[Qemu-devel] [PATCH WIP 03/30] qcow: add a 'keyid' parameter to qcow options

["Daniel P. Berrange" <berrange@redhat.com>]

Add a 'keyid' parameter that refers to the ID of a
QCryptoSecret instance that provides the encryption key.
eg

 $QEMU \
    -object secret,id=sec0,filename=/home/berrange/encrypted.pw \
    -drive file=/home/berrange/encrypted.qcow,keyid=sec0

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 block/qcow.c         | 94 +++++++++++++++++++++++++++++++++++++++-------------
 qapi/block-core.json | 17 +++++++++-
 2 files changed, 87 insertions(+), 24 deletions(-)

diff --git a/block/qcow.c b/block/qcow.c
index 635085e..719ed7c 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -27,6 +27,7 @@
 #include <zlib.h>
 #include "qapi/qmp/qerror.h"
 #include "crypto/cipher.h"
+#include "crypto/secret.h"
 #include "migration/migration.h"
 
 /**************************************************************/
@@ -40,6 +41,8 @@
 
 #define QCOW_OFLAG_COMPRESSED (1LL << 63)
 
+#define QCOW_OPT_KEY_ID "keyid"
+
 typedef struct QCowHeader {
     uint32_t magic;
     uint32_t version;
@@ -92,6 +95,43 @@ static int qcow_probe(const uint8_t *buf, int buf_size, const char *filename)
         return 0;
 }
 
+static QCryptoCipher *qcow_get_cipher_from_key(const char *key,
+                                               Error **errp)
+{
+    uint8_t keybuf[16];
+    int len, i;
+
+    memset(keybuf, 0, 16);
+    len = strlen(key);
+    if (len > 16) {
+        len = 16;
+    }
+    /* XXX: we could compress the chars to 7 bits to increase
+       entropy */
+    for (i = 0; i < len; i++) {
+        keybuf[i] = key[i];
+    }
+
+    return qcrypto_cipher_new(
+        QCRYPTO_CIPHER_ALG_AES_128,
+        QCRYPTO_CIPHER_MODE_CBC,
+        keybuf, G_N_ELEMENTS(keybuf),
+        errp);
+}
+
+static QemuOptsList qcow_runtime_opts = {
+    .name = "qcow",
+    .head = QTAILQ_HEAD_INITIALIZER(qcow_runtime_opts.head),
+    .desc = {
+        {
+            .name = QCOW_OPT_KEY_ID,
+            .type = QEMU_OPT_STRING,
+            .help = "ID of the secret that provides the encryption key",
+        },
+        { /* end of list */ }
+    },
+};
+
 static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
                      Error **errp)
 {
@@ -99,6 +139,10 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
     unsigned int len, i, shift;
     int ret;
     QCowHeader header;
+    QemuOpts *opts = NULL;
+    const char *keyid;
+    char *key;
+    Error *local_err = NULL;
 
     ret = bdrv_pread(bs->file->bs, 0, &header, sizeof(header));
     if (ret < 0) {
@@ -147,6 +191,32 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    opts = qemu_opts_create(&qcow_runtime_opts, NULL, 0, &error_abort);
+    qemu_opts_absorb_qdict(opts, options, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    keyid = qemu_opt_get(opts, QCOW_OPT_KEY_ID);
+    if (keyid) {
+        key = qcrypto_secret_lookup_as_utf8(keyid,
+                                            errp);
+        if (!key) {
+            ret = -ENOENT;
+            goto fail;
+        }
+
+        s->cipher = qcow_get_cipher_from_key(key,
+                                             errp);
+        g_free(key);
+        if (!s->cipher) {
+            ret = -ENOSYS;
+            goto fail;
+        }
+    }
+
     if (header.crypt_method > QCOW_CRYPT_AES) {
         error_setg(errp, "invalid encryption method in qcow header");
         ret = -EINVAL;
@@ -261,33 +331,11 @@ static int qcow_reopen_prepare(BDRVReopenState *state,
 static int qcow_set_key(BlockDriverState *bs, const char *key)
 {
     BDRVQcowState *s = bs->opaque;
-    uint8_t keybuf[16];
-    int len, i;
-    Error *err;
 
-    memset(keybuf, 0, 16);
-    len = strlen(key);
-    if (len > 16)
-        len = 16;
-    /* XXX: we could compress the chars to 7 bits to increase
-       entropy */
-    for(i = 0;i < len;i++) {
-        keybuf[i] = key[i];
-    }
     assert(bs->encrypted);
-
     qcrypto_cipher_free(s->cipher);
-    s->cipher = qcrypto_cipher_new(
-        QCRYPTO_CIPHER_ALG_AES_128,
-        QCRYPTO_CIPHER_MODE_CBC,
-        keybuf, G_N_ELEMENTS(keybuf),
-        &err);
-
+    s->cipher = qcow_get_cipher_from_key(key, NULL);
     if (!s->cipher) {
-        /* XXX would be nice if errors in this method could
-         * be properly propagate to the caller. Would need
-         * the bdrv_set_key() API signature to be fixed. */
-        error_free(err);
         return -1;
     }
     return 0;
diff --git a/qapi/block-core.json b/qapi/block-core.json
index a07b13f..d3cc129 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1693,6 +1693,21 @@
             'mode':  'Qcow2OverlapCheckMode' } }
 
 ##
+# @BlockdevOptionsQcow
+#
+# Driver specific block device options for qcow.
+#
+# @keyid:                 #optional ID of the "secret" object providing the
+#                         AES decryption key.
+#
+# Since: 2.5
+##
+{ 'struct': 'BlockdevOptionsQcow',
+  'base': 'BlockdevOptionsGenericCOWFormat',
+  'data': { '*keyid': 'str' } }
+
+
+##
 # @BlockdevOptionsQcow2
 #
 # Driver specific block device options for qcow2.
@@ -1956,7 +1971,7 @@
       'null-co':    'BlockdevOptionsNull',
       'parallels':  'BlockdevOptionsGenericFormat',
       'qcow2':      'BlockdevOptionsQcow2',
-      'qcow':       'BlockdevOptionsGenericCOWFormat',
+      'qcow':       'BlockdevOptionsQcow',
       'qed':        'BlockdevOptionsGenericCOWFormat',
       'quorum':     'BlockdevOptionsQuorum',
       'raw':        'BlockdevOptionsGenericFormat',
-- 
2.5.0