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Populate LUKS partition usage (#760080) 

Populate the used, unused and unallocated figures in the Partition
object for a LUKS formatted partition.  See comment in
luks::set_used_sectors() for the rational of what is used, unused and
unallocated.

As that rational mentions, a LUKS header does not store the size of the
encrypted data and is assumed to extend to the end of the partition by
the tools which start the mapping.

An underlying block device of 128 MiB (131072 KiB).
    # sfdisk -s /dev/sde
    131072

An active LUKS mapping at offset 2 MiB (4096 512-byte sectors) and
length 126 MiB (129024 KiB, 258048 512-byte sectors).
    # sfdisk -s /dev/mapper/sde_crypt
    129024
    # cryptsetup status sde_crypt
    /dev/mapper/sde_crypt is active.
      type:  LUKS1
      cipher:  aes-cbc-essiv:sha256
      keysize: 256 bits
      device:  /dev/sde
      offset:  4096 sectors
      size:    258048 sectors
      mode:    read/write

No size/length reported when dumping the LUKS header, just (payload)
offset.
    # cryptsetup luksDump /dev/sde
    LUKS header information for /dev/sde

    Version:        1
    Cipher name:    aes
    Cipher mode:    cbc-essiv:sha256
    Hash spec:      sha1
    Payload offset: 4096
    MK bits:        256
    MK digest:      7f fb ba 40 7e ba e4 3b 2f c6 d0 93 7b f7 05 49 7b 72 d4 ad
    MK salt:        4a 5b 54 f9 7b 67 af 6e ef 16 31 0a fe d9 7e 5f
                    c3 66 dc 8a ed e0 07 f4 45 c3 7c 1a 8d 7d ac f4
    MK iterations:  37750
    UUID:           0a337705-434a-4994-a842-5b4351cb3778
    ...

Shrink the LUKS mapping to 64 MiB (65536 KiB, 131072 512-byte sectors).
    # cryptsetup resize --size 131072 sde_crypt
    # sfdisk -s /dev/mapper/sde_crypt
    65536
    # cryptsetup status sde_crypt
    /dev/mapper/sde_crypt is active.
      type:  LUKS1
      cipher:  aes-cbc-essiv:sha256
      keysize: 256 bits
      device:  /dev/sde
      offset:  4096 sectors
      size:    131072 sectors
      mode:    read/write

Stop and start the LUKS mapping.
    # cryptsetup luksClose sde_crypt
    # cryptsetup luksOpen /dev/sde sde_crypt

The size of the LUKS mapping is back to 126 MiB (129024 KiB, 258048
512-byte sectors), extending to the end of the partition.
    # sfdisk -s /dev/mapper/sde_crypt
    129024
    # cryptsetup status sde_crypt
    /dev/mapper/sde_crypt is active.
      type:  LUKS1
      cipher:  aes-cbc-essiv:sha256
      keysize: 256 bits
      device:  /dev/sde
      offset:  4096 sectors
      size:    258048 sectors
      mode:    read/write

Bug 760080 - Implement read-only LUKS support
This commit is contained in:
Mike Fleetwood 2015-11-15 13:14:54 +00:00 committed by Curtis Gedak
parent 317e444056
commit 317114ffcb
2 changed files with 52 additions and 0 deletions
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2
include/luks.h
View File

@ -19,6 +19,7 @@
#define GPARTED_LUKS_H
#include "../include/FileSystem.h"
#include "../include/Partition.h"
namespace GParted
{
@ -28,6 +29,7 @@ class luks : public FileSystem
public:
FS get_filesystem_support();
bool is_busy( const Glib::ustring & path );
void set_used_sectors( Partition & partition );
};
} //GParted

50
src/luks.cc
View File

@ -16,6 +16,7 @@
#include "../include/LUKS_Info.h"
#include "../include/Utils.h"
#include "../include/luks.h"
namespace GParted
@ -27,6 +28,8 @@ FS luks::get_filesystem_support()
fs.filesystem = FS_LUKS;
fs.busy = FS::EXTERNAL;
fs.read = FS::EXTERNAL;
fs.online_read = FS::EXTERNAL;
return fs;
}
@ -37,4 +40,51 @@ bool luks::is_busy( const Glib::ustring & path )
return ! mapping.name.empty();
}
void luks::set_used_sectors( Partition & partition )
{
// Rational for how used, unused and unallocated are set for LUKS partitions
//
// A LUKS formatted partition has metadata at the start, followed by the encrypted
// data. The LUKS format only records the offset at which the encrypted data
// starts. It does NOT record it's length. Therefore for inactive LUKS mappings
// the encrypted data is assumed to extend to the end of the partition. However
// an active device-mapper (encrypted) mapping does have a size and can be resized
// with the "cryptsetup resize" command.
//
// * Metadata is required and can't be shrunk so treat as used space.
// * Encrypted data, when active, is fully in use by the device-mapper encrypted
// mapping so must also be considered used space.
// * Any space after an active mapping, because it has been shrunk, is considered
// unallocated. This matches the equivalent with other file systems.
// * Nothing is considered unused space.
//
// Therefore for an active LUKS partition:
// used = LUKS data offset + LUKS data length
// unused = 0
// unallocated = remainder
//
// And for an inactive LUKS partition:
// used = partition size
// unused = 0
// unallocated = 0
//
// References:
// * LUKS On-Disk Format Specification
// https://gitlab.com/cryptsetup/cryptsetup/wikis/LUKS-standard/on-disk-format.pdf
// * cryptsetup(8)
LUKS_Mapping mapping = LUKS_Info::get_cache_entry( partition.get_path() );
if ( mapping.name.empty() )
{
// Inactive LUKS partition
T = partition.get_sector_length();
partition.set_sector_usage( T, 0 );
}
else
{
// Active LUKS partition
T = Utils::round( ( mapping.offset + mapping.length ) / double(partition.sector_size) );
partition.set_sector_usage( T, 0 );
}
}
} //GParted