Loading ...
Sorry, an error occurred while loading the content.

Re: [caplet] Re: ADsafe validation

Expand Messages
  • Mike Samuel
    On 21/03/2008, David-Sarah Hopwood ... Or a committee of evil geniuses. ... Caja deals with many of these problems by rewriting. We can deal perfectly well
    Message 1 of 16 , Mar 21, 2008
    • 0 Attachment
      On 21/03/2008, David-Sarah Hopwood
      <david.hopwood@...> wrote:
      >
      >
      >
      >
      >
      >
      >
      > Mike Samuel wrote:
      > > On 21/03/2008, David-Sarah Hopwood
      > > <david.hopwood@...> wrote:
      > >> Mike Samuel wrote:
      > >> > On 21/03/2008, Kris Zyp <kris@...> wrote:
      > >> >>
      > >> >>> Do we have a regression test suite of tricky examples?
      > >> >> That would be awesome.
      > >> >>
      > >> >>> For instance, I don't see the string "cc_on" in Kris' validator, but that feature
      > >> >>> tripped up ADsafe a few months ago.
      > >> >> Thanks for the heads, fixed it.
      > >> >
      > >> > Can you disallow @ outside of string literals entirely?
      > >> >
      > >> > What if ADSafe code is included in a container that has @cc_on, and
      > >> > does an @set that overrides a variable defined in the container?
      > >>
      > >> '@' does not appear anywhere in the ES3 grammar outside string literals,
      > >> regexp literals, and comments, right? Isn't ADsafe defined to be a subset
      > >> of ES3?
      > >>
      > >> (See ECMA-262 section 7.6; note that '@' is 'Punctuation' but not
      > >> 'Connector punctuation' in Unicode 2.1 [insert grumble about using such
      > >> an old Unicode version], so it is not valid in an identifier.)
      > >
      > > Yep. @ often appears in JSDoc style comments:
      > > http://jsdoc.sourceforge.net/#tagref so banning @ in comments might
      > > make some programmers grumble.
      > >
      > > It also indicates a conditional compilation directive in IE and I
      > > don't have a specific exploit in mind but I don't know whether
      > > blacklisting @cc_on is sufficient to avoid using conditional
      > > compilation to split or join tokens that otherwise appear separate.
      > >
      > > Perhaps either ban @ outside string/regexp contexts, or recommend that
      > > containers not allow @cc_on.
      >
      > I meant my point a bit more generally:
      >
      > Assume that any extension to strict ES3 is designed by an evil genius trying

      Or a committee of evil geniuses.


      > to break ADsafe (or Caja, or whatever), and you won't go far wrong. It's
      > impossible to review all of the browser extensions: they aren't adequately
      > documented, even if they were documented it would be too much work, and
      > many of them display total cluelessness about programming language design.

      Caja deals with many of these problems by rewriting. We can deal
      perfectly well with @ by stripping comments, and rewriting '@' to \x40
      in strings and regexps.

      ADSafe is a really elegant design, but my concern with the validation
      approach, besides blacklisting in general, is that it seems to accrete
      these rules which must seem arbitrary and hard to remember to coders.

      And if a vulnerability is discovered, a rewriter can add a new rewrite
      rule, and apply that to existing programs, whereas a validator might
      have to reject previously valid programs, which won't work until their
      creator actually looks at the program, learns the new rule, and
      applies it.


      > (Preprocessing features in client-side Javascript? What's the point of that?
      > Just preprocess it on the server.)

      This presupposes the existence of a server. If you're using a
      cut-rate hosting service that only serves of static files, then you
      need to do everything on the client.

      I agree though that preprocessing on the client is a little weird,
      since one of the typical goals of preprocessing is to avoid wasting
      bandwidth on code the client doesn't need -- the logic could otherwise
      just use the language's conditional constructs.


      > --
      > David-Sarah Hopwood
    • Kris Zyp
      ... Also, because with the new cross-site XHR and XDR capabilities, web sites can directly request the scripts from other sites, which can potentially be
      Message 2 of 16 , Mar 21, 2008
      • 0 Attachment
        
        > (Preprocessing features in client-side Javascript? What's the point of that?
        > Just preprocess it on the server.)
        Also, because with the new cross-site XHR and XDR capabilities, web sites can directly request the scripts from other sites, which can potentially be significantly faster than sending them through your proxy (and incurring queuing against your own connection limit on the client). This could also reduces the burden on the server, always nice to offload to the infinitely scalable client (a new cpu for each user).
        IMO, performance is going to be a critical part of the acceptance of secured JavaScript. I would bet that a large percentage of potential users won't find the benefit of secure JavaScript compelling enough if there site takes twice as long to load. Of course this belief is one of the reasons for wanting to create a small fast 5K-ish library.
        Even without the new cross-site XHR and XDR capabilities, I think ADsafe client side validation could have a use, since we do have cross-site requesting mechanisms that are safe (like CrossSafe/Subspace). However, CrossSafe can't safely bring scripts into the container, only data. With ADsafe, CrossSafe could bring those scripts across using existing widespread browser technology.
        However, I do certainly agree that many users will prefer the server-side validation. Has anyone created a server-side ADsafe validator yet, or is that another project waiting to be undertaken?
        Kris
      Your message has been successfully submitted and would be delivered to recipients shortly.