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Re: [Fwd: Re: ADsafe attack]

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  • David-Sarah Hopwood
    ... I m not convinced that it is sufficiently robust to just check for (this === window). This should work: function robustify(aType, methodName) { var proto =
    Message 1 of 11 , May 21, 2008
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      Douglas Crockford wrote:
      > I don't trust a blacklist approach to guard dot, so that would mean
      > outlawing dot except in a few specific cases, which would make use of
      > the language close to unbearable.
      >
      > So instead, I will fix Firefox:
      >
      > Array.prototype.concat = function () {
      > var concat = Array.prototype.concat;
      > return function () {
      > if (this === window) {
      > throw {
      > name: "ADsafe",
      > message: "ADsafe violation."
      > };
      > }
      > return concat.apply(this, arguments);
      > };
      > }();

      I'm not convinced that it is sufficiently robust to just check for
      (this === window). This should work:

      function robustify(aType, methodName) {
      var proto = aType.prototype;
      var oldMethod = proto[methodName];

      if ({}.__proto__ !== undefined) {
      aType.prototype[methodName] = function () {
      if (this.__proto__ !== proto) {
      throw {name: "ADsafe", message: "ADsafe violation."};
      }
      return oldMethod.apply(this, arguments);
      };
      } else {
      proto._type___ = proto;
      if (Object.dontEnum !== undefined) {
      Object.dontEnum(proto, '_type___');
      }
      aType.prototype[methodName] = function () {
      if (this._type___ !== proto) {
      throw {name: "ADsafe", message: "ADsafe violation."};
      }
      return oldMethod.apply(this, arguments);
      };
      }
      }

      robustify(Array, 'concat');

      However, without having a way to enumerate all of the functions,
      including undocumented ones, defined on the prototypes of
      {Object,Function,Array,String,Boolean,Number,Math,Date,RegExp,*Error},
      you still risk missing one that could potentially leak 'this'.

      Any chance of an Object.__allKeys__(object) method, which ignores
      DontEnum, in ES3.1?

      --
      David-Sarah Hopwood
    • Douglas Crockford
      ... We are considering an Object.keys method, but it will only return the own, enumerable property names.
      Message 2 of 11 , May 21, 2008
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        --- In caplet@yahoogroups.com, David-Sarah Hopwood <david.hopwood@...>
        wrote:
        > Any chance of an Object.__allKeys__(object) method, which ignores
        > DontEnum, in ES3.1?

        We are considering an Object.keys method, but it will only return the
        own, enumerable property names.
      • Douglas Crockford
        ... Why? The test is intended to reject invocations of the method as a function. What cases are missed?
        Message 3 of 11 , May 21, 2008
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          --- In caplet@yahoogroups.com, David-Sarah Hopwood <david.hopwood@...>
          wrote:
          > I'm not convinced that it is sufficiently robust to just check for
          > (this === window).

          Why? The test is intended to reject invocations of the method as a
          function. What cases are missed?
        • Mark S. Miller
          On Wed, May 21, 2008 at 12:02 PM, David-Sarah Hopwood ... Yes! The about-to-be-specified Object.getProperties(obj) will provide a reflective description of all
          Message 4 of 11 , May 21, 2008
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            On Wed, May 21, 2008 at 12:02 PM, David-Sarah Hopwood
            <david.hopwood@...> wrote:
            > Any chance of an Object.__allKeys__(object) method, which ignores
            > DontEnum, in ES3.1?

            Yes! The about-to-be-specified Object.getProperties(obj) will provide
            a reflective description of all an object's own properties. This
            operation itself will not be visible from Caja, and I wouldn't
            recommend that it be visible from ADsafe, but in both cases it's
            useful within the runtime libraries of these secure subsets, to help
            enforce useful properties, as you explain.


            --
            Cheers,
            --MarkM
          • David-Sarah Hopwood
            ... That s why I suggested a name using the __...__ convention. Otherwise, a subset language that does not do rewriting must do one of: - blacklist the name
            Message 5 of 11 , May 21, 2008
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              Mark S. Miller wrote:
              > On Wed, May 21, 2008 at 12:02 PM, David-Sarah Hopwood
              > <david.hopwood@...> wrote:
              >> Any chance of an Object.__allKeys__(object) method, which ignores
              >> DontEnum, in ES3.1?
              >
              > Yes! The about-to-be-specified Object.getProperties(obj) will provide
              > a reflective description of all an object's own properties. This
              > operation itself will not be visible from Caja, and I wouldn't
              > recommend that it be visible from ADsafe, but in both cases it's
              > useful within the runtime libraries of these secure subsets, to help
              > enforce useful properties, as you explain.

              That's why I suggested a name using the __...__ convention.

              Otherwise, a subset language that does not do rewriting must do one of:
              - blacklist the name 'getProperties', which is ugly;
              - rebind 'Object' when running subset code, which does not have
              well-defined semantics and may cause compatibility problems;
              - block access to 'Object', which would not otherwise be necessary.

              Actually, a better idea would be to move *all* of the methods proposed
              to be added to Object, to a new global 'Reflect'. Rebinding 'Reflect'
              in order to provide tamed versions of these operations when running
              subset code would not have the same problems as rebinding 'Object',
              since 'Reflect' is not used for anything else.

              --
              David-Sarah Hopwood
            • Douglas Crockford
              ... Mark came up with a better idea: ADsafe denies any access to Object.
              Message 6 of 11 , May 21, 2008
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                --- In caplet@yahoogroups.com, David-Sarah Hopwood <david.hopwood@...>
                wrote:
                > That's why I suggested a name using the __...__ convention.
                >
                > Otherwise, a subset language that does not do rewriting must do one of:
                > - blacklist the name 'getProperties', which is ugly;
                > - rebind 'Object' when running subset code, which does not have
                > well-defined semantics and may cause compatibility problems;
                > - block access to 'Object', which would not otherwise be necessary.
                >
                > Actually, a better idea would be to move *all* of the methods proposed
                > to be added to Object, to a new global 'Reflect'. Rebinding 'Reflect'
                > in order to provide tamed versions of these operations when running
                > subset code would not have the same problems as rebinding 'Object',
                > since 'Reflect' is not used for anything else.

                Mark came up with a better idea: ADsafe denies any access to Object.
              • David-Sarah Hopwood
                ... I don t want to have to do that in Jacaranda (where it would otherwise be safe to allow first-class access to Object). -- David-Sarah Hopwood
                Message 7 of 11 , May 21, 2008
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                  Douglas Crockford wrote:
                  > --- In caplet@yahoogroups.com, David-Sarah Hopwood <david.hopwood@...>
                  > wrote:
                  >> That's why I suggested a name using the __...__ convention.
                  >>
                  >> Otherwise, a subset language that does not do rewriting must do one of:
                  >> - blacklist the name 'getProperties', which is ugly;
                  >> - rebind 'Object' when running subset code, which does not have
                  >> well-defined semantics and may cause compatibility problems;
                  >> - block access to 'Object', which would not otherwise be necessary.
                  >>
                  >> Actually, a better idea would be to move *all* of the methods proposed
                  >> to be added to Object, to a new global 'Reflect'. Rebinding 'Reflect'
                  >> in order to provide tamed versions of these operations when running
                  >> subset code would not have the same problems as rebinding 'Object',
                  >> since 'Reflect' is not used for anything else.
                  >
                  > Mark came up with a better idea: ADsafe denies any access to Object.

                  I don't want to have to do that in Jacaranda (where it would otherwise
                  be safe to allow first-class access to Object).

                  --
                  David-Sarah Hopwood
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