CVE-2020-10704: libcli ldap: test recursion depth in ldap_decode_filter_tree

Add tests to check that ASN.1 ldap requests with deeply nested elements
are rejected.  Previously there was no check on the on the depth of
nesting and excessive nesting could cause a stack overflow.

Credit to OSS-Fuzz

REF: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20454
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14334

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

libcli/ldap/tests/ldap_message_test.c

@@ -0,0 +1,271 @@
+/*
+ * Unit tests for ldap_message.
+ *
+ *  Copyright (C) Catalyst.NET Ltd 2020
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/*
+ * from cmocka.c:
+ * These headers or their equivalents should be included prior to
+ * including
+ * this header file.
+ *
+ * #include <stdarg.h>
+ * #include <stddef.h>
+ * #include <setjmp.h>
+ *
+ * This allows test applications to use custom definitions of C standard
+ * library functions and types.
+ *
+ */
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+#include "lib/util/attr.h"
+#include "includes.h"
+#include "lib/util/asn1.h"
+#include "libcli/ldap/ldap_message.h"
+#include "libcli/ldap/ldap_proto.h"
+
+/*
+ * declare the internal cmocka cm_print so we can output messages in
+ * sub unit format
+ */
+void cm_print_error(const char * const format, ...);
+/*
+ * helper function and macro to compare an ldap error code constant with the
+ * coresponding nt_status code
+ */
+#define NT_STATUS_LDAP_V(code) (0xF2000000 | code)
+static void _assert_ldap_status_equal(
+	int a,
+	NTSTATUS b,
+	const char * const file,
+	const int line)
+{
+	_assert_int_equal(NT_STATUS_LDAP_V(a), NT_STATUS_V(b), file, line);
+}
+
+#define assert_ldap_status_equal(a, b) \
+	_assert_ldap_status_equal((a), (b), __FILE__, __LINE__)
+
+/*
+ * helper function and macro to assert there were no errors in the last
+ * file operation
+ */
+static void _assert_not_ferror(
+	FILE *f,
+	const char * const file,
+	const int line)
+{
+	if (f == NULL || ferror(f)) {
+		cm_print_error("ferror (%d) %s\n", errno, strerror(errno));
+		_fail(file, line);
+	}
+}
+
+#define assert_not_ferror(f) \
+	_assert_not_ferror((f), __FILE__, __LINE__)
+
+struct test_ctx {
+};
+
+static int setup(void **state)
+{
+	struct test_ctx *test_ctx;
+
+	test_ctx = talloc_zero(NULL, struct test_ctx);
+	*state = test_ctx;
+	return 0;
+}
+
+static int teardown(void **state)
+{
+	struct test_ctx *test_ctx = talloc_get_type_abort(*state,
+							  struct test_ctx);
+
+	TALLOC_FREE(test_ctx);
+	return 0;
+}
+
+/*
+ * Test that an empty request is handled correctly
+ */
+static void test_empty_input(void **state)
+{
+	struct test_ctx *test_ctx = talloc_get_type_abort(
+		*state,
+		struct test_ctx);
+	struct asn1_data *asn1;
+	struct ldap_message *ldap_msg;
+	NTSTATUS status;
+	uint8_t buf[0];
+	size_t len = 0;
+
+
+	asn1 = asn1_init(test_ctx, ASN1_MAX_TREE_DEPTH);
+	assert_non_null(asn1);
+
+	asn1_load_nocopy(asn1, buf, len);
+
+	ldap_msg = talloc(test_ctx, struct ldap_message);
+	assert_non_null(ldap_msg);
+
+	status = ldap_decode(asn1, samba_ldap_control_handlers(), ldap_msg);
+	assert_ldap_status_equal(LDAP_PROTOCOL_ERROR, status);
+}
+
+/*
+ * Check that a request is rejected it it's recursion depth exceeds
+ * the maximum value specified. This test uses a very deeply nested query,
+ * 10,000 or clauses.
+ *
+ */
+static void test_recursion_depth_large(void **state)
+{
+	struct test_ctx *test_ctx = talloc_get_type_abort(
+		*state,
+		struct test_ctx);
+	struct asn1_data *asn1;
+	struct ldap_message *ldap_msg;
+	NTSTATUS status;
+	FILE *f = NULL;
+	uint8_t *buffer = NULL;
+	const size_t BUFF_SIZE = 1048576;
+	size_t len;
+
+
+	/*
+	 * Load a test data file containg 10,000 or clauses in encoded as
+	 * an ASN.1 packet.
+	 */
+	buffer = talloc_zero_array(test_ctx, uint8_t, BUFF_SIZE);
+	f = fopen("./libcli/ldap/tests/data/10000-or.dat", "r");
+	assert_not_ferror(f);
+	len = fread(buffer, sizeof(uint8_t), BUFF_SIZE, f);
+	assert_not_ferror(f);
+	assert_true(len > 0);
+
+	asn1 = asn1_init(test_ctx, ASN1_MAX_TREE_DEPTH);
+	assert_non_null(asn1);
+	asn1_load_nocopy(asn1, buffer, len);
+
+	ldap_msg = talloc(test_ctx, struct ldap_message);
+	assert_non_null(ldap_msg);
+
+	status = ldap_decode(asn1, samba_ldap_control_handlers(), ldap_msg);
+	assert_ldap_status_equal(LDAP_PROTOCOL_ERROR, status);
+}
+
+/*
+ * Check that a request is not rejected it it's recursion depth equals the
+ * maximum value
+ */
+static void test_recursion_depth_equals_max(void **state)
+{
+	struct test_ctx *test_ctx = talloc_get_type_abort(
+		*state,
+		struct test_ctx);
+	struct asn1_data *asn1;
+	struct ldap_message *ldap_msg;
+	NTSTATUS status;
+	FILE *f = NULL;
+	uint8_t *buffer = NULL;
+	const size_t BUFF_SIZE = 1048576;
+	size_t len;
+
+
+	buffer = talloc_zero_array(test_ctx, uint8_t, BUFF_SIZE);
+	f = fopen("./libcli/ldap/tests/data/ldap-recursive.dat", "r");
+	assert_not_ferror(f);
+	len = fread(buffer, sizeof(uint8_t), BUFF_SIZE, f);
+	assert_not_ferror(f);
+	assert_true(len > 0);
+
+	asn1 = asn1_init(test_ctx, 4);
+	assert_non_null(asn1);
+	asn1_load_nocopy(asn1, buffer, len);
+
+	ldap_msg = talloc(test_ctx, struct ldap_message);
+	assert_non_null(ldap_msg);
+
+	status = ldap_decode(asn1, samba_ldap_control_handlers(), ldap_msg);
+	assert_true(NT_STATUS_IS_OK(status));
+}
+
+/*
+ * Check that a request is rejected it it's recursion depth is greater than the
+ * maximum value
+ */
+static void test_recursion_depth_greater_than_max(void **state)
+{
+	struct test_ctx *test_ctx = talloc_get_type_abort(
+		*state,
+		struct test_ctx);
+	struct asn1_data *asn1;
+	struct ldap_message *ldap_msg;
+	NTSTATUS status;
+	FILE *f = NULL;
+	uint8_t *buffer = NULL;
+	const size_t BUFF_SIZE = 1048576;
+	size_t len;
+
+
+	buffer = talloc_zero_array(test_ctx, uint8_t, BUFF_SIZE);
+	f = fopen("./libcli/ldap/tests/data/ldap-recursive.dat", "r");
+	assert_not_ferror(f);
+	len = fread(buffer, sizeof(uint8_t), BUFF_SIZE, f);
+	assert_not_ferror(f);
+	assert_true(len > 0);
+
+	asn1 = asn1_init(test_ctx, 3);
+	assert_non_null(asn1);
+	asn1_load_nocopy(asn1, buffer, len);
+
+	ldap_msg = talloc(test_ctx, struct ldap_message);
+	assert_non_null(ldap_msg);
+
+	status = ldap_decode(asn1, samba_ldap_control_handlers(), ldap_msg);
+	assert_ldap_status_equal(LDAP_PROTOCOL_ERROR, status);
+}
+
+int main(_UNUSED_ int argc, _UNUSED_ const char **argv)
+{
+	const struct CMUnitTest tests[] = {
+		cmocka_unit_test_setup_teardown(
+			test_empty_input,
+			setup,
+			teardown),
+		cmocka_unit_test_setup_teardown(
+			test_recursion_depth_large,
+			setup,
+			teardown),
+		cmocka_unit_test_setup_teardown(
+			test_recursion_depth_equals_max,
+			setup,
+			teardown),
+		cmocka_unit_test_setup_teardown(
+			test_recursion_depth_greater_than_max,
+			setup,
+			teardown),
+	};
+
+	cmocka_set_message_output(CM_OUTPUT_SUBUNIT);
+	return cmocka_run_group_tests(tests, NULL, NULL);
+}

libcli/ldap/wscript_build

@@ -6,3 +6,18 @@ bld.SAMBA_LIBRARY('cli-ldap-common',
                   private_headers='ldap_message.h ldap_errors.h ldap_ndr.h',
                   deps='samba-util asn1util NDR_SECURITY tevent',
                   private_library=True)
+
+bld.SAMBA_BINARY(
+    'test_ldap_message',
+    source='tests/ldap_message_test.c',
+    deps='''
+        cmocka
+        talloc
+        ldb
+        samba-util
+        asn1util
+        NDR_SECURITY
+        cli-ldap
+    ''',
+    for_selftest=True
+)

selftest/knownfail.d/ldap_message

@@ -0,0 +1,2 @@
+^libcli.ldap.ldap_message.test_recursion_depth_greater_than_max\(none\)
+^libcli.ldap.ldap_message.test_recursion_depth_large\(none\)

source4/selftest/tests.py

@@ -1376,6 +1376,8 @@ plantestsuite("librpc.ndr.ndr", "none",
               [os.path.join(bindir(), "test_ndr")])
 plantestsuite("librpc.ndr.ndr_macros", "none",
               [os.path.join(bindir(), "test_ndr_macros")])
+plantestsuite("libcli.ldap.ldap_message", "none",
+              [os.path.join(bindir(), "test_ldap_message")])
 
 # process restart and limit tests, these break the environment so need to run
 # in their own specific environment