crypto: use /dev/[u]random as a final fallback random source

If neither gcrypt or gnutls are available to provide a
cryptographic random number generator, fallback to consuming
bytes directly from /dev/[u]random.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

diff --git a/crypto/Makefile.objs b/crypto/Makefile.objs
index 1f86f4f07f3f2315487e333199c8c78e6059a14d..febffba31366ca1f0e835c4a30dd647a06e4275d 100644 (file)
--- a/crypto/Makefile.objs
+++ b/crypto/Makefile.objs
@@ -12,6 +12,7 @@ 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
+crypto-obj-$(if $(CONFIG_GCRYPT),n,$(if $(CONFIG_GNUTLS_RND),n,y)) += random-platform.o
 crypto-obj-y += pbkdf.o
 crypto-obj-$(CONFIG_NETTLE_KDF) += pbkdf-nettle.o
 crypto-obj-$(if $(CONFIG_NETTLE_KDF),n,$(CONFIG_GCRYPT_KDF)) += pbkdf-gcrypt.o
@@ -28,6 +29,5 @@ crypto-obj-y += block-luks.o
 # Let the userspace emulators avoid linking gnutls/etc
 crypto-aes-obj-y = aes.o
 
-stub-obj-y += random-stub.o
 stub-obj-y += pbkdf-stub.o
 stub-obj-y += hash-stub.o

diff --git a/crypto/random-platform.c b/crypto/random-platform.c
new file mode 100644 (file)
index 0000000..82b755a
--- /dev/null
+++ b/crypto/random-platform.c
@@ -0,0 +1,64 @@
+/*
+ * 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)
+{
+    int fd;
+    int ret = -1;
+    int got;
+
+    /* TBD perhaps also add support for BSD getentropy / Linux
+     * getrandom syscalls directly */
+    fd = open("/dev/urandom", O_RDONLY);
+    if (fd == -1 && errno == ENOENT) {
+        fd = open("/dev/random", O_RDONLY);
+    }
+
+    if (fd < 0) {
+        error_setg(errp, "No /dev/urandom or /dev/random found");
+        return -1;
+    }
+
+    while (buflen > 0) {
+        got = read(fd, buf, buflen);
+        if (got < 0) {
+            error_setg_errno(errp, errno,
+                             "Unable to read random bytes");
+            goto cleanup;
+        } else if (!got) {
+            error_setg(errp,
+                       "Unexpected EOF reading random bytes");
+            goto cleanup;
+        }
+        buflen -= got;
+        buf += got;
+    }
+
+    ret = 0;
+ cleanup:
+    close(fd);
+    return ret;
+}

diff --git a/crypto/random-stub.c b/crypto/random-stub.c
deleted file mode 100644 (file)
index 63bbf41..0000000
--- a/crypto/random-stub.c
+++ /dev/null
@@ -1,31 +0,0 @@
-/*
- * 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;
-}