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only maintain one question RR key per transaction and other fixes
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We do so for Unicast DNS and LLMNR anyway, let's also do this for mDNS,
and simplify things.
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Let's simplify things and only maintain a single RR key per transaction
object, instead of a full DnsQuestion. Unicast DNS and LLMNR don't
support multiple questions per packet anway, and Multicast DNS suggests
coalescing questions beyond a single dns query, across the whole system.
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It shouldn't happen that we try to resolve IPv4 addresses via LLMNR on
IPv6 and vice versa, but let's explicitly verify that we don't turn an
IPv4 LLMNR lookup into an IPv6 TCP connection.
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We explicitly need to turn off name compression when marshalling or
demarshalling RRs for bus transfer, since they otherwise refer to packet
offsets that reference packets that are not transmitted themselves.
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With this change we'll now also generate synthesized RRs for the local
LLMNR hostname (first label of system hostname), the local mDNS hostname
(first label of system hostname suffixed with .local), the "gateway"
hostname and all the reverse PTRs. This hence takes over part of what
nss-myhostname already implemented.
Local hostnames resolve to the set of local IP addresses. Since the
addresses are possibly on different interfaces it is necessary to change
the internal DnsAnswer object to track per-RR interface indexes, and to
change the bus API to always return the interface per-address rather than
per-reply. This change also patches the existing clients for resolved
accordingly (nss-resolve + systemd-resolve-host).
This also changes the routing logic for queries slightly: we now ensure
that the local hostname is never resolved via LLMNR, thus making it
trustable on the local system.
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Following our usual logic of treating NULL arrays as empty arrays (for
example, see strv.c) do the same for questions too.
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Delete unnecessary checks before some function calls
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The following functions return immediately if a null pointer was passed.
* calendar_spec_free
* link_address_free
* manager_free
* sd_bus_unref
* sd_journal_close
* udev_monitor_unref
* udev_unref
It is therefore not needed that a function caller repeats a corresponding check.
This issue was fixed by using the software Coccinelle 1.0.1.
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We should never allow leaking of "localhost" queries onto the network,
even if there's an explicit domain rotue set for this.
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Let's make sure that clients querying resolved via the bus for A, AAAA
or PTR records for "localhost" get a synthesized, local reply, so that
we do not hit the network.
This makes part of nss-myhostname redundant, if used in conjunction.
However, given that nss-resolve shall be optional we need to keep this
code in both places for now.
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Previously, if the event loop never ran before sd_event_now() would
fail. With this change it will instead fall back to invoking now(). This
way, the function cannot fail anymore, except for programming error when
invoking it with wrong parameters.
This takes into account the fact that many callers did not handle the
error condition correctly, and if the callers did, then they kept simply
invoking now() as fall back on their own. Hence let's shorten the code
using this call, and make things more robust, and let's just fall back
to now() internally.
Whether now() is used or the cache timestamp may still be detected via
the return value of sd_event_now(). If > 0 is returned, then the fall
back to now() was used, if == 0 is returned, then the cached value was
returned.
This patch also simplifies many of the invocations of sd_event_now():
the manual fall back to now() can be removed. Also, in cases where the
call is invoked withing void functions we can now protect the invocation
via assert_se(), acknowledging the fact that the call cannot fail
anymore except for programming errors with the parameters.
This change is inspired by #841.
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With the exponential backoff, we can perform more requests in the same amount of time,
so bump this a bit.
In case of large RTT this may be necessary in order not to regress, and in case
of large packet-loss it will make us more robust. The latter is particularly
relevant once we start probing for features (and hence may see packet-loss
until we settle on the right feature level).
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Rather than fixing this to 5s for unicast DNS and 1s for LLMNR, start
at a tenth of those values and increase exponentially until the old
values are reached. For LLMNR the recommended timeout for IEEE802
networks (which basically means all of the ones we care about) is 100ms,
so that should be uncontroversial. For unicast DNS I have found no
recommended value. However, it seems vastly more likely that hitting a
500ms timeout is casued by a packet loss, rather than the RTT genuinely
being greater than 500ms, so taking this as a startnig value seems
reasonable to me.
In the common case this greatly reduces the latency due to normal packet
loss. Moreover, once we get support for probing for features, this means
that we can send more packets before degrading the feature level whilst
still allowing us to settle on the correct feature level in a reasonable
timeframe.
The timeouts are tracked per server (or per scope for the multicast
protocols), and once a server (or scope) receives a successfull package
the timeout is reset. We also track the largest RTT for the given
server/scope, and always start our timouts at twice the largest
observed RTT.
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We cannot rely on CLOCK_BOOTTIME being supported by the kernel, so fallack
to CLOCK_MONOTONIC if the former is not supported.
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resolved: never attempt to resolve loopback addresses via DNS/LLMNR/mDNS
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We already refuse to resolve "localhost", hence we should also refuse
resolving "127.0.0.1" and friends.
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The NSEC type itself must at least be in the bitmap, so NSEC records with empty
bitmaps must be bogus.
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We were tracking the bit offset inside each byte, rather than inside the whole bitmap.
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We were counting the number of bits set rather than the number of bytes they occupied.
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Let's optimize things a bit and properly compare DNS question arrays,
instead of checking if they are mutual supersets. This also makes ANY
query handling more accurate.
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This is handled by the kernel now that the socket is connect()ed.
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This was a bug.
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As we have connect()ed to the desired DNS server, we no longer need to pass
control messages manually when sending packets. Simplify the logic accordingly.
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This function emits the UDP packet via the scope, but first it will
determine the current server (and connect to it) and store the
server in the transaction.
This should not change the behavior, but simplifies the code.
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No functional change, but makes follow-up patch clearer.
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With access to the server when creating the socket, we can connect()
to the server and hence simplify message sending and receiving in
follow-up patches.
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Close the socket when changing the server in a transaction, in
order for it to be reopened with the right server when we send
the next packet.
This fixes a regression where we could get stuck with a failing
server.
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This was only ever used by LLMNR, so don't request this for unicast DNS packets.
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A transaction can only have one socket at a time, so no need to distinguish these.
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Assigning a TPYE enum value to a class variable is certainly wrong.
However, they both have the same value, so the result was correct
nevertheless.
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We were stopping the transaction, but we need to stop processing the packet alltogether.
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A size_t was being accessed as a char* due to the order of arguments being inverted.
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We were appending rather than reading the bitmap.
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We can never read past the end of the packet, so this seems impossible
to exploit, but let's error out early as reading past the end of the
current RR is clearly an error.
Found by Lennart, based on patch by Daniel.
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Rename the field to make this clearer.
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Most blobs (keys, signatures, ...) should have a specific size given by
the relevant algorithm. However, as we don't use/verify the algorithms
yet, let's just ensure that we don't read out zero-length data in cases
where this does not make sense.
The only exceptions, where zero-length data is allowed are in the NSEC3
salt field, and the generic data (which we don't know anything about,
so better not make any assumptions).
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resolve: unify memdup() code when parsing RRs
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resolved: make sure we alway initialize *start in dns_packet_append_t…
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dns_packet_append_type_window()
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Let's make dns_packet_read_public_key() more generic by renaming it to
dns_packet_read_memdup() (which more accurately describes what it
does...). Then, patch all cases where we memdup() RR data to use this
new call.
This specifically checks for zero-length objects, and handles them
gracefully. It will set zero length payload fields as a result.
Special care should be taken to ensure that any code using this call
can handle the returned allocated field to be NULL if the size is
specified as 0!
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resolve: fix two minor memory leaks
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strv_extend() already strdup()s internally, no need to to this twice.
(Also, was missing OOM check...).
Use strv_consume() when we already have a string allocated whose
ownership we want to pass to the strv.
This fixes 50f1e641a93cacfc693b0c3d300bee5df0c8c460.
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