linux/net/sctp
Daniel Borkmann b58537a1f5 net: sctp: fix permissions for rto_alpha and rto_beta knobs
Commit 3fd091e73b ("[SCTP]: Remove multiple levels of msecs
to jiffies conversions.") has silently changed permissions for
rto_alpha and rto_beta knobs from 0644 to 0444. The purpose of
this was to discourage users from tweaking rto_alpha and
rto_beta knobs in production environments since they are key
to correctly compute rtt/srtt.

RFC4960 under section 6.3.1. RTO Calculation says regarding
rto_alpha and rto_beta under rule C3 and C4:

  [...]
  C3)  When a new RTT measurement R' is made, set

       RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|

       and

       SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'

       Note: The value of SRTT used in the update to RTTVAR
       is its value before updating SRTT itself using the
       second assignment. After the computation, update
       RTO <- SRTT + 4 * RTTVAR.

  C4)  When data is in flight and when allowed by rule C5
       below, a new RTT measurement MUST be made each round
       trip. Furthermore, new RTT measurements SHOULD be
       made no more than once per round trip for a given
       destination transport address. There are two reasons
       for this recommendation: First, it appears that
       measuring more frequently often does not in practice
       yield any significant benefit [ALLMAN99]; second,
       if measurements are made more often, then the values
       of RTO.Alpha and RTO.Beta in rule C3 above should be
       adjusted so that SRTT and RTTVAR still adjust to
       changes at roughly the same rate (in terms of how many
       round trips it takes them to reflect new values) as
       they would if making only one measurement per
       round-trip and using RTO.Alpha and RTO.Beta as given
       in rule C3. However, the exact nature of these
       adjustments remains a research issue.
  [...]

While it is discouraged to adjust rto_alpha and rto_beta
and not further specified how to adjust them, the RFC also
doesn't explicitly forbid it, but rather gives a RECOMMENDED
default value (rto_alpha=3, rto_beta=2). We have a couple
of users relying on the old permissions before they got
changed. That said, if someone really has the urge to adjust
them, we could allow it with a warning in the log.

Fixes: 3fd091e73b ("[SCTP]: Remove multiple levels of msecs to jiffies conversions.")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-15 01:17:32 -07:00
..
associola.c sctp: Fix sk_ack_backlog wrap-around problem 2014-06-12 10:27:14 -07:00
auth.c net: sctp: cache auth_enable per endpoint 2014-04-18 18:32:00 -04:00
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 net: sctp: migrate most recently used transport to ktime 2014-06-11 12:23:17 -07:00
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: Eliminate no_check from protosw 2014-05-23 16:28:53 -04:00
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 net: rename local_df to ignore_df 2014-05-12 14:03:41 -04:00
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 snmp: fix some left over of snmp stats 2014-05-14 15:33:47 -04:00
protocol.c net: Eliminate no_check from protosw 2014-05-23 16:28:53 -04:00
sm_make_chunk.c ktime: add ktime_after and ktime_before helper 2014-06-11 12:23:17 -07:00
sm_sideeffect.c net: sctp: Don't transition to PF state when transport has exhausted 'Path.Max.Retrans'. 2014-04-27 23:41:14 -04:00
sm_statefuns.c net: sctp: cache auth_enable per endpoint 2014-04-18 18:32:00 -04:00
sm_statetable.c sctp: fix checkpatch errors with indent 2013-12-26 13:47:48 -05:00
socket.c net: Split sk_no_check into sk_no_check_{rx,tx} 2014-05-23 16:28:53 -04:00
ssnmap.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
sysctl.c net: sctp: fix permissions for rto_alpha and rto_beta knobs 2014-06-15 01:17:32 -07:00
transport.c net: sctp: migrate most recently used transport to ktime 2014-06-11 12:23:17 -07:00
tsnmap.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
ulpevent.c Revert "net: sctp: Fix a_rwnd/rwnd management to reflect real state of the receiver's buffer" 2014-04-14 16:26:48 -04:00
ulpqueue.c sctp: add support for busy polling to sctp protocol 2014-04-20 18:18:55 -04:00