Add possibility to change key size (optionally by shrinking device).

man/cryptsetup-reencrypt.8

@@ -50,6 +50,18 @@ lines are always prefixed by '#'.
 .B "\-\-cipher, \-c" \fI<cipher-spec>\fR
 Set the cipher specification string.
 .TP
+.B "\-\-key-size, \-s \fI<bits>\fR"
+Set key size in bits. The argument has to be a multiple of  8.
+
+The possible key-sizes are limited by the cipher and mode used. 
+
+If you are increasing key size, there must be enough space in the LUKS header
+for enlarged keyslots (data offset must be large enough) or reencryption
+cannot be performed.
+
+If there is not enough space for keyslots with new key size,
+you can destructively shrink device with \-\-reduce-device-size option.
+.TP
 .B "\-\-hash, \-h \fI<hash-spec>\fR"
 Specifies the hash used in the LUKS key setup scheme and volume key digest.
 .TP
@@ -64,17 +76,17 @@ Define which kernel random number generator will be used to create the volume ke
 .TP
 .B "\-\-key-file, \-d \fIname\fR"
 Read the passphrase from file.
-.br
+
 WARNING: \-\-key-file option can be used only if there only one active keyslot,
 or alternatively, also if \-\-key-slot option is specified (then all other keyslots
 will be disabled in new LUKS device).
 
-If this option is not used, cryptswtup-reencrypt will ask for all active keyslot
+If this option is not used, cryptsetup-reencrypt will ask for all active keyslot
 passphrases.
 .TP
 .B "\-\-key-slot, \-S <0-7>"
 Specify which key slot is used.
-.br
+
 WARNING: All other keyslots will be disabled if this option is used.
 .TP
 .B "\-\-keyfile-offset \fIvalue\fR"
@@ -90,12 +102,28 @@ Number of retries for invalid passphrase entry.
 .TP
 .B "\-\-block-size, \-B \fIvalue\fR"
 Use re-encryption block size of <value> in MiB.
-.br
+
 Values can be between 1 and 64 MiB.
 .TP
+.B "\-\-reduce-device-size \fInumber of 512 bytes sectors\fR"
+Enlarge data offset for specified value of sectors by shrinking
+device size.
+
+This means that last sectors on the original device will be lost,
+ciphertext data will be effectively shifted by specified
+number of sectors.
+
+It can be usefull if you e.g. added some space to underlying
+partition (so last sectors contains no data).
+
+WARNING: This is destructive operation and cannot be reverted.
+Use with extreme care - shrinked filesystems are usually unrecoverable.
+
+You cannot shrink device more than by 64 MiB (131072 sectors).
+.TP
 .B "\-\-use-directio"
 Use direct-io (O_DIRECT) for all read/write data operations.
-.br
+
 Usefull if direct-io operations perform better than normal buffered
 operations (e.g. in virtual environments).
 .TP

src/cryptsetup_reencrypt.c

@@ -55,11 +55,13 @@ static int opt_version_mode = 0;
 static int opt_random = 0;
 static int opt_urandom = 0;
 static int opt_bsize = 4;
+static int opt_reduce_device_size = 0;
 static int opt_directio = 0;
 static int opt_fsync = 0;
 static int opt_write_log = 0;
 static int opt_tries = 3;
 static int opt_key_slot = CRYPT_ANY_SLOT;
+static int opt_key_size = 0;
 
 static const char **action_argv;
 
@@ -277,19 +279,36 @@ out:
 	return r;
 }
 
-static int create_empty_header(const char *new_file, const char *old_file)
+static int create_empty_header(const char *new_file, const char *old_file,
+			       uint64_t data_sector)
 {
 	struct stat st;
 	ssize_t size;
 	int fd, r = 0;
 	char *buf;
 
+	/* Never create header > 4MiB */
+	if (data_sector > 8192)
+		data_sector = 8192;
+
+	/* new header file of the same size as old backup */
 	if (stat(old_file, &st) == -1 ||
 		 (st.st_mode & S_IFMT) != S_IFREG ||
 		 (st.st_size > 16 * 1024 * 1024))
 		return -EINVAL;
 	size = st.st_size;
 
+	/*
+	 * if requesting key size change, try to use offset
+	 * here can be enough space to fit new key.
+	 */
+	if (opt_key_size)
+		size = data_sector * SECTOR_SIZE;
+
+	/* if reducing size, be sure we have enough space */
+	if (opt_reduce_device_size)
+		size += (opt_reduce_device_size * SECTOR_SIZE);
+
 	log_dbg("Creating empty file %s of size %lu.", new_file, (unsigned long)size);
 
 	if (!(buf = malloc(size)))
@@ -499,13 +518,16 @@ static int backup_luks_headers(struct reenc_ctx *rc)
 		goto out;
 	log_verbose(_("LUKS header backup of device %s created.\n"), rc->device);
 
-	if ((r = create_empty_header(rc->header_file_new, rc->header_file_org)))
+	if ((r = create_empty_header(rc->header_file_new, rc->header_file_org,
+		crypt_get_data_offset(cd))))
 		goto out;
 
 	params.hash = opt_hash ?: DEFAULT_LUKS1_HASH;
 	params.data_alignment = crypt_get_data_offset(cd);
+	params.data_alignment += opt_reduce_device_size;
 	params.data_device = rc->device;
 
+
 	if ((r = crypt_init(&cd_new, rc->header_file_new)))
 		goto out;
 
@@ -529,7 +551,9 @@ static int backup_luks_headers(struct reenc_ctx *rc)
 			opt_cipher ? cipher : crypt_get_cipher(cd),
 			opt_cipher ? cipher_mode : crypt_get_cipher_mode(cd),
 			crypt_get_uuid(cd),
-			NULL, crypt_get_volume_key_size(cd), &params)))
+			NULL,
+			opt_key_size ? opt_key_size / 8 : crypt_get_volume_key_size(cd),
+			&params)))
 		goto out;
 	log_verbose(_("New LUKS header for device %s created.\n"), rc->device);
 
@@ -760,7 +784,7 @@ static int copy_data(struct reenc_ctx *rc)
 	}
 
 	/* Check size */
-	if (ioctl(fd_old, BLKGETSIZE64, &rc->device_size) < 0) {
+	if (ioctl(fd_new, BLKGETSIZE64, &rc->device_size) < 0) {
 		log_err(_("Cannot get device size.\n"));
 		goto out;
 	}
@@ -975,7 +999,7 @@ static int initialize_context(struct reenc_ctx *rc, const char *device)
 	}
 
 	if (!rc->in_progress) {
-		if (1 /*opt_new */)
+		if (!opt_reduce_device_size)
 			rc->reencrypt_direction = FORWARD;
 		else {
 			rc->reencrypt_direction = BACKWARD;
@@ -998,7 +1022,7 @@ static void destroy_context(struct reenc_ctx *rc)
 	if ((rc->reencrypt_direction == FORWARD &&
 	     rc->device_offset == rc->device_size) ||
 	    (rc->reencrypt_direction == BACKWARD &&
-	     rc->device_offset == 0)) {
+	     (rc->device_offset == 0 || rc->device_offset == (uint64_t)~0))) {
 		unlink(rc->log_file);
 		unlink(rc->header_file_org);
 		unlink(rc->header_file_new);
@@ -1091,6 +1115,7 @@ int main(int argc, const char **argv)
 		{ "debug",             '\0', POPT_ARG_NONE, &opt_debug,                 0, N_("Show debug messages"), NULL },
 		{ "block-size",        'B',  POPT_ARG_INT, &opt_bsize,                  0, N_("Reencryption block size"), N_("MiB") },
 		{ "cipher",            'c',  POPT_ARG_STRING, &opt_cipher,              0, N_("The cipher used to encrypt the disk (see /proc/crypto)"), NULL },
+		{ "key-size",          's',  POPT_ARG_INT, &opt_key_size,               0, N_("The size of the encryption key"), N_("BITS") },
 		{ "hash",              'h',  POPT_ARG_STRING, &opt_hash,                0, N_("The hash used to create the encryption key from the passphrase"), NULL },
 		{ "key-file",          'd',  POPT_ARG_STRING, &opt_key_file,            0, N_("Read the key from a file."), NULL },
 		{ "iter-time",         'i',  POPT_ARG_INT, &opt_iteration_time,         0, N_("PBKDF2 iteration time for LUKS (in ms)"), N_("msecs") },
@@ -1104,6 +1129,7 @@ int main(int argc, const char **argv)
 		{ "key-slot",          'S',  POPT_ARG_INT, &opt_key_slot,               0, N_("Use only this slot (others will be disabled)."), NULL },
 		{ "keyfile-offset",   '\0',  POPT_ARG_LONG, &opt_keyfile_offset,        0, N_("Number of bytes to skip in keyfile"), N_("bytes") },
 		{ "keyfile-size",      'l',  POPT_ARG_LONG, &opt_keyfile_size,          0, N_("Limits the read from keyfile"), N_("bytes") },
+		{ "reduce-device-size",'\0', POPT_ARG_INT, &opt_reduce_device_size,     0, N_("Reduce data device size (move data start). DANGEROUS!"), N_("SECTORS") },
 		POPT_TABLEEND
 	};
 	poptContext popt_context;
@@ -1153,6 +1179,16 @@ int main(int argc, const char **argv)
 		      _("Only values between 1MiB and 64 MiB allowed for reencryption block size."),
 		      poptGetInvocationName(popt_context));
 
+	if (opt_reduce_device_size > 64 * 1024 * 1024 / SECTOR_SIZE)
+		usage(popt_context, EXIT_FAILURE,
+		      _("Maximum device reduce size is 64 MiB."),
+		      poptGetInvocationName(popt_context));
+
+	if (opt_key_size % 8)
+		usage(popt_context, EXIT_FAILURE,
+		      _("Key size must be a multiple of 8 bits"),
+		      poptGetInvocationName(popt_context));
+
 	if (opt_debug) {
 		opt_verbose = 1;
 		crypt_set_debug_level(-1);