Re: [xml] Security fix for libxml2

[Mike Hommey <mh glandium org>]

On Sun, Aug 24, 2008 at 10:51:59AM +0200, Daniel Veillard wrote:
> On Sun, Aug 24, 2008 at 10:15:41AM +0200, Mike Hommey wrote:
> > On Wed, Aug 20, 2008 at 07:00:51PM +0200, Daniel Veillard wrote:
> > >   Bad news, when checking against recursive entities expansion problem
> > > back when it was made official (c.f. the billion laught attack circa
> > > 2004) I had checked for the normal recursion, but when happening in
> > > an attribute avlue the resource consumption is way faster and the
> > > recursion detection in place is not sufficient to catch the problem.
> > >
> > >   Basically when this happen within an attribute just checking for
> > > a recursion depth is not sufficient, and the only good method I could
> > > find was to count the number of entities replacement taking place while
> > > parsing a given document, and drop parsing after half a million
> > > substitution. I think it's a fair default processand what the patches
> > > below implements for various libxml2 versions, but i can understand that
> > > in some case that may be problematic. So i intend in the next release
> > > (2.7.0 hopefully available soon) to add a parser flag removing the
> > > hardcoded limits (there is also a maximum document depth in place).
> > >
> > >   Distributions have been made aware of the problem for a couple of
> > > weeks and updates should be available soon from normal update channels
> > > I'm updating SVN with the fix too,
> >
> > FWIW, this patch broke binary compatibility with librsvg, which,
> > foolishly, create xmlEntity objects "by hand" with a
> > malloc(sizeof(xmlEntity)), in rsvg_entity_decl, which is sets as SAX
> > entity handler.
>
>   Yup:
>     http://bugzilla.gnome.org/show_bug.cgi?id=549087
>     https://bugzilla.redhat.com/show_bug.cgi?id=459830
>
> I have some backward compatible patches on that last bug
>
> > I hope there aren't any more surprises with other libraries or programs.
>
>   yeah, it's a serious problem, I made data structure available
> to help with fast access to the trees, but people have abused it,
> I hope there isn't too many of those.
>   I hope librsvg get fixed, because I would really prefer the clean
> solution in the upcoming 2.7.0 release.

FWIW, strigi is also impacted.
http://websvn.kde.org/trunk/kdesupport/strigi/src/streamanalyzer/fieldpropertiesdb.cpp?view=markup
(look for "new xmlEntity")

Mike