Capture LUKS mapping master encryption key location (#59)

ISSUE OVERVIEW

When GParted tries to resize an open LUKS encryption mapping and the
volume (master) key was stored in the kernel keyring service [1] it
fails like this:

    Check and repair file system ([Encrypted] ext4) on /dev/...(ERROR)
    + calibrate /dev/sdd1                                      (SUCCESS)
    + check file system on /dev/mapper/sdd1_crypt for errors...(SUCCESS)
    + grow encryption volume to fill the partition             (ERROR)
      + cryptsetup -v resize 'sdd1_crypt'                      (ERROR)
          Command failed with code -1 (wrong or missing parameters).
          Nothing to read on input.

This error occurs with cryptsetup >= 2.0, kernel >= 4.10 and LUKS2
format because the crypt Device-Mapper target no longer has the volume
key so cryptsetup resize prompts for a passphrase, but GParted doesn't
provide it.

THIS COMMIT

Additionally capture the location of the volume (master) key location
for active encryption mappings.  Do this the using the same method that
cryptsetup uses [2][3].  Namely if the first character of the KEY is a
":" then the key *was* stored in the kernel keyring service, otherwise
it *is* store in the Device-Mapper crypt target as previously.

    # echo -n badpassword | cryptsetup luksFormat --type luks1 /dev/sdb1 -
    # echo -n badpassword | cryptsetup luksOpen /dev/sdb1 sdb1_crypt
    # cryptsetup status sdb1_crypt | egrep 'type|key location'
      type:         LUKS1
      key location: dm-crypt

    # echo -n badpassword | cryptsetup luksFormat --type luks2 /dev/sdb2 -
    # echo -n badpassword | cryptsetup luksOpen /dev/sdb2 sdb2_crypt
    # cryptsetup status sdb2_crypt | egrep 'type|key location'
      type:         LUKS2
      key location: keyring

    # dmsetup table --target crypt
    sdb1_crypt: 0 520192 crypt aes-xts-plain64 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0 8:17 4096
    sdb2_crypt: 0 491520 crypt aes-xts-plain64 :64:logon:cryptsetup:3d040240-97ba-4559-af98-72c3be500498-d0 0 8:18 32768
                                               ^
First character of the KEY field --------------'

[1] Integration with the kernel keyring service
    https://gitlab.com/cryptsetup/cryptsetup/blob/v2.0.0/docs/Keyring.txt
    "
    Starting with cryptsetup 2.0 we load [Volume Key] VK in kernel
    keyring by default for LUKSv2 devices ...

    In summary, the key description visible in dm-crypt table line is a
    reference to VK that usually no longer exists in kernel keyring
    service if you used cryptsetup to for device activation.
    "

[2] cryptsetup/v2.3.5/lib/libdevmapper.c:_dm_target_query_crypt()
    https://gitlab.com/cryptsetup/cryptsetup/-/blob/v2.3.5/lib/libdevmapper.c#L2031
        if (key_[0] == ':')
            *act_flags |= CRYPT_ACTIVATE_KEYRING_KEY;

[3] cryptsetup/v2.3.5/src/cryptsetup.c:action_status()
    https://gitlab.com/cryptsetup/cryptsetup/-/blob/v2.3.5/src/cryptsetup.c#L839
        log_std("  key location: %s\n", (cad.flags & CRYPT_ACTIVATE_KEYRING_KEY) ? "keyring" : "dm-crypt");

Closes #59 - Resize of LUKS2 encrypted file system fails with "Nothing
             to read on input"

include/LUKS_Info.h

@@ -34,12 +34,19 @@
 namespace GParted
 {
 
+enum KeyLocation
+{
+	KEYLOC_DMCrypt = 0,  // Master encryption key is stored in DeviceMapper crypt target
+	KEYLOC_KeyRing       // Master encryption key was stored in kernel Key Ring
+};
+
 struct LUKS_Mapping
 {
 	Glib::ustring name;       // Name of the dm-crypt mapping
 	BlockSpecial  container;  // Underlying block device containing the LUKS mapping
 	Byte_Value    offset;     // Offset to the start of the mapping in the underlying block device
 	Byte_Value    length;     // Length of the mapping in the underlying block device
+	KeyLocation   key_loc;    // Location where the master encryption key is stored
 };
 
 class LUKS_Info

src/LUKS_Info.cc

@@ -72,7 +72,7 @@ void LUKS_Info::load_cache()
 	// _status() function:
 	//     https://git.fedorahosted.org/cgit/lvm2.git/tree/tools/dmsetup.c?id=v2_02_118#n1715
 	// Field 5 onwards are called parameters and documented in the kernel source:
-	//     https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/device-mapper/dm-crypt.txt?id=v4.0
+	//     https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/device-mapper/dm-crypt.txt?id=v5.0
 
 	std::vector<Glib::ustring> lines;
 	Utils::tokenize( output, lines, "\n" );
@@ -83,6 +83,7 @@ void LUKS_Info::load_cache()
 		Utils::tokenize( lines[i], fields, " " );
 		const unsigned DMCRYPT_FIELD_Name    = 0;
 		const unsigned DMCRYPT_FIELD_length  = 2;
+		const unsigned DMCRYPT_FIELD_key     = 5;
 		const unsigned DMCRYPT_FIELD_devpath = 7;
 		const unsigned DMCRYPT_FIELD_offset  = 8;
 
@@ -126,6 +127,16 @@ void LUKS_Info::load_cache()
 		else
 			continue;
 
+		// Extract LUKS mapping master key location.  Following the cryptsetup
+		// implementation method; first character of KEY field is ":" means the
+		// master key was stored in the kernel key ring, otherwise it is stored in
+		// the Device-Mapper crypt target itself.
+		// * cryptsetup/v2.3.5/lib/libdevmapper.c:_dm_target_query_crypt()
+		//   https://gitlab.com/cryptsetup/cryptsetup/-/blob/v2.3.5/lib/libdevmapper.c#L2031
+		// * cryptsetup/v2.3.5/src/cryptsetup.c:action_status()
+		//   https://gitlab.com/cryptsetup/cryptsetup/-/blob/v2.3.5/src/cryptsetup.c#L839
+		luks_map.key_loc = (fields[DMCRYPT_FIELD_key][0] == ':') ? KEYLOC_KeyRing : KEYLOC_DMCrypt;
+
 		luks_mapping_cache.push_back( luks_map );
 	}
 }