[3.19.y-ckt stable] Patch "sctp: fix the transports round robin issue when init is retransmitted" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    sctp: fix the transports round robin issue when init is retransmitted

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt18.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 640b8bf3f4acc2496df7e4f6a003934c8ff7787e Mon Sep 17 00:00:00 2001
From: Xin Long <lucien.xin at gmail.com>
Date: Thu, 10 Mar 2016 15:31:57 +0800
Subject: sctp: fix the transports round robin issue when init is retransmitted

commit 39d2adebf137de5f900843f69f5e500932e31047 upstream.

prior to this patch, at the beginning if we have two paths in one assoc,
they may have the same params other than the last_time_heard, it will try
the paths like this:

1st cycle
  try trans1 fail.
  then trans2 is selected.(cause it's last_time_heard is after trans1).

2nd cycle:
  try  trans2 fail
  then trans2 is selected.(cause it's last_time_heard is after trans1).

3rd cycle:
  try  trans2 fail
  then trans2 is selected.(cause it's last_time_heard is after trans1).

....

trans1 will never have change to be selected, which is not what we expect.
we should keeping round robin all the paths if they are just added at the
beginning.

So at first every tranport's last_time_heard should be initialized 0, so
that we ensure they have the same value at the beginning, only by this,
all the transports could get equal chance to be selected.

Then for sctp_trans_elect_best, it should return the trans_next one when
*trans == *trans_next, so that we can try next if it fails,  but now it
always return trans. so we can fix it by exchanging these two params when
we calls sctp_trans_elect_tie().

Fixes: 4c47af4d5eb2 ('net: sctp: rework multihoming retransmission path selection to rfc4960')
Signed-off-by: Xin Long <lucien.xin at gmail.com>
Acked-by: Daniel Borkmann <daniel at iogearbox.net>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/sctp/associola.c | 2 +-
 net/sctp/transport.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 26d06db..d016bd5 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1257,7 +1257,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
 	if (score_curr > score_best)
 		return curr;
 	else if (score_curr == score_best)
-		return sctp_trans_elect_tie(curr, best);
+		return sctp_trans_elect_tie(best, curr);
 	else
 		return best;
 }
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index a0a4318..f45b05d 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -72,7 +72,7 @@ static struct sctp_transport *sctp_transport_init(struct net *net,
 	 */
 	peer->rto = msecs_to_jiffies(net->sctp.rto_initial);

-	peer->last_time_heard = ktime_get();
+	peer->last_time_heard = ktime_set(0, 0);
 	peer->last_time_ecne_reduced = jiffies;

 	peer->param_flags = SPP_HB_DISABLE |
--
2.7.4