++ = encode[n & 0x3f];
  97             break;
  98         }
  99         i++;
 100     }
 101     *str = 0;
 102 }
 103
 104 char *
 105 __user_local_dirname(uid_t uid, dirhelper_which_t which, char *path, size_t pathlen)
 106 {
 107     uuid_t uuid;
 108     char str[ENCODEDSIZE + 1];
 109     int res;
 110
 111     if(which < 0 || which > DIRHELPER_USER_LOCAL_LAST) {
 112         errno = EINVAL;
 113         return NULL;
 114     }
 115
 116     res = mbr_uid_to_uuid(uid, uuid);
 117     if(res != 0) {
 118         errno = res;
 119         return NULL;
 120     }
 121
 122     //
 123     // We partition the namespace so that we don't end up with too
 124     // many users in a single directory.  With 4096 buckets, we
 125     // could scale to 1,000,000 users while keeping the average
 126     // number of files in a single directory below 250
 127     //
 128     encode_uuid_uid(uuid, uid, str);
 129     res = snprintf(path, pathlen,
 130         "%s%.*s/%s/%s",
 131         VAR_FOLDERS_PATH, BUCKETLEN, str, str, subdirs[which]);
 132     if(res >= pathlen) {
 133         errno = EINVAL;
 134         return NULL; /* buffer too small */
 135     }
 136     return path;
 137 }
 138
 139 __private_extern__ char *
 140 _dirhelper(dirhelper_which_t which, char *path, size_t pathlen)
 141 {
 142     static char userdir[PATH_MAX];
 143     static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
 144     int res;
 145     struct stat sb;
 146
 147     if(which < 0 || which > DIRHELPER_USER_LOCAL_LAST) {
 148         errno = EINVAL;
 149         return NULL;
 150     }
 151
 152     if(!*userdir) {
 153         MUTEX_LOCK(&lock);
 154         if(!*userdir) {
 155             mach_port_t mp;
 156
 157             if(bootstrap_look_up(bootstrap_port, DIRHELPER_BOOTSTRAP_NAME, &mp) != KERN_SUCCESS) {
 158                 errno = EPERM;
 159                 MUTEX_UNLOCK(&lock);
 160                 return NULL;
 161             }
 162             if(__user_local_dirname(geteuid(), DIRHELPER_USER_LOCAL, userdir, sizeof(userdir)) == NULL) {
 163 server_error:
 164                 mach_port_deallocate(mach_task_self(), mp);
 165                 MUTEX_UNLOCK(&lock);
 166                 return NULL;
 167             }
 168             /*
 169              * check if userdir exists, and if not, call
 170              * __dirhelper_create_user_local to create it
 171              * (we have to check again afterwards).
 172              */
 173             if(stat(userdir, &sb) < 0) {
 174                 if(errno != ENOENT) { /* some unknown error */
 175                     *userdir = 0;
 176                     goto server_error;
 177                 }
 178                 if(__dirhelper_create_user_local(mp) != KERN_SUCCESS) {
 179                     errno = EPERM;
 180                     *userdir = 0;
 181                     goto server_error;
 182                 }
 183                 /* double check that the directory really got created */
 184                 if(stat(userdir, &sb) < 0) {
 185                     *userdir = 0;
 186                     goto server_error;
 187                 }
 188             }
 189             mach_port_deallocate(mach_task_self(), mp);
 190         }
 191         MUTEX_UNLOCK(&lock);
 192     }
 193
 194     if(pathlen < strlen(userdir) + strlen(subdirs[which]) + 1) {
 195         errno = EINVAL;
 196         return NULL; /* buffer too small */
 197     }
 198     strcpy(path, userdir);
 199     strcat(path, subdirs[which]);
 200
 201     /*
 202      * now for subdirectories, create it with the appropriate permissions
 203      * if it doesn't already exist.
 204      */
 205     if(which != DIRHELPER_USER_LOCAL) {
 206         res = mkdir(path, modes[which]);
 207         if(res != 0 && errno != EEXIST)
 208             return NULL;
 209     }
 210
 211     return path;
 212 }