[Parted-maintainers] Bug#349718: parted: last partition in EFI GPT
overlaps alternate table
Kalle Olavi Niemitalo
kon at iki.fi
Tue Jan 24 20:56:53 GMT 2006
Package: parted
Version: 1.6.25.1-1
Severity: grave
I overwrote a USB disk with shred, created an EFI GPT disk label
and two partitions with parted, used the partitions, shredded the
second of them again, made a new file system there, and copied
data to it. The next time I reconnected the disk, I was
surprised by this warning from Linux:
Jan 24 20:13:49 [kernel] SCSI device sda: 312581808 512-byte hdwr sectors (160042 MB)
- Last output repeated twice -
Jan 24 20:13:50 [kernel] Alternate GPT is invalid, using primary GPT.
Jan 24 20:13:50 [kernel] p1 p2
I then renamed the second partition with parted, in order to make
it rewrite the disk label and partition tables. This got rid of
the warning, but when I looked at the end of /dev/sda2, I saw
that the end of the partition had become overwritten with the
partition table. Because I was using ReiserFS with a 4096-byte
blocksize, the overwritten part was fortunately not part of the
file system. However, if this had been an MD or LVM partition,
important metadata could have been overwritten.
Next, I studied linux-2.6/fs/partitions/efi.h and examined the
on-disk structures with dd | hd | less. In the following
listing, the numbers at the left margin are LBA:byterange in
hexadecimal; all other numbers are in C syntax.
00000001:000-007 __le64 signature = "EFI PART";
00000001:008-00B __le32 revision = 0x00010000;
00000001:00C-00F __le32 header_size = 0x0000005c;
00000001:010-013 __le32 header_crc32 = 0x97529bc4;
00000001:014-017 __le32 reserved1 = 0;
00000001:018-01F __le64 my_lba = 1;
00000001:020-027 __le64 alternate_lba = 0x0000000012a19eaf;
00000001:028-02F __le64 first_usable_lba = 0x0000000000000022;
00000001:030-037 __le64 last_usable_lba = 0x0000000012a19e8e;
00000001:038-047 efi_guid_t disk_guid;
00000001:048-04F __le64 partition_entry_lba = 2;
00000001:050-053 __le32 num_partition_entries = 0x00000080;
00000001:054-057 __le32 sizeof_partition_entry = 0x00000080;
00000001:058-05B __le32 partition_entry_array_crc32 = 0x85c3221e;
00000002:000-00F efi_guid_t partition_type_guid = PARTITION_BASIC_DATA_GUID;
00000002:010-01F efi_guid_t unique_partition_guid;
00000002:020-027 __le64 starting_lba = 0x0000000000000022;
00000002:028-02F __le64 ending_lba = 0x000000000003d090;
00000002:030-037 gpt_entry_attributes attributes = 0;
00000002:038-07F efi_char16_t[36] partition_name = L"USB~2 clear";
00000002:080-08F efi_guid_t partition_type_guid = PARTITION_BASIC_DATA_GUID;
00000002:090-09F efi_guid_t unique_partition_guid;
00000002:0A0-0A7 __le64 starting_lba = 0x000000000003d091;
00000002:0A8-0AF __le64 ending_lba = 0x0000000012a19e8e;
00000002:0B0-0B7 gpt_entry_attributes attributes = 0;
00000002:0B8-0FF efi_char16_t[] partition_name = L"USB~2 cipher";
12a19e8e:000-00F efi_guid_t partition_type_guid = PARTITION_BASIC_DATA_GUID;
12a19e8e:010-01F efi_guid_t unique_partition_guid;
12a19e8e:020-027 __le64 starting_lba = 0x0000000000000022;
12a19e8e:028-02F __le64 ending_lba = 0x000000000003d090;
12a19e8e:030-037 gpt_entry_attributes attributes = 0;
12a19e8e:038-07F efi_char16_t[36] partition_name = L"USB~2 clear";
12a19e8e:080-08F efi_guid_t partition_type_guid = PARTITION_BASIC_DATA_GUID;
12a19e8e:090-09F efi_guid_t unique_partition_guid;
12a19e8e:0A0-0A7 __le64 starting_lba = 0x000000000003d091;
12a19e8e:0A8-0AF __le64 ending_lba = 0x0000000012a19e8e;
12a19e8e:0B0-0B7 gpt_entry_attributes attributes = 0;
12a19e8e:0B8-0FF efi_char16_t[36] partition_name = L"USB~2 cipher";
12a19e8e:100-1FF = 0;
12a19e8f:000-12a19ead:1FF = 0;
12a19eae:000-1FF = garbage;
12a19eaf:000 __le64 signature = "EFI PART";
12a19eaf:008 __le32 revision = 0x00010000;
12a19eaf:00C __le32 header_size = 0x0000005c;
12a19eaf:010 __le32 header_crc32 = 0x6de2756c;
12a19eaf:014 __le32 reserved1 = 0;
12a19eaf:018 __le64 my_lba = 0x0000000012a19eaf;
12a19eaf:020 __le64 alternate_lba = 1;
12a19eaf:028 __le64 first_usable_lba = 0x0000000000000022;
12a19eaf:030 __le64 last_usable_lba = 0x0000000012a19e8e;
12a19eaf:038 efi_guid_t disk_guid;
12a19eaf:048 __le64 partition_entry_lba = 0x0000000012a19e8e;
12a19eaf:050 __le32 num_partition_entries = 0x00000080;
12a19eaf:054 __le32 sizeof_partition_entry = 0x00000080;
12a19eaf:058 __le32 partition_entry_array_crc32 = 0x85c3221e;
Note that:
* last_usable_lba = 0x12a19e8e in both the primary and alternate
gpt_header structures.
* ending_lba = 0x12a19e8e for the second partition in both the
primary and alternate partition table.
* partition_entry_lba = 0x12a19e8e in the alternate gpt_header
structure.
* LBA 0x12a19e8e actually contains the beginning of the alternate
partition table. The table is 0x80*0x80 = 0x4000 bytes long,
so it needs 0x20 blocks (each 0x200 bytes).
* LBA 0x12a19eae between the alternative partition table and the
alternative gpt_header is random garbage, presumably from the
whole-disk shred run.
I think this means parted should have placed the alternative
partition table at the LBA range 0x12a19e8f-0x12a19eae, rather
than 0x12a19e8e-0x12a19ead.
I have now shrunk the partition by one block, so it'll be safe
regardless of which file system I may use in the future. The
last_usable_lba fields are still dangerously wrong, though.
-- System Information:
Debian Release: testing/unstable
APT prefers unstable
APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable')
Architecture: i386 (i686)
Shell: /bin/sh linked to /bin/bash
Kernel: Linux 2.6.12-1-k7
Locale: LANG=fi_FI.UTF-8, LC_CTYPE=fi_FI.UTF-8 (charmap=UTF-8)
Versions of packages parted depends on:
ii libc6 2.3.5-6 GNU C Library: Shared libraries an
ii libncurses5 5.4-3 Shared libraries for terminal hand
ii libparted1.6-13 1.6.25.1-1 The GNU Parted disk partitioning s
ii libreadline5 5.0-10 GNU readline and history libraries
parted recommends no packages.
-- no debconf information
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