RE: [PATCH 1/4] sctp: fix association hangs due to off-by-oneerrors in sctp_tsnmap_grow()

[Roberts, Lee A.]

Vlad,

> -----Original Message-----
> From: Roberts, Lee A.
> Sent: Thursday, February 21, 2013 11:00 AM
> To: 'Vlad Yasevich'
> Cc: linux-sctp@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: RE: [PATCH 1/4] sctp: fix association hangs due to off-by-one errors in sctp_tsnmap_grow()
> 
> Vlad,
> 
> > -----Original Message-----
> > From: Vlad Yasevich [mailto:vyasevich@xxxxxxxxx]
> > Sent: Thursday, February 21, 2013 10:19 AM
> > To: Roberts, Lee A.
> > Cc: linux-sctp@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH 1/4] sctp: fix association hangs due to off-by-one errors in sctp_tsnmap_grow()
> >
> > On 02/21/2013 11:44 AM, Roberts, Lee A. wrote:
> > > From: Lee A. Roberts <lee.roberts@xxxxxx>
> > >
> > > Resolve SCTP association hangs observed during SCTP stress
> > > testing.  Observable symptoms include communications hangs
> > > with data being held in the association lobby (ordering)
> > > queue.  Close examination of reassembly/ordering queues shows
> > > duplicated packets.
> > >
> > > In sctp_tsnmap_grow(), correct off-by-one errors when copying
> > > and resizing the tsnmap.  If max_tsn_seen is in the LSB of the
> > > word, this bit can be lost, causing the corresponding packet
> > > to be transmitted again and to be entered as a duplicate into
> > > the SCTP reassembly/ordering queues.
> > >
> > > Patch applies to linux-3.8 kernel.
> > >
> > > Signed-off-by: Lee A. Roberts <lee.roberts@xxxxxx>
> > > ---
> > >   net/sctp/tsnmap.c |    5 +++--
> > >   1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff -uprN -X linux-3.8-vanilla/Documentation/dontdiff linux-3.8-vanilla/net/sctp/tsnmap.c linux-
> > 3.8-SCTP+1/net/sctp/tsnmap.c
> > > --- linux-3.8-vanilla/net/sctp/tsnmap.c	2013-02-18 16:58:34.000000000 -0700
> > > +++ linux-3.8-SCTP+1/net/sctp/tsnmap.c	2013-02-20 08:01:02.555223259 -0700
> > > @@ -369,14 +369,15 @@ static int sctp_tsnmap_grow(struct sctp_
> > >   	if (gap >= SCTP_TSN_MAP_SIZE)
> >
> > No that I think about this a bit more, this should be gap + 1.  If you
> > do that, you might as well call sctp_tsnmap_grow() with gap+1 as
> > argument and then can just use the 'gap' everywhere inside.
> 
> I think the calculation of "gap" in sctp_tsnmap_mark() should change:
> 
> -	gap = tsn - map->base_tsn;
> +	gap = tsn - map->cumulative_tsn_ack_point;
> 

Oops, this breaks the logic that follows.  Using "gap + 1" in the call should work.
I sent an updated patch (v3).

                                    - Lee

> >
> > >   		return 0;
> > >
> > > -	inc = ALIGN((gap - map->len),BITS_PER_LONG) + SCTP_TSN_MAP_INCREMENT;
> > > +	inc = ALIGN((gap - map->len + 1), BITS_PER_LONG)
> > > +		+ SCTP_TSN_MAP_INCREMENT;
> > >   	len = min_t(u16, map->len + inc, SCTP_TSN_MAP_SIZE);
> > >
> > >   	new = kzalloc(len>>3, GFP_ATOMIC);
> > >   	if (!new)
> > >   		return 0;
> > >
> > > -	bitmap_copy(new, map->tsn_map, map->max_tsn_seen - map->base_tsn);
> > > +	bitmap_copy(new, map->tsn_map, map->max_tsn_seen - map->base_tsn + 1);
> >
> > Can simplify that this by using map->cumulative_tsn_ack_point instead of
> > base_tsn.
> >
> > -vlad
> >
> 
> I changed the code to use "cumulative_tsn_ack_point" in an updated version
> of the patch.
> 
>                                          -- Lee
> 
> > >   	kfree(map->tsn_map);
> > >   	map->tsn_map = new;
> > >   	map->len = len;
> > > --
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> > >

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