crypto: add QCryptoSecret object class for password/key handling

Introduce a new QCryptoSecret object class which will be used
for providing passwords and keys to other objects which need
sensitive credentials.

The new object can provide secret values directly as properties,
or indirectly via a file. The latter includes support for file
descriptor passing syntax on UNIX platforms. Ordinarily passing
secret values directly as properties is insecure, since they
are visible in process listings, or in log files showing the
CLI args / QMP commands. It is possible to use AES-256-CBC to
encrypt the secret values though, in which case all that is
visible is the ciphertext.  For ad hoc developer testing though,
it is fine to provide the secrets directly without encryption
so this is not explicitly forbidden.

The anticipated scenario is that libvirtd will create a random
master key per QEMU instance (eg /var/run/libvirt/qemu/$VMNAME.key)
and will use that key to encrypt all passwords it provides to
QEMU via '-object secret,....'.  This avoids the need for libvirt
(or other mgmt apps) to worry about file descriptor passing.

It also makes life easier for people who are scripting the
management of QEMU, for whom FD passing is significantly more
complex.

Providing data inline (insecure, only for ad hoc dev testing)

  $QEMU -object secret,id=sec0,data=letmein

Providing data indirectly in raw format

  printf "letmein" > mypasswd.txt
  $QEMU -object secret,id=sec0,file=mypasswd.txt

Providing data indirectly in base64 format

  $QEMU -object secret,id=sec0,file=mykey.b64,format=base64

Providing data with encryption

  $QEMU -object secret,id=master0,file=mykey.b64,format=base64 \
        -object secret,id=sec0,data=[base64 ciphertext],\
	           keyid=master0,iv=[base64 IV],format=base64

Note that 'format' here refers to the format of the ciphertext
data. The decrypted data must always be in raw byte format.

More examples are shown in the updated docs.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

1 files changed, 148 insertions, 0 deletions

diff --git a/include/crypto/secret.h b/include/crypto/secret.h
new file mode 100644
index 0000000000..913519ae27
--- /dev/null
+++ b/include/crypto/secret.h
@@ -0,0 +1,148 @@
+/*
+ * QEMU crypto secret support
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef QCRYPTO_SECRET_H__
+#define QCRYPTO_SECRET_H__
+
+#include "qemu-common.h"
+#include "qapi/error.h"
+#include "qom/object.h"
+
+#define TYPE_QCRYPTO_SECRET "secret"
+#define QCRYPTO_SECRET(obj)                  \
+    OBJECT_CHECK(QCryptoSecret, (obj), TYPE_QCRYPTO_SECRET)
+
+typedef struct QCryptoSecret QCryptoSecret;
+typedef struct QCryptoSecretClass QCryptoSecretClass;
+
+/**
+ * QCryptoSecret:
+ *
+ * The QCryptoSecret object provides storage of secrets,
+ * which may be user passwords, encryption keys or any
+ * other kind of sensitive data that is represented as
+ * a sequence of bytes.
+ *
+ * The sensitive data associated with the secret can
+ * be provided directly via the 'data' property, or
+ * indirectly via the 'file' property. In the latter
+ * case there is support for file descriptor passing
+ * via the usual /dev/fdset/NN syntax that QEMU uses.
+ *
+ * The data for a secret can be provided in two formats,
+ * either as a UTF-8 string (the default), or as base64
+ * encoded 8-bit binary data. The latter is appropriate
+ * for raw encryption keys, while the former is appropriate
+ * for user entered passwords.
+ *
+ * The data may be optionally encrypted with AES-256-CBC,
+ * and the decryption key provided by another
+ * QCryptoSecret instance identified by the 'keyid'
+ * property. When passing sensitive data directly
+ * via the 'data' property it is strongly recommended
+ * to use the AES encryption facility to prevent the
+ * sensitive data being exposed in the process listing
+ * or system log files.
+ *
+ * Providing data directly, insecurely (suitable for
+ * ad hoc developer testing only)
+ *
+ *  $QEMU -object secret,id=sec0,data=letmein
+ *
+ * Providing data indirectly:
+ *
+ *  # printf "letmein" > password.txt
+ *  # $QEMU \
+ *      -object secret,id=sec0,file=password.txt
+ *
+ * Using a master encryption key with data.
+ *
+ * The master key needs to be created as 32 secure
+ * random bytes (optionally base64 encoded)
+ *
+ *  # openssl rand -base64 32 > key.b64
+ *  # KEY=$(base64 -d key.b64 | hexdump  -v -e '/1 "%02X"')
+ *
+ * Each secret to be encrypted needs to have a random
+ * initialization vector generated. These do not need
+ * to be kept secret
+ *
+ *  # openssl rand -base64 16 > iv.b64
+ *  # IV=$(base64 -d iv.b64 | hexdump  -v -e '/1 "%02X"')
+ *
+ * A secret to be defined can now be encrypted
+ *
+ *  # SECRET=$(printf "letmein" |
+ *             openssl enc -aes-256-cbc -a -K $KEY -iv $IV)
+ *
+ * When launching QEMU, create a master secret pointing
+ * to key.b64 and specify that to be used to decrypt
+ * the user password
+ *
+ *  # $QEMU \
+ *      -object secret,id=secmaster0,format=base64,file=key.b64 \
+ *      -object secret,id=sec0,keyid=secmaster0,format=base64,\
+ *          data=$SECRET,iv=$(<iv.b64)
+ *
+ * When encrypting, the data can still be provided via an
+ * external file, in which case it is possible to use either
+ * raw binary data, or base64 encoded. This example uses
+ * raw format
+ *
+ *  # printf "letmein" |
+ *       openssl enc -aes-256-cbc -K $KEY -iv $IV -o pw.aes
+ *  # $QEMU \
+ *      -object secret,id=secmaster0,format=base64,file=key.b64 \
+ *      -object secret,id=sec0,keyid=secmaster0,\
+ *          file=pw.aes,iv=$(<iv.b64)
+ *
+ * Note that the ciphertext can be in either raw or base64
+ * format, as indicated by the 'format' parameter, but the
+ * plaintext resulting from decryption is expected to always
+ * be in raw format.
+ */
+
+struct QCryptoSecret {
+    Object parent_obj;
+    uint8_t *rawdata;
+    size_t rawlen;
+    QCryptoSecretFormat format;
+    char *data;
+    char *file;
+    char *keyid;
+    char *iv;
+};
+
+
+struct QCryptoSecretClass {
+    ObjectClass parent_class;
+};
+
+
+extern int qcrypto_secret_lookup(const char *secretid,
+                                 uint8_t **data,
+                                 size_t *datalen,
+                                 Error **errp);
+extern char *qcrypto_secret_lookup_as_utf8(const char *secretid,
+                                           Error **errp);
+extern char *qcrypto_secret_lookup_as_base64(const char *secretid,
+                                             Error **errp);
+
+#endif /* QCRYPTO_SECRET_H__ */