Tom Gundersen [Thu, 10 Dec 2015 18:57:41 +0000 (19:57 +0100)]
resolved: cache - don't flush the cache of mDNS records unneccesarily
When the DNS_RESOURCE_KEY_CACHE_FLUSH flag is not set for an mDNS packet, we should not flush
the cache for RRs with matching keys. However, we were unconditionally flushing the cache
also for these packets.
Now mark all packets as cache_flush by default, except for these mDNS packets, and respect
that flag in the cache handling.
Tom Gundersen [Thu, 3 Dec 2015 20:40:06 +0000 (21:40 +0100)]
resolved: cache - rework which RR types we apply redirection to
The logic of dns_cache_get() is now:
- look up the precise key;
- look up NXDOMAIN item;
- if an RR type that may be redirected
(i.e., not CNAME, DNAME, RRSIG, NSEC, NSEC3, SIG, KEY, or
NXT) look up a correpsonding CNAME or DNAME record;
- look up a corresponding NSEC record;
Before this change we would give up before potentially finding
negative cache entries for DNAME, CNAME and NSEC records, we
would return NSEC records for aliases where we had DNAME or CNAME
records available and we would incorrectly try to redirect DNSSEC RRs.
Tom Gundersen [Wed, 2 Dec 2015 17:46:32 +0000 (18:46 +0100)]
resolved: cache - do negative caching only on the canonical name
Apart from dropping redundant information, this fixes an issue
where, due to broken DNS servers, we can only be certain of whether
an apparent NODATA response is in fact an NXDOMAIN response after
explicitly resolving the canonical name. This issue is outlined in
RFC2308. Moreover, by caching NXDOMAIN for an existing name, we
would mistakenly return NXDOMAIN for types which should not be
redirected. I.e., a query for AAAA on test-nx-1.jklm.no correctly
returns NXDOMAIN, but a query for CNAME should return the record
and a query for DNAME should return NODATA.
Note that this means we will not cache an NXDOMAIN response in the
presence of redirection, meaning one redundant roundtrip in case the
name is queried again.
The current code is not compatible with current dkr protocols anyway,
and dkr has a different focus ("microservices") than nspawn anyway
("whole machine containers"), hence drop support for it, we cannot
reasonably keep this up to date, and it creates the impression we'd
actually care for the microservices usecase.
Jorgen Schaefer [Thu, 10 Dec 2015 12:24:45 +0000 (13:24 +0100)]
Use /proc/net/sockstat6 to detect IPv6 support
The file /sys/module/ipv6 does not exist in all container
implementations (e.g. Virtuozzo). Using /proc/net/sockstat6
detects IPv6 support reliably in these environments, too.
This file does not exist when the kernel is not compiled with
IPv6 support, or if IPv6 support is disabled, so simply checking
for existence should be a suitable check.
resolved: chase DNSKEY/DS RRs when doing look-ups with DNSSEC enabled
This adds initial support for validating RRSIG/DNSKEY/DS chains when
doing lookups. Proof-of-non-existance, or proof-of-unsigned-zones is not
implemented yet.
With this change DnsTransaction objects will generate additional
DnsTransaction objects when looking for DNSKEY or DS RRs to validate an
RRSIG on a response. DnsTransaction objects are thus created for three
reasons now:
1) Because a user asked for something to be resolved, i.e. requested by
a DnsQuery/DnsQueryCandidate object.
2) As result of LLMNR RR probing, requested by a DnsZoneItem.
3) Because another DnsTransaction requires the requested RRs for
validation of its own response.
DnsTransactions are shared between all these users, and are GC
automatically as soon as all of these users don't need a specific
transaction anymore.
To unify the handling of these three reasons for existance for a
DnsTransaction, a new common naming is introduced: each DnsTransaction
now tracks its "owners" via a Set* object named "notify_xyz", containing
all owners to notify on completion.
A new DnsTransaction state is introduced called "VALIDATING" that is
entered after a response has been receieved which needs to be validated,
as long as we are still waiting for the DNSKEY/DS RRs from other
DnsTransactions.
This patch will request the DNSKEY/DS RRs bottom-up, and then validate
them top-down.
Caching of RRs is now only done after verification, so that the cache is
not poisoned with known invalid data.
The "DnsAnswer" object gained a substantial number of new calls, since
we need to add/remove RRs to it dynamically now.
When increasing the DnsAnswer array, don't operate piecemeal, grow the
array exponentially.
This way, the default logic for DnsAnswer allocations matches the
behaviour for GREEDY_REALLOC and suchlike, and we can reduce the number
of necessary allocations.
resolved: when parsing DNS packets, handle OPT RR specially
As soon as we encounter the OPT RR while parsing, store it in a special
field in the DnsPacket structure. That way, we won't be confused if we
iterate through RRs, and can check that there's really only one of these
RRs around.
resolved: refuse modifying DnsAnswer objects that have more than one reference
DnsAnswer objects should be considered immutable after having passed to
more than one user, i.e. with a reference counter > 1. Enforce that in
code, so that we can track down misuses easier.
"Contrary to what the comment said, we always verify redirect chains in
full, and cache all the CNAME records. There is therefore no need to
do extra negative caching along a CNAME chain."
This simply steals @teg's commit since we'll touch the SOA matching case
in a later patch, and rather want this bit gone, so that we don't have
to "fix" it, only to remove it later on.
resolved: when outputting RRs in text form, append a trailing dot to owner names
After all, that's how this is done in DNS, and is particularly important
if we look a DS/DNSKEY RRs for the root zone itself, where the owner
name would otherwise be shown as completely empty (i.e. missing).
resolved: shortcut RR comparisons if pointers match
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.
Daniel Mack [Wed, 9 Dec 2015 12:09:35 +0000 (13:09 +0100)]
resolved: add more linked packets for overlong known answers
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.
Daniel Mack [Wed, 9 Dec 2015 10:55:54 +0000 (11:55 +0100)]
resolved: add dns_packet_set_flags()
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.
Daniel Mack [Mon, 30 Nov 2015 23:53:42 +0000 (00:53 +0100)]
resolved: add dns_cache_export_to_packet()
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.
Daniel Mack [Mon, 30 Nov 2015 11:47:11 +0000 (12:47 +0100)]
resolved: implement query coalescing
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.
Daniel Mack [Mon, 30 Nov 2015 21:35:51 +0000 (22:35 +0100)]
resolved: add 'next_attempt_after' field to DnsTransaction
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.
Daniel Mack [Mon, 30 Nov 2015 18:06:36 +0000 (19:06 +0100)]
resolved: split dns_transaction_go()
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.
Daniel Mack [Sat, 11 Jul 2015 00:44:59 +0000 (20:44 -0400)]
resolved: add mDNS packet dispatcher
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.
Daniel Mack [Fri, 28 Aug 2015 14:48:37 +0000 (16:48 +0200)]
resolved: handle mDNS timeouts per transaction
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.
Daniel Mack [Tue, 25 Aug 2015 15:57:58 +0000 (17:57 +0200)]
resolved: short-cut jitter callbacks for LLMNR and mDNS
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.
Daniel Mack [Tue, 24 Nov 2015 14:45:15 +0000 (15:45 +0100)]
resolved: add cache flush flag to DnsResourceKey
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.
David Herrmann [Mon, 7 Dec 2015 17:34:05 +0000 (18:34 +0100)]
basic: add RB-Tree implementation
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.
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.
Fixes:
$ ./autogen.sh
$ ./configure ... --disable-timesyncd
$ make distcheck
...
make[1]: *** No rule to make target 'src/timesync/timesyncd-gperf.gperf', needed by 'src/timesync/timesyncd-gperf.c'. Stop.
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