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The IPv6 temporary address generation uses a variable called DESYNC_FACTOR to prevent hosts updating the addresses at the same time. Quoting RFC 4941: ... The value DESYNC_FACTOR is a random value (different for each client) that ensures that clients don't synchronize with each other and generate new addresses at exactly the same time ... DESYNC_FACTOR is defined as: DESYNC_FACTOR -- A random value within the range 0 - MAX_DESYNC_FACTOR. It is computed once at system start (rather than each time it is used) and must never be greater than (TEMP_VALID_LIFETIME - REGEN_ADVANCE). First, I believe the RFC has a typo in it and meant to say: "and must never be greater than (TEMP_PREFERRED_LIFETIME - REGEN_ADVANCE)" The reason is that at various places in the RFC, DESYNC_FACTOR is used in a calculation like (TEMP_PREFERRED_LIFETIME - DESYNC_FACTOR) or (TEMP_PREFERRED_LIFETIME - REGEN_ADVANCE - DESYNC_FACTOR). It needs to be smaller than (TEMP_PREFERRED_LIFETIME - REGEN_ADVANCE) for the result of these calculations to be larger than zero. It's never used in a calculation together with TEMP_VALID_LIFETIME. I already submitted an errata to the rfc-editor: https://www.rfc-editor.org/errata_search.php?rfc=4941 The Linux implementation of DESYNC_FACTOR is very wrong: max_desync_factor is used in places DESYNC_FACTOR should be used. max_desync_factor is initialized to the RFC-recommended value for MAX_DESYNC_FACTOR (600) but the whole point is to get a _random_ value. And nothing ensures that the value used is not greater than (TEMP_PREFERRED_LIFETIME - REGEN_ADVANCE), which leads to underflows. The effect can easily be observed when setting the temp_prefered_lft sysctl e.g. to 60. The preferred lifetime of the temporary addresses will be bogus. TEMP_PREFERRED_LIFETIME and REGEN_ADVANCE are not constants and can be influenced by these three sysctls: regen_max_retry, dad_transmits and temp_prefered_lft. Thus, the upper bound for desync_factor needs to be re-calculated each time a new address is generated and if desync_factor is larger than the new upper bound, a new random value needs to be re-generated. And since we already have max_desync_factor configurable per interface, we also need to calculate and store desync_factor per interface. Signed-off-by: Jiri Bohac <jbohac@suse.cz> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| batman-adv | ||
| bluetooth | ||
| bridge | ||
| caif | ||
| can | ||
| ceph | ||
| core | ||
| dcb | ||
| dccp | ||
| decnet | ||
| dns_resolver | ||
| dsa | ||
| ethernet | ||
| hsr | ||
| ieee802154 | ||
| ipv4 | ||
| ipv6 | ||
| ipx | ||
| irda | ||
| iucv | ||
| kcm | ||
| key | ||
| l2tp | ||
| l3mdev | ||
| lapb | ||
| llc | ||
| mac80211 | ||
| mac802154 | ||
| mpls | ||
| ncsi | ||
| netfilter | ||
| netlabel | ||
| netlink | ||
| netrom | ||
| nfc | ||
| openvswitch | ||
| packet | ||
| phonet | ||
| qrtr | ||
| rds | ||
| rfkill | ||
| rose | ||
| rxrpc | ||
| sched | ||
| sctp | ||
| strparser | ||
| sunrpc | ||
| switchdev | ||
| tipc | ||
| unix | ||
| vmw_vsock | ||
| wimax | ||
| wireless | ||
| x25 | ||
| xfrm | ||
| compat.c | ||
| Kconfig | ||
| Makefile | ||
| socket.c | ||
| sysctl_net.c | ||