-- RestrictedExecution.lua (Part of the new Secure Headers implementation)
--
-- This contains the necessary (and sufficient) code to support
-- 'restricted execution' for code provided via attributes, intended
-- for use in the secure header implementations. It provides a fairly
-- isolated execution environment and is constructed to maintain local
-- control over the important elements of the execution environment.
--
-- Daniel Stephens (iriel@vigilance-committee.org)
-- Nevin Flanagan (alestane@comcast.net)
---------------------------------------------------------------------------

-- Localizes for functions that are frequently called or need to be
-- assuredly un-replaceable or unhookable.
local type = type;
local error = error;
local scrub = scrub;
local issecure = issecure;
local rawset = rawset;
local setfenv = setfenv;
local loadstring = loadstring;
local setmetatable = setmetatable;
local getmetatable = getmetatable;
local pcall = pcall;
local tostring = tostring;
local next = next;
local unpack = unpack;
local newproxy = newproxy;
local select = select;
local wipe = wipe;
local tonumber = tonumber;

local t_insert = table.insert;
local t_maxn = table.maxn;
local t_concat = table.concat;
local t_sort = table.sort;
local t_remove = table.remove;

local s_gsub = string.gsub;

local IsFrameHandle = IsFrameHandle;

---------------------------------------------------------------------------
-- RESTRICTED CLOSURES

local function SelfScrub(self)
	if self ~= nil and IsFrameHandle(self) then
		return self;
	end
	return nil;
end

-- closure, err = BuildRestrictedClosure(body, env, signature)
--
-- body      -- The function body (defaults to "")
-- env       -- The execution environment (defaults to {})
-- signature -- The function signature (defaults to "self,...")
--
-- Returns the constructed closure, or nil and an error
local function BuildRestrictedClosure(body, env, signature)
	body = tostring(body) or "";
	signature = tostring(signature) or "self,...";
	if type(env) ~= "table" then
		env = {};
	end

	if body:match("function") then
		-- NOTE - This is overzealous but it keeps it simple
		return nil, "The function keyword is not permitted";
	end

	if body:match("[{}]") then
		-- NOTE - This is overzealous but it keeps it simple
		return nil, "Direct table creation is not permitted";
	end

	if signature:match("function") then
		-- NOTE - This is overzealous but it keeps it simple
		return nil, "The function keyword is not permitted";
	end

	if not signature:match("^[a-zA-Z_0-9, ]*[.]*$") then
		-- NOTE - This is overzealous but it keeps it simple
		return nil, "Signature contains invalid characters (" .. signature .. ")";
	end

	-- Include a \n before end to stop shenanigans with comments
	local def, err =
		loadstring("return function (" .. signature .. ") " .. body .. "\nend", body);
	if def == nil then
		return nil, err;
	end

	-- Use a completely empty environment here to be absolutely
	-- sure to avoid tampering during function definition.
	setfenv(def, {});
	def = def();
	-- Double check that the definition did infact return a function
	if type(def) ~= "function" then
		return nil, "Invalid body";
	end
	-- Set the desired environment on the resulting closure.
	setfenv(def, env);

	-- And then return a 'safe' wrapped invocation for the closure.
	return function(self, ...) return def(SelfScrub(self), scrub(...)) end;
end

-- factory = CreateClosureFactory(env, signature)
--
-- env -- The desired environment table for the closures
-- signature -- The function signature for the closures
--
-- Returns a 'factory table' which is keyed by function bodies, and
-- has restricted closure values. It's weak-keyed and uses an __index
-- metamethod that automatically creates necessary closures on demand.
local function CreateClosureFactory(env, signature)
	local function metaIndex(t, k)
		if type(k) == "string" then
			local closure, err = BuildRestrictedClosure(k, env, signature);
			if not closure then
				-- Put the error into a closure to avoid constantly
				-- re-parsing it
				err = tostring(err or "Closure creation failed");
				closure = function() error(err) end;
			end
			if issecure() then
				t[k] = closure;
			end
			return closure;
		end
		error("Invalid closure body type (" .. type(k) .. ")");
		return nil;
	end

	local ret = {};
	setmetatable(ret, { __index = metaIndex, __mode = "k" });
	return ret;
end

---------------------------------------------------------------------------
-- RESTRICTED TABLES
--
-- Provides fully proxied tables with restrictions on their contents.
--

-- Mapping table from restricted table 'proxy' to the 'real' storage
local LOCAL_Restricted_Tables = {};
setmetatable(LOCAL_Restricted_Tables, { __mode="k" });

-- Metatable common to all restricted tables (This introduces one
-- level of indirection in every use as a means to share the same
-- metatable between all instances)
local LOCAL_Restricted_Table_Meta = {
	__index = function(t, k)
				  local real = LOCAL_Restricted_Tables[t];
				  return real[k];
			  end,

	__newindex = function(t, k, v)
					 local real = LOCAL_Restricted_Tables[t];
					 if not issecure() then
						 error("Cannot insecurely modify restricted table");
						 return;
					 end
					 local tv = type(v);
					 if ((tv ~= "string") and (tv ~= "number")
						 and (tv ~= "boolean") and (tv ~= "nil")
							 and ((tv ~= "userdata")
								  or not (LOCAL_Restricted_Tables[v]
										  or  IsFrameHandle(v)))) then
						 error("Invalid value type '" .. tv .. "'");
						 return;
					 end
					 local tk = type(k);
					 if ((tk ~= "string") and (tk ~= "number")
						 and (tk ~= "boolean")
							 and ((tk ~= "userdata")
								  or not (IsFrameHandle(k)))) then
						 error("Invalid key type '" .. tk .. "'");
						 return;
					 end
					 real[k] = v;
				 end,

	__len = function(t)
				local real = LOCAL_Restricted_Tables[t];
				return #real;
			end,

	__metatable = false, -- False means read-write proxy
}

local LOCAL_Readonly_Restricted_Tables = {};
setmetatable(LOCAL_Readonly_Restricted_Tables, { __mode="k" });

local function CheckReadonlyValue(ret)
	if type(ret) == "userdata" then
		if LOCAL_Restricted_Tables[ret] then
			if getmetatable(ret) then
				return ret;
			end
			return LOCAL_Readonly_Restricted_Tables[ret];
		end
	end
	return ret;
end

-- Metatable common to all read-only restricted tables (This also introduces
-- indirection so that a single metatable is viable)
local LOCAL_Readonly_Restricted_Table_Meta = {
	__index = function(t, k)
				  local real = LOCAL_Restricted_Tables[t];
				  return CheckReadonlyValue(real[k]);
			  end,

	__newindex = function(t, k, v)
					 error("Table is read-only");
				 end,

	__len = function(t)
				local real = LOCAL_Restricted_Tables[t];
				return #real;
			end,

	__metatable = true, -- True means read-only proxy
}


local LOCAL_Restricted_Prototype = newproxy(true);
local LOCAL_Readonly_Restricted_Prototype = newproxy(true);
do
	local meta = getmetatable(LOCAL_Restricted_Prototype);
	for k, v in pairs(LOCAL_Restricted_Table_Meta) do
		meta[k] = v;
	end

	meta = getmetatable(LOCAL_Readonly_Restricted_Prototype);
	for k, v in pairs(LOCAL_Readonly_Restricted_Table_Meta) do
		meta[k] = v;
	end
end

local function RestrictedTable_Readonly_index(t, k)
	local real = LOCAL_Restricted_Tables[k];
	if not real then return; end
	if not issecure() then
		error("Cannot create restricted tables from insecure code");
		return;
	end

	local ret = newproxy(LOCAL_Readonly_Restricted_Prototype);
	LOCAL_Restricted_Tables[ret] = real;
	t[k] = ret;
	return ret;
end

getmetatable(LOCAL_Readonly_Restricted_Tables).__index
	= RestrictedTable_Readonly_index;

-- table = RestrictedTable_create(...)
--
-- Create a new, restricted table, populating it from ... if
-- necessary, similar to the way the normal table constructor
-- works.
local function RestrictedTable_create(...)
	local ret = newproxy(LOCAL_Restricted_Prototype);
	if not issecure() then
		error("Cannot create restricted tables from insecure code");
		return;
	end
	LOCAL_Restricted_Tables[ret] = {};

	-- Use this loop to ensure that the contents of the new
	-- table are all allowed
	for i = 1, select('#', ...) do
		ret[i] = select(i, ...);
	end

	return ret;
end

-- table = GetReadonlyRestrictedTable(otherTable)
--
-- Given a restricted table, return a read-only proxy to the same
-- table (which will be itself, if it's already read-only)
function GetReadonlyRestrictedTable(ref)
	if LOCAL_Restricted_Tables[ref] then
		if getmetatable(ref) then
			return ref;
		end
		return LOCAL_Readonly_Restricted_Tables[ref];
	end
	error("Invalid restricted table");
end

-- key = RestrictedTable_next(table [,key])
--
-- An implementation of the next function,  which is
-- aware of restricted and normal tables and behaves consistently
-- for both.
local function RestrictedTable_next(T, k)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		if getmetatable(T) then
			local idx, val = next(PT, k);
			if val ~= nil then
				return idx, CheckReadonlyValue(val);
			else
				return idx, val;
			end
		else
			return next(PT, k);
		end
	end
	return next(T, k);
end

-- iterfunc, table, key = RestrictedTable_pairs(table)
--
-- An implementation of the pairs function, which is aware
-- of and iterates over both restricted and normal tables.
local function RestrictedTable_pairs(T)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		-- v
		return RestrictedTable_next, T, nil;
	end
	return pairs(T);
end

-- key, value = RestrictedTable_ipairsaux(table, prevkey)
--
-- Iterator function for internal use by restricted table ipairs
local function RestrictedTable_ipairsaux(T, i)
	i = i + 1;
	local v = T[i];
	if (v) then
		return i, v;
	end
end

-- iterfunc, table, key = RestrictedTable_ipairs(table)
--
-- An implementation of the ipairs function, which is aware
-- of and iterates over both restricted and normal tables.
local function RestrictedTable_ipairs(T)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		return RestrictedTable_ipairsaux, T, 0;
	end
	return ipairs(T);
end

-- Recursive helper to ensure all values from a list are properly converted
-- to read-only proxies
local RestrictedTable_unpack_ro;
function RestrictedTable_unpack_ro(...)
	local n = select('#', ...);
	if n == 0 then
		return;
	end
	return CheckReadonlyValue(...), RestrictedTable_unpack_ro(select(2, ...));
end

-- ... = RestrictedTable_unpack(table)
--
-- An implementation of unpack which unpacks both restricted
-- and normal tables.
local function RestrictedTable_unpack(T)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		if getmetatable(T) then
			return RestrictedTable_unpack_ro(unpack(PT));
		end
		return unpack(PT)
	end
	return unpack(T);
end

-- table = RestrictedTable_wipe(table)
--
-- A restricted aware implementation of wipe()
local function RestrictedTable_wipe(T)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		if getmetatable(T) then
			error("Cannot wipe a read-only table");
			return;
		end
		if not issecure() then
			error("Cannot insecurely modify restricted table");
			return;
		end
		wipe(PT);
		return T;
	end
	return wipe(T);
end

-- RestrictedTable_maxn(table)
--
-- A restricted aware implementation of table.maxn()
local function RestrictedTable_maxn(T)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		return t_maxn(PT);
	end
	return t_maxn(T);
end

-- RestrictedTable_concat(table)
--
-- A restricted aware implementation of table.concat()
local function RestrictedTable_concat(T)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		return t_concat(PT);
	end
	return t_concat(T);
end

-- RestrictedTable_sort(table, func)
--
-- A restricted aware implementation of table.sort()
local function RestrictedTable_sort(T, func)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		if getmetatable(T) then
			error("Cannot sort a read-only table");
			return;
		end
		if not issecure() then
			error("Cannot insecurely modify restricted table");
			return;
		end
		t_sort(PT, func);
		return;
	end
	t_sort(T, func);
end

-- RestrictedTable_insert(table [,pos], val)
--
-- A restricted aware implementation of table.insert()
local function RestrictedTable_insert(T, ...)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		if getmetatable(T) then
			error("Cannot insert into a read-only table");
			return;
		end
		local pos, val;
		if select('#', ...) == 1 then
			local val = ...;
			T[#PT + 1] = val;
			return;
		end
		pos, val = ...;
		pos = tonumber(pos);
		t_insert(PT, pos, nil);
		-- Leverage protections present on regular indexing
		T[pos] = val;
		return;
	end
	return t_insert(T, ...);
end

-- val = RestrictedTable_remove(table, pos)
--
-- A restricted aware implementation of table.remove()
local function RestrictedTable_remove(T, pos)
	local PT = LOCAL_Restricted_Tables[T];
	if (PT) then
		if getmetatable(T) then
			error("Cannot remove from a read-only table");
			return;
		end
		if not issecure() then
			error("Cannot insecurely modify restricted table");
			return;
		end
		return CheckReadonlyValue(t_remove(PT, pos));
	end
	return t_remove(T, pos);
end

-- objtype = RestrictedTable_type(obj)
--
-- A version of type which returns 'table' for restricted tables
local function RestrictedTable_type(obj)
	local t = type(obj);
	if t == "userdata" then
		if LOCAL_Restricted_Tables[obj] then
			t = "table";
		end
	end
	return t;
end

-- ns = RestrictedTable_rtgsub(s, pattern, repl, n)
--
-- A version of string.gsub which is able to be passed restricted tables
local function RestrictedTable_rtgsub(s, pattern, repl, n)
	local t = type(repl);
	if t == "userdata" then
		local PT = LOCAL_Restricted_Tables[repl];
		return s_gsub(s, pattern, PT, n);
	end
	return s_gsub(s, pattern, repl, n);
end

-- Export these functions so that addon code can use them if desired
-- and so that the handlers can create these tables
rtable = {
	next = RestrictedTable_next;
	pairs = RestrictedTable_pairs;
	ipairs = RestrictedTable_ipairs;
	unpack = RestrictedTable_unpack;
	newtable = RestrictedTable_create;

	maxn = RestrictedTable_maxn;
	insert = RestrictedTable_insert;
	remove = RestrictedTable_remove;
	sort = RestrictedTable_sort;
	concat = RestrictedTable_concat;
	wipe = RestrictedTable_wipe;

	type = RestrictedTable_type;
	rtgsub = RestrictedTable_rtgsub;
};

-- Add this version of gsub to the string metatable
string.rtgsub = RestrictedTable_rtgsub;

local LOCAL_Table_Namespace = {
	table = {
		maxn = RestrictedTable_maxn;
		insert = RestrictedTable_insert;
		remove = RestrictedTable_remove;
		sort = RestrictedTable_sort;
		concat = RestrictedTable_concat;
		wipe = RestrictedTable_wipe;
		new = RestrictedTable_create;
	}
};

---------------------------------------------------------------------------
-- RESTRICTED ENVIRONMENT
--
-- environment, manageFunc = CreateRestrictedEnvironment(baseEnvironment)
--
-- baseEnvironment -- The base environment table (containing functions)
--
-- environment     -- The new restricted environment table
-- manageFunc      -- Management function to set/clear working and proxy
--                    environments.
--
-- The management function takes two parameters
--    manageFunc(set, workingTable, controlHandle)
--
-- set is a boolean;  If it's true then the working table is set to the
-- specified value (pushing any previous environment onto a stack). If
-- it's false then the working table is unset (and restored from stack).
--
-- The working table should be a restricted table, or an immutable object.
--
-- The controlHandle is an optional object which is made available to
-- the restricted code with the name 'control'.
--
-- The management function monitors calls to get and set in order to prevent
-- re-entrancy (i.e. calls to get and set must be balanced, and one cannot
-- switch working tables in the middle).
local function CreateRestrictedEnvironment(base)
	if type(base) ~= "table" then base = {}; end

	local working, control, depth = nil, nil, 0;
	local workingStack, controlStack = {}, {};

	local result = {};
	local meta_index;

	local function meta_index(t, k)
		local v = base[k] or working[k];
		if v == nil then
			if k == "control" then return control; end
		end
		return v;
	end;

	local function meta_newindex(t, k, v)
		working[k] = v;
	end

	local meta = {
		__index = meta_index,
		__newindex = meta_newindex,
		__metatable = false;
		__environment = false;
	}

	setmetatable(result, meta);

	local function manage(set, newWorking, newControl)
		if set then
			if depth == 0 then
				depth = 1;
			else
				workingStack[depth] = working;
				controlStack[depth] = control;

				depth = depth + 1;
			end
			working = newWorking;
			control = newControl;
		else
			if depth == 0 then
				error("Attempted to release unused environment");
				return;
			end

			if working ~= newWorking then
				error("Working environment mismatch at release");
				return;
			end

			if control ~= newControl then
				error("Control handle mismatch at release");
				return;
			end

			depth = depth - 1;
			if depth == 0 then
				working = nil;
				control = nil;
			else
				working = workingStack[depth];
				control = controlStack[depth];
				workingStack[depth] = nil;
				controlStack[depth] = nil;
			end
		end
	end

	return result, manage;
end

---------------------------------------------------------------------------
-- AVAILABLE FUNCTIONS
--
-- The current implementation has a single set of functions (aka a single
-- base environment), this initializes that environment by creating a master
-- base environment table, and then creating a restricted environment
-- around that. If the RESTRICTED_FUNCTIONS_SCOPE table exists when
-- this file is executed then its contents are added to the environment.
--
-- It is expected that any functions that are to be placed into this
-- environment have been carefully written to not return arbtirary tables,
-- functions, or userdata back to the caller.
--
-- One can use function(...) return scrub(realFunction(...)) end to wrap
-- those functions one doesn't trust.

-- A metatable to prevent tampering with the environment tables.
local LOCAL_No_Secure_Update_Meta = {
	__newindex = function() end;
	__metatable = false;
};

local LOCAL_Restricted_Global_Functions = {
	newtable = RestrictedTable_create;
	pairs = RestrictedTable_pairs;
	ipairs = RestrictedTable_ipairs;
	next = RestrictedTable_next;
	unpack = RestrictedTable_unpack;

	-- Table methods
	wipe = RestrictedTable_wipe;
	tinsert = RestrictedTable_insert;
	tremove = RestrictedTable_remove;

	-- Synthetic restricted-table-aware 'type'
	type = RestrictedTable_type;

	-- Restricted table aware gsub
	rtgsub = RestrictedTable_rtgsub;
};

-- A helper function to recursively copy and protect scopes
local PopulateGlobalFunctions
function PopulateGlobalFunctions(src, dest)
	for k, v in pairs(src) do
		if type(k) == "string" then
			local tv = type(v);
			if (tv == "function") or (tv == "number") or (tv == "string") or (tv == "boolean") then
				dest[k] = v;
			elseif tv == "table" then
				local subdest = {};
				PopulateGlobalFunctions(v, subdest);
				setmetatable(subdest, LOCAL_No_Secure_Update_Meta);
				local dproxy = newproxy(true);
				local dproxy_meta = getmetatable(dproxy);
				dproxy_meta.__index = subdest;
				dproxy_meta.__metatable = false;
				dest[k] = dproxy;
			end
		end
	end
end

-- Import any functions initialized by other/earier files
if RESTRICTED_FUNCTIONS_SCOPE then
	PopulateGlobalFunctions(RESTRICTED_FUNCTIONS_SCOPE,
							LOCAL_Restricted_Global_Functions);
	RESTRICTED_FUNCTIONS_SCOPE = nil;
end
PopulateGlobalFunctions(LOCAL_Table_Namespace,
						LOCAL_Restricted_Global_Functions);

-- Create the environment
local LOCAL_Function_Environment, LOCAL_Function_Environment_Manager =
	CreateRestrictedEnvironment(LOCAL_Restricted_Global_Functions);

-- Protect from injection via the string metatable index
-- Assume for now that 'string' is relatively clean
local strmeta = getmetatable("x");
local newmetaindex = {};
for k, v in pairs(string) do newmetaindex[k] = v; end
setmetatable(newmetaindex, {
				 __index = function(t,k)
							   if not issecure() then
								   return string[k];
							   end
						   end;
				 __metatable = false;
			 });
strmeta.__index = newmetaindex;
strmeta.__metatable = string;
strmeta = nil;
newmetaindex = nil;

---------------------------------------------------------------------------
-- CLOSURE FACTORIES
--
-- An automatically populating table keyed by function signature with
-- values that are closure factories for those signatures.

local LOCAL_Closure_Factories = { };

local function ClosureFactories_index(t, signature)
	if type(signature) ~= "string" then
		return;
	end

	local factory = CreateClosureFactory(LOCAL_Function_Environment, signature);

	if not issecure() then
		error("Cannot declare closure factories from insecure code");
		return;
	end

	t[signature] = factory;
	return factory;
end

setmetatable(LOCAL_Closure_Factories, { __index = ClosureFactories_index });

---------------------------------------------------------------------------
-- FUNCTION CALL

-- A helper method to release the restricted environment environment before
-- returning from the function call.
local function ReleaseAndReturn(workingEnv, ctrlHandle, pcallFlag, ...)
	-- Tampering at this point will irrevocably taint the protected
	-- environment, for now that's a handy protective measure.
	LOCAL_Function_Environment_Manager(false, workingEnv, ctrlHandle);
	if pcallFlag then
		return ...;
	end
	error("Call failed: " .. tostring( (...) ) );
end

-- ? = CallRestrictedClosure(signature, workingEnv, onupdate, body, ...)
--
-- Invoke a managed closure, looking its definition up from a factory
-- and managing its environment during execution.
--
-- signature  -- function signature
-- workingEnv -- the working environment, must be a restricted table
-- ctrlHandle -- a control handle
-- body       -- function body
-- ...        -- any arguments to pass to the executing closure
--
-- Returns whatever the restricted closure returns
function CallRestrictedClosure(signature, workingEnv, ctrlHandle, body, ...)
	if not LOCAL_Restricted_Tables[workingEnv] then
		error("Invalid working environment");
		return;
	end

	signature = tostring(signature);
	local factory = LOCAL_Closure_Factories[signature];
	if not factory then
		error("Invalid signature '" .. signature .. "'");
		return;
	end

	local closure = factory[body];
	if not closure then
		-- Expect factory to have thrown an error
		return;
	end

	if not issecure() then
		error("Cannot call restricted closure from insecure code");
		return;
	end

	if type(ctrlHandle) ~= "userdata" then
		ctrlHandle = nil;
	end

	LOCAL_Function_Environment_Manager(true, workingEnv, ctrlHandle);
	return ReleaseAndReturn(workingEnv, ctrlHandle, pcall( closure, ... ) );
end
