filters/partition/partition-mbr.c

   1 /* nbdkit
   2  * Copyright Red Hat
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
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   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <stdint.h>
  38 #include <inttypes.h>
  39 #include <string.h>
  40 #include <errno.h>
  41
  42 #include <nbdkit-filter.h>
  43
  44 #include "byte-swapping.h"
  45 #include "isaligned.h"
  46
  47 #include "partition.h"
  48
  49 /* See also linux.git/block/partitions/msdos.c:is_extended_partition */
  50 #define is_extended(byte) ((byte) == 0x5 || (byte) == 0xf || (byte) == 0x85)
  51
  52 struct mbr_partition {
  53   uint8_t part_type_byte;
  54   uint32_t start_sector;
  55   uint32_t nr_sectors;
  56 };
  57
  58 static void
  59 get_mbr_partition (uint8_t *sector, int i, struct mbr_partition *part)
  60 {
  61   int offset = 0x1BE + i*0x10;
  62
  63   part->part_type_byte = sector[offset+4];
  64   memcpy (&part->start_sector, &sector[offset+8], 4);
  65   part->start_sector = le32toh (part->start_sector);
  66   memcpy (&part->nr_sectors, &sector[offset+0xC], 4);
  67   part->nr_sectors = le32toh (part->nr_sectors);
  68 }
  69
  70 int
  71 find_mbr_partition (nbdkit_next *next,
  72                     int64_t size, uint8_t *mbr,
  73                     int64_t *offset_r, int64_t *range_r)
  74 {
  75   int i;
  76   struct mbr_partition partition;
  77   uint32_t ep_start_sector, ep_nr_sectors;
  78   uint64_t ebr, next_ebr;
  79   uint8_t sector[SECTOR_SIZE];
  80
  81   /* Primary partition. */
  82   if (partnum <= 4) {
  83     for (i = 0; i < 4; ++i) {
  84       get_mbr_partition (mbr, i, &partition);
  85       if (partition.nr_sectors > 0 &&
  86           partition.part_type_byte != 0 &&
  87           !is_extended (partition.part_type_byte) &&
  88           partnum == i+1) {
  89         *offset_r = partition.start_sector * (int64_t) SECTOR_SIZE;
  90         *range_r = partition.nr_sectors * (int64_t) SECTOR_SIZE;
  91         return 0;
  92       }
  93     }
  94
  95     /* Not found falls through to error case at the end of the function. */
  96   }
  97
  98   /* Logical partition. */
  99   else {
 100     /* Find the extended partition in the primary partition table. */
 101     for (i = 0; i < 4; ++i) {
 102       get_mbr_partition (mbr, i, &partition);
 103       if (partition.nr_sectors > 0 &&
 104           is_extended (partition.part_type_byte)) {
 105         goto found_extended;
 106       }
 107     }
 108     nbdkit_error ("MBR logical partition selected, "
 109                   "but there is no extended partition in the partition table");
 110     return -1;
 111
 112   found_extended:
 113     ep_start_sector = partition.start_sector;
 114     ep_nr_sectors = partition.nr_sectors;
 115     ebr = ep_start_sector * (uint64_t)SECTOR_SIZE;
 116
 117     /* This loop will terminate eventually because we only accept
 118      * links which strictly increase the EBR pointer.  There are valid
 119      * partition tables which do odd things like arranging the
 120      * partitions in reverse order, but we will not accept them here.
 121      */
 122     for (i = 5; ; ++i) {
 123       /* Check that the ebr is aligned and pointing inside the disk
 124        * and doesn't point to the MBR.
 125        */
 126       if (!IS_ALIGNED (ebr, SECTOR_SIZE) ||
 127           ebr < SECTOR_SIZE || ebr >= size-SECTOR_SIZE) {
 128         nbdkit_error ("invalid EBR chain: "
 129                       "next EBR boot sector is located outside disk boundary");
 130         return -1;
 131       }
 132
 133       /* Read the EBR sector. */
 134       nbdkit_debug ("partition: reading EBR at %" PRIi64, ebr);
 135       if (next->pread (next, sector, sizeof sector, ebr, 0, &errno) == -1)
 136         return -1;
 137
 138       if (partnum == i) {
 139         uint64_t offset, range;
 140
 141         /* First entry in EBR points to the logical partition. */
 142         get_mbr_partition (sector, 0, &partition);
 143
 144         /* The first entry start sector is relative to the EBR. */
 145         offset = ebr + partition.start_sector * (uint64_t)SECTOR_SIZE;
 146         range = partition.nr_sectors * (uint64_t)SECTOR_SIZE;
 147
 148         /* Logical partition cannot be before the corresponding EBR,
 149          * and it cannot extend beyond the enclosing extended
 150          * partition.
 151          */
 152         if (offset <= ebr ||
 153             offset + range >
 154             ((uint64_t)ep_start_sector + ep_nr_sectors) * SECTOR_SIZE) {
 155           nbdkit_error ("logical partition start or size out of range "
 156                         "(offset=%" PRIu64 ", range=%" PRIu64 ", "
 157                         "ep:startsect=%" PRIu32 ", ep:nrsects=%" PRIu32 ")",
 158                         offset, range, ep_start_sector, ep_nr_sectors);
 159           return -1;
 160         }
 161         *offset_r = offset;
 162         *range_r = range;
 163         return 0;
 164       }
 165
 166       /* Second entry in EBR links to the next EBR. */
 167       get_mbr_partition (sector, 1, &partition);
 168
 169       /* All zeroes means the end of the chain. */
 170       if (partition.start_sector == 0 && partition.nr_sectors == 0)
 171         break;
 172
 173       /* The second entry start sector is relative to the start to the
 174        * extended partition.
 175        */
 176       next_ebr =
 177         ((uint64_t)ep_start_sector + partition.start_sector) * SECTOR_SIZE;
 178
 179       /* Make sure the next EBR > current EBR. */
 180       if (next_ebr <= ebr) {
 181         nbdkit_error ("invalid EBR chain: "
 182                       "next EBR %" PRIu64 " <= current EBR %" PRIu64,
 183                       next_ebr, ebr);
 184         return -1;
 185       }
 186       ebr = next_ebr;
 187     }
 188   }
 189
 190   nbdkit_error ("MBR partition %d not found", partnum);
 191   return -1;
 192 }