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This is preparation for making our Varlink API a public API. Since our
Varlink API is built on top of our JSON API we need to make that public
first (it's a nice API, but JSON APIs there are already enough, this is
purely about the Varlink angle).
I made most of the json.h APIs public, and just placed them in
sd-json.h. Sometimes I wasn't so sure however, since the underlying data
structures would have to be made public too. If in doubt I didn#t risk
it, and moved the relevant API to src/libsystemd/sd-json/json-util.h
instead (without any sd_* symbol prefixes).
This is mostly a giant search/replace patch.
The name resolver.arpa is reserved for RFC9462 "Discovery of Designated
Resolvers" (DDR). This relies on regular dns queries for SVCB records at
the special use domain name _dns.resolver.arpa. Unfortunately, older
nameservers (or broken ones) won't know about this SUDN and will likely
return NXDOMAIN. If this is cached, the cache entry will become an
impediment for any clients trying to discover designated resolvers
through the stub-resolver, or potentially even sd-resolved itself, were
it to implement DDR.
The RFC recommendation is that "clients MUST NOT perform A or AAAA
queries for resolver.arpa", and "resolvers SHOULD respond to queries of
any type other than SVCB for _dns.resolver.arpa. with NODATA and queries
of any type for any domain name under resolver.arpa with NODATA." which
should help avoid potential compatibility issues. This enforces that
condition within sd-resolved, and avoids caching any such erroneous
NXDOMAIN.
The RFC also recommends requests for this domain should never be
forwarded, to prevent authentication failures. Since there isn't much
point in establishing secure communication to the local stub, we still
allow SVCB to be forwarded from the stub, in case the client cares to
implement some other authentication method and understands the
consequences of skipping the local stub. Normal clients are not
expected to implement DDR, but this change will protect sd-resolved's
own caches in case they try.
Although A and AAAA are prohibited, I think validating resolvers
might reasonably query for dnssec records, even though the resolver.arpa
zone does not exist (it is declared to be a locally served zone). For
this reason, I have also added resolver.arpa to the builtin dnssec NTA.
RFC6762 10.1 says that queriers receiving a Multicast DNS response with a TTL
of zero SHOULD record a TTL of 1 and then delete the record one second later.
Added a timer event to trigger a callback to clean-up the cache one second after
a goodbye packet is received. The callback also checks for any cache entries
expiring within the next one second and schedules follow-up cleanup callbacks
accordingly.
When we receive a goodby packet about a host, and we have a cache entry about
the host, we do not immediately remove the cache entry, but update it with TTL 1.
See RFC 6762 section 10.1 and 3755027c2cada70345c96787a9b5569994dd23ed.
If we receive a request soon after the goodby packet, previously the
entry was included in the known answers section of the reply. But such
information should not be appended.
Follow-up for 3755027c2cada70345c96787a9b5569994dd23ed.
Otherwise, the check below is always fail.
```
if (FLAGS_SET(query_flags, SD_RESOLVED_NO_STALE) && j->until_valid < current)
```
Follow-up for 5ed91481abea382dc486507556e5cdf0f36b796f.
Initialize until_valid is properly for negative response, the cached negative responses can be used to answer the queries before contacting upstream server.
serve stale feature to keep the DNS resource records beyond TTL to return them as stale records in case of upstream server is not reachable or returns negative response.
SD_RESOLVED_NO_STALE flag has been added to disable serving stale records via dbus.
added serve stale test cases to TEST-75-RESOLVED
Fixes: #21815
This adds a simple varlink call io.systemd.Resolve.Monitor.DumpCache to
the existing io.systemd.Resolve.Monitor service. It compiles a JSON
object containing the per-scope cache entries and returns it.
Replaces: #20053#19104Fixes: #14796
Otherwise, if we have many cached entries or pending transactions with
TYPE_ANY, then dns_transaction_make_packet_mdns() fails with -EMSGSIZE.
This also fixes use-after-free.
Fixes#23894.
Since we don't need the error value, and the buffer is allocated with a fixed
size, the whole logic provided by in_addr_to_string() becomes unnecessary, so
it's enough to wrap inet_ntop() directly.
inet_ntop() can only fail with ENOSPC. But we specify a buffer that is supposed
to be large enough, so this should never fail. A bunch of tests of this are added.
This allows all the wrappers like strna(), strnull(), strempty() to be dropped.
The guard of 'if (DEBUG_LOGGING)' can be dropped from around log_debug(),
because log_debug() implements the check outside of the function call. But
log_link_debug() does not, so it we need it to avoid unnecessary evaluation of
the formatting.
Let's raise our supported baseline a bit: CLOCK_BOOTTIME started to work
with timerfd in kernel 3.15 (i.e. back in 2014), let's require support
for it now.
This will raise our baseline only modestly from 3.13 → 3.15.
Also,
- drop unnecessary +1 from buffer size, as IF_NAMESIZE or IFNAMSIZ
includes the nul at the end.
- format_ifname() does not update buffer on failure,
- introduces format_ifname_alloc(), FORMAT_IFNAME(), and their friends.
LLVM 13 introduced `-Wunused-but-set-variable` diagnostic flag, which
trips over some intentionally set-but-not-used variables or variables
attached to cleanup handlers with side effects (`_cleanup_umask_`,
`_cleanup_(notify_on_cleanup)`, `_cleanup_(restore_sigsetp)`, etc.):
```
../src/basic/process-util.c:1257:46: error: variable 'saved_ssp' set but not used [-Werror,-Wunused-but-set-variable]
_cleanup_(restore_sigsetp) sigset_t *saved_ssp = NULL;
^
1 error generated.
```
The issue was introduced in the refactoring in 775ae35403f8f3c01b7ac13387fe8aac1759993f.
We would pass an initialized value to a helper function. We would only *use*
it if it was initialized. But the mere passing of an unitialized variable is
UB, so let's not do that. This silences a gcc warning.
rr is asserted upon a few lines above, no need to check for null.
Coverity-found issue, CID 1450844
CID 1450844: Null pointer dereferences (REVERSE_INULL)
Null-checking "rr" suggests that it may be null, but it has already
been dereferenced on all paths leading to the check.
When responding from DNS cache, let's slightly tweak how the TTL is
lowered: as before let's round down when converting from our internal µs
to the external seconds. (This is preferable, since records should
better be cached too short instead of too long.) Let's avoid rounding
down to zero though, since that has special semantics in many cases (in
particular mDNS). Let's just use 1s in that case.
We nowadays cache full answer RRset combinations instead of just the
exact matching rrset. This means we should not cache RRs that are not
immediate answers to our question for longer then their own RRs. Or in
other words: let's determine the shortest TTL of all RRs in the whole
answer, and use that as cache lifetime.
I started working on this because I wanted to change how
DEFINE_TRIVIAL_CLEANUP_FUNC is defined. Even independently of that change, it's
nice to make make things more consistent and predictable.
Let's introduce a new flag that indicates whether the response was
acquired in "confidential" mode, i.e. via encrypted DNS-over-TLS, or
synthesized locally.
Fixes: #12859
Let's use the same flags type we use for client communication, i.e.
instead of "bool answer_authenticated", let's use "uint64_t
answer_query_flags", with the SD_RESOLVED_AUTHENTICATED flag.
This is mostly just search/replace, i.e. a refactoring, no change in
behaviour.
This becomes useful once in a later commit SD_RESOLVED_CONFIDENTIAL is
added to indicate resolution that either were encrypted (DNS-over-TLS)
or never left the local system.
This substantially beefs up the local DNS stub feature set in order to
allow local clients to do DNSSEC validation through the stub.
Previously we'd return NOTIMP if we'd get a DO or DO+CD lookup. With
this change we'll instead:
1. If we get DO+CD requests (i.e. DNSSEC with no local checking) we'll
proxy DNS queries and response mostly unmodified to/from upstream DNS
servers if possible (this is called "bypass" mode). We will patch in
new request IDs, (and patch them back out on reply), so that we can
sanely keep track of things. We'll also maintain a minimal local
cache for such lookups, always keeping the whole DNS packets in it
(if we reply from cache we'll patch the TTLs of all included RRs).
2. If we get DO requests without CD (i.e. DNSSEC with local checking)
we'll resolve and validate locally. In this mode we will not proxy
packets, but generate our own. We will however cache the combination
of answer RRs (along with their packet section assignments) we got
back in the cache, and use this information to generate reply packets
from the DNS stub.
In both cases: if we determine a lookup is to be answered from LLMNR or
mDNS we'll always revert to non-DNSSEC, non-proxy operation as before.
Answers will lack the DO bit then, since the data cannot be validated
via DNSSEC by the clients.
To make this logic more debuggable, this also adds query flags for
turning off RR sources. i.e. cache/network/zone/trust anchor/local
synthesis may now be disabled individually for each lookup.
The cache is substantially updated to make all this work: in addition to
caching simple RRs for lookup RR keys, we'll now cache the whole packets
and the whole combination of RRs, so that we can answer DO and DO+CD
replies sensibly according to the rules described above. This sounds
wasteful, but given that the
DnsResourceRecord/DnsResourceKey/DnsAnswer/DnsPacket
objects are all ref-counted and we try to merge references the actual
additional memory used should be limited (but this might be something to
optimize further later on).
To implement classic RR key lookups and new-style packet proxy lookups
(i.e. the ones necessary for DO+CD packet proxying, as described above)
DnsTransaction and DnsQuery objects now always maintain either a
DnsResourceKey/DnsQuestion as lookup key or a DnsPacket for "bypass"
mode.
Fixes: #4621#17218
The more fields DnsAnswerItem gains the less sense it makes to pass
every field of it as separate parameter to an iterator macro. Let's
simplify things here, in preparation of adding more fields to the
structure later on: let's just return the structure itself in the loop,
rather than the individual fields.
GetMulticastHosts() returns an array of hostnames/addresses discovered via
LLMNR or Multicast DNS. It does not trigger any discovery on its own.
Instead, it simply returns whatever is already in resolved's cache.
Apparently 30s is a bit too long for some cases, see #5552. But not
caching SERVFAIL at all also breaks stuff, see explanation in
201d99584ed7af8078bb243ce2587e5455074713.
Let's try to find some middle ground, by lowering the cache timeout to
10s. This should be ample for the problem
201d99584ed7af8078bb243ce2587e5455074713 attackes, but not as long as
half a miute, as #5552 complains.
Fixes: #5552
