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rexec.py
"""Restricted execution facilities. The class RExec exports methods r_exec(), r_eval(), r_execfile(), and r_import(), which correspond roughly to the built-in operations exec, eval(), execfile() and import, but executing the code in an environment that only exposes those built-in operations that are deemed safe. To this end, a modest collection of 'fake' modules is created which mimics the standard modules by the same names. It is a policy decision which built-in modules and operations are made available; this module provides a reasonable default, but derived classes can change the policies e.g. by overriding or extending class variables like ok_builtin_modules or methods like make_sys(). XXX To do: - r_open should allow writing tmp dir - r_exec etc. with explicit globals/locals? (Use rexec("exec ... in ...")?) """ from warnings import warnpy3k warnpy3k("the rexec module has been removed in Python 3.0", stacklevel=2) del warnpy3k import sys import __builtin__ import os import ihooks import imp __all__ = ["RExec"] class FileBase: ok_file_methods = ('fileno', 'flush', 'isatty', 'read', 'readline', 'readlines', 'seek', 'tell', 'write', 'writelines', 'xreadlines', '__iter__') class FileWrapper(FileBase): # XXX This is just like a Bastion -- should use that! def __init__(self, f): for m in self.ok_file_methods: if not hasattr(self, m) and hasattr(f, m): setattr(self, m, getattr(f, m)) def close(self): self.flush() TEMPLATE = """ def %s(self, *args): return getattr(self.mod, self.name).%s(*args) """ class FileDelegate(FileBase): def __init__(self, mod, name): self.mod = mod self.name = name for m in FileBase.ok_file_methods + ('close',): exec TEMPLATE % (m, m) class RHooks(ihooks.Hooks): def __init__(self, *args): # Hacks to support both old and new interfaces: # old interface was RHooks(rexec[, verbose]) # new interface is RHooks([verbose]) verbose = 0 rexec = None if args and type(args[-1]) == type(0): verbose = args[-1] args = args[:-1] if args and hasattr(args[0], '__class__'): rexec = args[0] args = args[1:] if args: raise TypeError, "too many arguments" ihooks.Hooks.__init__(self, verbose) self.rexec = rexec def set_rexec(self, rexec): # Called by RExec instance to complete initialization self.rexec = rexec def get_suffixes(self): return self.rexec.get_suffixes() def is_builtin(self, name): return self.rexec.is_builtin(name) def init_builtin(self, name): m = __import__(name) return self.rexec.copy_except(m, ()) def init_frozen(self, name): raise SystemError, "don't use this" def load_source(self, *args): raise SystemError, "don't use this" def load_compiled(self, *args): raise SystemError, "don't use this" def load_package(self, *args): raise SystemError, "don't use this" def load_dynamic(self, name, filename, file): return self.rexec.load_dynamic(name, filename, file) def add_module(self, name): return self.rexec.add_module(name) def modules_dict(self): return self.rexec.modules def default_path(self): return self.rexec.modules['sys'].path # XXX Backwards compatibility RModuleLoader = ihooks.FancyModuleLoader RModuleImporter = ihooks.ModuleImporter class RExec(ihooks._Verbose): """Basic restricted execution framework. Code executed in this restricted environment will only have access to modules and functions that are deemed safe; you can subclass RExec to add or remove capabilities as desired. The RExec class can prevent code from performing unsafe operations like reading or writing disk files, or using TCP/IP sockets. However, it does not protect against code using extremely large amounts of memory or processor time. """ ok_path = tuple(sys.path) # That's a policy decision ok_builtin_modules = ('audioop', 'array', 'binascii', 'cmath', 'errno', 'imageop', 'marshal', 'math', 'md5', 'operator', 'parser', 'select', 'sha', '_sre', 'strop', 'struct', 'time', '_weakref') ok_posix_names = ('error', 'fstat', 'listdir', 'lstat', 'readlink', 'stat', 'times', 'uname', 'getpid', 'getppid', 'getcwd', 'getuid', 'getgid', 'geteuid', 'getegid') ok_sys_names = ('byteorder', 'copyright', 'exit', 'getdefaultencoding', 'getrefcount', 'hexversion', 'maxint', 'maxunicode', 'platform', 'ps1', 'ps2', 'version', 'version_info') nok_builtin_names = ('open', 'file', 'reload', '__import__') ok_file_types = (imp.C_EXTENSION, imp.PY_SOURCE) def __init__(self, hooks = None, verbose = 0): """Returns an instance of the RExec class. The hooks parameter is an instance of the RHooks class or a subclass of it. If it is omitted or None, the default RHooks class is instantiated. Whenever the RExec module searches for a module (even a built-in one) or reads a module's code, it doesn't actually go out to the file system itself. Rather, it calls methods of an RHooks instance that was passed to or created by its constructor. (Actually, the RExec object doesn't make these calls --- they are made by a module loader object that's part of the RExec object. This allows another level of flexibility, which can be useful when changing the mechanics of import within the restricted environment.) By providing an alternate RHooks object, we can control the file system accesses made to import a module, without changing the actual algorithm that controls the order in which those accesses are made. For instance, we could substitute an RHooks object that passes all filesystem requests to a file server elsewhere, via some RPC mechanism such as ILU. Grail's applet loader uses this to support importing applets from a URL for a directory. If the verbose parameter is true, additional debugging output may be sent to standard output. """ raise RuntimeError, "This code is not secure in Python 2.2 and later" ihooks._Verbose.__init__(self, verbose) # XXX There's a circular reference here: self.hooks = hooks or RHooks(verbose) self.hooks.set_rexec(self) self.modules = {} self.ok_dynamic_modules = self.ok_builtin_modules list = [] for mname in self.ok_builtin_modules: if mname in sys.builtin_module_names: list.append(mname) self.ok_builtin_modules = tuple(list) self.set_trusted_path() self.make_builtin() self.make_initial_modules() # make_sys must be last because it adds the already created # modules to its builtin_module_names self.make_sys() self.loader = RModuleLoader(self.hooks, verbose) self.importer = RModuleImporter(self.loader, verbose) def set_trusted_path(self): # Set the path from which dynamic modules may be loaded. # Those dynamic modules must also occur in ok_builtin_modules self.trusted_path = filter(os.path.isabs, sys.path) def load_dynamic(self, name, filename, file): if name not in self.ok_dynamic_modules: raise ImportError, "untrusted dynamic module: %s" % name if name in sys.modules: src = sys.modules[name] else: src = imp.load_dynamic(name, filename, file) dst = self.copy_except(src, []) return dst def make_initial_modules(self): self.make_main() self.make_osname() # Helpers for RHooks def get_suffixes(self): return [item # (suff, mode, type) for item in imp.get_suffixes() if item[2] in self.ok_file_types] def is_builtin(self, mname): return mname in self.ok_builtin_modules # The make_* methods create specific built-in modules def make_builtin(self): m = self.copy_except(__builtin__, self.nok_builtin_names) m.__import__ = self.r_import m.reload = self.r_reload m.open = m.file = self.r_open def make_main(self): self.add_module('__main__') def make_osname(self): osname = os.name src = __import__(osname) dst = self.copy_only(src, self.ok_posix_names) dst.environ = e = {} for key, value in os.environ.items(): e[key] = value def make_sys(self): m = self.copy_only(sys, self.ok_sys_names) m.modules = self.modules m.argv = ['RESTRICTED'] m.path = map(None, self.ok_path) m.exc_info = self.r_exc_info m = self.modules['sys'] l = self.modules.keys() + list(self.ok_builtin_modules) l.sort() m.builtin_module_names = tuple(l) # The copy_* methods copy existing modules with some changes def copy_except(self, src, exceptions): dst = self.copy_none(src) for name in dir(src): setattr(dst, name, getattr(src, name)) for name in exceptions: try: delattr(dst, name) except AttributeError: pass return dst def copy_only(self, src, names): dst = self.copy_none(src) for name in names: try: value = getattr(src, name) except AttributeError: continue setattr(dst, name, value) return dst def copy_none(self, src): m = self.add_module(src.__name__) m.__doc__ = src.__doc__ return m # Add a module -- return an existing module or create one def add_module(self, mname): m = self.modules.get(mname) if m is None: self.modules[mname] = m = self.hooks.new_module(mname) m.__builtins__ = self.modules['__builtin__'] return m # The r* methods are public interfaces def r_exec(self, code): """Execute code within a restricted environment. The code parameter must either be a string containing one or more lines of Python code, or a compiled code object, which will be executed in the restricted environment's __main__ module. """ m = self.add_module('__main__') exec code in m.__dict__ def r_eval(self, code): """Evaluate code within a restricted environment. The code parameter must either be a string containing a Python expression, or a compiled code object, which will be evaluated in the restricted environment's __main__ module. The value of the expression or code object will be returned. """ m = self.add_module('__main__') return eval(code, m.__dict__) def r_execfile(self, file): """Execute the Python code in the file in the restricted environment's __main__ module. """ m = self.add_module('__main__') execfile(file, m.__dict__) def r_import(self, mname, globals={}, locals={}, fromlist=[]): """Import a module, raising an ImportError exception if the module is considered unsafe. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. """ return self.importer.import_module(mname, globals, locals, fromlist) def r_reload(self, m): """Reload the module object, re-parsing and re-initializing it. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. """ return self.importer.reload(m) def r_unload(self, m): """Unload the module. Removes it from the restricted environment's sys.modules dictionary. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. """ return self.importer.unload(m) # The s_* methods are similar but also swap std{in,out,err} def make_delegate_files(self): s = self.modules['sys'] self.delegate_stdin = FileDelegate(s, 'stdin') self.delegate_stdout = FileDelegate(s, 'stdout') self.delegate_stderr = FileDelegate(s, 'stderr') self.restricted_stdin = FileWrapper(sys.stdin) self.restricted_stdout = FileWrapper(sys.stdout) self.restricted_stderr = FileWrapper(sys.stderr) def set_files(self): if not hasattr(self, 'save_stdin'): self.save_files() if not hasattr(self, 'delegate_stdin'): self.make_delegate_files() s = self.modules['sys'] s.stdin = self.restricted_stdin s.stdout = self.restricted_stdout s.stderr = self.restricted_stderr sys.stdin = self.delegate_stdin sys.stdout = self.delegate_stdout sys.stderr = self.delegate_stderr def reset_files(self): self.restore_files() s = self.modules['sys'] self.restricted_stdin = s.stdin self.restricted_stdout = s.stdout self.restricted_stderr = s.stderr def save_files(self): self.save_stdin = sys.stdin self.save_stdout = sys.stdout self.save_stderr = sys.stderr def restore_files(self): sys.stdin = self.save_stdin sys.stdout = self.save_stdout sys.stderr = self.save_stderr def s_apply(self, func, args=(), kw={}): self.save_files() try: self.set_files() r = func(*args, **kw) finally: self.restore_files() return r def s_exec(self, *args): """Execute code within a restricted environment. Similar to the r_exec() method, but the code will be granted access to restricted versions of the standard I/O streams sys.stdin, sys.stderr, and sys.stdout. The code parameter must either be a string containing one or more lines of Python code, or a compiled code object, which will be executed in the restricted environment's __main__ module. """ return self.s_apply(self.r_exec, args) def s_eval(self, *args): """Evaluate code within a restricted environment. Similar to the r_eval() method, but the code will be granted access to restricted versions of the standard I/O streams sys.stdin, sys.stderr, and sys.stdout. The code parameter must either be a string containing a Python expression, or a compiled code object, which will be evaluated in the restricted environment's __main__ module. The value of the expression or code object will be returned. """ return self.s_apply(self.r_eval, args) def s_execfile(self, *args): """Execute the Python code in the file in the restricted environment's __main__ module. Similar to the r_execfile() method, but the code will be granted access to restricted versions of the standard I/O streams sys.stdin, sys.stderr, and sys.stdout. """ return self.s_apply(self.r_execfile, args) def s_import(self, *args): """Import a module, raising an ImportError exception if the module is considered unsafe. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. Similar to the r_import() method, but has access to restricted versions of the standard I/O streams sys.stdin, sys.stderr, and sys.stdout. """ return self.s_apply(self.r_import, args) def s_reload(self, *args): """Reload the module object, re-parsing and re-initializing it. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. Similar to the r_reload() method, but has access to restricted versions of the standard I/O streams sys.stdin, sys.stderr, and sys.stdout. """ return self.s_apply(self.r_reload, args) def s_unload(self, *args): """Unload the module. Removes it from the restricted environment's sys.modules dictionary. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. Similar to the r_unload() method, but has access to restricted versions of the standard I/O streams sys.stdin, sys.stderr, and sys.stdout. """ return self.s_apply(self.r_unload, args) # Restricted open(...) def r_open(self, file, mode='r', buf=-1): """Method called when open() is called in the restricted environment. The arguments are identical to those of the open() function, and a file object (or a class instance compatible with file objects) should be returned. RExec's default behaviour is allow opening any file for reading, but forbidding any attempt to write a file. This method is implicitly called by code executing in the restricted environment. Overriding this method in a subclass is used to change the policies enforced by a restricted environment. """ mode = str(mode) if mode not in ('r', 'rb'): raise IOError, "can't open files for writing in restricted mode" return open(file, mode, buf) # Restricted version of sys.exc_info() def r_exc_info(self): ty, va, tr = sys.exc_info() tr = None return ty, va, tr def test(): import getopt, traceback opts, args = getopt.getopt(sys.argv[1:], 'vt:') verbose = 0 trusted = [] for o, a in opts: if o == '-v': verbose = verbose+1 if o == '-t': trusted.append(a) r = RExec(verbose=verbose) if trusted: r.ok_builtin_modules = r.ok_builtin_modules + tuple(trusted) if args: r.modules['sys'].argv = args r.modules['sys'].path.insert(0, os.path.dirname(args[0])) else: r.modules['sys'].path.insert(0, "") fp = sys.stdin if args and args[0] != '-': try: fp = open(args[0]) except IOError, msg: print "%s: can't open file %r" % (sys.argv[0], args[0]) return 1 if fp.isatty(): try: import readline except ImportError: pass import code class RestrictedConsole(code.InteractiveConsole): def runcode(self, co): self.locals['__builtins__'] = r.modules['__builtin__'] r.s_apply(code.InteractiveConsole.runcode, (self, co)) try: RestrictedConsole(r.modules['__main__'].__dict__).interact() except SystemExit, n: return n else: text = fp.read() fp.close() c = compile(text, fp.name, 'exec') try: r.s_exec(c) except SystemExit, n: return n except: traceback.print_exc() return 1 if __name__ == '__main__': sys.exit(test())
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