Re: [PATCH 1/4] sctp: fix association hangs due to off-by-one errorsin sctp_tsnmap_grow()

From: Vlad Yasevich
Date: Thu Feb 21 2013 - 12:18:59 EST

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.

return 0;

- inc = ALIGN((gap - map->len),BITS_PER_LONG) + SCTP_TSN_MAP_INCREMENT;
+ inc = ALIGN((gap - map->len + 1), BITS_PER_LONG)
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.


map->tsn_map = new;
map->len = len;
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