Re: [PATCH 02/13] qcrypto-luks: implement encryption key management

[Markus Armbruster]

Reviewing just the QAPI schema.

Maxim Levitsky <address@hidden> writes:

> Next few patches will expose that functionality
> to the user.
>
> Signed-off-by: Maxim Levitsky <address@hidden>
> ---
>  crypto/block-luks.c | 374 +++++++++++++++++++++++++++++++++++++++++++-
>  qapi/crypto.json    |  50 +++++-
>  2 files changed, 421 insertions(+), 3 deletions(-)
>
> diff --git a/crypto/block-luks.c b/crypto/block-luks.c
> index 4861db810c..349e95fed3 100644
> --- a/crypto/block-luks.c
> +++ b/crypto/block-luks.c
> @@ -32,6 +32,7 @@
>  #include "qemu/uuid.h"
>  
>  #include "qemu/coroutine.h"
> +#include "qemu/bitmap.h"
>  
>  /*
>   * Reference for the LUKS format implemented here is
> @@ -70,6 +71,9 @@ typedef struct QCryptoBlockLUKSKeySlot 
> QCryptoBlockLUKSKeySlot;
>  
>  #define QCRYPTO_BLOCK_LUKS_SECTOR_SIZE 512LL
>  
> +#define QCRYPTO_BLOCK_LUKS_DEFAULT_ITER_TIME_MS 2000
> +#define QCRYPTO_BLOCK_LUKS_ERASE_ITERATIONS 40
> +
>  static const char qcrypto_block_luks_magic[QCRYPTO_BLOCK_LUKS_MAGIC_LEN] = {
>      'L', 'U', 'K', 'S', 0xBA, 0xBE
>  };
> @@ -219,6 +223,9 @@ struct QCryptoBlockLUKS {
>  
>      /* Hash algorithm used in pbkdf2 function */
>      QCryptoHashAlgorithm hash_alg;
> +
> +    /* Name of the secret that was used to open the image */
> +    char *secret;
>  };
>  
>  
> @@ -1069,6 +1076,112 @@ qcrypto_block_luks_find_key(QCryptoBlock *block,
>      return -1;
>  }
>  
> +/*
> + * Returns true if a slot i is marked as active
> + * (contains encrypted copy of the master key)
> + */
> +static bool
> +qcrypto_block_luks_slot_active(const QCryptoBlockLUKS *luks,
> +                               unsigned int slot_idx)
> +{
> +    uint32_t val = luks->header.key_slots[slot_idx].active;
> +    return val ==  QCRYPTO_BLOCK_LUKS_KEY_SLOT_ENABLED;
> +}
> +
> +/*
> + * Returns the number of slots that are marked as active
> + * (slots that contain encrypted copy of the master key)
> + */
> +static unsigned int
> +qcrypto_block_luks_count_active_slots(const QCryptoBlockLUKS *luks)
> +{
> +    size_t i = 0;
> +    unsigned int ret = 0;
> +
> +    for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> +        if (qcrypto_block_luks_slot_active(luks, i)) {
> +            ret++;
> +        }
> +    }
> +    return ret;
> +}
> +
> +/*
> + * Finds first key slot which is not active
> + * Returns the key slot index, or -1 if it doesn't exist
> + */
> +static int
> +qcrypto_block_luks_find_free_keyslot(const QCryptoBlockLUKS *luks)
> +{
> +    size_t i;
> +
> +    for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> +        if (!qcrypto_block_luks_slot_active(luks, i)) {
> +            return i;
> +        }
> +    }
> +    return -1;
> +
> +}
> +
> +/*
> + * Erases an keyslot given its index
> + * Returns:
> + *    0 if the keyslot was erased successfully
> + *   -1 if a error occurred while erasing the keyslot
> + *
> + */
> +static int
> +qcrypto_block_luks_erase_key(QCryptoBlock *block,
> +                             unsigned int slot_idx,
> +                             QCryptoBlockWriteFunc writefunc,
> +                             void *opaque,
> +                             Error **errp)
> +{
> +    QCryptoBlockLUKS *luks = block->opaque;
> +    QCryptoBlockLUKSKeySlot *slot = &luks->header.key_slots[slot_idx];
> +    g_autofree uint8_t *garbagesplitkey = NULL;
> +    size_t splitkeylen = luks->header.master_key_len * slot->stripes;
> +    size_t i;
> +
> +    assert(slot_idx < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS);
> +    assert(splitkeylen > 0);
> +
> +    garbagesplitkey = g_new0(uint8_t, splitkeylen);
> +
> +    /* Reset the key slot header */
> +    memset(slot->salt, 0, QCRYPTO_BLOCK_LUKS_SALT_LEN);
> +    slot->iterations = 0;
> +    slot->active = QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED;
> +
> +    qcrypto_block_luks_store_header(block,  writefunc, opaque, errp);
> +
> +    /*
> +     * Now try to erase the key material, even if the header
> +     * update failed
> +     */
> +    for (i = 0; i < QCRYPTO_BLOCK_LUKS_ERASE_ITERATIONS; i++) {
> +        if (qcrypto_random_bytes(garbagesplitkey, splitkeylen, errp) < 0) {
> +            /*
> +             * If we failed to get the random data, still write
> +             * at least zeros to the key slot at least once
> +             */
> +            if (i > 0) {
> +                return -1;
> +            }
> +        }
> +
> +        if (writefunc(block,
> +                      slot->key_offset_sector * 
> QCRYPTO_BLOCK_LUKS_SECTOR_SIZE,
> +                      garbagesplitkey,
> +                      splitkeylen,
> +                      opaque,
> +                      errp) != splitkeylen) {
> +            return -1;
> +        }
> +    }
> +    return 0;
> +}
>  
>  static int
>  qcrypto_block_luks_open(QCryptoBlock *block,
> @@ -1099,6 +1212,7 @@ qcrypto_block_luks_open(QCryptoBlock *block,
>  
>      luks = g_new0(QCryptoBlockLUKS, 1);
>      block->opaque = luks;
> +    luks->secret = g_strdup(options->u.luks.key_secret);
>  
>      if (qcrypto_block_luks_load_header(block, readfunc, opaque, errp) < 0) {
>          goto fail;
> @@ -1164,6 +1278,7 @@ qcrypto_block_luks_open(QCryptoBlock *block,
>   fail:
>      qcrypto_block_free_cipher(block);
>      qcrypto_ivgen_free(block->ivgen);
> +    g_free(luks->secret);
>      g_free(luks);
>      return -1;
>  }
> @@ -1204,7 +1319,7 @@ qcrypto_block_luks_create(QCryptoBlock *block,
>  
>      memcpy(&luks_opts, &options->u.luks, sizeof(luks_opts));
>      if (!luks_opts.has_iter_time) {
> -        luks_opts.iter_time = 2000;
> +        luks_opts.iter_time = QCRYPTO_BLOCK_LUKS_DEFAULT_ITER_TIME_MS;
>      }
>      if (!luks_opts.has_cipher_alg) {
>          luks_opts.cipher_alg = QCRYPTO_CIPHER_ALG_AES_256;
> @@ -1244,6 +1359,8 @@ qcrypto_block_luks_create(QCryptoBlock *block,
>                     optprefix ? optprefix : "");
>          goto error;
>      }
> +    luks->secret = g_strdup(options->u.luks.key_secret);
> +
>      password = qcrypto_secret_lookup_as_utf8(luks_opts.key_secret, errp);
>      if (!password) {
>          goto error;
> @@ -1471,10 +1588,260 @@ qcrypto_block_luks_create(QCryptoBlock *block,
>      qcrypto_block_free_cipher(block);
>      qcrypto_ivgen_free(block->ivgen);
>  
> +    g_free(luks->secret);
>      g_free(luks);
>      return -1;
>  }
>  
> +/*
> + * Given LUKSKeyslotUpdate command, return @slots_bitmap with all slots
> + * that will be updated with new password (or erased)
> + * returns number of affected slots
> + */
> +static int qcrypto_block_luks_get_slots_bitmap(QCryptoBlock *block,
> +                                               QCryptoBlockReadFunc readfunc,
> +                                               void *opaque,
> +                                               const LUKSKeyslotUpdate 
> *command,
> +                                               unsigned long *slots_bitmap,
> +                                               Error **errp)
> +{
> +    const QCryptoBlockLUKS *luks = block->opaque;
> +    size_t i;
> +    int ret = 0;
> +
> +    if (command->has_keyslot) {
> +        /* keyslot set, select only this keyslot */
> +        int keyslot = command->keyslot;
> +
> +        if (keyslot < 0 || keyslot >= QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS) {
> +            error_setg(errp,
> +                       "Invalid slot %u specified, must be between 0 and %u",
> +                       keyslot, QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS - 1);
> +            goto error;
> +        }
> +        bitmap_set(slots_bitmap, keyslot, 1);
> +        ret++;
> +
> +    } else if (command->has_old_secret) {
> +        /* initially select all active keyslots */
> +        for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> +            if (qcrypto_block_luks_slot_active(luks, i)) {
> +                bitmap_set(slots_bitmap, i, 1);
> +                ret++;
> +            }
> +        }
> +    } else {
> +        /* find a free keyslot */
> +        int slot = qcrypto_block_luks_find_free_keyslot(luks);
> +
> +        if (slot == -1) {
> +            error_setg(errp,
> +                       "Can't add a keyslot - all key slots are in use");
> +            goto error;
> +        }
> +        bitmap_set(slots_bitmap, slot, 1);
> +        ret++;
> +    }
> +
> +    if (command->has_old_secret) {
> +        /* now deselect all keyslots that don't contain the password */
> +        g_autofree uint8_t *tmpkey = g_new0(uint8_t,
> +                                            luks->header.master_key_len);
> +
> +        for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> +            g_autofree char *old_password = NULL;
> +            int rv;
> +
> +            if (!test_bit(i, slots_bitmap)) {
> +                continue;
> +            }
> +
> +            old_password = qcrypto_secret_lookup_as_utf8(command->old_secret,
> +                                                         errp);
> +            if (!old_password) {
> +                goto error;
> +            }
> +
> +            rv = qcrypto_block_luks_load_key(block,
> +                                             i,
> +                                             old_password,
> +                                             tmpkey,
> +                                             readfunc,
> +                                             opaque,
> +                                             errp);
> +            if (rv == -1)
> +                goto error;
> +            else if (rv == 0) {
> +                bitmap_clear(slots_bitmap, i, 1);
> +                ret--;
> +            }
> +        }
> +    }
> +    return ret;
> +error:
> +    return -1;
> +}
> +
> +/*
> + * Apply a single keyslot update command as described in @command
> + * Optionally use @unlock_secret to retrieve the master key
> + */
> +static int
> +qcrypto_block_luks_apply_keyslot_update(QCryptoBlock *block,
> +                                        QCryptoBlockReadFunc readfunc,
> +                                        QCryptoBlockWriteFunc writefunc,
> +                                        void *opaque,
> +                                        LUKSKeyslotUpdate *command,
> +                                        const char *unlock_secret,
> +                                        uint8_t **master_key,
> +                                        bool force,
> +                                        Error **errp)
> +{
> +    QCryptoBlockLUKS *luks = block->opaque;
> +    g_autofree unsigned long *slots_bitmap = NULL;
> +    int64_t iter_time = QCRYPTO_BLOCK_LUKS_DEFAULT_ITER_TIME_MS;
> +    int slot_count;
> +    size_t i;
> +    char *new_password;
> +    bool erasing;
> +
> +    slots_bitmap = bitmap_new(QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS);
> +    slot_count = qcrypto_block_luks_get_slots_bitmap(block, readfunc, opaque,
> +                                                     command, slots_bitmap,
> +                                                     errp);
> +    if (slot_count == -1) {
> +        goto error;
> +    }
> +    /* no matching slots, so nothing to do */
> +    if (slot_count == 0) {
> +        error_setg(errp, "Requested operation didn't match any slots");
> +        goto error;
> +    }
> +    /*
> +     * slot is erased when the password is set to null, or empty string
> +     * (for compatibility with command line)
> +     */
> +    erasing = command->new_secret->type == QTYPE_QNULL ||
> +              strlen(command->new_secret->u.s) == 0;
> +
> +    /* safety checks */
> +    if (!force) {
> +        if (erasing) {
> +            if (slot_count == qcrypto_block_luks_count_active_slots(luks)) {
> +                error_setg(errp,
> +                           "Requested operation will erase all active 
> keyslots"
> +                           " which will erase all the data in the image"
> +                           " irreversibly - refusing operation");
> +                goto error;
> +            }
> +        } else {
> +            for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> +                if (!test_bit(i, slots_bitmap)) {
> +                    continue;
> +                }
> +                if (qcrypto_block_luks_slot_active(luks, i)) {
> +                    error_setg(errp,
> +                               "Refusing to overwrite active slot %zu - "
> +                               "please erase it first", i);
> +                    goto error;
> +                }
> +            }
> +        }
> +    }
> +
> +    /* setup the data needed for storing the new keyslot */
> +    if (!erasing) {
> +        /* Load the master key if it wasn't already loaded */
> +        if (!*master_key) {
> +            g_autofree char *old_password;
> +            old_password = qcrypto_secret_lookup_as_utf8(unlock_secret,  
> errp);
> +            if (!old_password) {
> +                goto error;
> +            }
> +            *master_key = g_new0(uint8_t, luks->header.master_key_len);
> +
> +            if (qcrypto_block_luks_find_key(block, old_password, *master_key,
> +                                            readfunc, opaque, errp) < 0) {
> +                error_append_hint(errp, "Failed to retrieve the master key");
> +                goto error;
> +            }
> +        }
> +        new_password = 
> qcrypto_secret_lookup_as_utf8(command->new_secret->u.s,
> +                                                     errp);
> +        if (!new_password) {
> +            goto error;
> +        }
> +        if (command->has_iter_time) {
> +            iter_time = command->iter_time;
> +        }
> +    }
> +
> +    /* new apply the update */
> +    for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> +        if (!test_bit(i, slots_bitmap)) {
> +            continue;
> +        }
> +        if (erasing) {
> +            if (qcrypto_block_luks_erase_key(block, i,
> +                                             writefunc,
> +                                             opaque,
> +                                             errp)) {
> +                error_append_hint(errp, "Failed to erase keyslot %zu", i);
> +                goto error;
> +            }
> +        } else {
> +            if (qcrypto_block_luks_store_key(block, i,
> +                                             new_password,
> +                                             *master_key,
> +                                             iter_time,
> +                                             writefunc,
> +                                             opaque,
> +                                             errp)) {
> +                error_append_hint(errp, "Failed to write to keyslot %zu", i);
> +                goto error;
> +            }
> +        }
> +    }
> +    return 0;
> +error:
> +    return -EINVAL;
> +}
> +
> +static int
> +qcrypto_block_luks_amend_options(QCryptoBlock *block,
> +                                 QCryptoBlockReadFunc readfunc,
> +                                 QCryptoBlockWriteFunc writefunc,
> +                                 void *opaque,
> +                                 QCryptoBlockAmendOptions *options,
> +                                 bool force,
> +                                 Error **errp)
> +{
> +    QCryptoBlockLUKS *luks = block->opaque;
> +    QCryptoBlockAmendOptionsLUKS *options_luks = &options->u.luks;
> +    LUKSKeyslotUpdateList *ptr;
> +    g_autofree uint8_t *master_key = NULL;
> +    int ret;
> +
> +    char *unlock_secret = options_luks->has_unlock_secret ?
> +                          options_luks->unlock_secret :
> +                          luks->secret;
> +
> +    for (ptr = options_luks->keys; ptr; ptr = ptr->next) {
> +        ret = qcrypto_block_luks_apply_keyslot_update(block, readfunc,
> +                                                      writefunc, opaque,
> +                                                      ptr->value,
> +                                                      unlock_secret,
> +                                                      &master_key,
> +                                                      force, errp);
> +
> +        if (ret != 0) {
> +            goto error;
> +        }
> +    }
> +    return 0;
> +error:
> +    return -1;
> +}
>  
>  static int qcrypto_block_luks_get_info(QCryptoBlock *block,
>                                         QCryptoBlockInfo *info,
> @@ -1523,7 +1890,9 @@ static int qcrypto_block_luks_get_info(QCryptoBlock 
> *block,
>  
>  static void qcrypto_block_luks_cleanup(QCryptoBlock *block)
>  {
> -    g_free(block->opaque);
> +    QCryptoBlockLUKS *luks = block->opaque;
> +    g_free(luks->secret);
> +    g_free(luks);
>  }
>  
>  
> @@ -1560,6 +1929,7 @@ qcrypto_block_luks_encrypt(QCryptoBlock *block,
>  const QCryptoBlockDriver qcrypto_block_driver_luks = {
>      .open = qcrypto_block_luks_open,
>      .create = qcrypto_block_luks_create,
> +    .amend = qcrypto_block_luks_amend_options,
>      .get_info = qcrypto_block_luks_get_info,
>      .cleanup = qcrypto_block_luks_cleanup,
>      .decrypt = qcrypto_block_luks_decrypt,
> diff --git a/qapi/crypto.json b/qapi/crypto.json
> index 9faebd03d4..e83847c71e 100644
> --- a/qapi/crypto.json
> +++ b/qapi/crypto.json
> @@ -1,6 +1,8 @@
>  # -*- Mode: Python -*-
>  #
>  
> +{ 'include': 'common.json' }
> +
>  ##
>  # = Cryptography
>  ##
> @@ -310,6 +312,52 @@
>    'discriminator': 'format',
>    'data': { 'luks': 'QCryptoBlockInfoLUKS' } }
>  
> +##
> +# @LUKSKeyslotUpdate:
> +#
> +# @keyslot:         If specified, will update only keyslot with this index
> +#
> +# @old-secret:      If specified, will only update keyslots that
> +#                   can be opened with password which is contained in
> +#                   QCryptoSecret with @old-secret ID
> +#
> +#                   If neither @keyslot nor @old-secret is specified,
> +#                   first empty keyslot is selected for the update
> +#
> +# @new-secret:      The ID of a QCryptoSecret object providing a new 
> decryption
> +#                   key to place in all matching keyslots.
> +#                   null/empty string erases all matching keyslots

I hate making the empty string do something completely different than a
non-empty string.

What about making @new-secret optional, and have absent @new-secret
erase?

> +#                                                                  unless
> +#                   last valid keyslot is erased.

Leaves me to wonder what happens when I try.  If I read your code
correctly, it's an error.  Suggest "You cannot erase the last valid
keyslot".

Not documented here: "Refusing to overwrite active slot".

> +#
> +# @iter-time:       number of milliseconds to spend in
> +#                   PBKDF passphrase processing

Default?

> +# Since: 5.0
> +##
> +{ 'struct': 'LUKSKeyslotUpdate',
> +  'data': {
> +           '*keyslot': 'int',
> +           '*old-secret': 'str',
> +           'new-secret' : 'StrOrNull',
> +           '*iter-time' : 'int' } }
> +
> +
> +##
> +# @QCryptoBlockAmendOptionsLUKS:
> +#
> +# The options that can be changed on existing luks encrypted device
> +# @keys:           list of keyslot updates to perform
> +#                  (updates are performed in order)
> +# @unlock-secret:  use this secret to retrieve the current master key
> +#                  if not given will use the same secret as one

"as the one"?

> +#                  that was used to open the image
> +#
> +# Since: 5.0
> +##
> +{ 'struct': 'QCryptoBlockAmendOptionsLUKS',
> +  'data' : {
> +            'keys': ['LUKSKeyslotUpdate'],
> +             '*unlock-secret' : 'str' } }
> +
>  
>  
>  ##
> @@ -324,4 +372,4 @@
>    'base': 'QCryptoBlockOptionsBase',
>    'discriminator': 'format',
>    'data': {
> -            } }
> +          'luks': 'QCryptoBlockAmendOptionsLUKS' } }