linux/net/sctp
Daniel Borkmann 4c47af4d5e net: sctp: rework multihoming retransmission path selection to rfc4960
Problem statement: 1) both paths (primary path1 and alternate
path2) are up after the association has been established i.e.,
HB packets are normally exchanged, 2) path2 gets inactive after
path_max_retrans * max_rto timed out (i.e. path2 is down completely),
3) now, if a transmission times out on the only surviving/active
path1 (any ~1sec network service impact could cause this like
a channel bonding failover), then the retransmitted packets are
sent over the inactive path2; this happens with partial failover
and without it.

Besides not being optimal in the above scenario, a small failure
or timeout in the only existing path has the potential to cause
long delays in the retransmission (depending on RTO_MAX) until
the still active path is reselected. Further, when the T3-timeout
occurs, we have active_patch == retrans_path, and even though the
timeout occurred on the initial transmission of data, not a
retransmit, we end up updating retransmit path.

RFC4960, section 6.4. "Multi-Homed SCTP Endpoints" states under
6.4.1. "Failover from an Inactive Destination Address" the
following:

  Some of the transport addresses of a multi-homed SCTP endpoint
  may become inactive due to either the occurrence of certain
  error conditions (see Section 8.2) or adjustments from the
  SCTP user.

  When there is outbound data to send and the primary path
  becomes inactive (e.g., due to failures), or where the SCTP
  user explicitly requests to send data to an inactive
  destination transport address, before reporting an error to
  its ULP, the SCTP endpoint should try to send the data to an
  alternate __active__ destination transport address if one
  exists.

  When retransmitting data that timed out, if the endpoint is
  multihomed, it should consider each source-destination address
  pair in its retransmission selection policy. When retransmitting
  timed-out data, the endpoint should attempt to pick the most
  divergent source-destination pair from the original
  source-destination pair to which the packet was transmitted.

  Note: Rules for picking the most divergent source-destination
  pair are an implementation decision and are not specified
  within this document.

So, we should first reconsider to take the current active
retransmission transport if we cannot find an alternative
active one. If all of that fails, we can still round robin
through unkown, partial failover, and inactive ones in the
hope to find something still suitable.

Commit 4141ddc02a ("sctp: retran_path update bug fix") broke
that behaviour by selecting the next inactive transport when
no other active transport was found besides the current assoc's
peer.retran_path. Before commit 4141ddc02a, we would have
traversed through the list until we reach our peer.retran_path
again, and in case that is still in state SCTP_ACTIVE, we would
take it and return. Only if that is not the case either, we
take the next inactive transport.

Besides all that, another issue is that transports in state
SCTP_UNKNOWN could be preferred over transports in state
SCTP_ACTIVE in case a SCTP_ACTIVE transport appears after
SCTP_UNKNOWN in the transport list yielding a weaker transport
state to be used in retransmission.

This patch mostly reverts 4141ddc02a, but also rewrites
this function to introduce more clarity and strictness into
the code. A strict priority of transport states is enforced
in this patch, hence selection is active > unkown > partial
failover > inactive.

Fixes: 4141ddc02a ("sctp: retran_path update bug fix")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Acked-by: Vlad Yasevich <yasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-02-22 00:26:05 -05:00
..
associola.c net: sctp: rework multihoming retransmission path selection to rfc4960 2014-02-22 00:26:05 -05:00
auth.c sctp: fix checkpatch errors with open brace '{' and trailing statements 2013-12-26 13:47:48 -05:00
bind_addr.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
chunk.c sctp: fix checkpatch errors with space required or prohibited 2013-12-26 13:47:47 -05:00
command.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
debug.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
endpointola.c sctp: remove macros sctp_local_bh_{disable|enable} 2014-01-21 18:40:40 -08:00
input.c sctp: remove macros sctp_bh_[un]lock_sock 2014-01-21 18:41:36 -08:00
inqueue.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
ipv6.c net: sctp: fix initialization of local source address on accepted ipv6 sockets 2014-02-06 21:18:06 -08:00
Kconfig net: sctp: get rid of SCTP_DBG_TSNS entirely 2013-07-02 00:08:03 -07:00
Makefile sctp: implement sctp association probing module 2010-04-30 22:41:09 -04:00
objcnt.c sctp: fix checkpatch errors with (foo*)|foo * bar|foo* bar 2013-12-26 13:47:47 -05:00
output.c sctp: move skb_dst_set() a bit downwards in sctp_packet_transmit() 2013-12-31 14:31:44 -05:00
outqueue.c Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-01-06 17:37:45 -05:00
primitive.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
probe.c sctp: loading sctp when load sctp_probe 2013-12-16 20:04:27 -05:00
proc.c sctp: remove macros sctp_local_bh_{disable|enable} 2014-01-21 18:40:40 -08:00
protocol.c sctp: remove macros sctp_bh_[un]lock_sock 2014-01-21 18:41:36 -08:00
sm_make_chunk.c sctp: make sctp_addto_chunk_fixed local 2014-01-13 14:42:30 -08:00
sm_sideeffect.c net: sctp: Potentially-Failed state should not be reached from unconfirmed state 2014-02-20 13:24:56 -05:00
sm_statefuns.c net: sctp: Fix a_rwnd/rwnd management to reflect real state of the receiver's buffer 2014-02-17 00:16:56 -05:00
sm_statetable.c sctp: fix checkpatch errors with indent 2013-12-26 13:47:48 -05:00
socket.c net: sctp: fix sctp_connectx abi for ia32 emulation/compat mode 2014-02-18 16:06:48 -05:00
ssnmap.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
sysctl.c sctp: optimize the sctp_sysctl_net_register 2014-02-13 17:08:29 -05:00
transport.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-12-09 20:20:14 -05:00
tsnmap.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
ulpevent.c net: sctp: Fix a_rwnd/rwnd management to reflect real state of the receiver's buffer 2014-02-17 00:16:56 -05:00
ulpqueue.c sctp: fix checkpatch errors with open brace '{' and trailing statements 2013-12-26 13:47:48 -05:00