libddwaf is Datadog's implementation of a Web Application Firewall (WAF) engine, with a goal of low performance and memory overhead, and embeddability in a wide variety of language runtimes through a C API.
libddwaf follows Semantic Versioning 2.0, with a slight twist.
libddwaf is a heir to libsqreen, the latter which was semantically versioned using 0.y.z:
Major version zero (0.y.z) is for initial development. Anything MAY change at any time. The public API SHOULD NOT be considered stable.
To mark the break between libsqreen and libddwaf (which involved a lot of renaming and changes), it was decided to bump the major version, but some time was needed still to stabilise the public API. Therefore libddwaf's 1.y.z is operating following semver's usual 0.y.z, with minor y meaning "breaking change" and patch z meaning "bugfix".
In addition libddwaf's "unstable" marker on releases means the API may evolve and have breaking changes on minor versions. Nonetheless its codebase and resulting binaries are considered production-ready as the "unstable" marker only applies to libddwaf's public API.
Since libddwaf should not be used directly and is wrapped by binding libraries to various languages, any such low-level C API change is handled by Datadog internally and isolated by the higher level binding code, which aims to provide a much stabler high level language-oriented API. In any case, the binding library dependency is directly consumed by the Datadog tracing client libraries, and should there be a breaking change in the binding API it would be handled as gracefully as technically possible within the tracing client library level, and properly handled using the tracing client library dependency verssion constraints so that it picks only compatible versions of the binding library.
This project is built using cmake.
On Linux and Darwin, the following should produce a static and a dynamic library inside of build:
mkdir -p build && cd build
cmake ..
make -j4
A cross-platform way to achieve the same result (e.g on Windows):
cmake -E make_directory build
cd build
cmake ..
cmake --build . --target all -j4
And a more involved example, with specific targets, building, then running the test suite along with debug information:
cmake -E make_directory build packages
cd build
cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=.. -DCPACK_PACKAGE_DIRECTORY=../packages ..
cmake --build . --config RelWithDebInfo --verbose --target libddwaf_shared --target libddwaf_static --target waf_test -j
cd ../tests
../build/tests/waf_test
The general process is as follows:
- Load processing rules as a
ddwaf_objectdata structure into the WAF engine. This returns a handler. - Start a context with the returned handler.
- Prepare input to test against the rules into a
ddwaf_objectdata structure. - Perform a run against the input in the context.
- Optionally perform subsequent runs against additional input in the same context. Only newly relevant rules are checked against.
- Discard context and/or handler as needed.
The full example can be found here.
#include<yaml-cpp/yaml.h>
#include"ddwaf.h"constexpr std::string_view waf_rule = R"(version: "2.1"rules: - id: "1" name: rule 1 tags: type: flow1 category: test conditions: - operator: match_regex parameters: inputs: - address: arg1 regex: .* - operator: match_regex parameters: inputs: - address: arg2 regex: .* on_match: [ block ])";
intmain()
{
auto alloc = ddwaf_get_default_allocator();
YAML::Node doc = YAML::Load(waf_rule.data());
auto rule = doc.as<ddwaf_object>();
ddwaf_builder builder = ddwaf_builder_init();
ddwaf_object diagnostics;
bool success = ddwaf_builder_add_or_update_config(builder, "config", 6, &rule, &diagnostics);
ddwaf_object_destroy(&rule, alloc);
ddwaf_object_destroy(&diagnostics, alloc);
if (!success) {
ddwaf_builder_destroy(builder);
returnEXIT_FAILURE;
}
ddwaf_handle handle = ddwaf_builder_build_instance(builder);
ddwaf_builder_destroy(builder);
if (handle == nullptr) {
returnEXIT_FAILURE;
}
ddwaf_context context = ddwaf_context_init(handle, alloc);
if (context == nullptr) {
ddwaf_destroy(handle);
returnEXIT_FAILURE;
}
ddwaf_object root;
ddwaf_object_set_map(&root, 2, alloc);
ddwaf_object *arg1 = ddwaf_object_insert_literal_key(&root, "arg1", 4, alloc);
ddwaf_object_set_string_literal(arg1, "string 1", 8);
ddwaf_object *arg2 = ddwaf_object_insert_literal_key(&root, "arg2", 4, alloc);
ddwaf_object_set_string_literal(arg2, "string 2", 8);
ddwaf_object ret;
auto code = ddwaf_context_eval(context, &root, alloc, &ret, 1000000/* microseconds */);
std::cout << "Output second run: " << code << '\n';
if (code == DDWAF_MATCH) {
YAML::Emitter out(std::cout);
out.SetIndent(2);
out.SetMapFormat(YAML::Block);
out.SetSeqFormat(YAML::Block);
out << object_to_yaml(ret);
}
ddwaf_object_destroy(&ret, alloc);
ddwaf_context_destroy(context);
ddwaf_destroy(handle);
returnEXIT_SUCCESS;
}namespaceYAML {
template <>
structas_if<ddwaf_object, void>
{
explicitas_if(const Node& node_) : node(node_) {}
static ddwaf_object yaml_to_object_helper(const Node& node, ddwaf_allocator alloc)
{
ddwaf_object arg;
switch (node.Type())
{
case NodeType::Sequence:
ddwaf_object_set_array(&arg, 0, alloc);
break;
case NodeType::Map:
ddwaf_object_set_map(&arg, 0, alloc);
break;
case NodeType::Scalar:
{
auto scalar = node.Scalar();
ddwaf_object_set_string(&arg, scalar.c_str(), scalar.length(), alloc);
break;
}
case NodeType::Null:
ddwaf_object_set_null(&arg);
break;
case NodeType::Undefined:
default:
ddwaf_object_set_invalid(&arg);
break;
}
return arg;
}
ddwaf_object operator()() const
{
auto alloc = ddwaf_get_default_allocator();
std::list<std::tuple<ddwaf_object *, YAML::Node, YAML::Node::const_iterator>> stack;
ddwaf_object root = yaml_to_object_helper(node, alloc);
if (root.type == DDWAF_OBJ_MAP || root.type == DDWAF_OBJ_ARRAY) {
stack.emplace_back(&root, node, node.begin());
}
while (!stack.empty()) {
auto current_depth = stack.size();
auto &[parent_obj, parent_node, it] = stack.back();
for (; it != parent_node.end(); ++it) {
YAML::Node child_node = parent_node.IsMap() ? it->second : *it;
auto child_obj = yaml_to_object_helper(child_node, alloc);
ddwaf_object *child_ptr = nullptr;
if (parent_obj->type == DDWAF_OBJ_MAP) {
auto key = it->first.as<std::string>();
child_ptr = ddwaf_object_insert_key(parent_obj, key.c_str(), key.size(), alloc);
*child_ptr = child_obj;
} elseif (parent_obj->type == DDWAF_OBJ_ARRAY) {
child_ptr = ddwaf_object_insert(parent_obj, alloc);
*child_ptr = child_obj;
}
if (child_obj.type == DDWAF_OBJ_MAP || child_obj.type == DDWAF_OBJ_ARRAY) {
stack.emplace_back(child_ptr, child_node, child_node.begin());
++it;
break;
}
}
if (current_depth == stack.size()) {
stack.pop_back();
}
}
return root;
}
const Node& node;
};
} // namespace YAMLnamespace {
YAML::Node object_to_yaml_helper(const ddwaf_object &obj)
{
YAML::Node output;
switch (obj.type) {
caseDDWAF_OBJ_BOOL:
output = ddwaf_object_get_bool(&obj);
break;
caseDDWAF_OBJ_SIGNED:
output = ddwaf_object_get_signed(&obj);
break;
caseDDWAF_OBJ_UNSIGNED:
output = ddwaf_object_get_unsigned(&obj);
break;
caseDDWAF_OBJ_FLOAT:
output = ddwaf_object_get_float(&obj);
break;
caseDDWAF_OBJ_STRING:
caseDDWAF_OBJ_LITERAL_STRING:
caseDDWAF_OBJ_SMALL_STRING:
{
size_t length;
constchar* str = ddwaf_object_get_string(&obj, &length);
output = std::string{str, length};
}
break;
caseDDWAF_OBJ_MAP:
output = YAML::Load("{}");
break;
caseDDWAF_OBJ_ARRAY:
output = YAML::Load("[]");
break;
caseDDWAF_OBJ_INVALID:
caseDDWAF_OBJ_NULL:
output = YAML::Null;
break;
};
return output;
}
} // namespaceYAML::Node object_to_yaml(const ddwaf_object &obj)
{
std::list<std::tuple<const ddwaf_object &, YAML::Node, std::size_t>> stack;
YAML::Node root = object_to_yaml_helper(obj);
if (obj.type == DDWAF_OBJ_MAP || obj.type == DDWAF_OBJ_ARRAY) {
stack.emplace_back(obj, root, 0);
}
while (!stack.empty()) {
auto current_depth = stack.size();
auto &[parent_obj, parent_node, index] = stack.back();
size_t size = ddwaf_object_get_size(&parent_obj);
for (; index < size; ++index) {
const ddwaf_object *child_obj = nullptr;
if (parent_obj.type == DDWAF_OBJ_MAP) {
child_obj = ddwaf_object_at_value(&parent_obj, index);
auto *key_obj = ddwaf_object_at_key(&parent_obj, index);
size_t key_len;
constchar* key_str = ddwaf_object_get_string(key_obj, &key_len);
std::string key{key_str, key_len};
auto child_node = object_to_yaml_helper(*child_obj);
parent_node[key] = child_node;
if (child_obj->type == DDWAF_OBJ_MAP || child_obj->type == DDWAF_OBJ_ARRAY) {
stack.emplace_back(*child_obj, child_node, 0);
++index;
break;
}
} elseif (parent_obj.type == DDWAF_OBJ_ARRAY) {
child_obj = ddwaf_object_at_value(&parent_obj, index);
auto child_node = object_to_yaml_helper(*child_obj);
parent_node.push_back(child_node);
if (child_obj->type == DDWAF_OBJ_MAP || child_obj->type == DDWAF_OBJ_ARRAY) {
stack.emplace_back(*child_obj, child_node, 0);
++index;
break;
}
}
}
if (current_depth == stack.size()) {
stack.pop_back();
}
}
return root;
}The following rule:
version: 2.1rules:
- id: crs-042-001name: Detect a script tagtags:
category: attack_attempttype: xssconditions:
- operator: match_regexparameters:
regex: "^<script>"inputs:
- address: http.server.queryapplied to the http.server.query value http://localhost/?q=<script>alert() hello world produces the following result:
- rule:
id: crs-042-001name: Detect a script tagtags:
category: attack_attempttype: xssrule_matches:
- operator: match_regexoperator_value: ^<script>parameters:
- address: http.server.querykey_path:
- qvalue: <script>alert() hello worldhighlight:
- <script>