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