Alias: Restore recursion limit and limit memory use

The (faulty) detection of recursive Aliases was removed in
a656fd06930541103c70297825d6f5f5956ecc45, claiming that "our nesting
limit will catch issues now."  However, nested Aliases weren't actually
increasing the nesting level.

Actually increasing the nesting level when an alias is executed restores
the intended behavior.  Additionally, limiting the size of the
expanded arguments to an alias prevents exponential growth of memory
usage for certain malicious inputs/aliases.

Signed-off-by: James McCoy <vega.james@gmail.com>

plugins/Alias/plugin.py

@@ -1,6 +1,6 @@
 ###
 # Copyright (c) 2002-2004, Jeremiah Fincher
-# Copyright (c) 2009-2010, James McCoy
+# Copyright (c) 2014, James McCoy
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
@@ -78,9 +78,6 @@ def getArgs(args, required=1, optional=0, wildcard=0):
 class AliasError(Exception):
     pass
 
-class RecursiveAlias(AliasError):
-    pass
-
 dollarRe = re.compile(r'\$(\d+)')
 def findBiggestDollar(alias):
     dollars = dollarRe.findall(alias)
@@ -156,7 +153,11 @@ def makeNewAlias(name, alias):
                         return True
                 return False
             everythingReplace(tokens)
-        self.Proxy(irc, msg, tokens)
+        # Limit memory use by constraining the size of the message being passed
+        # in to the alias.  Also tracking nesting to avoid endless recursion.
+        maxLength = conf.supybot.reply.maximumLength()
+        tokens = [t[:maxLength] for t in tokens]
+        self.Proxy(irc, msg, tokens, nested=irc.nested + 1)
     flexargs = ''
     if biggestDollar and (wildcard or biggestAt):
         flexargs = ' at least'
@@ -258,11 +259,8 @@ class Alias(callbacks.Plugin):
             (currentAlias, locked, _) = self.aliases[name]
             if locked and currentAlias != alias:
                 raise AliasError, format('Alias %q is locked.', name)
-        try:
-            f = makeNewAlias(name, alias)
-            f = new.instancemethod(f, self, Alias)
-        except RecursiveAlias:
-            raise AliasError, 'You can\'t define a recursive alias.'
+        f = makeNewAlias(name, alias)
+        f = new.instancemethod(f, self, Alias)
         aliasGroup = self.registryValue('aliases', value=False)
         if name in self.aliases:
             # We gotta remove it so its value gets updated.