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    SubjectRE: [PATCH 1/4] sctp: fix association hangs due to off-by-one errors in sctp_tsnmap_grow()
    Date
    Vlad,

    > -----Original Message-----
    > From: Vlad Yasevich [mailto:vyasevich@gmail.com]
    > Sent: Thursday, February 21, 2013 10:19 AM
    > To: Roberts, Lee A.
    > Cc: linux-sctp@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.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@hp.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@hp.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;
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > >



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