radare2/shlr/grub/partmap/msdos.c

/* pc.c - Read PC style partition tables.  */
/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2002,2004,2005,2006,2007,2008,2009  Free Software Foundation, Inc.
 *
 *  GRUB is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  GRUB is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <r_types.h>
#include <grub/partition.h>
#include <grub/msdos_partition.h>
#include <grub/disk.h>
#include <grub/mm.h>
#include <grub/misc.h>
#include <grub/dl.h>
#include <grubfs.h>

struct grub_partition_map grub_msdos_partition_map;


static grub_err_t
pc_partition_map_iterate (grub_disk_t disk,
			  int (*hook) (grub_disk_t disk,
				       const grub_partition_t partition,
				       void *closure),
			  void *closure)
{
	int i;
	struct grub_msdos_partition_entry *e;
	struct grub_partition p;
	struct grub_msdos_partition_mbr mbr;
	int labeln = 0;
	grub_disk_addr_t lastaddr;
	grub_disk_addr_t ext_offset;

	p.offset = 0;
	ext_offset = 0;
	p.number = -1;
	p.partmap = &grub_msdos_partition_map;

	/* Any value different than `p.offset' will satisfy the check during
	   first loop.  */
	lastaddr = !p.offset;

	for (;;) {
		/* Read the MBR.  */
		if (grub_disk_read (disk, p.offset, 0, sizeof (mbr), &mbr))
			goto finish;

		/* This is our loop-detection algorithm. It works the following way:
		   It saves last position which was a power of two. Then it compares the
		   saved value with a current one. This way it's guaranteed that the loop
		   will be broken by at most third walk.
		 */
		if (labeln && lastaddr == p.offset) {
			return grub_error (GRUB_ERR_BAD_PART_TABLE, "loop detected");
		}

		labeln++;
		if ((labeln & (labeln - 1)) == 0)
			lastaddr = p.offset;

		/* Check if it is valid.  */
		if (mbr.signature != grub_cpu_to_le16 (GRUB_PC_PARTITION_SIGNATURE)) {
			fprintf (stderr, "msdos: no signature\n");
			return grub_error (GRUB_ERR_BAD_PART_TABLE, "no signature");
		}

		for (i = 0; i < 4; i++)
			if (mbr.entries[i].flag & 0x7f) {
				fprintf (stderr, "msdos: bad boot flag\n");
				return grub_error (GRUB_ERR_BAD_PART_TABLE, "bad boot flag");
			}

		/* Analyze DOS partitions.  */
		for (p.index = 0; p.index < 4; p.index++) {
			e = mbr.entries + p.index;

			p.start = p.offset + grub_le_to_cpu32 (e->start);
			p.len = grub_le_to_cpu32 (e->length);

			p.msdostype = e->type;
			grub_dprintf ("partition",
					"partition %d: flag 0x%x, type 0x%x, start 0x%"PFMT64x", len 0x%"PFMT64x"\n",
					p.index, e->flag, e->type,
					(ut64) p.start,
					(ut64) p.len);

			/* If this is a GPT partition, this MBR is just a dummy.  */
			if (e->type == GRUB_PC_PARTITION_TYPE_GPT_DISK && p.index == 0)
				return grub_error (GRUB_ERR_BAD_PART_TABLE, "dummy mbr");

			/* If this partition is a normal one, call the hook.  */
			if (! grub_msdos_partition_is_empty (e->type)
					&& ! grub_msdos_partition_is_extended (e->type))
			{
				p.number++;

				if (hook (disk, &p, closure)) {
					fprintf (stderr, "msdos: hook fail\n");
					return grub_errno;
				}
			} else if (p.number < 4)
				/* If this partition is a logical one, shouldn't increase the
				   partition number.  */
				p.number++;
		}

		/* Find an extended partition.  */
		for (i = 0; i < 4; i++) {
			e = mbr.entries + i;

			if (grub_msdos_partition_is_extended (e->type)) {
				p.offset = ext_offset + grub_le_to_cpu32 (e->start);
				if (! ext_offset)
					ext_offset = p.offset;
				break;
			}
		}

		/* If no extended partition, the end.  */
		if (i == 4)
			break;
	}
finish:
	return grub_errno;
}


/* Partition map type.  */
struct grub_partition_map grub_msdos_partition_map =
  {
    .name = "msdos",
    .iterate = pc_partition_map_iterate,
  };