third_party/jinja2/sandbox.py

   1 # -*- coding: utf-8 -*-
   2 """
   3     jinja2.sandbox
   4     ~~~~~~~~~~~~~~
   5
   6     Adds a sandbox layer to Jinja as it was the default behavior in the old
   7     Jinja 1 releases.  This sandbox is slightly different from Jinja 1 as the
   8     default behavior is easier to use.
   9
  10     The behavior can be changed by subclassing the environment.
  11
  12     :copyright: (c) 2010 by the Jinja Team.
  13     :license: BSD.
  14 """
  15 import operator
  16 from jinja2.environment import Environment
  17 from jinja2.exceptions import SecurityError
  18 from jinja2._compat import string_types, function_type, method_type, \
  19      traceback_type, code_type, frame_type, generator_type, PY2
  20
  21
  22 #: maximum number of items a range may produce
  23 MAX_RANGE = 100000
  24
  25 #: attributes of function objects that are considered unsafe.
  26 UNSAFE_FUNCTION_ATTRIBUTES = set(['func_closure', 'func_code', 'func_dict',
  27                                   'func_defaults', 'func_globals'])
  28
  29 #: unsafe method attributes.  function attributes are unsafe for methods too
  30 UNSAFE_METHOD_ATTRIBUTES = set(['im_class', 'im_func', 'im_self'])
  31
  32 #: unsafe generator attirbutes.
  33 UNSAFE_GENERATOR_ATTRIBUTES = set(['gi_frame', 'gi_code'])
  34
  35 # On versions > python 2 the special attributes on functions are gone,
  36 # but they remain on methods and generators for whatever reason.
  37 if not PY2:
  38     UNSAFE_FUNCTION_ATTRIBUTES = set()
  39
  40 import warnings
  41
  42 # make sure we don't warn in python 2.6 about stuff we don't care about
  43 warnings.filterwarnings('ignore', 'the sets module', DeprecationWarning,
  44                         module='jinja2.sandbox')
  45
  46 from collections import deque
  47
  48 _mutable_set_types = (set,)
  49 _mutable_mapping_types = (dict,)
  50 _mutable_sequence_types = (list,)
  51
  52
  53 # on python 2.x we can register the user collection types
  54 try:
  55     from UserDict import UserDict, DictMixin
  56     from UserList import UserList
  57     _mutable_mapping_types += (UserDict, DictMixin)
  58     _mutable_set_types += (UserList,)
  59 except ImportError:
  60     pass
  61
  62 # if sets is still available, register the mutable set from there as well
  63 try:
  64     from sets import Set
  65     _mutable_set_types += (Set,)
  66 except ImportError:
  67     pass
  68
  69 #: register Python 2.6 abstract base classes
  70 try:
  71     from collections import MutableSet, MutableMapping, MutableSequence
  72     _mutable_set_types += (MutableSet,)
  73     _mutable_mapping_types += (MutableMapping,)
  74     _mutable_sequence_types += (MutableSequence,)
  75 except ImportError:
  76     pass
  77
  78 _mutable_spec = (
  79     (_mutable_set_types, frozenset([
  80         'add', 'clear', 'difference_update', 'discard', 'pop', 'remove',
  81         'symmetric_difference_update', 'update'
  82     ])),
  83     (_mutable_mapping_types, frozenset([
  84         'clear', 'pop', 'popitem', 'setdefault', 'update'
  85     ])),
  86     (_mutable_sequence_types, frozenset([
  87         'append', 'reverse', 'insert', 'sort', 'extend', 'remove'
  88     ])),
  89     (deque, frozenset([
  90         'append', 'appendleft', 'clear', 'extend', 'extendleft', 'pop',
  91         'popleft', 'remove', 'rotate'
  92     ]))
  93 )
  94
  95
  96 def safe_range(*args):
  97     """A range that can't generate ranges with a length of more than
  98     MAX_RANGE items.
  99     """
 100     rng = range(*args)
 101     if len(rng) > MAX_RANGE:
 102         raise OverflowError('range too big, maximum size for range is %d' %
 103                             MAX_RANGE)
 104     return rng
 105
 106
 107 def unsafe(f):
 108     """Marks a function or method as unsafe.
 109
 110     ::
 111
 112         @unsafe
 113         def delete(self):
 114             pass
 115     """
 116     f.unsafe_callable = True
 117     return f
 118
 119
 120 def is_internal_attribute(obj, attr):
 121     """Test if the attribute given is an internal python attribute.  For
 122     example this function returns `True` for the `func_code` attribute of
 123     python objects.  This is useful if the environment method
 124     :meth:`~SandboxedEnvironment.is_safe_attribute` is overridden.
 125
 126     >>> from jinja2.sandbox import is_internal_attribute
 127     >>> is_internal_attribute(lambda: None, "func_code")
 128     True
 129     >>> is_internal_attribute((lambda x:x).func_code, 'co_code')
 130     True
 131     >>> is_internal_attribute(str, "upper")
 132     False
 133     """
 134     if isinstance(obj, function_type):
 135         if attr in UNSAFE_FUNCTION_ATTRIBUTES:
 136             return True
 137     elif isinstance(obj, method_type):
 138         if attr in UNSAFE_FUNCTION_ATTRIBUTES or \
 139            attr in UNSAFE_METHOD_ATTRIBUTES:
 140             return True
 141     elif isinstance(obj, type):
 142         if attr == 'mro':
 143             return True
 144     elif isinstance(obj, (code_type, traceback_type, frame_type)):
 145         return True
 146     elif isinstance(obj, generator_type):
 147         if attr in UNSAFE_GENERATOR_ATTRIBUTES:
 148             return True
 149     return attr.startswith('__')
 150
 151
 152 def modifies_known_mutable(obj, attr):
 153     """This function checks if an attribute on a builtin mutable object
 154     (list, dict, set or deque) would modify it if called.  It also supports
 155     the "user"-versions of the objects (`sets.Set`, `UserDict.*` etc.) and
 156     with Python 2.6 onwards the abstract base classes `MutableSet`,
 157     `MutableMapping`, and `MutableSequence`.
 158
 159     >>> modifies_known_mutable({}, "clear")
 160     True
 161     >>> modifies_known_mutable({}, "keys")
 162     False
 163     >>> modifies_known_mutable([], "append")
 164     True
 165     >>> modifies_known_mutable([], "index")
 166     False
 167
 168     If called with an unsupported object (such as unicode) `False` is
 169     returned.
 170
 171     >>> modifies_known_mutable("foo", "upper")
 172     False
 173     """
 174     for typespec, unsafe in _mutable_spec:
 175         if isinstance(obj, typespec):
 176             return attr in unsafe
 177     return False
 178
 179
 180 class SandboxedEnvironment(Environment):
 181     """The sandboxed environment.  It works like the regular environment but
 182     tells the compiler to generate sandboxed code.  Additionally subclasses of
 183     this environment may override the methods that tell the runtime what
 184     attributes or functions are safe to access.
 185
 186     If the template tries to access insecure code a :exc:`SecurityError` is
 187     raised.  However also other exceptions may occour during the rendering so
 188     the caller has to ensure that all exceptions are catched.
 189     """
 190     sandboxed = True
 191
 192     #: default callback table for the binary operators.  A copy of this is
 193     #: available on each instance of a sandboxed environment as
 194     #: :attr:`binop_table`
 195     default_binop_table = {
 196         '+':        operator.add,
 197         '-':        operator.sub,
 198         '*':        operator.mul,
 199         '/':        operator.truediv,
 200         '//':       operator.floordiv,
 201         '**':       operator.pow,
 202         '%':        operator.mod
 203     }
 204
 205     #: default callback table for the unary operators.  A copy of this is
 206     #: available on each instance of a sandboxed environment as
 207     #: :attr:`unop_table`
 208     default_unop_table = {
 209         '+':        operator.pos,
 210         '-':        operator.neg
 211     }
 212
 213     #: a set of binary operators that should be intercepted.  Each operator
 214     #: that is added to this set (empty by default) is delegated to the
 215     #: :meth:`call_binop` method that will perform the operator.  The default
 216     #: operator callback is specified by :attr:`binop_table`.
 217     #:
 218     #: The following binary operators are interceptable:
 219     #: ``//``, ``%``, ``+``, ``*``, ``-``, ``/``, and ``**``
 220     #:
 221     #: The default operation form the operator table corresponds to the
 222     #: builtin function.  Intercepted calls are always slower than the native
 223     #: operator call, so make sure only to intercept the ones you are
 224     #: interested in.
 225     #:
 226     #: .. versionadded:: 2.6
 227     intercepted_binops = frozenset()
 228
 229     #: a set of unary operators that should be intercepted.  Each operator
 230     #: that is added to this set (empty by default) is delegated to the
 231     #: :meth:`call_unop` method that will perform the operator.  The default
 232     #: operator callback is specified by :attr:`unop_table`.
 233     #:
 234     #: The following unary operators are interceptable: ``+``, ``-``
 235     #:
 236     #: The default operation form the operator table corresponds to the
 237     #: builtin function.  Intercepted calls are always slower than the native
 238     #: operator call, so make sure only to intercept the ones you are
 239     #: interested in.
 240     #:
 241     #: .. versionadded:: 2.6
 242     intercepted_unops = frozenset()
 243
 244     def intercept_unop(self, operator):
 245         """Called during template compilation with the name of a unary
 246         operator to check if it should be intercepted at runtime.  If this
 247         method returns `True`, :meth:`call_unop` is excuted for this unary
 248         operator.  The default implementation of :meth:`call_unop` will use
 249         the :attr:`unop_table` dictionary to perform the operator with the
 250         same logic as the builtin one.
 251
 252         The following unary operators are interceptable: ``+`` and ``-``
 253
 254         Intercepted calls are always slower than the native operator call,
 255         so make sure only to intercept the ones you are interested in.
 256
 257         .. versionadded:: 2.6
 258         """
 259         return False
 260
 261
 262     def __init__(self, *args, **kwargs):
 263         Environment.__init__(self, *args, **kwargs)
 264         self.globals['range'] = safe_range
 265         self.binop_table = self.default_binop_table.copy()
 266         self.unop_table = self.default_unop_table.copy()
 267
 268     def is_safe_attribute(self, obj, attr, value):
 269         """The sandboxed environment will call this method to check if the
 270         attribute of an object is safe to access.  Per default all attributes
 271         starting with an underscore are considered private as well as the
 272         special attributes of internal python objects as returned by the
 273         :func:`is_internal_attribute` function.
 274         """
 275         return not (attr.startswith('_') or is_internal_attribute(obj, attr))
 276
 277     def is_safe_callable(self, obj):
 278         """Check if an object is safely callable.  Per default a function is
 279         considered safe unless the `unsafe_callable` attribute exists and is
 280         True.  Override this method to alter the behavior, but this won't
 281         affect the `unsafe` decorator from this module.
 282         """
 283         return not (getattr(obj, 'unsafe_callable', False) or
 284                     getattr(obj, 'alters_data', False))
 285
 286     def call_binop(self, context, operator, left, right):
 287         """For intercepted binary operator calls (:meth:`intercepted_binops`)
 288         this function is executed instead of the builtin operator.  This can
 289         be used to fine tune the behavior of certain operators.
 290
 291         .. versionadded:: 2.6
 292         """
 293         return self.binop_table[operator](left, right)
 294
 295     def call_unop(self, context, operator, arg):
 296         """For intercepted unary operator calls (:meth:`intercepted_unops`)
 297         this function is executed instead of the builtin operator.  This can
 298         be used to fine tune the behavior of certain operators.
 299
 300         .. versionadded:: 2.6
 301         """
 302         return self.unop_table[operator](arg)
 303
 304     def getitem(self, obj, argument):
 305         """Subscribe an object from sandboxed code."""
 306         try:
 307             return obj[argument]
 308         except (TypeError, LookupError):
 309             if isinstance(argument, string_types):
 310                 try:
 311                     attr = str(argument)
 312                 except Exception:
 313                     pass
 314                 else:
 315                     try:
 316                         value = getattr(obj, attr)
 317                     except AttributeError:
 318                         pass
 319                     else:
 320                         if self.is_safe_attribute(obj, argument, value):
 321                             return value
 322                         return self.unsafe_undefined(obj, argument)
 323         return self.undefined(obj=obj, name=argument)
 324
 325     def getattr(self, obj, attribute):
 326         """Subscribe an object from sandboxed code and prefer the
 327         attribute.  The attribute passed *must* be a bytestring.
 328         """
 329         try:
 330             value = getattr(obj, attribute)
 331         except AttributeError:
 332             try:
 333                 return obj[attribute]
 334             except (TypeError, LookupError):
 335                 pass
 336         else:
 337             if self.is_safe_attribute(obj, attribute, value):
 338                 return value
 339             return self.unsafe_undefined(obj, attribute)
 340         return self.undefined(obj=obj, name=attribute)
 341
 342     def unsafe_undefined(self, obj, attribute):
 343         """Return an undefined object for unsafe attributes."""
 344         return self.undefined('access to attribute %r of %r '
 345                               'object is unsafe.' % (
 346             attribute,
 347             obj.__class__.__name__
 348         ), name=attribute, obj=obj, exc=SecurityError)
 349
 350     def call(__self, __context, __obj, *args, **kwargs):
 351         """Call an object from sandboxed code."""
 352         # the double prefixes are to avoid double keyword argument
 353         # errors when proxying the call.
 354         if not __self.is_safe_callable(__obj):
 355             raise SecurityError('%r is not safely callable' % (__obj,))
 356         return __context.call(__obj, *args, **kwargs)
 357
 358
 359 class ImmutableSandboxedEnvironment(SandboxedEnvironment):
 360     """Works exactly like the regular `SandboxedEnvironment` but does not
 361     permit modifications on the builtin mutable objects `list`, `set`, and
 362     `dict` by using the :func:`modifies_known_mutable` function.
 363     """
 364
 365     def is_safe_attribute(self, obj, attr, value):
 366         if not SandboxedEnvironment.is_safe_attribute(self, obj, attr, value):
 367             return False
 368         return not modifies_known_mutable(obj, attr)