Conditional rules (#364)

* Add ability to skip rules for unknown filters

Add the ability to skip a rule if its condition refers to a filtercheck
that doesn't exist. This allows defining a rules file that contains new
conditions that can still has limited backward compatibility with older
falco versions.

When compiling a filter, return a list of filtercheck names that are
present in the ast (which also includes filterchecks from any
macros). This set of filtercheck names is matched against the set of
filterchecks known to sinsp, expressed as lua patterns, and in the
global table defined_filters. If no match is found, the rule loader
throws an error.

The pattern changes slightly depending on whether the filter has
arguments or not. Two filters (proc.apid/proc.aname) can work with or
without arguments, so both styles of patterns are used.

If the rule has an attribute "skip-if-unknown-filter", the rule will be
skipped instead.

* Unit tests for skipping unknown filter

New unit test for skipping unknown filter. Test cases:

 - A rule that refers to an unknown filter results in an error.
 - A rule that refers to an unknown filter, but has
   "skip-if-unknown-filter: true", can be read, but doesn't match any events.
 - A rule that refers to an unknown filter, but has
   "skip-if-unknown-filter: false", returns an error.

Also test the case of a filtercheck like evt.arg.xxx working properly
with the embedded patterns as well as proc.aname/apid which work both ways.

test/falco_tests.yaml

@@ -713,3 +713,30 @@ trace_files: !mux
       - open_dev_null: 1
         dev_null: 0
     trace_file: trace_files/cat_write.scap
+
+  skip_unknown_noevt:
+    detect: False
+    stdout_contains: Skipping rule "Contains Unknown Event And Skipping" that contains unknown filter proc.nobody
+    rules_file:
+      - rules/skip_unknown_evt.yaml
+    trace_file: trace_files/cat_write.scap
+
+  skip_unknown_prefix:
+    detect: False
+    rules_file:
+      - rules/skip_unknown_prefix.yaml
+    trace_file: trace_files/cat_write.scap
+
+  skip_unknown_error:
+    exit_status: 1
+    stderr_contains: Rule "Contains Unknown Event And Not Skipping" contains unknown filter proc.nobody. Exiting.
+    rules_file:
+      - rules/skip_unknown_error.yaml
+    trace_file: trace_files/cat_write.scap
+
+  skip_unknown_unspec_error:
+    exit_status: 1
+    stderr_contains: Rule "Contains Unknown Event And Unspecified" contains unknown filter proc.nobody. Exiting.
+    rules_file:
+      - rules/skip_unknown_unspec.yaml
+    trace_file: trace_files/cat_write.scap

test/rules/skip_unknown_error.yaml

@@ -0,0 +1,6 @@
+- rule: Contains Unknown Event And Not Skipping
+  desc: Contains an unknown event
+  condition: proc.nobody=cat
+  output: Never
+  skip-if-unknown-filter: false
+  priority: INFO

test/rules/skip_unknown_evt.yaml

@@ -0,0 +1,6 @@
+- rule: Contains Unknown Event And Skipping
+  desc: Contains an unknown event
+  condition: evt.type=open and proc.nobody=cat
+  output: Never
+  skip-if-unknown-filter: true
+  priority: INFO

test/rules/skip_unknown_prefix.yaml

@@ -0,0 +1,8 @@
+- rule: Contains Prefix of Filter
+  desc: Testing matching filter prefixes
+  condition: >
+    evt.type=open and evt.arg.path="foo" and evt.arg[0]="foo"
+    and proc.aname="ls" and proc.aname[1]="ls"
+    and proc.apid=10 and proc.apid[1]=10
+  output: Never
+  priority: INFO

test/rules/skip_unknown_unspec.yaml

@@ -0,0 +1,5 @@
+- rule: Contains Unknown Event And Unspecified
+  desc: Contains an unknown event
+  condition: proc.nobody=cat
+  output: Never
+  priority: INFO

userspace/engine/lua/compiler.lua

@@ -322,6 +322,21 @@ function get_evttypes_syscalls(name, ast, source, warn_evttypes)
    return evttypes, syscallnums
 end
 
+function get_filters(ast)
+
+   local filters = {}
+
+   function cb(node)
+      if node.type == "FieldName" then
+	 filters[node.value] = 1
+      end
+   end
+
+   parser.traverse_ast(ast.filter.value, {FieldName=1} , cb)
+
+   return filters
+end
+
 function compiler.expand_lists_in(source, list_defs)
 
    for name, def in pairs(list_defs) do
@@ -408,7 +423,9 @@ function compiler.compile_filter(name, source, macro_defs, list_defs, warn_evtty
 
    evttypes, syscallnums = get_evttypes_syscalls(name, ast, source, warn_evttypes)
 
-   return ast, evttypes, syscallnums
+   filters = get_filters(ast)
+
+   return ast, evttypes, syscallnums, filters
 end
 
 

userspace/engine/lua/rule_loader.lua

@@ -275,6 +275,12 @@ function load_rules(rules_content, rules_mgr, verbose, all_events, extra, replac
 	    error ("Missing name in rule")
 	 end
 
+	 -- By default, if a rule's condition refers to an unknown
+	 -- filter like evt.type, etc the loader throws an error.
+	 if v['skip-if-unknown-filter'] == nil then
+	    v['skip-if-unknown-filter'] = false
+	 end
+
 	 -- Possibly append to the condition field of an existing rule
 	 append = false
 
@@ -378,9 +384,34 @@ function load_rules(rules_content, rules_mgr, verbose, all_events, extra, replac
 	 warn_evttypes = v['warn_evttypes']
       end
 
-      local filter_ast, evttypes, syscallnums = compiler.compile_filter(v['rule'], v['condition'],
-									state.macros, state.lists,
-									warn_evttypes)
+      local filter_ast, evttypes, syscallnums, filters = compiler.compile_filter(v['rule'], v['condition'],
+										 state.macros, state.lists,
+										 warn_evttypes)
+
+      -- If a filter in the rule doesn't exist, either skip the rule
+      -- or raise an error, depending on the value of
+      -- skip-if-unknown-filter.
+      for filter, _ in pairs(filters) do
+	 found = false
+
+	 for pat, _ in pairs(defined_filters) do
+	    if string.match(filter, pat) ~= nil then
+	       found = true
+	       break
+	    end
+	 end
+
+	 if not found then
+	    if v['skip-if-unknown-filter'] then
+	       if verbose then
+		  print("Skipping rule \""..v['rule'].."\" that contains unknown filter "..filter)
+	       end
+	       goto next_rule
+	    else
+	       error("Rule \""..v['rule'].."\" contains unknown filter "..filter)
+	    end
+	 end
+      end
 
       if (filter_ast.type == "Rule") then
 	 state.n_rules = state.n_rules + 1
@@ -452,6 +483,8 @@ function load_rules(rules_content, rules_mgr, verbose, all_events, extra, replac
       else
 	 error ("Unexpected type in load_rule: "..filter_ast.type)
       end
+
+      ::next_rule::
    end
 
    if verbose then

userspace/engine/rules.cpp

@@ -258,6 +258,63 @@ void falco_rules::load_rules(const string &rules_content,
 
 		lua_setglobal(m_ls, m_lua_ignored_syscalls.c_str());
 
+		// Create a table containing all filtercheck names.
+		lua_newtable(m_ls);
+
+		vector<const filter_check_info*> fc_plugins;
+		sinsp::get_filtercheck_fields_info(&fc_plugins);
+
+		for(uint32_t j = 0; j < fc_plugins.size(); j++)
+		{
+			const filter_check_info* fci = fc_plugins[j];
+
+			if(fci->m_flags & filter_check_info::FL_HIDDEN)
+			{
+				continue;
+			}
+
+			for(int32_t k = 0; k < fci->m_nfields; k++)
+			{
+				const filtercheck_field_info* fld = &fci->m_fields[k];
+
+				if(fld->m_flags & EPF_TABLE_ONLY ||
+				   fld->m_flags & EPF_PRINT_ONLY)
+				{
+					continue;
+				}
+
+				// Some filters can work with or without an argument
+				std::set<string> flexible_filters = {
+					"^proc.aname",
+					"^proc.apid"
+				};
+
+				std::list<string> fields;
+				std::string field_base = string("^") + fld->m_name;
+
+				if(fld->m_flags & EPF_REQUIRES_ARGUMENT ||
+				   flexible_filters.find(field_base) != flexible_filters.end())
+				{
+					fields.push_back(field_base + "[%[%.]");
+				}
+
+				if(!(fld->m_flags & EPF_REQUIRES_ARGUMENT) ||
+				   flexible_filters.find(field_base) != flexible_filters.end())
+				{
+					fields.push_back(field_base + "$");
+				}
+
+				for(auto &field : fields)
+				{
+					lua_pushstring(m_ls, field.c_str());
+					lua_pushnumber(m_ls, 1);
+					lua_settable(m_ls, -3);
+				}
+			}
+		}
+
+		lua_setglobal(m_ls, m_lua_defined_filters.c_str());
+
 		lua_pushstring(m_ls, rules_content.c_str());
 		lua_pushlightuserdata(m_ls, this);
 		lua_pushboolean(m_ls, (verbose ? 1 : 0));

userspace/engine/rules.h

@@ -56,6 +56,7 @@ class falco_rules
 	string m_lua_load_rules = "load_rules";
 	string m_lua_ignored_syscalls = "ignored_syscalls";
 	string m_lua_ignored_events = "ignored_events";
+	string m_lua_defined_filters = "defined_filters";
 	string m_lua_events = "events";
 	string m_lua_syscalls = "syscalls";
 	string m_lua_describe_rule = "describe_rule";