[3.13.y.z extended stable] Patch "net: sctp: Potentially-Failed state should not be reached from unconfirmed state" has been added to staging queue

[Kamal Mostafa]

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

    net: sctp: Potentially-Failed state should not be reached from unconfirmed state

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.4.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 133467507527bba47deef08f1db265bfeee2bfde Mon Sep 17 00:00:00 2001
From: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext at nsn.com>
Date: Thu, 20 Feb 2014 14:13:04 +0100
Subject: net: sctp: Potentially-Failed state should not be reached from
 unconfirmed state

commit 7cce3b75682ff898c935c17d186983cbf3ed393e upstream.

In current implementation it is possible to reach PF state from unconfirmed.
We can interpret sctp-failover-02 in a way that PF state is meant to be reached
only from active state, in the end, this is when entering PF state makes sense.
Here are few quotes from sctp-failover-02, but regardless of these, same
understanding can be reached from whole section 5:

Section 5.1, quickfailover guide:
    "The PF state is an intermediate state between Active and Failed states."

    "Each time the T3-rtx timer expires on an active or idle
    destination, the error counter of that destination address will
    be incremented.  When the value in the error counter exceeds
    PFMR, the endpoint should mark the destination transport address as PF."

There are several concrete reasons for such interpretation. For start, rfc4960
does not take into concern quickfailover algorithm. Therefore, quickfailover
must comply to 4960. Point where this compliance can be argued is following
behavior:
When PF is entered, association overall error counter is incremented for each
missed HB. This is contradictory to rfc4960, as address, while in unconfirmed
state, is subjected to probing, and while it is probed, it should not increment
association overall error counter. This has as a consequence that we might end
up in situation in which we drop association due path failure on unconfirmed
address, in case we have wrong configuration in a way:
Association.Max.Retrans == Path.Max.Retrans.

Another reason is that entering PF from unconfirmed will cause a loss of address
confirmed event when address is once (if) confirmed. This is fine from failover
guide point of view, but it is not consistent with behavior preceding failover
implementation and recommendation from 4960:

5.4.  Path Verification
   Whenever a path is confirmed, an indication MAY be given to the upper
   layer.

Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext at nsn.com>
Acked-by: Vlad Yasevich <vyasevich at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/sctp/sm_sideeffect.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index 1a6eef3..04b1398 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -496,11 +496,12 @@ static void sctp_do_8_2_transport_strike(sctp_cmd_seq_t *commands,
 	}

 	/* If the transport error count is greater than the pf_retrans
-	 * threshold, and less than pathmaxrtx, then mark this transport
-	 * as Partially Failed, ee SCTP Quick Failover Draft, secon 5.1,
-	 * point 1
+	 * threshold, and less than pathmaxrtx, and if the current state
+	 * is not SCTP_UNCONFIRMED, then mark this transport as Partially
+	 * Failed, see SCTP Quick Failover Draft, section 5.1
 	 */
 	if ((transport->state != SCTP_PF) &&
+	   (transport->state != SCTP_UNCONFIRMED) &&
 	   (asoc->pf_retrans < transport->pathmaxrxt) &&
 	   (transport->error_count > asoc->pf_retrans)) {

--
1.9.1