crypto: qcrypto_random_bytes() now works on windows w/o any other crypto libs

If no crypto library is included in the build, QEMU uses
qcrypto_random_bytes() to generate random data. That function tried to open
/dev/urandom or /dev/random and if opening both files failed it errored out.

Those files obviously do not exist on windows, so there the code uses
CryptGenRandom().

Furthermore there was some refactoring and a new function
qcrypto_random_init() was introduced. If a proper crypto library (gnutls or
libgcrypt) is included in the build, this function does nothing. If neither
is included it initializes the (platform specific) handles that are used by
qcrypto_random_bytes().
Either:
* a handle to /dev/urandom | /dev/random on unix like systems
* a handle to a cryptographic service provider on windows

Signed-off-by: Geert Martin Ijewski <gm.ijewski@web.de>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

crypto/init.c

@@ -32,6 +32,8 @@
 #include <gcrypt.h>
 #endif
 
+#include "crypto/random.h"
+
 /* #define DEBUG_GNUTLS */
 
 /*
@@ -146,5 +148,9 @@ int qcrypto_init(Error **errp)
     gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0);
 #endif
 
+    if (qcrypto_random_init(errp) < 0) {
+        return -1;
+    }
+
     return 0;
 }

crypto/random-gcrypt.c

@@ -31,3 +31,5 @@ int qcrypto_random_bytes(uint8_t *buf,
     gcry_randomize(buf, buflen, GCRY_STRONG_RANDOM);
     return 0;
 }
+
+int qcrypto_random_init(Error **errp G_GNUC_UNUSED) { return 0; }

crypto/random-gnutls.c

@@ -41,3 +41,6 @@ int qcrypto_random_bytes(uint8_t *buf,
 
     return 0;
 }
+
+
+int qcrypto_random_init(Error **errp G_GNUC_UNUSED) { return 0; }

crypto/random-platform.c

@@ -22,14 +22,16 @@
 
 #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;
+#ifdef _WIN32
+#include <Wincrypt.h>
+static HCRYPTPROV hCryptProv;
+#else
+static int fd; /* a file handle to either /dev/urandom or /dev/random */
+#endif
 
+int qcrypto_random_init(Error **errp)
+{
+#ifndef _WIN32
     /* TBD perhaps also add support for BSD getentropy / Linux
      * getrandom syscalls directly */
     fd = open("/dev/urandom", O_RDONLY);
@@ -41,6 +43,25 @@ int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
         error_setg(errp, "No /dev/urandom or /dev/random found");
         return -1;
     }
+#else
+    if (!CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL,
+                             CRYPT_SILENT | CRYPT_VERIFYCONTEXT)) {
+        error_setg_win32(errp, GetLastError(),
+                         "Unable to create cryptographic provider");
+        return -1;
+    }
+#endif
+
+    return 0;
+}
+
+int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
+                         size_t buflen G_GNUC_UNUSED,
+                         Error **errp)
+{
+#ifndef _WIN32
+    int ret = -1;
+    int got;
 
     while (buflen > 0) {
         got = read(fd, buf, buflen);
@@ -59,6 +80,14 @@ int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
 
     ret = 0;
  cleanup:
-    close(fd);
     return ret;
+#else
+    if (!CryptGenRandom(hCryptProv, buflen, buf)) {
+        error_setg_win32(errp, GetLastError(),
+                         "Unable to read random bytes");
+        return -1;
+    }
+
+    return 0;
+#endif
 }

include/crypto/random.h

@@ -40,5 +40,14 @@ int qcrypto_random_bytes(uint8_t *buf,
                          size_t buflen,
                          Error **errp);
 
+/**
+ * qcrypto_random_init:
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Initializes the handles used by qcrypto_random_bytes
+ *
+ * Returns 0 on success, -1 on error
+ */
+int qcrypto_random_init(Error **errp);
 
 #endif /* QCRYPTO_RANDOM_H */