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Following our coding style on success we should initialize all return
parameters of a function. We missed to cases for dns_cache_lookup() (but
covered all others), fix them too.
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Some domains (such as us.ynuf.alipay.com) almost appear as if they actively
want to sabotage our DNSSEC work. Specifically, they unconditionally
return SERVFAIL on SOA lookups and always only after a 1s delay (at
least). This is pretty bad for our validation logic, as we use SOA
lookups to distuingish zones from non-terminal names. Moreover, SERVFAIL
is an error that is typically returned if we send requests a server
doesn't grok, and thus is reason for us to downgrade our protocol and
try again. In case of these zones this means we'll accept the SERVFAIL
response only after a full iterative downgrade to our lowest feature
level: TCP. In combination with the 1s delays this has the effect of
making us hit our transaction timeout way to easily.
As first attempt to improve the situation: let's start caching SERVFAIL
responses in our cache, after the full downgrade for a short period of
time.
Conceptually this is exposed as "weird rcode" caching, but for now we
only consider SERVFAIL a "weird rcode" worthy of caching. Later on we
might want to add more.
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See the section 10.2 of RFC6762 for details.
Signed-off-by: Dmitry Rozhkov <dmitry.rozhkov@linux.intel.com>
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resolved fixes for handling SERVFAIL errors from servers
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This way we don't log complaints about packets without SOA in case we are not
caching it anyway because the rcode is not SUCCESS or NXDOMAIN...
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When we return the full RR wire data, let's make sure the TTL included in it is
adjusted by the time the RR sat in the cache.
As an optimization we do this only for ResolveRecord() and not for
ResolveHostname() and friends, since adjusting the TTL means copying the RR
object, and we don#t want to do that if there's no reason to.
(ResolveHostname() and friends don't return the TTL hence there's no reason to
in that case)
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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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CID #1351544, #1351545.
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When the buffer is allocated on the stack we do not have to check for
failure everywhere. This is especially useful in debug statements, because
we can put dns_resource_key_to_string() call in the debug statement, and
we do not need a seperate if (log_level >= LOG_DEBUG) for the conversion.
dns_resource_key_to_string() is changed not to provide any whitespace
padding. Most callers were stripping the whitespace with strstrip(),
and it did not look to well anyway. systemd-resolve output is not column
aligned anymore.
The result of the conversion is not stored in DnsTransaction object
anymore. It is used only for debugging, so it seems fine to generate it
when needed.
Various debug statements are extended to provide more information.
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This fixes formatting of root domain in debug messages:
Old:
systemd-resolved[10049]: Requesting DS to validate transaction 19313 (., DNSKEY with key tag: 19036).
New:
systemd-resolved[10049]: Requesting DS to validate transaction 19313 (, DNSKEY with key tag: 19036).
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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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Fixes: #2361
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When using NSEC/NSEC3 RRs from the cache to derive existance of arbitrary RRs, we should not get confused by the fact
that NSEC/NSEC3 RRs exist twice at zone cuts: once in the parent zone, and once in the child zone. For most RR types we
should only consult the latter since that's where the beef is. However, for DS lookups we have to check the former.
This change makes sure we never cache NSEC/NSEC3 RRs from any parent zone of a zone-cut. It also makes sure that when
we look for a DS RR in the cache we never consider any cached NSEC RR, as those are now always from the child zone.
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Quite often we read the same RR key multiple times from the same message. Try to replace them by a single object when
we notice this. Do so again when we add things to the cache.
This should reduce memory consumption a tiny bit.
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When storing negative responses, clamp the SOA minimum TTL (as suggested
by RFC2308) to the TTL of the NSEC/NSEC3 RRs we used to prove
non-existance, if it there is any.
This is necessary since otherwise an attacker might put together a faked
negative response for one of our question including a high-ttl SOA RR
for any parent zone, and we'd use trust the TTL.
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This makes sure that we also honour the RRSIG expiry for negative
caching.
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When we verified a signature, fix up the RR's TTL to the original TTL
mentioned in the signature, and store the signature expiry information
in the RR, too. Then, use that when adding RRs to the cache.
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This collects statistical data about transactions, dnssec verifications
and the cache, and exposes it over the bus. The systemd-resolve-host
tool learns new options to query these statistics and reset them.
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Let's simplify usage and memory management of DnsResourceRecord's
dns_resource_record_to_string() call: cache the formatted string as
part of the object, and return it on subsequent calls, freeing it when
the DnsResourceRecord itself is freed.
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entries
We use ANY RR keys to store NXDOMAIN information, but we previously
didn't flush out old ANY RR items in the cache when adding new entries.
Fix that.
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Let's abstract which RRs shall honour CNAMEs, and which ones should not.
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In most of the other call, we called similar functions that remove the
data structure link-ups to other objects "unlink", hence we should here,
too.
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Given that we already have dns_cache_remove_by_rr() this makes clearer
what the operation actually does.
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This adds a new DnsAnswer item flag "DNS_ANSWER_SHARED_OWNER" which is
set for mDNS RRs that lack the cache-flush bit. The cache-flush bit is
removed from the DnsResourceRecord object in favour of this.
This also splits out the code that removes previous entries when adding
new positive ones into a new separate call dns_cache_remove_previous().
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After all we want to allow NULL DnsAnswer objects as equivalent to empty
ones, hence we should use the right checks everywhere.
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Make sure the cache never altes the authenticated bit of RRs stored in
it, and drops it for RRs when passing it out again.
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Let's use dns_cache_remove() rather than
dns_cache_item_remove_and_free() to destroy the cache, since the former
requires far fewer hash table lookups.
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When we receieve a TTL=0 RR, then let's only flush that specific RR and
not the whole RRset.
On mDNS with RRsets that a shared-owner this is how specific RRs are
removed from the set, hence support this. And on non-mDNS the whole
RRset will already be removed much earlier in dns_cache_put() hence
there's no reason remove it again.
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We should never use the TTL of an unauthenticated SOA to cache an
authenticated RR.
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We call it anyway as one of the first calls in dns_cache_put(), hence
there's no reason to do this multiple times.
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Let's keep entries for longer and more of them. After all, due to the
DNSSEC hookup the amount of RRs we need to store is much higher now.
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OK to be unsigned
This large patch adds a couple of mechanisms to ensure we get NSEC3 and
proof-of-unsigned support into place. Specifically:
- Each item in an DnsAnswer gets two bit flags now:
DNS_ANSWER_AUTHENTICATED and DNS_ANSWER_CACHEABLE. The former is
necessary since DNS responses might contain signed as well as unsigned
RRsets in one, and we need to remember which ones are signed and which
ones aren't. The latter is necessary, since not we need to keep track
which RRsets may be cached and which ones may not be, even while
manipulating DnsAnswer objects.
- The .n_answer_cachable of DnsTransaction is dropped now (it used to
store how many of the first DnsAnswer entries are cachable), and
replaced by the DNS_ANSWER_CACHABLE flag instead.
- NSEC3 proofs are implemented now (lacking support for the wildcard
part, to be added in a later commit).
- Support for the "AD" bit has been dropped. It's unsafe, and now that
we have end-to-end authentication we don't need it anymore.
- An auxiliary DnsTransaction of a DnsTransactions is now kept around as
least as long as the latter stays around. We no longer remove the
auxiliary DnsTransaction as soon as it completed. THis is necessary,
as we now are interested not only in the RRsets it acquired but also
in its authentication status.
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This is in the fast path, so let's not do all this work unneccessarily.
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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.
This fixes 90325e8c2e559a21ef0bc2f26b844c140faf8020.
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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.
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Some DNS servers will hand out negative answers without SOA records,
these can not be cached, so log about that fact.
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An NXDOMAIN entry means there are no RRs of any type for a name,
so only cache by CLASS + NAME, rather than CLASS + NAME + TYPE.
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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.
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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.
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Quoting @teg:
"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.
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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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