K8s audit evts (#450)

* Add new json/webserver libs, embedded webserver

Add two new external libraries:

 - nlohmann-json is a better json library that has stronger use of c++
   features like type deduction, better conversion from stl structures,
   etc. We'll use it to hold generic json objects instead of jsoncpp.

 - civetweb is an embeddable webserver that will allow us to accept
   posted json data.

New files webserver.{cpp,h} start an embedded webserver that listens for
POSTS on a configurable url and passes the json data to the falco
engine.

New falco config items are under webserver:
  - enabled: true|false. Whether to start the embedded webserver or not.
  - listen_port. Port that webserver listens on
  - k8s_audit_endpoint: uri on which to accept POSTed k8s audit events.

(This commit doesn't compile entirely on its own, but we're grouping
these related changes into one commit for clarity).

* Don't use relative paths to find lua code

You can look directly below PROJECT_SOURCE_DIR.

* Reorganize compiler lua code

The lua compiler code is generic enough to work on more than just
sinsp-based rules, so move the parts of the compiler related to event
types and filterchecks out into a standalone lua file
sinsp_rule_utils.lua.

The checks for event types/filterchecks are now done from rule_loader,
and are dependent on a "source" attribute of the rule being
"sinsp". We'll be adding additional types of events next that come from
sources other than system calls.

* Manage separate syscall/k8s audit rulesets

Add the ability to manage separate sets of rules (syscall and
k8s_audit). Stop using the sinsp_evttype_filter object from the sysdig
repo, replacing it with falco_ruleset/falco_sinsp_ruleset from
ruleset.{cpp,h}. It has the same methods to add rules, associate them
with rulesets, and (for syscall) quickly find the relevant rules for a
given syscall/event type.

At the falco engine level, there are new parallel interfaces for both
types of rules (syscall and k8s_audit) to:
  - add a rule: add_k8s_audit_filter/add_sinsp_filter
  - match an event against rules, possibly returning a result:
    process_sinsp_event/process_k8s_audit_event

At the rule loading level, the mechanics of creating filterchecks
objects is handled two factories (sinsp_filter_factory and
json_event_filter_factory), both of which are held by the engine.

* Handle multiple rule types when parsing rules

Modify the steps of parsing a rule's filter expression to handle
multiple types of rules. Notable changes:

 - In the rule loader/ast traversal, pass a filter api object down,
   which is passed back up in the lua parser api calls like nest(),
   bool_op(), rel_expr(), etc.
 - The filter api object is either the sinsp factory or k8s audit
   factory, depending on the rule type.
 - When the rule is complete, the complete filter is passed to the
   engine using either add_sinsp_filter()/add_k8s_audit_filter().

* Add multiple output formatting types

Add support for multiple output formatters. Notable changes:

 - The falco engine is passed along to falco_formats to gain access to
   the engine's factories.
 - When creating a formatter, the source of the rule is passed along
   with the format string, which controls which kind of output formatter
   is created.

Also clean up exception handling a bit so all lua callbacks catch all
exceptions and convert them into lua errors.

* Add support for json, k8s audit filter fields

With some corresponding changes in sysdig, you can now create general
purpose filter fields and events, which can be tied together with
nesting, expressions, and relational operators. The classes here
represent an instance of these fields devoted to generic json objects as
well as k8s audit events. Notable changes:

 - json_event: holds a json object, used by all of the below

 - json_event_filter_check: Has the ability to extract values out of a
   json_event object and has the ability to define macros that associate
   a field like "group.field" with a json pointer expression that
   extracts a single property's value out of the json object. The basic
   field definition also allows creating an index
   e.g. group.field[index], where a std::function is responsible for
   performing the indexing. This class has virtual void methods so it
   must be overridden.

 - jevt_filter_check: subclass of json_event_filter_check and defines
   the following fields:
     - jevt.time/jevt.rawtime: extracts the time from the underlying json object.
     - jevt.value[<json pointer>]: general purpose way to extract any
       json value out of the underlying object. <json pointer> is a json
       pointer expression
     - jevt.obj: Return the entire object, stringified.

 - k8s_audit_filter_check: implements fields that extract values from
   k8s audit events. Most of the implementation is in the form of macros
   like ka.user.name, ka.uri, ka.target.name, etc. that just use json
   pointers to extact the appropriate value from a k8s audit event. More
   advanced fields like ka.uri.param, ka.req.container.image use
   indexing to extract individual values out of maps or arrays.

 - json_event_filter_factory: used by things like the lua parser api,
   output formatter, etc to create the necessary objects and return
   them.

  - json_event_formatter: given a format string, create the necessary
    fields that will be used to create a resolved string when given a
    json_event object.

* Add ability to list fields

Similar to sysdig's -l option, add --list (<source>) to list the fields
supported by falco. With no source specified, will print all
fields. Source can be "syscall" for inspector fields e.g. what is
supported by sysdig, or "k8s_audit" to list fields supported only by the
k8s audit support in falco.

* Initial set of k8s audit rules

Add an initial set of k8s audit rules. They're broken into 3 classes of
rules:

 - Suspicious activity: this includes things like:
    - A disallowed k8s user performing an operation
    - A disallowed container being used in a pod.
    - A pod created with a privileged pod.
    - A pod created with a sensitive mount.
    - A pod using host networking
    - Creating a NodePort Service
    - A configmap containing private credentials
    - A request being made by an unauthenticated user.
    - Attach/exec to a pod. (We eventually want to also do privileged
      pods, but that will require some state management that we don't
      currently have).
    - Creating a new namespace outside of an allowed set
    - Creating a pod in either of the kube-system/kube-public namespaces
    - Creating a serviceaccount in either of the kube-system/kube-public
      namespaces
    - Modifying any role starting with "system:"
    - Creating a clusterrolebinding to the cluster-admin role
    - Creating a role that wildcards verbs or resources
    - Creating a role with writable permissions/pod exec permissions.
 - Resource tracking. This includes noting when a deployment, service,
    - configmap, cluster role, service account, etc are created or destroyed.
 - Audit tracking: This tracks all audit events.

To support these rules, add macros/new indexing functions as needed to
support the required fields and ways to index the results.

* Add ability to read trace files of k8s audit evts

Expand the use of the -e flag to cover both .scap files containing
system calls as well as jsonl files containing k8s audit events:

If a trace file is specified, first try to read it using the
inspector. If that throws an exception, try to read the first line as
json. If both fail, return an error.

Based on the results of the open, the main loop either calls
do_inspect(), looping over system events, or
read_k8s_audit_trace_file(), reading each line as json and passing it to
the engine and outputs.

* Example showing how to enable k8s audit logs.

An example of how to enable k8s audit logging for minikube.

* Add unit tests for k8s audit support

Initial unit test support for k8s audit events. A new multiplex file
falco_k8s_audit_tests.yaml defines the tests. Traces (jsonl files) are
in trace_files/k8s_audit and new rules files are in
test/rules/k8s_audit.

Current test cases include:

- User outside allowed set
- Creating disallowed pod.
- Creating a pod explicitly on the allowed list
- Creating a pod w/ a privileged container (or second container), or a
  pod with no privileged container.
- Creating a pod w/ a sensitive mount container (or second container), or a
  pod with no sensitive mount.
- Cases for a trace w/o the relevant property + the container being
  trusted, and hostnetwork tests.
- Tests that create a Service w/ and w/o a NodePort type.
- Tests for configmaps: tries each disallowed string, ensuring each is
  detected, and the other has a configmap with no disallowed string,
  ensuring it is not detected.
- The anonymous user creating a namespace.
- Tests for all kactivity rules e.g. those that create/delete
  resources as compared to suspicious activity.
- Exec/Attach to Pod
- Creating a namespace outside of an allowed set
- Creating a pod/serviceaccount in kube-system/kube-public namespaces
- Deleting/modifying a system cluster role
- Creating a binding to the cluster-admin role
- Creating a cluster role binding that wildcards verbs or resources
- Creating a cluster role with write/pod exec privileges

* Don't manually install gcc 4.8

gcc 4.8 should already be installed by default on the vm we use for
travis.

userspace/engine/formats.cpp

@@ -25,6 +25,7 @@ limitations under the License.
 
 
 sinsp* falco_formats::s_inspector = NULL;
+falco_engine *falco_formats::s_engine = NULL;
 bool falco_formats::s_json_output = false;
 bool falco_formats::s_json_include_output_property = true;
 sinsp_evt_formatter_cache *falco_formats::s_formatters = NULL;
@@ -38,9 +39,14 @@ const static struct luaL_reg ll_falco [] =
 	{NULL,NULL}
 };
 
-void falco_formats::init(sinsp* inspector, lua_State *ls, bool json_output, bool json_include_output_property)
+void falco_formats::init(sinsp* inspector,
+			 falco_engine *engine,
+			 lua_State *ls,
+			 bool json_output,
+			 bool json_include_output_property)
 {
 	s_inspector = inspector;
+	s_engine = engine;
 	s_json_output = json_output;
 	s_json_include_output_property = json_include_output_property;
 	if(!s_formatters)
@@ -53,31 +59,57 @@ void falco_formats::init(sinsp* inspector, lua_State *ls, bool json_output, bool
 
 int falco_formats::formatter(lua_State *ls)
 {
-	string format = luaL_checkstring(ls, 1);
-	sinsp_evt_formatter* formatter;
+	string source = luaL_checkstring(ls, -2);
+	string format = luaL_checkstring(ls, -1);
+
 	try
 	{
-		formatter = new sinsp_evt_formatter(s_inspector, format);
-		lua_pushlightuserdata(ls, formatter);
+		if(source == "syscall")
+		{
+			sinsp_evt_formatter* formatter;
+			formatter = new sinsp_evt_formatter(s_inspector, format);
+			lua_pushlightuserdata(ls, formatter);
+		}
+		else
+		{
+			json_event_formatter *formatter;
+			formatter = new json_event_formatter(s_engine->json_factory(), format);
+			lua_pushlightuserdata(ls, formatter);
+		}
 	}
 	catch(sinsp_exception& e)
 	{
 		luaL_error(ls, "Invalid output format '%s': '%s'", format.c_str(), e.what());
 	}
+	catch(falco_exception& e)
+	{
+		luaL_error(ls, "Invalid output format '%s': '%s'", format.c_str(), e.what());
+	}
 
 	return 1;
 }
 
 int falco_formats::free_formatter(lua_State *ls)
 {
-	if (!lua_islightuserdata(ls, -1))
+	if (!lua_islightuserdata(ls, -1) ||
+	    !lua_isstring(ls, -2))
+
 	{
 		luaL_error(ls, "Invalid argument passed to free_formatter");
 	}
 
-	sinsp_evt_formatter *formatter = (sinsp_evt_formatter *) lua_topointer(ls, 1);
+	string source = luaL_checkstring(ls, -2);
 
-	delete(formatter);
+	if(source == "syscall")
+	{
+		sinsp_evt_formatter *formatter = (sinsp_evt_formatter *) lua_topointer(ls, -1);
+		delete(formatter);
+	}
+	else
+	{
+		json_event_formatter *formatter = (json_event_formatter *) lua_topointer(ls, -1);
+		delete(formatter);
+	}
 
 	return 0;
 }
@@ -100,57 +132,64 @@ int falco_formats::format_event (lua_State *ls)
 	if (!lua_isstring(ls, -1) ||
 	    !lua_isstring(ls, -2) ||
 	    !lua_isstring(ls, -3) ||
-	    !lua_islightuserdata(ls, -4)) {
+	    !lua_isstring(ls, -4) ||
+	    !lua_islightuserdata(ls, -5)) {
 		lua_pushstring(ls, "Invalid arguments passed to format_event()");
 		lua_error(ls);
 	}
-	sinsp_evt* evt = (sinsp_evt*)lua_topointer(ls, 1);
+	gen_event* evt = (gen_event*)lua_topointer(ls, 1);
 	const char *rule = (char *) lua_tostring(ls, 2);
-	const char *level = (char *) lua_tostring(ls, 3);
-	const char *format = (char *) lua_tostring(ls, 4);
+	const char *source = (char *) lua_tostring(ls, 3);
+	const char *level = (char *) lua_tostring(ls, 4);
+	const char *format = (char *) lua_tostring(ls, 5);
 
 	string sformat = format;
 
-	try {
-		s_formatters->tostring(evt, sformat, &line);
+	if(strcmp(source, "syscall") == 0)
+	{
+		try {
+			s_formatters->tostring((sinsp_evt *) evt, sformat, &line);
 
-		if(s_json_output)
-		{
-			switch(s_inspector->get_buffer_format())
+			if(s_json_output)
 			{
-				case sinsp_evt::PF_NORMAL:
-					s_inspector->set_buffer_format(sinsp_evt::PF_JSON);
-					break;
-				case sinsp_evt::PF_EOLS:
-					s_inspector->set_buffer_format(sinsp_evt::PF_JSONEOLS);
-					break;
-				case sinsp_evt::PF_HEX:
-					s_inspector->set_buffer_format(sinsp_evt::PF_JSONHEX);
-					break;
-				case sinsp_evt::PF_HEXASCII:
-					s_inspector->set_buffer_format(sinsp_evt::PF_JSONHEXASCII);
-					break;
-				case sinsp_evt::PF_BASE64:
-					s_inspector->set_buffer_format(sinsp_evt::PF_JSONBASE64);
-					break;
-				default:
-					// do nothing
-					break;
-			}
-			s_formatters->tostring(evt, sformat, &json_line);
+				s_inspector->set_buffer_format(sinsp_evt::PF_JSON);
+				s_formatters->tostring((sinsp_evt *) evt, sformat, &json_line);
 
-			// The formatted string might have a leading newline. If it does, remove it.
-			if (json_line[0] == '\n')
-			{
-				json_line.erase(0, 1);
+				// The formatted string might have a leading newline. If it does, remove it.
+				if (json_line[0] == '\n')
+				{
+					json_line.erase(0, 1);
+				}
+
+				s_inspector->set_buffer_format(sinsp_evt::PF_NORMAL);
 			}
 		}
+		catch (sinsp_exception& e)
+		{
+			string err = "Invalid output format '" + sformat + "': '" + string(e.what()) + "'";
+			lua_pushstring(ls, err.c_str());
+			lua_error(ls);
+		}
 	}
-	catch (sinsp_exception& e)
+	else
 	{
-		string err = "Invalid output format '" + sformat + "': '" + string(e.what()) + "'";
-		lua_pushstring(ls, err.c_str());
-		lua_error(ls);
+		try {
+
+			json_event_formatter formatter(s_engine->json_factory(), sformat);
+
+			line = formatter.tostring((json_event *) evt);
+
+			if(s_json_output)
+			{
+				json_line = formatter.tojson((json_event *) evt);
+			}
+		}
+		catch (exception &e)
+		{
+			string err = "Invalid output format '" + sformat + "': '" + string(e.what()) + "'";
+			lua_pushstring(ls, err.c_str());
+			lua_error(ls);
+		}
 	}
 
 	// For JSON output, the formatter returned a json-as-text