File

util/format.lua @ 12591:494577d883ff

util.table: Fix inaccurate comment Probably a duplicate of the comment next to Lmove, recorded by mistake Lpack can probably be removed at some point in the near future once we are confident it is not used anywhere.
author Kim Alvefur <zash@zash.se>
date Mon, 11 Jul 2022 20:02:10 +0200
parent 12590:5eaf77114fdb
child 12781:22066b02887f
line wrap: on
line source

--
-- A string.format wrapper that gracefully handles invalid arguments since
-- certain format string and argument combinations may cause errors or other
-- issues like log spoofing
--
-- Provides some protection from e.g. CAPEC-135, CWE-117, CWE-134, CWE-93

local tostring = tostring;
local unpack = table.unpack;
local pack = table.pack;
local valid_utf8 = require "util.encodings".utf8.valid;
local type = type;
local dump = require "util.serialization".new("debug");
local num_type = math.type or function (n)
	return n % 1 == 0 and n <= 9007199254740992 and n >= -9007199254740992 and "integer" or "float";
end

-- In Lua 5.3+ these formats throw an error if given a float
local expects_integer = { c = true, d = true, i = true, o = true, u = true, X = true, x = true, };
-- In Lua 5.2 these throw an error given a negative number
local expects_positive = { o = true; u = true; x = true; X = true };
-- Printable Unicode replacements for control characters
local control_symbols = {
	-- 0x00 .. 0x1F --> U+2400 .. U+241F, 0x7F --> U+2421
	["\000"] = "\226\144\128", ["\001"] = "\226\144\129", ["\002"] = "\226\144\130",
	["\003"] = "\226\144\131", ["\004"] = "\226\144\132", ["\005"] = "\226\144\133",
	["\006"] = "\226\144\134", ["\007"] = "\226\144\135", ["\008"] = "\226\144\136",
	["\009"] = "\226\144\137", ["\010"] = "\226\144\138", ["\011"] = "\226\144\139",
	["\012"] = "\226\144\140", ["\013"] = "\226\144\141", ["\014"] = "\226\144\142",
	["\015"] = "\226\144\143", ["\016"] = "\226\144\144", ["\017"] = "\226\144\145",
	["\018"] = "\226\144\146", ["\019"] = "\226\144\147", ["\020"] = "\226\144\148",
	["\021"] = "\226\144\149", ["\022"] = "\226\144\150", ["\023"] = "\226\144\151",
	["\024"] = "\226\144\152", ["\025"] = "\226\144\153", ["\026"] = "\226\144\154",
	["\027"] = "\226\144\155", ["\028"] = "\226\144\156", ["\029"] = "\226\144\157",
	["\030"] = "\226\144\158", ["\031"] = "\226\144\159", ["\127"] = "\226\144\161",
};
local supports_p = pcall(string.format, "%p", ""); -- >= Lua 5.4

local function format(formatstring, ...)
	local args = pack(...);
	local args_length = args.n;

	-- format specifier spec:
	-- 1. Start: '%%'
	-- 2. Flags: '[%-%+ #0]'
	-- 3. Width: '%d?%d?'
	-- 4. Precision: '%.?%d?%d?'
	-- 5. Option: '[cdiouxXaAeEfgGqs%%]'
	--
	-- The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a number as argument, whereas q and s expect a string.
	-- This function does not accept string values containing embedded zeros, except as arguments to the q option.
	-- a and A are only in Lua 5.2+
	-- Lua 5.4 adds a p format that produces a pointer


	-- process each format specifier
	local i = 0;
	formatstring = formatstring:gsub("%%[^cdiouxXaAeEfgGpqs%%]*[cdiouxXaAeEfgGpqs%%]", function(spec)
		if spec == "%%" then return end
		i = i + 1;
		local arg = args[i];

		if arg == nil then
			args[i] = "nil";
			return "(%s)";
		end

		local option = spec:sub(-1);
		local t = type(arg);

		if option == "s" and t == "string" and not arg:find("[%z\1-\31\128-\255]") then
			-- No UTF-8 or control characters, assumed to be the common case.
			return
		elseif t == "number" then
			if option == "g" or (option == "d" and num_type(arg) == "integer") then return end
		elseif option == "s" and t ~= "string" then
			arg = tostring(arg);
			t = "string";
		end

		if option ~= "s" and option ~= "q" and option ~= "p" then
			-- all other options expect numbers
			if t ~= "number" then
				-- arg isn't number as expected?
				arg = tostring(arg);
				option = "s";
				spec = "[%s]";
				t = "string";
			elseif expects_integer[option] and num_type(arg) ~= "integer" then
				args[i] = tostring(arg);
				return "[%s]";
			elseif expects_positive[option] and arg < 0 then
				args[i] = tostring(arg);
				return "[%s]";
			else
				return -- acceptable number
			end
		end


		if option == "p" and not supports_p then
			arg = tostring(arg);
			option = "s";
			spec = "[%s]";
			t = "string";
		end

		if t == "string" and option ~= "p" then
			if not valid_utf8(arg) then
				option = "q";
			elseif option ~= "q" then -- gets fully escaped in the next block
				-- Prevent funny things with ASCII control characters and ANSI escape codes (CWE-117)
				-- Also ensure embedded newlines can't look like another log line (CWE-93)
				args[i] = arg:gsub("[%z\1-\8\11-\31\127]", control_symbols):gsub("\n\t?", "\n\t");
				return spec;
			end
		end

		if option == "q" then
			args[i] = dump(arg);
			return "%s";
		end

		if option == "p" and (t == "boolean" or t == "number") then
			args[i] = tostring(arg);
			return "[%s]";
		end
	end);

	-- process extra args
	while i < args_length do
		i = i + 1;
		local arg = args[i];
		if arg == nil then
			args[i] = "(nil)";
		else
			args[i] = tostring(arg):gsub("[%z\1-\8\11-\31\127]", control_symbols):gsub("\n\t?", "\n\t");
		end
		formatstring = formatstring .. " [%s]"
	end

	return formatstring:format(unpack(args));
end

return {
	format = format;
};