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annotate util/format.lua @ 12181:783056b4e448 0.11 0.11.12

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util.xml: Do not allow doctypes, comments or processing instructions Yes. This is as bad as it sounds. CVE pending. In Prosody itself, this only affects mod_websocket, which uses util.xml to parse the <open/> frame, thus allowing unauthenticated remote DoS using Billion Laughs. However, third-party modules using util.xml may also be affected by this. This commit installs handlers which disallow the use of doctype declarations and processing instructions without any escape hatch. It, by default, also introduces such a handler for comments, however, there is a way to enable comments nontheless. This is because util.xml is used to parse human-facing data, where comments are generally a desirable feature, and also because comments are generally harmless.
author Jonas Schäfer <jonas@wielicki.name>
date Mon, 10 Jan 2022 18:23:54 +0100
parents e88db5668cfb
children 3da6cc927ee6
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1 --
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2 -- A string.format wrapper that gracefully handles invalid arguments
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3 --
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4
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5 local tostring = tostring;
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6 local select = select;
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7 local unpack = table.unpack or unpack; -- luacheck: ignore 113/unpack
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8 local type = type;
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9
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10 local function format(formatstring, ...)
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11 local args, args_length = { ... }, select('#', ...);
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12
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13 -- format specifier spec:
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14 -- 1. Start: '%%'
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15 -- 2. Flags: '[%-%+ #0]'
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16 -- 3. Width: '%d?%d?'
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17 -- 4. Precision: '%.?%d?%d?'
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18 -- 5. Option: '[cdiouxXaAeEfgGqs%%]'
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19 --
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20 -- 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.
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21 -- This function does not accept string values containing embedded zeros, except as arguments to the q option.
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22 -- a and A are only in Lua 5.2+
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24
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25 -- process each format specifier
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26 local i = 0;
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27 formatstring = formatstring:gsub("%%[^cdiouxXaAeEfgGqs%%]*[cdiouxXaAeEfgGqs%%]", function(spec)
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28 if spec ~= "%%" then
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29 i = i + 1;
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30 local arg = args[i];
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31 if arg == nil then -- special handling for nil
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32 arg = "<nil>"
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33 args[i] = "<nil>";
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34 end
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35
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36 local option = spec:sub(-1);
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37 if option == "q" or option == "s" then -- arg should be string
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38 args[i] = tostring(arg);
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39 elseif type(arg) ~= "number" then -- arg isn't number as expected?
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40 args[i] = tostring(arg);
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41 spec = "[%s]";
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42 end
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43 end
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44 return spec;
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45 end);
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46
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47 -- process extra args
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48 while i < args_length do
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49 i = i + 1;
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50 local arg = args[i];
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51 if arg == nil then
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52 args[i] = "<nil>";
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53 else
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54 args[i] = tostring(arg);
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55 end
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56 formatstring = formatstring .. " [%s]"
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57 end
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58
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59 return formatstring:format(unpack(args));
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60 end
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61
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62 return {
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63 format = format;
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64 };