Re: [PATCH net] sctp: fix SSN comparision

["'Marcelo Ricardo Leitner'" <marcelo.leitner@gmail.com>]

On Mon, Sep 19, 2016 at 10:41:34AM +0000, David Laight wrote:
> From: 'Marcelo Ricardo Leitner'
> > Sent: 16 September 2016 18:22
> ...
> >         frags = sack->variable;
> > -       gap = tsn - ctsn;
> > -       for (i = 0; i < ntohs(sack->num_gap_ack_blocks); ++i) {
> > -               if (TSN_lte(ntohs(frags[i].gab.start), gap) &&
> > -                   TSN_lte(gap, ntohs(frags[i].gab.end)))
> > +       blocks = ntohs(sack->num_gap_ack_blocks);
> > +       for (i = 0; i < blocks; ++i) {
> > +               if (TSN_lte(ctsn + ntohs(frags[i].gab.start), tsn) &&
> > +                   TSN_lte(tsn, ctsn + ntohs(frags[i].gab.end)))
> >                         goto pass;
> 
> I think I now understand what all the values are!
> The correct test is just:
> 			if (gap > ntohs(frags[i].gab.start) &&
> 			    gap <= ntohs(frags[i].gab.end))
> (I think the ends are right).
> gab.start/end are 16bit unsigned offsets from ctsn.
> All the module arithmetic is sorted out when 'tsn' is converted to an
> offset from ctsn. 'gap' is a very bad name for the tsn_offset.

Yep! I like this approach, thanks.
And in case tsn is actually smaller than ctsn in this code, than that's
another bug actually, so I think your suggestion covers all the cases.

Though the ends are both inclusive.
Handy https://tools.ietf.org/html/rfc4960#section-3.3.4 if you want.

> 
> Looks like gap.start/end should be saved in host order though.

I lost you here. gab.start/end you mean? Saved?

  Marcelo