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authorDaniel Borkmann <dborkman@redhat.com>2014-06-15 00:59:14 +0200
committerDavid S. Miller <davem@davemloft.net>2014-06-15 01:17:32 -0700
commitb58537a1f5629bdc98a8b9dc2051ce0e952f6b4b (patch)
tree48ac36dadd2e162b27ead7bdd630d0efa1e0ea0d /MAINTAINERS
parente4f7ae930afafd4d9d67449657fefe51010c3349 (diff)
downloadlinux-stericsson-b58537a1f5629bdc98a8b9dc2051ce0e952f6b4b.tar.gz
net: sctp: fix permissions for rto_alpha and rto_beta knobs
Commit 3fd091e73b81 ("[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: 3fd091e73b81 ("[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>
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