Lib/rexec.py

   1 """Restricted execution facilities.
   2
   3 The class RExec exports methods r_exec(), r_eval(), r_execfile(), and
   4 r_import(), which correspond roughly to the built-in operations
   5 exec, eval(), execfile() and import, but executing the code in an
   6 environment that only exposes those built-in operations that are
   7 deemed safe.  To this end, a modest collection of 'fake' modules is
   8 created which mimics the standard modules by the same names.  It is a
   9 policy decision which built-in modules and operations are made
  10 available; this module provides a reasonable default, but derived
  11 classes can change the policies e.g. by overriding or extending class
  12 variables like ok_builtin_modules or methods like make_sys().
  13
  14 XXX To do:
  15 - r_open should allow writing tmp dir
  16 - r_exec etc. with explicit globals/locals? (Use rexec("exec ... in ...")?)
  17
  18 """
  19
  20
  21 import sys
  22 import __builtin__
  23 import os
  24 import ihooks
  25
  26 __all__ = ["RExec"]
  27
  28 class FileBase:
  29
  30     ok_file_methods = ('fileno', 'flush', 'isatty', 'read', 'readline',
  31             'readlines', 'seek', 'tell', 'write', 'writelines')
  32
  33
  34 class FileWrapper(FileBase):
  35
  36     # XXX This is just like a Bastion -- should use that!
  37
  38     def __init__(self, f):
  39         self.f = f
  40         for m in self.ok_file_methods:
  41             if not hasattr(self, m) and hasattr(f, m):
  42                 setattr(self, m, getattr(f, m))
  43
  44     def close(self):
  45         self.flush()
  46
  47
  48 TEMPLATE = """
  49 def %s(self, *args):
  50         return apply(getattr(self.mod, self.name).%s, args)
  51 """
  52
  53 class FileDelegate(FileBase):
  54
  55     def __init__(self, mod, name):
  56         self.mod = mod
  57         self.name = name
  58
  59     for m in FileBase.ok_file_methods + ('close',):
  60         exec TEMPLATE % (m, m)
  61
  62
  63 class RHooks(ihooks.Hooks):
  64
  65     def __init__(self, *args):
  66         # Hacks to support both old and new interfaces:
  67         # old interface was RHooks(rexec[, verbose])
  68         # new interface is RHooks([verbose])
  69         verbose = 0
  70         rexec = None
  71         if args and type(args[-1]) == type(0):
  72             verbose = args[-1]
  73             args = args[:-1]
  74         if args and hasattr(args[0], '__class__'):
  75             rexec = args[0]
  76             args = args[1:]
  77         if args:
  78             raise TypeError, "too many arguments"
  79         ihooks.Hooks.__init__(self, verbose)
  80         self.rexec = rexec
  81
  82     def set_rexec(self, rexec):
  83         # Called by RExec instance to complete initialization
  84         self.rexec = rexec
  85
  86     def is_builtin(self, name):
  87         return self.rexec.is_builtin(name)
  88
  89     def init_builtin(self, name):
  90         m = __import__(name)
  91         return self.rexec.copy_except(m, ())
  92
  93     def init_frozen(self, name): raise SystemError, "don't use this"
  94     def load_source(self, *args): raise SystemError, "don't use this"
  95     def load_compiled(self, *args): raise SystemError, "don't use this"
  96     def load_package(self, *args): raise SystemError, "don't use this"
  97
  98     def load_dynamic(self, name, filename, file):
  99         return self.rexec.load_dynamic(name, filename, file)
 100
 101     def add_module(self, name):
 102         return self.rexec.add_module(name)
 103
 104     def modules_dict(self):
 105         return self.rexec.modules
 106
 107     def default_path(self):
 108         return self.rexec.modules['sys'].path
 109
 110
 111 # XXX Backwards compatibility
 112 RModuleLoader = ihooks.FancyModuleLoader
 113 RModuleImporter = ihooks.ModuleImporter
 114
 115
 116 class RExec(ihooks._Verbose):
 117
 118     """Restricted Execution environment."""
 119
 120     ok_path = tuple(sys.path)           # That's a policy decision
 121
 122     ok_builtin_modules = ('audioop', 'array', 'binascii',
 123                           'cmath', 'errno', 'imageop',
 124                           'marshal', 'math', 'md5', 'operator',
 125                           'parser', 'regex', 'pcre', 'rotor', 'select',
 126                           'sha', '_sre', 'strop', 'struct', 'time')
 127
 128     ok_posix_names = ('error', 'fstat', 'listdir', 'lstat', 'readlink',
 129                       'stat', 'times', 'uname', 'getpid', 'getppid',
 130                       'getcwd', 'getuid', 'getgid', 'geteuid', 'getegid')
 131
 132     ok_sys_names = ('ps1', 'ps2', 'copyright', 'version',
 133                     'platform', 'exit', 'maxint')
 134
 135     nok_builtin_names = ('open', 'file', 'reload', '__import__')
 136
 137     def __init__(self, hooks = None, verbose = 0):
 138         ihooks._Verbose.__init__(self, verbose)
 139         # XXX There's a circular reference here:
 140         self.hooks = hooks or RHooks(verbose)
 141         self.hooks.set_rexec(self)
 142         self.modules = {}
 143         self.ok_dynamic_modules = self.ok_builtin_modules
 144         list = []
 145         for mname in self.ok_builtin_modules:
 146             if mname in sys.builtin_module_names:
 147                 list.append(mname)
 148         self.ok_builtin_modules = tuple(list)
 149         self.set_trusted_path()
 150         self.make_builtin()
 151         self.make_initial_modules()
 152         # make_sys must be last because it adds the already created
 153         # modules to its builtin_module_names
 154         self.make_sys()
 155         self.loader = RModuleLoader(self.hooks, verbose)
 156         self.importer = RModuleImporter(self.loader, verbose)
 157
 158     def set_trusted_path(self):
 159         # Set the path from which dynamic modules may be loaded.
 160         # Those dynamic modules must also occur in ok_builtin_modules
 161         self.trusted_path = filter(os.path.isabs, sys.path)
 162
 163     def load_dynamic(self, name, filename, file):
 164         if name not in self.ok_dynamic_modules:
 165             raise ImportError, "untrusted dynamic module: %s" % name
 166         if sys.modules.has_key(name):
 167             src = sys.modules[name]
 168         else:
 169             import imp
 170             src = imp.load_dynamic(name, filename, file)
 171         dst = self.copy_except(src, [])
 172         return dst
 173
 174     def make_initial_modules(self):
 175         self.make_main()
 176         self.make_osname()
 177
 178     # Helpers for RHooks
 179
 180     def is_builtin(self, mname):
 181         return mname in self.ok_builtin_modules
 182
 183     # The make_* methods create specific built-in modules
 184
 185     def make_builtin(self):
 186         m = self.copy_except(__builtin__, self.nok_builtin_names)
 187         m.__import__ = self.r_import
 188         m.reload = self.r_reload
 189         m.open = m.file = self.r_open
 190
 191     def make_main(self):
 192         m = self.add_module('__main__')
 193
 194     def make_osname(self):
 195         osname = os.name
 196         src = __import__(osname)
 197         dst = self.copy_only(src, self.ok_posix_names)
 198         dst.environ = e = {}
 199         for key, value in os.environ.items():
 200             e[key] = value
 201
 202     def make_sys(self):
 203         m = self.copy_only(sys, self.ok_sys_names)
 204         m.modules = self.modules
 205         m.argv = ['RESTRICTED']
 206         m.path = map(None, self.ok_path)
 207         m.exc_info = self.r_exc_info
 208         m = self.modules['sys']
 209         l = self.modules.keys() + list(self.ok_builtin_modules)
 210         l.sort()
 211         m.builtin_module_names = tuple(l)
 212
 213     # The copy_* methods copy existing modules with some changes
 214
 215     def copy_except(self, src, exceptions):
 216         dst = self.copy_none(src)
 217         for name in dir(src):
 218             setattr(dst, name, getattr(src, name))
 219         for name in exceptions:
 220             try:
 221                 delattr(dst, name)
 222             except AttributeError:
 223                 pass
 224         return dst
 225
 226     def copy_only(self, src, names):
 227         dst = self.copy_none(src)
 228         for name in names:
 229             try:
 230                 value = getattr(src, name)
 231             except AttributeError:
 232                 continue
 233             setattr(dst, name, value)
 234         return dst
 235
 236     def copy_none(self, src):
 237         m = self.add_module(src.__name__)
 238         m.__doc__ = src.__doc__
 239         return m
 240
 241     # Add a module -- return an existing module or create one
 242
 243     def add_module(self, mname):
 244         if self.modules.has_key(mname):
 245             return self.modules[mname]
 246         self.modules[mname] = m = self.hooks.new_module(mname)
 247         m.__builtins__ = self.modules['__builtin__']
 248         return m
 249
 250     # The r* methods are public interfaces
 251
 252     def r_exec(self, code):
 253         m = self.add_module('__main__')
 254         exec code in m.__dict__
 255
 256     def r_eval(self, code):
 257         m = self.add_module('__main__')
 258         return eval(code, m.__dict__)
 259
 260     def r_execfile(self, file):
 261         m = self.add_module('__main__')
 262         execfile(file, m.__dict__)
 263
 264     def r_import(self, mname, globals={}, locals={}, fromlist=[]):
 265         return self.importer.import_module(mname, globals, locals, fromlist)
 266
 267     def r_reload(self, m):
 268         return self.importer.reload(m)
 269
 270     def r_unload(self, m):
 271         return self.importer.unload(m)
 272
 273     # The s_* methods are similar but also swap std{in,out,err}
 274
 275     def make_delegate_files(self):
 276         s = self.modules['sys']
 277         self.delegate_stdin = FileDelegate(s, 'stdin')
 278         self.delegate_stdout = FileDelegate(s, 'stdout')
 279         self.delegate_stderr = FileDelegate(s, 'stderr')
 280         self.restricted_stdin = FileWrapper(sys.stdin)
 281         self.restricted_stdout = FileWrapper(sys.stdout)
 282         self.restricted_stderr = FileWrapper(sys.stderr)
 283
 284     def set_files(self):
 285         if not hasattr(self, 'save_stdin'):
 286             self.save_files()
 287         if not hasattr(self, 'delegate_stdin'):
 288             self.make_delegate_files()
 289         s = self.modules['sys']
 290         s.stdin = self.restricted_stdin
 291         s.stdout = self.restricted_stdout
 292         s.stderr = self.restricted_stderr
 293         sys.stdin = self.delegate_stdin
 294         sys.stdout = self.delegate_stdout
 295         sys.stderr = self.delegate_stderr
 296
 297     def reset_files(self):
 298         self.restore_files()
 299         s = self.modules['sys']
 300         self.restricted_stdin = s.stdin
 301         self.restricted_stdout = s.stdout
 302         self.restricted_stderr = s.stderr
 303
 304
 305     def save_files(self):
 306         self.save_stdin = sys.stdin
 307         self.save_stdout = sys.stdout
 308         self.save_stderr = sys.stderr
 309
 310     def restore_files(self):
 311         sys.stdin = self.save_stdin
 312         sys.stdout = self.save_stdout
 313         sys.stderr = self.save_stderr
 314
 315     def s_apply(self, func, args=(), kw=None):
 316         self.save_files()
 317         try:
 318             self.set_files()
 319             if kw:
 320                 r = apply(func, args, kw)
 321             else:
 322                 r = apply(func, args)
 323         finally:
 324             self.restore_files()
 325         return r
 326
 327     def s_exec(self, *args):
 328         return self.s_apply(self.r_exec, args)
 329
 330     def s_eval(self, *args):
 331         return self.s_apply(self.r_eval, args)
 332
 333     def s_execfile(self, *args):
 334         return self.s_apply(self.r_execfile, args)
 335
 336     def s_import(self, *args):
 337         return self.s_apply(self.r_import, args)
 338
 339     def s_reload(self, *args):
 340         return self.s_apply(self.r_reload, args)
 341
 342     def s_unload(self, *args):
 343         return self.s_apply(self.r_unload, args)
 344
 345     # Restricted open(...)
 346
 347     def r_open(self, file, mode='r', buf=-1):
 348         if mode not in ('r', 'rb'):
 349             raise IOError, "can't open files for writing in restricted mode"
 350         return open(file, mode, buf)
 351
 352     # Restricted version of sys.exc_info()
 353
 354     def r_exc_info(self):
 355         ty, va, tr = sys.exc_info()
 356         tr = None
 357         return ty, va, tr
 358
 359
 360 def test():
 361     import getopt, traceback
 362     opts, args = getopt.getopt(sys.argv[1:], 'vt:')
 363     verbose = 0
 364     trusted = []
 365     for o, a in opts:
 366         if o == '-v':
 367             verbose = verbose+1
 368         if o == '-t':
 369             trusted.append(a)
 370     r = RExec(verbose=verbose)
 371     if trusted:
 372         r.ok_builtin_modules = r.ok_builtin_modules + tuple(trusted)
 373     if args:
 374         r.modules['sys'].argv = args
 375         r.modules['sys'].path.insert(0, os.path.dirname(args[0]))
 376     else:
 377         r.modules['sys'].path.insert(0, "")
 378     fp = sys.stdin
 379     if args and args[0] != '-':
 380         try:
 381             fp = open(args[0])
 382         except IOError, msg:
 383             print "%s: can't open file %s" % (sys.argv[0], `args[0]`)
 384             return 1
 385     if fp.isatty():
 386         print "*** RESTRICTED *** Python", sys.version
 387         print 'Type "help", "copyright", "credits" or "license" ' \
 388               'for more information.'
 389
 390         while 1:
 391             try:
 392                 try:
 393                     s = raw_input('>>> ')
 394                 except EOFError:
 395                     print
 396                     break
 397                 if s and s[0] != '#':
 398                     s = s + '\n'
 399                     c = compile(s, '<stdin>', 'single')
 400                     r.s_exec(c)
 401             except SystemExit, n:
 402                 return n
 403             except:
 404                 traceback.print_exc()
 405     else:
 406         text = fp.read()
 407         fp.close()
 408         c = compile(text, fp.name, 'exec')
 409         try:
 410             r.s_exec(c)
 411         except SystemExit, n:
 412             return n
 413         except:
 414             traceback.print_exc()
 415             return 1
 416
 417
 418 if __name__ == '__main__':
 419     sys.exit(test())