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>

7 files changed, 189 insertions, 3 deletions

diff --git a/configure.ac b/configure.ac
index bce0d9f7ab..4ae4c0bc4e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -248,6 +248,14 @@ AC_ARG_ENABLE(tests,
     enable_tests=$enableval, enable_tests=$enable_tools)
 AM_CONDITIONAL(ENABLE_TESTS, test "$enable_tests" != "no")
 
+AC_ARG_ENABLE(fuzzer-target,
+  AS_HELP_STRING([--enable-fuzzer-target], [make a library intended for testing - not production]),
+    enable_fuzzer_target=$enableval, enable_fuzzer_target=no)
+AM_CONDITIONAL(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION, test "$enable_fuzzer_target" != "no")
+if test "$enable_fuzzer_target" != "no";then
+	AC_DEFINE([FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION], 1, [Enable fuzzer target -not for production])
+fi
+
 GTK_DOC_CHECK(1.1)
 AM_GNU_GETTEXT([external])
 AM_GNU_GETTEXT_VERSION([0.19])
@@ -1043,3 +1051,9 @@ AC_MSG_WARN([[
 *** applications to link, do not enable static linking.
 ]])
 fi
+
+if test "$enable_fuzzer_target" != "no";then
+AC_MSG_WARN([[
+*** This version of the library is for fuzzying purposes and is intentionally broken!
+]])
+fi
diff --git a/devel/fuzz/README.md b/devel/fuzz/README.md
index 575f80e091..0d94bbae15 100644
--- a/devel/fuzz/README.md
+++ b/devel/fuzz/README.md
@@ -18,7 +18,7 @@ using other projects like openssl.
 Use the following commands on top dir:
 
 ```
-$ CC="afl-gcc" ./configure
+$ CC="afl-gcc" ./configure --enable-fuzzer-target
 $ make -j$(nproc)
 $ cd devel/fuzz
 $ make gnutls_pkcs7_parser_fuzzer
diff --git a/lib/handshake.c b/lib/handshake.c
index 8dc3fa58ec..d0e3d497bd 100644
--- a/lib/handshake.c
+++ b/lib/handshake.c
@@ -186,9 +186,14 @@ static int create_tls_random(uint8_t * dst)
 	 * system's time.
 	 */
 
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
+	/* When fuzzying avoid timing dependencies */
+	memset(dst, 1, 4);
+#else
 	tim = gnutls_time(NULL);
 	/* generate server random value */
 	_gnutls_write_uint32(tim, dst);
+#endif
 
 	ret =
 	    gnutls_rnd(GNUTLS_RND_NONCE, &dst[3], GNUTLS_RANDOM_SIZE - 3);
@@ -793,11 +798,18 @@ static int _gnutls_recv_finished(gnutls_session_t session)
 		goto cleanup;
 	}
 
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
+	/* When fuzzying allow to proceed without verifying the handshake
+	 * consistency */
+# warning This is unsafe for production builds
+
+#else
 	if (memcmp(vrfy, data, data_size) != 0) {
 		gnutls_assert();
 		ret = GNUTLS_E_ERROR_IN_FINISHED_PACKET;
 		goto cleanup;
 	}
+#endif
 
 	ret = _gnutls_ext_sr_finished(session, data, data_size, 1);
 	if (ret < 0) {
diff --git a/lib/nettle/Makefile.am b/lib/nettle/Makefile.am
index 12d7f016ea..c7196ae307 100644
--- a/lib/nettle/Makefile.am
+++ b/lib/nettle/Makefile.am
@@ -53,6 +53,10 @@ libcrypto_la_SOURCES += sysrng-linux.c
 endif
 endif
 
+if FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+libcrypto_la_SOURCES += rnd-fuzzer.c
+endif
+
 if ENABLE_FIPS140
 libcrypto_la_SOURCES += rnd-fips.c int/drbg-aes-self-test.c \
 	int/drbg-aes.c int/drbg-aes.h
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,
+};
diff --git a/lib/random.c b/lib/random.c
index 2fe82adc7d..0c05dbe187 100644
--- a/lib/random.c
+++ b/lib/random.c
@@ -37,6 +37,9 @@
 # error Unsupported platform
 #endif
 
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
+extern gnutls_crypto_rnd_st _gnutls_fuzz_rnd_ops;
+#endif
 
 /* Per thread context of random generator, and a flag to indicate initialization */
 static _Thread_local void *gnutls_rnd_ctx;
@@ -100,7 +103,13 @@ int _gnutls_rnd_preinit(void)
 {
 	int ret;
 
-#ifdef ENABLE_FIPS140
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
+# warning Insecure PRNG is enabled
+	ret = gnutls_crypto_rnd_register(100, &_gnutls_fuzz_rnd_ops);
+	if (ret < 0)
+		return ret;
+
+#elif defined(ENABLE_FIPS140)
 	/* The FIPS140 random generator is only enabled when we are compiled
 	 * with FIPS support, _and_ the system requires FIPS140.
 	 */
diff --git a/lib/x509/common.h b/lib/x509/common.h
index eafc7a515b..1a27666076 100644
--- a/lib/x509/common.h
+++ b/lib/x509/common.h
@@ -30,9 +30,14 @@
 #include <fips.h>
 
 #define MAX_STRING_LEN 512
+
+#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
+# define MAX_ITER_COUNT 10*1024
+#else
 /* Set a maximum iteration count over which we refuse to
  * decode a file. That is to prevent DoS. */
-#define MAX_ITER_COUNT (10*1024*1024)
+# define MAX_ITER_COUNT (10*1024*1024)
+#endif
 
 #define GNUTLS_XML_SHOW_ALL 1