The RA's Retransmission Timer field was being ignored. This resolves the IPv6
Core Conformance test, v6LC.2.1.5 [1].
Retransmission Timer is a 32-bit unsigned integer. The time, in milliseconds,
between retransmitted Neighbor Solicitation messages. Used by the Address
Resolution and Neighbor Unreachability Detection (NUD) algorithm.
Support setting a default value for the neighbour retransmission timer value with:
[Network]
IPv6RetransmissionTimeSec=<int>
By default, upon receiving a Router Advertisement with the Retransmission Timer
field set to a non-zero value, it will update the kernel's retransmit timer value.
To disable this behaviour, configure the UseIPv6RetransmissionTime= under the
[IPv6AcceptRA] section.
[IPv6AcceptRA]
UseIPv6RetransmissionTime=<bool>
RFC4861: Neighbor Discovery in IPv6
* Section 4.2 RA Message Format.
* Section 6.3.4 Processing Received Router Advertisements
A Router Advertisement field (e.g., Cur Hop Limit, Reachable Time,
and Retrans Timer) may contain a value denoting that it is
unspecified. In such cases, the parameter should be ignored and the
host should continue using whatever value it is already using. In
particular, a host MUST NOT interpret the unspecified value as
meaning change back to the default value that was in use before the
first Router Advertisement was received.
The RetransTimer variable SHOULD be copied from the Retrans Timer
field, if the received value is non-zero.
References
[1] IPv6 Core Conformance Spec (PDF)
Currently `systemd-sysctl` binary is used in `systemd-sysctl.service`
which is mostly configured as `oneshot`. There are situations where one
would like to use systemd to maintain Sysctl configurations on a host,
using a configuration managers such as Chef or Puppet, by apply
configurations every X duration.
The problem with using `systemd-sysctl` is that it writes all the Sysctl
settings, even if the values for those settings have not changed. From
experience, we have observed that some Sysctl settings cause actions in
the kernel upon writing(like dropping caches) which in turn cause
undesired side effects.
This patch tries to minimize such side effects by comparing values
before writing.
let's do what we did for sysctl_write()/sysctl_write_ip_property() also
for the read paths: i.e. make one a wrapper of the other, and add more
careful input validation.
Let's add similar path validation to sysctl_read() as we already have in
sysctl_write().
Let's also drop the trailing newline from the returned string, like
sysctl_read_ip_property() already does it.
(I checked all users of this, they don't care)
It does the same stuff, let's use the same codepaths as much as we can.
And while we are at it, let's generate good error codes in case we are
called with unsupported parameters/let's validate stuff more that might
originate from user input.
The sysctl_write_ip_property() call already uses write_string_file(), so
let's do so here, too, to make the codepaths more uniform.
While we are at it, let's also validate the passed path a bit, since we
shouldn't allow sysctls with /../ or such in the name. Hence simplify
the path first, and then check if it is normalized, and refuse if not.
