If we get no response to three renews (unicast), switch to sending
rebinds (broadcast). Servers are supposed to always reply with
a DHCPACK or DHCPNAK even if the server doesn't update its internal
lease duration database, so this behavior should be RFC compliant.
'(c)' may not be a valid substitute for 'Copyright' in some legal
domains/interpretations. So be safe, since I obviously am asserting
copyright on my legal work.
It breaks with the existing whitelists on the latest glibc and is
just too much maintenance burden. It also causes the most questions
for new users.
Something like openbsd's pledge() would be fine, but I have no
intention of maintaining such a thing.
Most of the value-gain would come from disallowing high-risk
syscalls like ptrace() and the perf syscalls, anyway.
ndhc already uses extensive defense-in-depth and wasn't using
seccomp on non-(x86|x86-64) platforms, so it's not a huge loss.
If carrier is lost before network fingerprinting is complete, we
have a few problems; first, we don't know whether the network has
changed underneath us. Second, we've not yet configured the
interface properties, and it is not unlikely that doing so will
fail as the underlying network device may have been destroyed
and recreated during this time (eg, if ethtool has been run at
start-up time).
Thus, the safest reaction is to terminate and force a supervisor
respawn. It is best to do this once carrier recovers, not when
the carrier is lost, as it is more likely to minimize delays.
ARP packets aren't split across multiple receive events, so
reply_offset is pointless, and we implicitly assume that the
previous ARP packet data is still available after a forced sleep.
The gateway/router MAC fingerprinting could perhaps be done more
robustly in the face of suspend or carrier loss, but the time window
in which things could get confused is very small and I would rather
just rely on supervisor respawn in that case.
Even this case I don't think I've ever seen.
The previous approach would desynchronize the state machine if the
carrier is paused after receiving the lease but before sending the
announce, since we have received a lease already.
This change is an improvement but is still not ideal.
We instead check carrier status as needed. This approach is more
robust. For a simple example, imagine link state changes that happen
while the machine is suspended.
This is fairly tricky, but fopen() almost surely interally calls malloc
when it creates the FILE* that it returns. I did promise that
ndhc doesn't call malloc after initialization, besides what libc may
do internally, but it feels a bit dishonest given that fopen() is
basically sure to do so on any general-purpose libc.
Thus, eliminate it and just use direct POSIX i/o.
With the previous pidfile changes, ndhc doesn't use C fopen() at all.
In practice, this change won't really be noticeable as most libcs,
particularly with dynamic linking, will end up calling malloc themselves
during program initialization before main() is invoked.
