With new leaking queries features, the initialization of OS resolver can
now lead to data race if queries are resolving while re-initialization
happens.
To fix it, using an atomic pointer to store list of nameservers which
were initialized, making read/write to the list concurrently safe.
So it would work in more general case than just captive portal network,
which ctrld have supported recently.
Uses who may want no leaking behavior can use a config to turn off this
feature.
So it can be run regardless of ctrld current status. This prevents a
racy behavior when reset DNS task restores DNS settings of the system,
but current running ctrld process may revert it immediately.
For query domain that matches "uid.verify.controld.com" in cd mode, and
the uid has the same value with "--cd" flag, ctrld will fetch uid config
from ControlD API, using this config if valid.
This is useful for force syncing API without waiting until the API
reload ticker fire.
ControlD have global list of known captive portals that user can augment
with proper setup. However, this requires manual actions, and involving
restart ctrld for taking effects.
By allowing ctrld "leaks" DNS queries to OS resolver, this process
becomes automatically, the captive portal could intercept these queries,
and as long as it was passed, ctrld will resume normal operation.
Using netsh command will emit unexpected SOA queries, do not use it.
While at it, also ensure that local ipv6 will be added to nameservers
list on systems that require ipv6 local listener.
There are several issues with OS resolver right now:
- The list of nameservers are obtained un-conditionally from all
running interfaces.
- ControlD public DNS query is always be used if response ok.
This could lead to slow query time, and also incorrect result if a
domain is resolved differently between internal DNS and ControlD public
DNS.
To fix these problems:
- While initializing OS resolver, sending a test query to the
nameserver to ensure it will response. Unreachable nameserver will
not be used.
- Only use ControlD public DNS success response as last one, preferring
ok response from internal DNS servers.
While at it, also using standard package slices, since ctrld now
requires go1.21 as the minimum version.
So changes to DNS after ctrld stopped won't be reverted by the goroutine
itself. The problem happens rarely on darwin, because networksetup
command won't propagate config to /etc/resolv.conf if there is no
changes between multiple running.
The dns watchdog is spawned *after* DNS was set by ctrld, thus it should
use the currentStaticDNS for getting the static DNS, instead of relying
on currentDNS, which could be system wide instead of per interfaces.
On Darwin, modifying /etc/resolv.conf directly does not change interface
network settings. Thus the networksetup command uses to set DNS does not
do anything.
To fix this, after setting DNS using networksetup, re-check the content
of /etc/resolv.conf file to see if the nameservers are what we expected.
Otherwise, re-generate the file with proper nameservers.
Without reading the documentation, users may think that "ctrld start"
will just start ctrld service. However, this is not the case, and may
lead to unexpected result from user's point of view.
This commit changes "ctrld start" to just start already installed ctrld
service, so users won't lost what they did installed before. If there
are any arguments specified, performing the current behavior.
