fuzzer: added a fuzzer target

This allows to compile the library with flags which will add predictable
random generation and eliminate some crypto checks, in order for the
library to be used for testing (fuzzying).

Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>

1 files changed, 142 insertions, 0 deletions

diff --git a/lib/nettle/rnd-fuzzer.c b/lib/nettle/rnd-fuzzer.c
new file mode 100644
index 0000000000..b48601fabf
--- /dev/null
+++ b/lib/nettle/rnd-fuzzer.c
@@ -0,0 +1,142 @@
+/*
+ * Copyright (C) 2017 Red Hat
+ * Copyright (C) 1995-2017 Free Software Foundation, Inc.
+ * This file is part of the GNU C Library.
+ * Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, August 1995.
+ *
+ * This file is part of GnuTLS.
+ *
+ * Libgcrypt 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 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * Libgcrypt 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 program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <drbg-aes.h>
+#include <fips.h>
+
+#include "gnutls_int.h"
+#include "errors.h"
+#include <stdlib.h>
+#include <rnd-common.h>
+
+#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+# error 1
+#endif
+
+struct r48_rand_data {
+	unsigned short int __x[3];	/* Current state.  */
+	unsigned short int __old_x[3];	/* Old state.  */
+	unsigned short int __c;	/* Additive const. in congruential formula.  */
+	unsigned short int __init;	/* Flag for initializing.  */
+	__extension__ unsigned long long int __a;	/* Factor in congruential
+							   formula.  */
+};
+
+static int
+__r48_rand_iterate(unsigned short int xsubi[3], struct r48_rand_data *buffer)
+{
+	uint64_t X;
+	uint64_t result;
+
+	/* Initialize buffer, if not yet done.  */
+	if (unlikely(!buffer->__init)) {
+		buffer->__a = 0x5deece66dull;
+		buffer->__c = 0xb;
+		buffer->__init = 1;
+	}
+
+	/* Do the real work.  We choose a data type which contains at least
+	   48 bits.  Because we compute the modulus it does not care how
+	   many bits really are computed.  */
+
+	X = (uint64_t) xsubi[2] << 32 | (uint32_t) xsubi[1] << 16 | xsubi[0];
+
+	result = X * buffer->__a + buffer->__c;
+
+	xsubi[0] = result & 0xffff;
+	xsubi[1] = (result >> 16) & 0xffff;
+	xsubi[2] = (result >> 32) & 0xffff;
+
+	return 0;
+}
+
+static int
+r48_r(unsigned short int xsubi[3], struct r48_rand_data *buffer,
+      long int *result)
+{
+	/* Compute next state.  */
+	if (__r48_rand_iterate(xsubi, buffer) < 0)
+		return -1;
+
+	/* Store the result.  */
+	*result = (int32_t) ((xsubi[2] << 16) | xsubi[1]);
+
+	return 0;
+}
+
+static int r48(struct r48_rand_data *buffer, long int *result)
+{
+	return r48_r(buffer->__x, buffer, result);
+}
+
+/* This is a dummy random generator intended to be reproducible
+ * for use in fuzzying targets.
+ */
+
+static int _rngfuzz_init(void **_ctx)
+{
+	*_ctx = calloc(1, sizeof(struct r48_rand_data));
+
+	return 0;
+}
+
+static int _rngfuzz_rnd(void *_ctx, int level, void *buffer, size_t length)
+{
+	struct r48_rand_data *ctx = _ctx;
+	uint8_t *p = buffer;
+	long r;
+	unsigned i;
+
+	memset(ctx, 0, sizeof(*ctx));
+
+	for (i = 0; i < length; i++) {
+		r48(ctx, &r);
+		p[i] = r;
+	}
+	return 0;
+}
+
+static void _rngfuzz_deinit(void *_ctx)
+{
+	struct r48_rand_data *ctx = _ctx;
+
+	free(ctx);
+}
+
+static void _rngfuzz_refresh(void *_ctx)
+{
+	/* this is predictable RNG. Don't refresh */
+	return;
+}
+
+gnutls_crypto_rnd_st _gnutls_fuzz_rnd_ops = {
+	.init = _rngfuzz_init,
+	.deinit = _rngfuzz_deinit,
+	.rnd = _rngfuzz_rnd,
+	.rnd_refresh = _rngfuzz_refresh,
+	.self_test = NULL,
+};