Wireshark-dev: Re: [Wireshark-dev] [Wireshark-commits] rev 52578: /trunk/epan/ /trunk/epan/: pr
From: Jakub Zawadzki <[email protected]>
Date: Sun, 13 Oct 2013 09:54:40 +0200
> On Sun, Oct 13, 2013 at 12:54 AM,  <[email protected]> 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);

About tvb_offset_exists() comment, compute_offset() is not returning
exception when offset == tvb->length.

Kuba.