Re: [Wireshark-commits] rev 52578: /trunk/epan/ /trunk/epan/: proto.c tvbuff.c tvbuff.h

[Evan Huus <eapache () gmail com>]

On Sun, Oct 13, 2013 at 3:54 AM, Jakub Zawadzki
<darkjames-ws () darkjames pl> wrote:
> > On Sun, Oct 13, 2013 at 12:54 AM,  <eapache () wireshark org> wrote:
> > > http://anonsvn.wireshark.org/viewvc/viewvc.cgi?view=rev&revision=52578
> > >
> > > User: eapache
> > > Date: 2013/10/13 04:54 AM
> > >
> > > Log:
> [...]
> > >  All of this is (theoretically) unnecessary - simply checking the offset without
> > >  worrying about the length will still catch the very-long-loops, since it is the
> > >  offset that increases in each iteration, not the length.
> > >
> > >  All that to justify:
> > >  - implement tvb_ensure_offset_exists which throws an exception if the offset is
> > >    not within the tvb
> > >  - use it instead of all the complicated other logic in the pre-short-circuit
> > >    step of proto_tree_add_item and friends
> > >
> > >  This gives us back about 3/4 of the performance we lost in the original patch.
> > >  We're still ~2% slower than without any check, but this is the best I can think
> > >  of right now.
>
> On Sun, Oct 13, 2013 at 12:58:12AM -0400, Evan Huus wrote:
> > Jeff (and/or anyone else who cares) I'd appreciate a verification that
> > my logic here is correct, and that I've not accidentally undone your
> > good work.
>
> I think it's fine, unless in loops there're some weird offset integer overflows (which returns back to offset + 0), 
> like easy case:
>
>         proto_tree_add_item(..., offset, 0xfffffffe /* -2 */, ...); offset += (-2);
>         proto_tree_add_item(..., offset, +2, ...); offset += (+2);

You were right, the fuzz-bot found some infinite loops of this type,
so I reverted the change. I guess we're just going to have to take the
performance hit (sorry Anders).
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