netdev - RE: [PATCH 1/4] sctp: fix association hangs due to off-by-one errors in sctp_tsnmap

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Date:	Thu, 21 Feb 2013 18:00:24 +0000
From:	"Roberts, Lee A." <lee.roberts@...com>
To:	Vlad Yasevich <vyasevich@...il.com>
CC:	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
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@...il.com]
> Sent: Thursday, February 21, 2013 10:19 AM
> To: Roberts, Lee A.
> Cc: linux-sctp@...r.kernel.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> 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@...com>
> >
> > 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@...com>
> > ---
> >   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;

> 
> >   		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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