r was not initialized and would be used if "tcp" was the only option
used for the stub. We should initialize it to 0 to indicate that no
error happened in the udp case.
When running in a user namespace without private networking, resolved would
fail to start. There isn't much difference between EADDRINUSE and EPERM,
so treat them the same, except for the warning message text.
Make sure an error is always printed… When systemd-resolved is started in a
user namespace without private network, it would fail on setsockopt, but the
error wouldn't be particularly informative:
"Failed to start manager: permission denied."
DNS servers which have route-only domains should only be used for
the specified domains. Routing queries about other domains there is a privacy
violation, prone to fail (as that DNS server was not meant to be used for other
domains), and puts unnecessary load onto that server.
Introduce a new helper function dns_server_limited_domains() that checks if the
DNS server should only be used for some selected domains, i. e. has some
route-only domains without "~.". Use that when determining whether to query it
in the scope, and when writing resolv.conf.
Extend the test_route_only_dns() case to ensure that the DNS server limited to
~company does not appear in resolv.conf. Add test_route_only_dns_all_domains()
to ensure that a server that also has ~. does appear in resolv.conf as global
name server. These reproduce #3420.
Add a new test_resolved_domain_restricted_dns() test case that verifies that
domain-limited DNS servers are only being used for those domains. This
reproduces #3421.
Clarify what a "routing domain" is in the manpage.
Fixes#3420Fixes#3421
With commit 6f7da49d00 route-only domains do not get put into resolv.conf's
"search" list any more. Add a comment about the tri-state, to clarify its
semantics and why we are passing a bool parameter into an int type. Also add a
test case for it.
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.
Some upstream DNS servers return SERVFAIL if we ask them for DNSSEC RRs, which
some forwarding DNS servers pass on to us as SERVFAIL (other though as
NOERROR...). This is should not be considered a problem, as long as the domain
in question didn't have DNSSEC enabled. Hence: when making use of auxiliary
transactions accept those that return SERVFAIL.
There might be two reasons why we get a SERVFAIL response from our selected DNS
server: because this DNS server itself is bad, or because the DNS server
actually serving the zone upstream is bad. So far we immediately downgraded our
server feature level when getting SERVFAIL, under the assumption that the first
case is the only possible case. However, this meant we'd downgrade immediately
even if we encountered the second case described above.
With this commit handling of SERVFAIL is reworked. As soon as we get a SERVFAIL
on a transaction we retry the transaction with a lower feature level, without
changing the feature level tracked for the DNS server itself. If that fails
too, we downgrade further, and so on. If during this downgrading the SERVFAIL
goes away we assume that the DNS server we are talking to is bad, but the zone
is fine and propagate the detected feature level to the information we track
about the DNS server. Should the SERVFAIL not go away this way we let the
transaction fail and accept the SERVFAIL.
In order to improve compatibility with local clients that speak DNS directly
(and do not use NSS or our bus API) listen locally on 127.0.0.53:53 and process
any queries made that way.
Note that resolved does not implement a full DNS server on this port, but
simply enough to allow normal, local clients to resolve RRs through resolved.
Specifically it does not implement queries without the RD bit set (these are
requests where recursive lookups are explicitly disabled), and neither queries
with DNSSEC DO set in combination with DNSSEC CD (i.e. DNSSEC lookups with
validation turned off). It also refuses zone transfers and obsolete RR types.
All lookups done this way will be rejected with a clean error code, so that the
client side can repeat the query with a reduced feature set.
The code will set the DNSSEC AD flag however, depending on whether the data
resolved has been validated (or comes from a local, trusted source).
Lookups made via this mechanisms are propagated to LLMNR and mDNS as necessary,
but this is only partially useful as DNS packets cannot carry IP scope data
(i.e. the ifindex), and hence link-local addresses returned cannot be used
properly (and given that LLMNR/mDNS are mostly about link-local communication
this is quite a limitation). Also, given that DNS tends to use IDNA for
non-ASCII names, while LLMNR/mDNS uses UTF-8 lookups cannot be mapped 1:1.
In general this should improve compatibility with clients bypassing NSS but
it is highly recommended for clients to instead use NSS or our native bus API.
This patch also beefs up the DnsStream logic, as it reuses the code for local
TCP listening. DnsStream now provides proper reference counting for its
objects.
In order to avoid feedback loops resolved will no silently ignore 127.0.0.53
specified as DNS server when reading configuration.
resolved listens on 127.0.0.53:53 instead of 127.0.0.1:53 in order to leave
the latter free for local, external DNS servers or forwarders.
This also changes the "etc.conf" tmpfiles snippet to create a symlink from
/etc/resolv.conf to /usr/lib/systemd/resolv.conf by default, thus making this
stub the default mode of operation if /etc is not populated.
When we return the full RR wire data, let's make sure the TTL included in it is
adjusted by the time the RR sat in the cache.
As an optimization we do this only for ResolveRecord() and not for
ResolveHostname() and friends, since adjusting the TTL means copying the RR
object, and we don#t want to do that if there's no reason to.
(ResolveHostname() and friends don't return the TTL hence there's no reason to
in that case)
It's weird having a "negative" function link_is_unmanaged(), let's invert it
and get rid of the negation this way, by renaming it to link_is_managed().
Internally we stored this as a positive boolean already, hence let's do this
for the function too.
Let's split the code from the inner loop out, into its own function
link_update_dns_server_one(). This matches how things are already handled for
the search domain logic. Also, this is preparation for a later commit that
persists DNS server data pushed in via the bus.
The new command shows the per-link and global DNS configuration currently in
effect. This is useful to quickly see the DNS settings resolved acquired from
networkd and that was pushed into it via the bus APIs.
Internally, we store the per-link DNSSEC setting as -1 (invalid) if there's no
link-specific setting configured, and the global setting should be used. When
exporting this one the bus we really should export the effective DNSSEC
setting however, i.e. return the global one if there's non set per-link.
