Pass back warnings when loading rules

Add the notion of warnings when loading rules, which are printed if
verbose is true:

 - load_rules now returns a tuple (success, required engine version,
   error array, warnings array) instead of (true, required engine
   version) or (false, error string)
 - build_error/build_error_with_context now returns an array instead of
   string value.
 - warnings are combined across calls to load_rules_doc
 - Current warnings include:
   - a rule that contains an unknown filter
   - a macro not referred to by any rule
   - a list not referred to by any rule/macro/list

Any errors/warnings are concatenated into the exception if success was
false. Any errors/warnings will be printed if verbose is true.

Signed-off-by: Mark Stemm <mark.stemm@gmail.com>

userspace/engine/lua/rule_loader.lua

@@ -256,16 +256,18 @@ end
 function build_error(rules_lines, row, num_lines, err)
    local ret = err.."\n---\n"..get_lines(rules_lines, row, num_lines).."---"
 
-   return ret
+   return {ret}
 end
 
 function build_error_with_context(ctx, err)
    local ret = err.."\n---\n"..ctx.."---"
-   return ret
+   return {ret}
 end
 
 function load_rules_doc(rules_mgr, doc, load_state)
 
+   local warnings = {}
+
    -- Iterate over yaml list. In this pass, all we're doing is
    -- populating the set of rules, macros, and lists. We're not
    -- expanding/compiling anything yet. All that will happen in a
@@ -279,7 +281,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
 					load_state.indices[load_state.cur_item_idx])
 
       if (not (type(v) == "table")) then
-	 return false, build_error_with_context(context, "Unexpected element of type " ..type(v)..". Each element should be a yaml associative array.")
+	 return false, build_error_with_context(context, "Unexpected element of type " ..type(v)..". Each element should be a yaml associative array."), warnings
       end
 
       v['context'] = context
@@ -291,13 +293,13 @@ function load_rules_doc(rules_mgr, doc, load_state)
 	 end
 
 	 if falco_rules.engine_version(rules_mgr) < v['required_engine_version'] then
-	    return false, build_error_with_context(v['context'], "Rules require engine version "..v['required_engine_version']..", but engine version is "..falco_rules.engine_version(rules_mgr))
+	    return false, build_error_with_context(v['context'], "Rules require engine version "..v['required_engine_version']..", but engine version is "..falco_rules.engine_version(rules_mgr)), warnings
 	 end
 
       elseif (v['macro']) then
 
 	 if (v['macro'] == nil or type(v['macro']) == "table") then
-	    return false, build_error_with_context(v['context'], "Macro name is empty")
+	    return false, build_error_with_context(v['context'], "Macro name is empty"), warnings
 	 end
 
 	 if v['source'] == nil then
@@ -310,7 +312,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
 
 	 for j, field in ipairs({'condition'}) do
 	    if (v[field] == nil) then
-	       return false, build_error_with_context(v['context'], "Macro must have property "..field)
+	       return false, build_error_with_context(v['context'], "Macro must have property "..field), warnings
 	    end
 	 end
 
@@ -323,7 +325,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
 
 	 if append then
 	    if state.macros_by_name[v['macro']] == nil then
-	       return false, build_error_with_context(v['context'], "Macro " ..v['macro'].. " has 'append' key but no macro by that name already exists")
+	       return false, build_error_with_context(v['context'], "Macro " ..v['macro'].. " has 'append' key but no macro by that name already exists"), warnings
 	    end
 
 	    state.macros_by_name[v['macro']]['condition'] = state.macros_by_name[v['macro']]['condition'] .. " " .. v['condition']
@@ -338,7 +340,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
       elseif (v['list']) then
 
 	 if (v['list'] == nil or type(v['list']) == "table") then
-	    return false, build_error_with_context(v['context'], "List name is empty")
+	    return false, build_error_with_context(v['context'], "List name is empty"), warnings
 	 end
 
 	 if state.lists_by_name[v['list']] == nil then
@@ -347,7 +349,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
 
 	 for j, field in ipairs({'items'}) do
 	    if (v[field] == nil) then
-	       return false, build_error_with_context(v['context'], "List must have property "..field)
+	       return false, build_error_with_context(v['context'], "List must have property "..field), warnings
 	    end
 	 end
 
@@ -360,7 +362,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
 
 	 if append then
 	    if state.lists_by_name[v['list']] == nil then
-	       return false, build_error_with_context(v['context'], "List " ..v['list'].. " has 'append' key but no list by that name already exists")
+	       return false, build_error_with_context(v['context'], "List " ..v['list'].. " has 'append' key but no list by that name already exists"), warnings
 	    end
 
 	    for j, elem in ipairs(v['items']) do
@@ -373,7 +375,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
       elseif (v['rule']) then
 
 	 if (v['rule'] == nil or type(v['rule']) == "table") then
-	    return false, build_error_with_context(v['context'], "Rule name is empty")
+	    return false, build_error_with_context(v['context'], "Rule name is empty"), warnings
 	 end
 
 	 -- By default, if a rule's condition refers to an unknown
@@ -398,13 +400,13 @@ function load_rules_doc(rules_mgr, doc, load_state)
 	    -- For append rules, all you need is the condition
 	    for j, field in ipairs({'condition'}) do
 	       if (v[field] == nil) then
-		  return false, build_error_with_context(v['context'], "Rule must have property "..field)
+		  return false, build_error_with_context(v['context'], "Rule must have property "..field), warnings
 	       end
 	    end
 
 	    if state.rules_by_name[v['rule']] == nil then
 	       if state.skipped_rules_by_name[v['rule']] == nil then
-		  return false, build_error_with_context(v['context'], "Rule " ..v['rule'].. " has 'append' key but no rule by that name already exists")
+		  return false, build_error_with_context(v['context'], "Rule " ..v['rule'].. " has 'append' key but no rule by that name already exists"), warnings
 	       end
 	    else
 	       state.rules_by_name[v['rule']]['condition'] = state.rules_by_name[v['rule']]['condition'] .. " " .. v['condition']
@@ -417,7 +419,7 @@ function load_rules_doc(rules_mgr, doc, load_state)
 
 	    for j, field in ipairs({'condition', 'output', 'desc', 'priority'}) do
 	       if (v[field] == nil) then
-		  return false, build_error_with_context(v['context'], "Rule must have property "..field)
+		  return false, build_error_with_context(v['context'], "Rule must have property "..field), warnings
 	       end
 	    end
 
@@ -449,13 +451,18 @@ function load_rules_doc(rules_mgr, doc, load_state)
 	 -- Remove the context from the table, so the table is exactly what was parsed
 	 local context = v['context']
 	 v['context'] = nil
-	 return false, build_error_with_context(context, "Unknown rule object: "..table.tostring(v))
+	 return false, build_error_with_context(context, "Unknown rule object: "..table.tostring(v)), warnings
       end
    end
 
-   return true, ""
+   return true, {}, {}
 end
 
+-- Returns:
+-- - Load Result: bool
+-- - required engine version. will be nil when load result is false
+-- - List of Errors
+-- - List of Warnings
 function load_rules(sinsp_lua_parser,
 		    json_lua_parser,
 		    rules_content,
@@ -466,6 +473,8 @@ function load_rules(sinsp_lua_parser,
 		    replace_container_info,
 		    min_priority)
 
+   local warnings = {}
+
    local load_state = {lines={}, indices={}, cur_item_idx=0, min_priority=min_priority, required_engine_version=0}
 
    load_state.lines, load_state.indices = split_lines(rules_content)
@@ -487,36 +496,42 @@ function load_rules(sinsp_lua_parser,
       row = tonumber(row)
       col = tonumber(col)
 
-      return false, build_error(load_state.lines, row, 3, docs)
+      return false, nil, build_error(load_state.lines, row, 3, docs), warnings
    end
 
    if docs == nil then
       -- An empty rules file is acceptable
-      return true, load_state.required_engine_version
+      return true, load_state.required_engine_version, {}, warnings
    end
 
    if type(docs) ~= "table" then
-      return false, build_error(load_state.lines, 1, 1, "Rules content is not yaml")
+      return false, nil, build_error(load_state.lines, 1, 1, "Rules content is not yaml"), warnings
    end
 
    for docidx, doc in ipairs(docs) do
 
       if type(doc) ~= "table" then
-	 return false, build_error(load_state.lines, 1, 1, "Rules content is not yaml")
+	 return false, nil, build_error(load_state.lines, 1, 1, "Rules content is not yaml"), warnings
       end
 
       -- Look for non-numeric indices--implies that document is not array
       -- of objects.
       for key, val in pairs(doc) do
 	 if type(key) ~= "number" then
-	    return false, build_error(load_state.lines, 1, 1, "Rules content is not yaml array of objects")
+	    return false, nil, build_error(load_state.lines, 1, 1, "Rules content is not yaml array of objects"), warnings
 	 end
       end
 
-      res, errstr = load_rules_doc(rules_mgr, doc, load_state)
+      res, errors, doc_warnings = load_rules_doc(rules_mgr, doc, load_state)
+
+      if (doc_warnings ~= nil) then
+	 for idx, warning in pairs(doc_warnings) do
+	    table.insert(warnings, warning)
+	 end
+      end
 
       if not res then
-	 return res, errstr
+	 return res, nil, errors, warnings
       end
    end
 
@@ -556,7 +571,7 @@ function load_rules(sinsp_lua_parser,
       local status, ast = compiler.compile_macro(v['condition'], state.macros, state.lists)
 
       if status == false then
-	 return false, build_error_with_context(v['context'], ast)
+	 return false, nil, build_error_with_context(v['context'], ast), warnings
       end
 
       if v['source'] == "syscall" then
@@ -581,7 +596,7 @@ function load_rules(sinsp_lua_parser,
 								  state.macros, state.lists)
 
       if status == false then
-	 return false, build_error_with_context(v['context'], filter_ast)
+	 return false, nil, build_error_with_context(v['context'], filter_ast), warnings
       end
 
       local evtttypes = {}
@@ -631,12 +646,10 @@ function load_rules(sinsp_lua_parser,
 	 end
 
 	 if not found then
-	    if v['skip-if-unknown-filter'] then
+	    msg = "rule \""..v['rule'].."\" contains unknown filter "..filter
-	       if verbose then
+	    warnings[#warnings + 1] = msg
-		  print("Skipping rule \""..v['rule'].."\" that contains unknown filter "..filter)
+
-	       end
+	    if not v['skip-if-unknown-filter'] then
-	       goto next_rule
-	    else
 	       error("Rule \""..v['rule'].."\" contains unknown filter "..filter)
 	    end
 	 end
@@ -719,30 +732,30 @@ function load_rules(sinsp_lua_parser,
 	 formatter = formats.formatter(v['source'], v['output'])
 	 formats.free_formatter(v['source'], formatter)
       else
-	 return false, build_error_with_context(v['context'], "Unexpected type in load_rule: "..filter_ast.type)
+	 return false, nil, build_error_with_context(v['context'], "Unexpected type in load_rule: "..filter_ast.type), warnings
       end
 
       ::next_rule::
    end
 
-   if verbose then
+   -- Print info on any dangling lists or macros that were not used anywhere
-      -- Print info on any dangling lists or macros that were not used anywhere
+   for name, macro in pairs(state.macros) do
-      for name, macro in pairs(state.macros) do
+      if macro.used == false then
-	 if macro.used == false then
+	 msg = "macro "..name.." not refered to by any rule/macro"
-	    print("Warning: macro "..name.." not refered to by any rule/macro")
+	 warnings[#warnings + 1] = msg
-	 end
       end
+   end
 
-      for name, list in pairs(state.lists) do
+   for name, list in pairs(state.lists) do
-	 if list.used == false then
+      if list.used == false then
-	    print("Warning: list "..name.." not refered to by any rule/macro/list")
+	 msg = "list "..name.." not refered to by any rule/macro/list"
-	 end
+	 warnings[#warnings + 1] = msg
       end
    end
 
    io.flush()
 
-   return true, load_state.required_engine_version
+   return true, load_state.required_engine_version, {}, warnings
 end
 
 local rule_fmt = "%-50s %s"

userspace/engine/rules.cpp

@@ -14,8 +14,9 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+#include <sstream>
+
 #include "rules.h"
-#include "logger.h"
 
 extern "C" {
 #include "lua.h"
@@ -218,6 +219,31 @@ int falco_rules::engine_version(lua_State *ls)
 	return 1;
 }
 
+static std::list<std::string> get_lua_table_values(lua_State *ls, int idx)
+{
+	std::list<std::string> ret;
+
+	if (lua_isnil(ls, idx)) {
+		return ret;
+	}
+
+	lua_pushnil(ls);  /* first key */
+	while (lua_next(ls, idx-1) != 0) {
+                // key is at index -2, value is at index
+                // -1. We want the values.
+		if (! lua_isstring(ls, -1)) {
+			std::string err = "Non-string value in table of strings";
+			throw falco_exception(err);
+		}
+		ret.push_back(string(lua_tostring(ls, -1)));
+
+		// Remove value, keep key for next iteration
+		lua_pop(ls, 1);
+	}
+
+	return ret;
+}
+
 void falco_rules::load_rules(const string &rules_content,
 			     bool verbose, bool all_events,
 			     string &extra, bool replace_container_info,
@@ -423,7 +449,7 @@ void falco_rules::load_rules(const string &rules_content,
 		lua_pushstring(m_ls, extra.c_str());
 		lua_pushboolean(m_ls, (replace_container_info ? 1 : 0));
 		lua_pushnumber(m_ls, min_priority);
-		if(lua_pcall(m_ls, 9, 2, 0) != 0)
+		if(lua_pcall(m_ls, 9, 4, 0) != 0)
 		{
 			const char* lerr = lua_tostring(m_ls, -1);
 
@@ -432,20 +458,49 @@ void falco_rules::load_rules(const string &rules_content,
 			throw falco_exception(err);
 		}
 
-		// Either returns (true, required_engine_version), or (false, error string)
+		// Returns:
-		bool successful = lua_toboolean(m_ls, -2);
+		// Load result: bool
+		// required engine version: will be nil when load result is false
+		// array of errors
+		// array of warnings
+		bool successful = lua_toboolean(m_ls, -4);
+		required_engine_version = lua_tonumber(m_ls, -3);
+		std::list<std::string> errors = get_lua_table_values(m_ls, -2);
+		std::list<std::string> warnings = get_lua_table_values(m_ls, -1);
 
-		if(successful)
+		// Concatenate errors/warnings
+		std::ostringstream os;
+		if (errors.size() > 0)
 		{
-			required_engine_version = lua_tonumber(m_ls, -1);
+			os << errors.size() << " errors:" << std::endl;
-		}
+			for(auto err : errors)
-		else
+			{
-		{
+				os << err << std::endl;
-			std::string err = lua_tostring(m_ls, -1);
+			}
-			throw falco_exception(err);
 		}
 
-		lua_pop(m_ls, 2);
+		if (warnings.size() > 0)
+		{
+			os << warnings.size() << " warnings:" << std::endl;
+			for(auto warn : warnings)
+			{
+				os << warn << std::endl;
+			}
+		}
+
+		if(!successful)
+		{
+			throw falco_exception(os.str());
+		}
+
+		if (verbose && os.str() != "") {
+			// We don't really have a logging callback
+			// from the falco engine, but this would be a
+			// good place to use it.
+			fprintf(stderr, "When reading rules content: %s", os.str().c_str());
+		}
+
+		lua_pop(m_ls, 4);
 
 	} else {
 		throw falco_exception("No function " + m_lua_load_rules + " found in lua rule module");

userspace/falco/falco.cpp

@@ -813,7 +813,7 @@ int falco_init(int argc, char **argv)
 				}
 				catch(falco_exception &e)
 				{
-					printf("%s%s\n", prefix.c_str(), e.what());
+					printf("%s%s", prefix.c_str(), e.what());
 					throw;
 				}
 				printf("%sOk\n", prefix.c_str());
@@ -865,7 +865,15 @@ int falco_init(int argc, char **argv)
 			falco_logger::log(LOG_INFO, "Loading rules from file " + filename + ":\n");
 			uint64_t required_engine_version;
 
-			engine->load_rules_file(filename, verbose, all_events, required_engine_version);
+			try {
+				engine->load_rules_file(filename, verbose, all_events, required_engine_version);
+			}
+			catch(falco_exception &e)
+			{
+				std::string prefix = "Could not load rules file " + filename + ": ";
+
+				throw falco_exception(prefix + e.what());
+			}
 			required_engine_versions[filename] = required_engine_version;
 		}
 
@@ -1177,8 +1185,8 @@ int falco_init(int argc, char **argv)
 						falco_logger::log(LOG_ERR, "Unable to load the driver.\n");
 					}
 					open_f(inspector);
-				} 
+				}
-				else 
+				else
 				{
 					rethrow_exception(current_exception());
 				}
@@ -1287,7 +1295,7 @@ int falco_init(int argc, char **argv)
 
 		if(!trace_filename.empty() && !trace_is_scap)
 		{
-#ifndef MINIMAL_BUILD			
+#ifndef MINIMAL_BUILD
 			read_k8s_audit_trace_file(engine,
 						  outputs,
 						  trace_filename);