When a DnsServiceBrowser object is detached from the manager,
all queries, event sources, and then the reference to Manager should be
dropped. Otherwise, spurious query may be triggered for already
disconnected varlink.
manager_recv() sizes its buffer with next_datagram_size_fd(), which peeks at
the datagram with MSG_PEEK|MSG_TRUNC. That peek makes the kernel verify the UDP
checksum - which is the whole point of using it over FIONREAD - and hence also
drop the datagram when the checksum is bad. The datagram that woke the event
source can thus be gone by the time we peek at it, and the peek returns EAGAIN.
manager_recv() returned that error, while the recvmsg_safe() below, which can
fail the same way, already treats it as "no packet". The callers on the mDNS,
LLMNR and stub listening sockets pass a negative return on to the event loop,
which disables the event source, so a single datagram with a bad checksum -
something anyone on the link can send - stops resolved from receiving on that
socket for good. on_dns_packet() completes the transaction with -EAGAIN instead
of retrying it.
So return 0 on a transient error here too, like the other users of the helper
on an event source do. Disconnect errors are left as they are: they show up
here from ICMP errors on the connected UDP socket, and on_dns_packet() handles
them.
Currently they are marked as required, as resolved aborts on startup if
dns-over-tls is built in, even if it is not enabled in the config.
Change initialization to be done lazily on first use, so that if the
config is not enabled, it never runs, and the libraries are never
dlopened, so they can be downgraded to recommends.
resolved watches networkd state changes and RTNL updates separately. RTNL is
currently processed at SD_EVENT_PRIORITY_IMPORTANT, while networkd state
changes are processed later at SD_EVENT_PRIORITY_IMPORTANT+5.
If both are pending, an RTM_NEWADDR update can make a link relevant for
LLMNR/mDNS scope allocation before resolved has consumed the corresponding
networkd state update. This can let scope recalculation use stale per-link
settings until the networkd event is processed.
Run the networkd monitor source before RTNL by using
SD_EVENT_PRIORITY_IMPORTANT-5. This lets resolved consume current link settings
before reacting to RTNL address updates in the same event loop iteration.
Fixes#42079
Co-developed-by: OpenAI Codex <noreply@openai.com>
Add CacheSize= option to [Resolve] section of resolved.conf to allow
configuring the maximum number of entries in the per-scope DNS cache.
The default remains 4096 entries. Setting this to 0 disables caching
(similar to Cache=no).
CacheSize= is only read when Cache=yes or Cache=no-negative. When
Cache=no, caching is fully disabled regardless of CacheSize=.
Changes:
- Add cache_size field to Manager struct
- Parse CacheSize= from resolved.conf via gperf
- Thread cache_size through dns_cache_put() and helper functions
- Replace hard-coded CACHE_MAX with the configurable cache_size
- When cache_size is 0 or Cache=no, flush cache and skip caching
- Add man page documentation for the new option
- Add unit tests for cache size enforcement
Co-developed-by: Claude <claude@anthropic.com>
This addresses
https://github.com/systemd/systemd/pull/41213#pullrequestreview-4002247053
which I somehow missed earlier.
Claude found a real issue for the case of manager_etc_hosts_flush().
We'll do the equivalent change in manager_static_records_flush() too,
even though it's not really necessary there, simply to keep things
nicely mirrored.
This is an extension of the /etc/hosts concept, but can provide any kind
of RRs (well, actually, we only parse A/AAAA/PTR for now, but the
concept is open for more).
Fixes: #17791
When we are told to reload our configuration also flush out /etc/hosts
explicitly. This is particularly relevant since we suppress too frequent
reloads, and hence a synchronous way to force a reload is very useful.
The varlink API is currently missing the "DNSSEC supported" field, which
is required for to re-implement the existing resolvectl status output
with varlink instead of dbus.
Add this field to DNSConfiguration.
The current_dns_server_json object in dns_configuration_json_append() is
always NULL, because the logic to dump the current DNS server to JSON
was removed by mistake in a re-factoring commit. Add that logic back.
Fixes c6b6ac63ea ("resolve: drop unnecessary preparation of empty arrays").
When systemd-resolved is used in resolv.conf foreign mode, reloading the
systemd-resolved daemon does not read resolv.conf when not touched since
the last time resolved read the file. Since the DNS servers list is
flushed during a reload, resolved forgets about the servers
in /etc/resolv.conf
When reloading the daemon it is expected that all configuration is
reloaded regardless of the disk timestamps.
This introduces /run/systemd/resolve.hook/ as a new directory that local
(privileged) programs can bind a Varlink socket into. If they do they'll
get a method call for each attempted resolved lookup, which they can
then either process themselves (and generate new records for, or return
errors to block stuff) or let pass so that the regular resolution is
done.
Usecase for this is primarily two things:
1. in machined we can add local resolution of machine names to their IP
addresses, similar in fashion to nss-mymachines, but working also if
the non-NSS interfaces to name resolution are used, i.e. the local
DNS responder. In fact, I think we should eventually remove
nss-mymachines from our tree, as soon as this code in resolved is
setlled.
2. in networkd we can add local resolution of names specified in DHCP
leases we hand out.
But beyond that there should be many other uses, for example people
could write "dns firewalls" with this if they like where they
dynamically block certain names from resolution.
Fixes: #8518
We want to reuse these generic DNS concepts in resolved hook
implementations, hence move them to shared code.
(This also enables us to immediately remove som SVCB record handling
duplicate definitions.)
No real code changes, just some moving around of things.
On reload, resolved does not apply new DNSSEC= (or DNSOverTLS=) settings
on links, because the link unicast scopes are not re-created. However,
the servers and link states are updated correctly, so resolvectl and link
state files do show the new setting, leading users to believe the change
took effect immediately, the same way `resolvectl dnssec` does.
Fix this by freeing all of the link unicast scopes during reload, so
that they are re-created with the new settings in link_allocate_scopes().
Allow for mDNS service/domain/types browsing.
A client can connect to the backend via varlink and receive updates as the
requested service becomes available.
The interval between the first two queries MUST be at least one second,
the intervals between successive queries MUST increase by at least a factor of two.
When the interval between queries reaches or exceeds 60 minutes, a querier MAY cap
the interval to a maximum of 60 minutes, and perform subsequent queries at a
steady-state rate of one query per hour.
Delete expired cache entries one second after goodbye packet received
as per RFC6762 Section 10.1
Cache maintenance:
The querier should plan to issue a query at 80% of the record lifetime, and
then if no answer is received, at 85%, 90%, and 95%.
If an answer is received, then the remaining TTL is reset to the value given
in the answer, and this process repeats for as long as the Multicast DNS querier
has an ongoing interest in the record.
If no answer is received after four queries, the record is deleted when it
reaches 100% of its lifetime.
TODO:
Improve the DNS transaction logic when multiple clients subscribe to
the same service, ensuring that continuous queries are optimized.
Co-authored-by: Vishwanath Chandapur <vishwanath.chandapur@philips.com>
Prepare for upcoming mDNS browse services.
Distinguish between registered and discovered services to avoid confusion.
Co-authored-by: Vishwanath Chandapur <vishwanath.chandapur@philips.com>
Previously, the extra stub listners were stopped but new ones were not
started. Also, the main stub listners were not restarted, hence the
new settings were not applied. This fixes the above two issues.
Note, to fix the issue, we need to keep CAP_NET_BIND_SERVICE capability
to make it allow to bind stub listner later.
Fixes#37843.
- set defaults after all existing configs and setups cleared,
- mention failures are ignored in log messages,
- drop one redundant log message,
- do not return negative errno but exit event loop on critical failure.
This permits configuration of additional "delegates" which ensure that
lookups for certain DNS zones are routed to specific sets of DNS
servers, in addition to the routes we create for each network interface.
For now, this allows only static configuration, but eventually we should
open this up to IPC.
Fixes: #5573#14159#20485#21260#24532#32022
(Fixes#32022, because now redundant)
This new enum field is supposed to indicate why a DnsScope came to be.
For now it distinguishes two origins: the "global" one (which is what is
configured in resolved.conf) and "link" ones (which are synthesized for
each link).
The field as is is pretty redundant, the same information can be
determined from whether the .link field is set or not.
This is pretty much just preparation for later commits that add
statically configured additional DnsScopes whose origin shall be encoded
with this.
Currently, NOTIFY_READY from daemon-util.h conflicts with NOTIFY_READY
from NotifyState from service.h so let's rename the constants to avoid
the conflict.
Yu Watanabe
Armaan Sandhu
Luca Boccassi
elysia090
ishwarbb
Zbigniew Jędrzejewski-Szmek
Lennart Poettering
Michael Vogt
Daan De Meyer
Nick Rosbrook
Pasquale van Heumen
Daan De Meyer
Jelle van der Waa
Lennart Poettering
Vishal Chillara SrinivasandVishwanath Chandapur
Jelle van der Waa