This is much better handled by a user-land tool.
Proposed on tech-net here:
https://mail-index.netbsd.org/tech-net/2020/04/22/msg007766.html
Note that the ioctl SIOCGIFINFO_IN6 no longer sets flags. That now
needs to be done using the pre-existing SIOCSIFINFO_FLAGS ioctl.
Compat is fully provided where it makes sense, but trying to turn on
RA handling will obviously throw an error as it no longer exists.
Note that if you use IPv6 temporary addresses, this now needs to be
turned on in dhcpcd.conf(5) rather than in sysctl.conf(5).
rndctl -S triggers entropy consolidation, so whatever we gathered
during kernel startup -- interrupt timings, autoconf timings, &c. --
will be incorporated into the seed and into subsequent data read from
/dev/urandom, just like if rndctl -L had run at this boot, and the
seed will carry them into the next boot too.
But it still avoids frequently consolidating entropy on any regular
schedule, in order to continue to mitigate iterative-guessing
attacks.
- Teach rndctl to load the seed, but treat it as zero entropy, if the
medium is read-only or if the update fails.
- Teach rndctl to accept `-i' flag instructing it to ignore the
entropy estimate in the seed.
- Teach /etc/rc.d/random_seed to:
(a) assume nonlocal file systems are unsafe, and use -i, but
(b) assume / is safe, even if it is nonlocal.
If the medium is nonwritable, leave it to rndctl to detect that.
(Could use statvfs and check for ST_LOCAL in rndctl, I guess, but I
already implemented it this way.)
Treating nonlocal / as safe is a compromise: it's up to the operator
to secure the network for (e.g.) nfs mounts, but that's true whether
we're talking entropy or not -- if the adversary has access to the
network that you've mounted / from, they can do a lot more damage
anyway; this reduces warning fatigue for diskless systems, e.g. test
racks.
`rndctl -S' can replace the file just fine, and deleting it ahead of
time adds a window during which we can lose the seed altogether if
the system is interrupted by a crash or power outage.
XXX pullup
/netbsd/modules respectively instead of /netbsd and
/stand/<arch>/<version>/modules. This is only supported for x86,
and is turned off by default. To try it, add KERNEL_DIR=yes in your
/mk.conf and install a system from that build.
