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', '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         # but since re isn't normally built-in, we can add it at the end;
 158         # we need the imported to be set before this can be imported.
 159         self.make_re()
 160
 161     def set_trusted_path(self):
 162         # Set the path from which dynamic modules may be loaded.
 163         # Those dynamic modules must also occur in ok_builtin_modules
 164         self.trusted_path = filter(os.path.isabs, sys.path)
 165
 166     def load_dynamic(self, name, filename, file):
 167         if name not in self.ok_dynamic_modules:
 168             raise ImportError, "untrusted dynamic module: %s" % name
 169         if sys.modules.has_key(name):
 170             src = sys.modules[name]
 171         else:
 172             import imp
 173             src = imp.load_dynamic(name, filename, file)
 174         dst = self.copy_except(src, [])
 175         return dst
 176
 177     def make_initial_modules(self):
 178         self.make_main()
 179         self.make_osname()
 180
 181     # Helpers for RHooks
 182
 183     def is_builtin(self, mname):
 184         return mname in self.ok_builtin_modules
 185
 186     # The make_* methods create specific built-in modules
 187
 188     def make_builtin(self):
 189         m = self.copy_except(__builtin__, self.nok_builtin_names)
 190         m.__import__ = self.r_import
 191         m.reload = self.r_reload
 192         m.open = self.r_open
 193
 194     def make_main(self):
 195         m = self.add_module('__main__')
 196
 197     def make_osname(self):
 198         osname = os.name
 199         src = __import__(osname)
 200         dst = self.copy_only(src, self.ok_posix_names)
 201         dst.environ = e = {}
 202         for key, value in os.environ.items():
 203             e[key] = value
 204
 205     def make_re(self):
 206         dst = self.add_module("re")
 207         src = self.r_import("pre")
 208         for name in dir(src):
 209             if name != "__name__":
 210                 setattr(dst, name, getattr(src, name))
 211
 212     def make_sys(self):
 213         m = self.copy_only(sys, self.ok_sys_names)
 214         m.modules = self.modules
 215         m.argv = ['RESTRICTED']
 216         m.path = map(None, self.ok_path)
 217         m.exc_info = self.r_exc_info
 218         m = self.modules['sys']
 219         l = self.modules.keys() + list(self.ok_builtin_modules)
 220         l.sort()
 221         m.builtin_module_names = tuple(l)
 222
 223     # The copy_* methods copy existing modules with some changes
 224
 225     def copy_except(self, src, exceptions):
 226         dst = self.copy_none(src)
 227         for name in dir(src):
 228             setattr(dst, name, getattr(src, name))
 229         for name in exceptions:
 230             try:
 231                 delattr(dst, name)
 232             except AttributeError:
 233                 pass
 234         return dst
 235
 236     def copy_only(self, src, names):
 237         dst = self.copy_none(src)
 238         for name in names:
 239             try:
 240                 value = getattr(src, name)
 241             except AttributeError:
 242                 continue
 243             setattr(dst, name, value)
 244         return dst
 245
 246     def copy_none(self, src):
 247         m = self.add_module(src.__name__)
 248         m.__doc__ = src.__doc__
 249         return m
 250
 251     # Add a module -- return an existing module or create one
 252
 253     def add_module(self, mname):
 254         if self.modules.has_key(mname):
 255             return self.modules[mname]
 256         self.modules[mname] = m = self.hooks.new_module(mname)
 257         m.__builtins__ = self.modules['__builtin__']
 258         return m
 259
 260     # The r* methods are public interfaces
 261
 262     def r_exec(self, code):
 263         m = self.add_module('__main__')
 264         exec code in m.__dict__
 265
 266     def r_eval(self, code):
 267         m = self.add_module('__main__')
 268         return eval(code, m.__dict__)
 269
 270     def r_execfile(self, file):
 271         m = self.add_module('__main__')
 272         return execfile(file, m.__dict__)
 273
 274     def r_import(self, mname, globals={}, locals={}, fromlist=[]):
 275         return self.importer.import_module(mname, globals, locals, fromlist)
 276
 277     def r_reload(self, m):
 278         return self.importer.reload(m)
 279
 280     def r_unload(self, m):
 281         return self.importer.unload(m)
 282
 283     # The s_* methods are similar but also swap std{in,out,err}
 284
 285     def make_delegate_files(self):
 286         s = self.modules['sys']
 287         self.delegate_stdin = FileDelegate(s, 'stdin')
 288         self.delegate_stdout = FileDelegate(s, 'stdout')
 289         self.delegate_stderr = FileDelegate(s, 'stderr')
 290         self.restricted_stdin = FileWrapper(sys.stdin)
 291         self.restricted_stdout = FileWrapper(sys.stdout)
 292         self.restricted_stderr = FileWrapper(sys.stderr)
 293
 294     def set_files(self):
 295         if not hasattr(self, 'save_stdin'):
 296             self.save_files()
 297         if not hasattr(self, 'delegate_stdin'):
 298             self.make_delegate_files()
 299         s = self.modules['sys']
 300         s.stdin = self.restricted_stdin
 301         s.stdout = self.restricted_stdout
 302         s.stderr = self.restricted_stderr
 303         sys.stdin = self.delegate_stdin
 304         sys.stdout = self.delegate_stdout
 305         sys.stderr = self.delegate_stderr
 306
 307     def reset_files(self):
 308         self.restore_files()
 309         s = self.modules['sys']
 310         self.restricted_stdin = s.stdin
 311         self.restricted_stdout = s.stdout
 312         self.restricted_stderr = s.stderr
 313
 314
 315     def save_files(self):
 316         self.save_stdin = sys.stdin
 317         self.save_stdout = sys.stdout
 318         self.save_stderr = sys.stderr
 319
 320     def restore_files(self):
 321         sys.stdin = self.save_stdin
 322         sys.stdout = self.save_stdout
 323         sys.stderr = self.save_stderr
 324
 325     def s_apply(self, func, args=(), kw=None):
 326         self.save_files()
 327         try:
 328             self.set_files()
 329             if kw:
 330                 r = apply(func, args, kw)
 331             else:
 332                 r = apply(func, args)
 333         finally:
 334             self.restore_files()
 335         return r
 336
 337     def s_exec(self, *args):
 338         return self.s_apply(self.r_exec, args)
 339
 340     def s_eval(self, *args):
 341         return self.s_apply(self.r_eval, args)
 342
 343     def s_execfile(self, *args):
 344         return self.s_apply(self.r_execfile, args)
 345
 346     def s_import(self, *args):
 347         return self.s_apply(self.r_import, args)
 348
 349     def s_reload(self, *args):
 350         return self.s_apply(self.r_reload, args)
 351
 352     def s_unload(self, *args):
 353         return self.s_apply(self.r_unload, args)
 354
 355     # Restricted open(...)
 356
 357     def r_open(self, file, mode='r', buf=-1):
 358         if mode not in ('r', 'rb'):
 359             raise IOError, "can't open files for writing in restricted mode"
 360         return open(file, mode, buf)
 361
 362     # Restricted version of sys.exc_info()
 363
 364     def r_exc_info(self):
 365         ty, va, tr = sys.exc_info()
 366         tr = None
 367         return ty, va, tr
 368
 369
 370 def test():
 371     import sys, getopt, traceback
 372     opts, args = getopt.getopt(sys.argv[1:], 'vt:')
 373     verbose = 0
 374     trusted = []
 375     for o, a in opts:
 376         if o == '-v':
 377             verbose = verbose+1
 378         if o == '-t':
 379             trusted.append(a)
 380     r = RExec(verbose=verbose)
 381     if trusted:
 382         r.ok_builtin_modules = r.ok_builtin_modules + tuple(trusted)
 383     if args:
 384         r.modules['sys'].argv = args
 385         r.modules['sys'].path.insert(0, os.path.dirname(args[0]))
 386     else:
 387         r.modules['sys'].path.insert(0, "")
 388     fp = sys.stdin
 389     if args and args[0] != '-':
 390         try:
 391             fp = open(args[0])
 392         except IOError, msg:
 393             print "%s: can't open file %s" % (sys.argv[0], `args[0]`)
 394             return 1
 395     if fp.isatty():
 396         print "*** RESTRICTED *** Python", sys.version
 397         print sys.copyright
 398         while 1:
 399             try:
 400                 try:
 401                     s = raw_input('>>> ')
 402                 except EOFError:
 403                     print
 404                     break
 405                 if s and s[0] != '#':
 406                     s = s + '\n'
 407                     c = compile(s, '<stdin>', 'single')
 408                     r.s_exec(c)
 409             except SystemExit, n:
 410                 return n
 411             except:
 412                 traceback.print_exc()
 413     else:
 414         text = fp.read()
 415         fp.close()
 416         c = compile(text, fp.name, 'exec')
 417         try:
 418             r.s_exec(c)
 419         except SystemExit, n:
 420             return n
 421         except:
 422             traceback.print_exc()
 423             return 1
 424
 425
 426 if __name__ == '__main__':
 427     sys.exit(test())