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When iterating through RR lists we frequently end up comparing RRs and
RR keys with themselves, hence att a minor optimization to check ptr
values first, before doing a deep comparison.
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DNS RR types are uint16_t after all, treat them as such.
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Expose soft limits on the bus
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For mDNS, if we're unable to stuff all known answers into the given packet,
allocate a new one, push the RR into that one and link it to the current
one.
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In dns_scope_emit(), walk the list of additional packets and emit all of
them. Set the TC bit in all but the last of them.
This is specific to mDNS, so an assertion is triggered if used with other
protocols.
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For mDNS, we need to support the TC bit in case the list of known answers
exceed the maximum packet size.
For this, add a 'more' pointer to DnsPacket for an additional packet.
When a packet is unref'ed, the ->more packet is also unrefed, so it
sufficient to only keep track of the 1st packet in a chain.
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We need to support the TC bit in queries in case known answers exceed the
maximum packet size. Factor out the flags compilation to
dns_packet_set_flags() and make it externally available.
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sd_event_add_io() returns the error directly and does not mess with errno.
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DNS names ending with .local are specific to mDNS, so don't use them
on DNS scopes.
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Udev indentation
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basic: add RB-Tree implementation
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This new functions exports cached records of type PTR, SRV and TXT into
an existing DnsPacket. This is used in order to fill in known records
to mDNS queries, for known answer supression.
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Implement dns_transaction_make_packet_mdns(), a special version of
dns_transaction_make_packet() for mDNS which differs in many ways:
a) We coalesce queries of currently active transaction on the scope.
This is possible because mDNS actually allows many questions in a
to be sent in a single packet and it takes some burden from the
network.
b) Both A and AAAA query keys are broadcast on both IPv4 and IPv6
scopes, because other hosts might only respond on one of their
addresses but resolve both types.
c) We discard previously sent packages (t->sent) so we can start over
and coalesce pending transactions again.
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For each transaction, record when the earliest point in time when the
query packet may hit the wire. This is the same time stamp for which
the timer is scheduled in retries, except for the initial query packets
which are delayed by a random jitter. In this case, we denote that the
packet may actually be sent at the nominal time, without the jitter.
Transactions that share the same timestamp will also have identical
values in this field. It is used to coalesce pending queries in a later
patch.
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Split some code out of dns_transaction_go() so we can re-use it later from
different context. The new function dns_transaction_prepare_next_attempt()
takes care of preparing everything so that a new packet can conditionally
be formulated for a transaction.
This patch shouldn't cause any functional change.
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Add the packet dispatching routine for mDNS.
It differs to what LLMNR and DNS dispatchers do in the way it matches
incoming packets. In mDNS, we actually handle all incoming packets,
regardless whether we asked for them earlier or not.
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mDNS packet timeouts need to be handled per transaction, not per link.
Re-use the n_attempts field for this purpose, as packets timeouts should be
determined by starting at 1 second, and doubling the value on each try.
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When a jitter callback is issued instead of sending a DNS packet directly,
on_transaction_timeout() is invoked to 'retry' the transaction. However,
this function has side effects. For once, it increases the packet loss
counter on the scope, and it also unrefs/refs the server instances.
Fix this by tracking the jitter with two bool variables. One saying that
the initial jitter has been scheduled in the first place, and one that
tells us the delay packet has been sent.
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In mDNS, DNS_RESOURCE_KEY_CACHE_FLUSH denotes whether other records with the
same key should be flushed from the cache.
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MDNS has a 'key cache flush' flag for records which must be masked out for
the parsers to do our right thing. We will also use that flag later (in a
different patch) in order to alter the cache behavior.
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The logic is to kick off mDNS packets in a delayed way is mostly identical
to what LLMNR needs, except that the constants are different.
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Follow what LLMNR does, and create per-link DnsScope objects.
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Per link, join the mDNS multicast groups when the scope is created, and
leave it again when the scope goes away.
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Validate mDNS queries and responses by looking at some header fields,
add mDNS flags.
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Just hook up mDNS listeners with an empty packet dispather function,
introduce a config directive, man page updates etc.
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tests: add test-rlimit-util
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This adds an self-standing RB-Tree implementation to src/basic/. This
will be needed for NSEC RR lookups, since we need "close lookups", which
hashmaps (not even ordered-hashmaps) can give us in reasonable time.
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Otherwise emacs wants to use 2-space indentation and other
attrocities.
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We quite obviously check whether event->dev_db is nonnull, and
right after that call a function which asserts the same. Move
the call under the same if.
https://bugzilla.redhat.com/show_bug.cgi?id=1283971
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user-sessions: make sure /run/nologin has correct SELinux label
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Misc cleanups
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The next step of a general cleanup of our includes. This one mostly
adds missing includes but there are a few removals as well.
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https://github.com/systemd/systemd/issues/2016
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This adds a new SD_RESOLVED_AUTHENTICATED flag for responses we return
on the bus. When set, then the data has been authenticated. For now this
mostly reflects the DNSSEC AD bit, if DNSSEC=trust is set. As soon as
the client-side validation is complete it will be hooked up to this flag
too.
We also set this bit whenver we generated the data ourselves, for
example, because it originates in our local LLMNR zone, or from the
built-in trust anchor database.
The "systemd-resolve-host" tool has been updated to show the flag state
for the data it shows.
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When an RR type is not set in an NSEC, then the CNAME/DNAME types might
still be, hence check them too.
Otherwise we might end up refusing resolving of CNAME'd RRs if we cached
an NSEC before.
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files for now
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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.
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When doing DNSSEC lookups we need to know one or more DS or DNSKEY RRs
as trust anchors to validate lookups. With this change we add a
compiled-in trust anchor database, serving the root DS key as of today,
retrieved from:
https://data.iana.org/root-anchors/root-anchors.xml
The interface is kept generic, so that additional DS or DNSKEY RRs may
be served via the same interface, for example by provisioning them
locally in external files to support "islands" of security.
The trust anchor database becomes the fourth source of RRs we maintain,
besides, the network, the local cache, and the local zone.
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Previously, we'd never do any single-label or root domain lookups via
DNS, thus leaving single-label lookups to LLMNR and the search path
logic in order that single-label names don't leak too easily onto the
internet. With this change we open things up a bit, and only prohibit
A/AAAA lookups of single-label/root domains, but allow all other
lookups. This should provide similar protection, but allow us to resolve
DNSKEY+DS RRs for the top-level and root domains.
(This also simplifies handling of the search domain detection, and gets
rid of dns_scope_has_search_domains() in favour of
dns_scope_get_search_domains()).
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