[poppler] Poppler and MOAB-06-01-2007

Jeff Muizelaar jeff at infidigm.net
Thu Jan 11 08:24:49 PST 2007

On Thu, Jan 11, 2007 at 10:33:39AM -0500, Kristian Høgsberg wrote:
> On 1/11/07, Jeff Muizelaar <jeff at infidigm.net> wrote:
> >On Thu, Jan 11, 2007 at 08:45:48AM -0500, Kristian Høgsberg wrote:
> ...
> >> And the problem in this case is how to prevent looping when we have
> >> circular references in the page tree.  To prevent this we can do two
> >> things: the one idea that Albert doesn't like is to just limit the
> >> depth of the page tree.  We can either choose a fixed limit or use the
> >> total number of references as a limit.  If there is a page tree chain
> >> longer than, say, 1000, the document is most certainly malicious.  On
> >> the other hand, we can easily handle a recusion level of 1000, so we
> >> can detect it and bail out safely in that case.
> >>
> >> The other idea is to just put a 'visited' bit in each node of the page
> >> tree.  If wee see a page that already has the 'visited' bit set we
> >> know something is wrong and we can bail out right away.
> >
> >I looked at this idea first. However, I didn't see how it could fit
> >easily with the exisiting code structure. The solution I came with is to
> >have a bitmap of size XRef->size(), then for each object we visit mark
> >the bit corresponding to that object. If the bit is already set we know
> >that we have a loop in the tree.
> But why not just limit the recursion depth to XRef->size() calls?

Didn't think of that. Sounds like that would work just fine as well, and
should be even easier to implement.


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