crypto: add cryptographic random byte source

There are three backend impls provided. The preferred
is gnutls, which is backed by nettle in modern distros.
The gcrypt impl is provided for cases where QEMU build
against gnutls is disabled, but crypto is still desired.
No nettle impl is provided, since it is non-trivial to
use the nettle APIs for random numbers. Users of nettle
should ensure gnutls is enabled for QEMU.

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

1 files changed, 43 insertions, 0 deletions

diff --git a/crypto/random-gnutls.c b/crypto/random-gnutls.c
new file mode 100644
index 0000000000..04b45a8f8f
--- /dev/null
+++ b/crypto/random-gnutls.c
@@ -0,0 +1,43 @@
+/*
+ * QEMU Crypto random number provider
+ *
+ * Copyright (c) 2015-2016 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/>.
+ *
+ */
+
+#include "qemu/osdep.h"
+
+#include "crypto/random.h"
+
+#include <gnutls/gnutls.h>
+#include <gnutls/crypto.h>
+
+int qcrypto_random_bytes(uint8_t *buf,
+                         size_t buflen,
+                         Error **errp)
+{
+    int ret;
+
+    ret = gnutls_rnd(GNUTLS_RND_RANDOM, buf, buflen);
+
+    if (ret < 0) {
+        error_setg(errp, "Cannot get random bytes: %s",
+                   gnutls_strerror(ret));
+        return -1;
+    }
+
+    return 0;
+}