[Qemu-devel] [PATCH 09/13] qcrypto-luks: implement the encryption key management

[Maxim Levitsky]

Signed-off-by: Maxim Levitsky <address@hidden>
---
 crypto/block-luks.c | 374 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 373 insertions(+), 1 deletion(-)

diff --git a/crypto/block-luks.c b/crypto/block-luks.c
index 1997e92fe1..2c33643b52 100644
--- a/crypto/block-luks.c
+++ b/crypto/block-luks.c
@@ -72,6 +72,8 @@ typedef struct QCryptoBlockLUKSKeySlot 
QCryptoBlockLUKSKeySlot;
 
 #define QCRYPTO_BLOCK_LUKS_DEFAULT_ITER_TIME 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
 };
@@ -221,6 +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;
 };
 
 
@@ -1121,6 +1126,194 @@ qcrypto_block_luks_find_key(QCryptoBlock *block,
 }
 
 
+
+/*
+ * Returns true if a slot i is marked as containing as active
+ * (contains encrypted copy of the master key)
+ */
+
+static bool
+qcrypto_block_luks_slot_active(QCryptoBlockLUKS *luks, 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
+ * (contains encrypted copy of the master key)
+ */
+
+static int
+qcrypto_block_luks_count_active_slots(QCryptoBlockLUKS *luks)
+{
+    int i, 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 doesn't exist
+ */
+
+static int
+qcrypto_block_luks_find_free_keyslot(QCryptoBlockLUKS *luks)
+{
+    uint 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,
+                             uint slot_idx,
+                             QCryptoBlockWriteFunc writefunc,
+                             void *opaque,
+                             Error **errp)
+{
+    QCryptoBlockLUKS *luks = block->opaque;
+    QCryptoBlockLUKSKeySlot *slot = &luks->header.key_slots[slot_idx];
+    uint8_t *garbagekey = NULL;
+    size_t splitkeylen = masterkeylen(luks) * slot->stripes;
+    int i;
+    int ret = -1;
+
+    assert(slot_idx < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS);
+    assert(splitkeylen > 0);
+
+    garbagekey = g_malloc0(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(garbagekey, splitkeylen, errp) < 0) {
+
+                /*
+                 * If we failed to get the random data, still write
+                 * *something* to the key slot at least once
+                 */
+
+                if (i > 0) {
+                    goto cleanup;
+                }
+        }
+
+        if (writefunc(block, slot->key_offset * QCRYPTO_BLOCK_LUKS_SECTOR_SIZE,
+                  garbagekey,
+                  splitkeylen,
+                  opaque,
+                  errp) != splitkeylen) {
+            goto cleanup;
+        }
+    }
+
+    ret = 0;
+cleanup:
+    g_free(garbagekey);
+    return ret;
+}
+
+
+/*
+ * Erase all the keys that match the given password
+ * Will stop when only one keyslot is remaining
+ * Returns 0 is some keys were erased or -1 on failure
+ */
+
+static int
+qcrypto_block_luks_erase_matching_keys(QCryptoBlock *block,
+                             const char *password,
+                             QCryptoBlockReadFunc readfunc,
+                             QCryptoBlockWriteFunc writefunc,
+                             void *opaque,
+                             bool force,
+                             Error **errp)
+{
+    QCryptoBlockLUKS *luks = block->opaque;
+    uint i;
+    int rv, ret = -1;
+    uint8_t *masterkey;
+    uint erased_count = 0;
+    uint active_slot_count = qcrypto_block_luks_count_active_slots(luks);
+
+    masterkey = g_new0(uint8_t, masterkeylen(luks));
+
+    for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
+
+        /* refuse to erase last key if not forced */
+        if (!force && active_slot_count == 1) {
+            break;
+        }
+
+        rv = qcrypto_block_luks_load_key(block,
+                                         i,
+                                         password,
+                                         masterkey,
+                                         readfunc,
+                                         opaque,
+                                         errp);
+        if (rv < 0) {
+            goto cleanup;
+        }
+        if (rv == 0) {
+            continue;
+        }
+
+        rv = qcrypto_block_luks_erase_key(block, i, writefunc, opaque, errp);
+        if (rv < 0) {
+            goto cleanup;
+        }
+
+        erased_count++;
+        active_slot_count--;
+    }
+
+    if (!erased_count) {
+        error_setg(errp, "Didn't erase a keyslot, because no keyslots "
+                         "match the given password");
+        goto cleanup;
+    }
+
+    ret = 0;
+cleanup:
+    memset(masterkey, 0, masterkeylen(luks));
+    g_free(masterkey);
+    return ret;
+}
+
+
 static int
 qcrypto_block_luks_open(QCryptoBlock *block,
                         QCryptoBlockOpenOptions *options,
@@ -1151,6 +1344,7 @@ qcrypto_block_luks_open(QCryptoBlock *block,
 
     luks = g_new0(QCryptoBlockLUKS, 1);
     block->opaque = luks;
+    luks->secret = g_strdup(options->u.luks.key_secret);
 
     ret = qcrypto_block_luks_load_header(block, readfunc, opaque, errp);
     if (ret) {
@@ -1320,6 +1514,8 @@ qcrypto_block_luks_create(QCryptoBlock *block,
                    optprefix ? optprefix : "");
         return -1;
     }
+    luks->secret = options->u.luks.key_secret;
+
     password = qcrypto_secret_lookup_as_utf8(luks_opts.key_secret, errp);
     if (!password) {
         return -1;
@@ -1605,7 +1801,9 @@ 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);
 }
 
 
@@ -1638,6 +1836,179 @@ qcrypto_block_luks_encrypt(QCryptoBlock *block,
                                         offset, buf, len, errp);
 }
 
+static int
+qcrypto_block_luks_setup_encryption(QCryptoBlock *block,
+                                    QCryptoBlockReadFunc readfunc,
+                                    QCryptoBlockWriteFunc writefunc,
+                                    void *opaque,
+                                    enum BlkSetupEncryptionAction action,
+                                    QCryptoEncryptionSetupOptions *options,
+                                    bool force,
+                                    Error **errp)
+{
+    QCryptoBlockLUKS *luks = block->opaque;
+    char *old_password = NULL;
+    char *password = NULL;
+    const char *old_secret = luks->secret;
+    uint8_t *masterkey = NULL;
+    int slot = -1;
+    int ret = -1;
+    int64_t iter_time = QCRYPTO_BLOCK_LUKS_DEFAULT_ITER_TIME;
+
+    /* Read given slot and check it */
+    if (options->has_slot) {
+        slot = options->slot;
+        if (slot < 0 || slot >= QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS) {
+            error_setg(errp,
+                       "Given key slot %i is not supported by LUKS", slot);
+             goto cleanup;
+        }
+    }
+
+    if (options->has_iter_time) {
+        iter_time = options->iter_time;
+    }
+
+    switch (action) {
+
+    case BLK_UPDATE_ENCRYPTION:
+
+        /* Check that we are not overwriting an active slot */
+        if (!force && slot != -1 &&
+                    qcrypto_block_luks_slot_active(luks, slot)) {
+
+            error_setg(errp, "Can't update an active key slot %i",
+                       slot);
+            goto cleanup;
+        }
+
+        /* check that we have the passwords*/
+        if (!options->has_key_secret) {
+            error_setg(errp, "Can't add a key slot without a  password");
+            goto cleanup;
+        }
+
+        if (options->has_old_key_secret) {
+            old_secret = options->old_key_secret;
+        }
+
+        /* Read the old password */
+        old_password = qcrypto_secret_lookup_as_utf8(old_secret, errp);
+        if (!old_password) {
+            goto cleanup;
+        }
+
+        masterkey = g_new0(uint8_t, masterkeylen(luks));
+
+        /* Retrieve the master key*/
+        if (qcrypto_block_luks_find_key(block, old_password, masterkey,
+                                    readfunc, opaque, errp) < 0) {
+            error_append_hint(errp,
+                       "Old password that was given doesn't unlock the image");
+            goto cleanup;
+        }
+
+        /* Read the new password*/
+        password = qcrypto_secret_lookup_as_utf8(options->key_secret, errp);
+        if (!password) {
+            goto cleanup;
+        }
+
+        /* Find the new slot to write to */
+        if (slot == -1) {
+            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 cleanup;
+
+            }
+        }
+
+        /* Store the master key to the new slot */
+        if (qcrypto_block_luks_store_key(block, slot, password,
+                                     masterkey, iter_time,
+                                     writefunc, opaque, errp)) {
+
+            error_append_hint(errp, "Failed to store the keyslot %i", slot);
+            goto cleanup;
+        }
+        break;
+
+    case BLK_ERASE_ENCRYPTION:
+
+        /* Check that we are not erasing last key slot */
+        if (qcrypto_block_luks_count_active_slots(luks) <= 1) {
+
+            if (!force) {
+                error_setg(errp, "Only one slot active - can't erase");
+                goto cleanup;
+            }
+        }
+
+        if (slot != -1) {
+            /* Check that we are not erasing an inactive slot */
+            if (!qcrypto_block_luks_slot_active(luks, options->slot)) {
+                if (!force) {
+                    error_setg(errp, "Can't erase an inactive key slot %i",
+                               slot);
+                    goto cleanup;
+                }
+            }
+
+            /* Erase the given slot */
+            if (qcrypto_block_luks_erase_key(block, slot,
+                                             writefunc, opaque, errp)) {
+                goto cleanup;
+            }
+
+        } else {
+            if (!options->has_key_secret) {
+                error_setg(errp,
+                           "To erase a keyslot you have to specify either the"
+                           "slot index or a password "
+                           "(to erase all slots that match it)");
+                goto cleanup;
+            }
+
+            password = qcrypto_secret_lookup_as_utf8(options->key_secret, 
errp);
+            if (!password) {
+                goto cleanup;
+            }
+
+            if (qcrypto_block_luks_erase_matching_keys(block, password,
+                                                       readfunc, writefunc,
+                                                       opaque, force, errp)) {
+                goto cleanup;
+            }
+        }
+        break;
+
+    default:
+        goto cleanup;
+    }
+
+    ret = 0;
+cleanup:
+
+    if (old_password) {
+        memset(old_password, 0, strlen(old_password));
+        g_free(old_password);
+    }
+
+    if (password) {
+        memset(password, 0, strlen(password));
+        g_free(password);
+    }
+
+    if (masterkey) {
+        memset(masterkey, 0,  masterkeylen(luks));
+        g_free(masterkey);
+    }
+    return ret;
+}
+
 
 const QCryptoBlockDriver qcrypto_block_driver_luks = {
     .open = qcrypto_block_luks_open,
@@ -1647,4 +2018,5 @@ const QCryptoBlockDriver qcrypto_block_driver_luks = {
     .decrypt = qcrypto_block_luks_decrypt,
     .encrypt = qcrypto_block_luks_encrypt,
     .has_format = qcrypto_block_luks_has_format,
+    .setup_encryption = qcrypto_block_luks_setup_encryption,
 };
-- 
2.17.2