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: NFam Zheng <famz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

Makefile.objs

 #######################################################################
 # Common libraries for tools and emulators
-stub-obj-y = stubs/
+stub-obj-y = stubs/ crypto/
 util-obj-y = util/ qobject/ qapi/
 util-obj-y += qmp-introspect.o qapi-types.o qapi-visit.o qapi-event.o
 

configure

@@ -306,6 +306,7 @@ gtkabi=""
 gtk_gl="no"
 gnutls=""
 gnutls_hash=""
+gnutls_rnd=""
 nettle=""
 gcrypt=""
 vte=""
@@ -2201,6 +2202,13 @@ if test "$gnutls" != "no"; then
 	    gnutls_hash="no"
 	fi
 
+	# gnutls_rnd requires >= 2.11.0
+	if $pkg_config --exists "gnutls >= 2.11.0"; then
+	    gnutls_rnd="yes"
+	else
+	    gnutls_rnd="no"
+	fi
+
 	if $pkg_config --exists 'gnutls >= 3.0'; then
 	    gnutls_gcrypt=no
 	    gnutls_nettle=yes
@@ -2228,9 +2236,11 @@ if test "$gnutls" != "no"; then
     else
         gnutls="no"
         gnutls_hash="no"
+        gnutls_rnd="no"
     fi
 else
     gnutls_hash="no"
+    gnutls_rnd="no"
 fi
 
 
@@ -4714,6 +4724,7 @@ echo "GTK support       $gtk"
 echo "GTK GL support    $gtk_gl"
 echo "GNUTLS support    $gnutls"
 echo "GNUTLS hash       $gnutls_hash"
+echo "GNUTLS rnd        $gnutls_rnd"
 echo "libgcrypt         $gcrypt"
 if test "$nettle" = "yes"; then
     echo "nettle            $nettle ($nettle_version)"
@@ -5092,6 +5103,9 @@ fi
 if test "$gnutls_hash" = "yes" ; then
   echo "CONFIG_GNUTLS_HASH=y" >> $config_host_mak
 fi
+if test "$gnutls_rnd" = "yes" ; then
+  echo "CONFIG_GNUTLS_RND=y" >> $config_host_mak
+fi
 if test "$gcrypt" = "yes" ; then
   echo "CONFIG_GCRYPT=y" >> $config_host_mak
 fi

crypto/Makefile.objs

@@ -8,6 +8,10 @@ crypto-obj-y += tlscredsanon.o
 crypto-obj-y += tlscredsx509.o
 crypto-obj-y += tlssession.o
 crypto-obj-y += secret.o
+crypto-obj-$(CONFIG_GCRYPT) += random-gcrypt.o
+crypto-obj-$(if $(CONFIG_GCRYPT),n,$(CONFIG_GNUTLS_RND)) += random-gnutls.o
 
 # Let the userspace emulators avoid linking gnutls/etc
 crypto-aes-obj-y = aes.o
+
+stub-obj-y += random-stub.o

crypto/random-gcrypt.c

+/*
+ * 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 <gcrypt.h>
+
+int qcrypto_random_bytes(uint8_t *buf,
+                         size_t buflen,
+                         Error **errp G_GNUC_UNUSED)
+{
+    gcry_randomize(buf, buflen, GCRY_STRONG_RANDOM);
+    return 0;
+}

crypto/random-gnutls.c

+/*
+ * 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;
+}

crypto/random-stub.c

+/*
+ * 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"
+
+int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
+                         size_t buflen G_GNUC_UNUSED,
+                         Error **errp)
+{
+    error_setg(errp, "No random byte source provided in this build");
+    return -1;
+}

include/crypto/random.h

+/*
+ * 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/>.
+ *
+ */
+
+#ifndef QCRYPTO_RANDOM_H__
+#define QCRYPTO_RANDOM_H__
+
+#include "qemu-common.h"
+#include "qapi/error.h"
+
+
+/**
+ * qcrypto_random_bytes:
+ * @buf: the buffer to fill
+ * @buflen: length of @buf in bytes
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Fill @buf with @buflen bytes of cryptographically strong
+ * random data
+ *
+ * Returns 0 on sucess, -1 on error
+ */
+int qcrypto_random_bytes(uint8_t *buf,
+                         size_t buflen,
+                         Error **errp);
+
+
+#endif /* QCRYPTO_RANDOM_H__ */