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cpython/Lib/rexec.py
Guido van Rossum 7f7c3d0a9c Address SF bug #577530: del __builtins__ breaks out of rexec 
Using the suggestion there: add_module() forces __builtin__ back; this
fixes r_exec, r_eval, r_execfile.  The interactive console had to be
fixed separately, because it doesn't use r_exec, but relies on the
'locals' dict having the right __builtins__.  Fixed this by
subclassing InteractiveConsole and overriding runcode(), which does
the exec.  This changes the banner output slightly: instead of
starting with *** RESTRICTED ***, a subtler (RestrictedConsole) is
printed before the first >>> prompt.

Also import readline (if it exists) when the interactive console is
used, for more convenient input editing and history.

This does not mean that rexec is now considered safe!  But for those
willing to take the risk, it's safer than before.  (Note that a safety
analysis of the code module would be wise if you plan to use the
interactive console for real -- I've only ever used it to play with
restricted mode.)

This should be backported to 2.2 and 2.1.
2002-09-15 06:00:43 +00:00

583 lines
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"""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 ...")?)
"""
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')
class FileWrapper(FileBase):
# XXX This is just like a Bastion -- should use that!
def __init__(self, f):
self.f = 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 apply(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', 'regex', 'pcre', 'rotor', 'select',
'sha', '_sre', 'strop', 'struct', 'time')
ok_posix_names = ('error', 'fstat', 'listdir', 'lstat', 'readlink',
'stat', 'times', 'uname', 'getpid', 'getppid',
'getcwd', 'getuid', 'getgid', 'geteuid', 'getegid')
ok_sys_names = ('ps1', 'ps2', 'copyright', 'version',
'platform', 'exit', 'maxint')
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.
"""
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):
m = 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=None):
self.save_files()
try:
self.set_files()
if kw:
r = apply(func, args, kw)
else:
r = apply(func, args)
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.
"""
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 %s" % (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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