serve stale feature to keep the DNS resource records beyond TTL to return them as stale records in case of upstream server is not reachable or returns negative response.
SD_RESOLVED_NO_STALE flag has been added to disable serving stale records via dbus.
added serve stale test cases to TEST-75-RESOLVED
Fixes: #21815
The socket is only accessible to privileged clients anyway, no need to
add another (user unfriendly) restriction via opt-in setting. let's just
allow this for privileged clients, mirroring "busctl monitor", or
"tcpdump" and similar, which all just work if you have privs.
(This does not break API, since we never did a release witht the
"Monitor" dbus property or config setting in place, i.e. with
cb456374e0)
* The new varlink interface exposes a method to subscribe to DNS
resolutions on the system. The socket permissions are open for owner and
group only.
* Notifications are sent to subscriber(s), if any, after successful
resolution of A and AAAA records.
This feature could be used by applications for auditing/logging services
downstream of the resolver. It could also be used to asynchronously
update the firewall. For example, a system that has a tightly configured
firewall could open up connections selectively to known good hosts based
on a known allow-list of hostnames. Of course, updating the firewall
asynchronously will require other design considerations (such as
queueing packets in the user space while a verdict is made).
See also:
https://lists.freedesktop.org/archives/systemd-devel/2022-August/048202.htmlhttps://lists.freedesktop.org/archives/systemd-devel/2022-February/047441.html
Even though many of those scripts are very simple, it is easier to include
the header than to try to say whether each of those files is trivial enough
not to require one.
Change the resolved.conf Cache option to a tri-state "no, no-negative, yes" values.
If a lookup returns SERVFAIL systemd-resolved will cache the result for 30s (See 201d995),
however, there are several use cases on which this condition is not acceptable (See systemd#5552 comments)
and the only workaround would be to disable cache entirely or flush it , which isn't optimal.
This change adds the 'no-negative' option when set it avoids putting in cache
negative answers but still works the same heuristics for positive answers.
Signed-off-by: Jorge Niedbalski <jnr@metaklass.org>
In some cases, caching DNS results locally is not desirable, a it makes DNS
cache poisoning attacks a tad easier and also allows users on the system to
determine whether or not a particular domain got visited by another user. Thus
provide a new "Cache" resolved.conf option to disable it.
networkd previously knew an enum "ResolveSupport" for configuring
per-interface LLMNR support, resolved had a similar enum just called
"Support", with the same value and similar pasers.
Unify this, call the enum ResolveSupport, and port both daemons to it.
The setting controls which kind of DNSSEC validation is done: none at
all, trusting the AD bit, or client-side validation.
For now, no validation is implemented, hence the setting doesn't do much
yet, except of toggling the CD bit in the generated messages if full
client-side validation is requested.
With this change, we add a new object to resolved, "DnsSearchDomain="
which wraps a search domain. This is then used to introduce a global
search domain list, in addition to the existing per-link search domain
list which is reword to make use of this new object too.
This is preparation for implement proper unicast DNS search domain
support.
Let's use the same parser when parsing dns server information from
/etc/resolv.conf and our native configuration file.
Also, move all code that manages lists of dns servers to a single place.
resolved-dns-server.c
We now maintain two lists of DNS servers: system servers and fallback
servers.
system servers are used in combination with any per-link servers.
fallback servers are only used if there are no system servers or
per-link servers configured.
The system server list is supposed to be populated from a foreign tool's
/etc/resolv.conf (not implemented yet).
Also adds a configuration switch for LLMNR, that allows configuring
whether LLMNR shall be used simply for resolving or also for responding.
Let's turn resolved into a something truly useful: a fully asynchronous
DNS stub resolver that subscribes to network changes.
(More to come: caching, LLMNR, mDNS/DNS-SD, DNSSEC, IDN, NSS module)
Kiran Vemula
Lennart Poettering
Suraj Krishnan
Zbigniew Jędrzejewski-Szmek
Pavel Sapezhko
Susant Sahani
Daan De Meyer
Jorge Niedbalski
Yu Watanabe
Iwan Timmer
Shawn Landden
David Michael
Martin Pitt
Daniel Mack
Tom Gundersen