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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.
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After all, /etc/resolv.conf doesn't know the concept of "route-only domains",
hence the domains should really not appear there.
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changed via bus calls
This also moves log message generation into manager_write_resolv_conf(), so
that it is shorter to invoke the function, given that we have to invoke it at a
couple of additional places now.
Fixes: #3225
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Make sure we can parse DNS server addresses that use the "zone id" syntax for
local link addresses, i.e. "fe80::c256:27ff:febb:12f%wlp3s0", when reading
/etc/resolv.conf.
Also make sure we spit this out correctly again when writing /etc/resolv.conf
and via the bus.
Fixes: #3359
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Write comments about "too many search domains" and "Total length of all search
domains is too long" just once. Also put it on a separate line, as
resolv.conf(5) only specifies comments in a line by themselves.
This is ugly to do if write_resolv_conf_search() gets called once for every
search domain. So change it to receive the complete OrderedSet instead and do
the iteration by itself.
Add test cases to networkd-test.py.
https://launchpad.net/bugs/1588229
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Throughout the tree there's spurious use of spaces separating ++ and --
operators from their respective operands. Make ++ and -- operator
consistent with the majority of existing uses; discard the spaces.
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This should be handled fine now by .dir-locals.el, so need to carry that
stuff in every file.
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Otherwise it's unclear if it's /etc/resolv.conf or some
other file that is meant.
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This makes it easier to log information about a specific DnsServer object.
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After all /etc/resolv.conf is usually done when the network
configuration changes, which is a good reason to flush the global cache.
See: #2038
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If /etc/resolv.conf is missing, this should not result in the server
list to be cleared, after all the native data from resolved.conf
shouldn't be flushed out then. Hence flush out the data only if
/etc/resolv.conf exists, but we cannot read it for some reason.
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Let's split this out from the resolv.conf parser, so that this becomes
generically useful.
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This copies concepts we introduced for the DnsSearchDomain stuff, and
reworks the operations on lists of dns servers to be reusable and
generic for use both with the Link and the Manager object.
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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.
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Previously, there was a chance of memory corruption, because when
switching to the next DNS server we didn't care whether they linked list
of DNS servers was still valid.
Clean up lifecycle of the dns server logic:
- When a DnsServer object is still in the linked list of DnsServers for
a link or the manager, indicate so with a "linked" boolean field, and
never follow the linked list if that boolean is not set.
- When picking a DnsServer to use for a link ot manager, always
explicitly take a reference.
This also rearranges some logic, to make the tracking of dns servers by
link and globally more alike.
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No functional changes.
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