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DNS queries need timeout values to detect whether a DNS server is
unresponsive or, if the query is sent over UDP, whether a DNS message
was lost and has to be resent. The total time that it takes to answer a
query to arrive is t + RTT, where t is the maximum time that the DNS
server that is being queried needs to answer the query.
An authoritative server stores a copy of the zone that it serves in main
memory or secondary storage, so t is very small and therefore the time
that it takes to answer a query is almost entirely determined by the
RTT. Modern authoritative server software keeps its zones in main memory
and, for example, Knot DNS and NSD are able to answer in less than
100 µs [1]. So iterative resolvers continuously measure the RTT to
optimize their query timeouts and to resend queries more quickly if they
are lost.
systemd-resolved is a stub resolver: it forwards DNS queries to an
upstream resolver and waits for an answer. So the time that it takes for
systemd-resolved to answer a query is determined by the RTT and the time
that it takes the upstream resolver to answer the query.
It seems common for iterative resolver software to set a total timeout
for the query. Such total timeout subsumes the timeout of all queries
that the iterative has to make to answer a query. For example, BIND
seems to use a default timeout of 10 s.
At the moment systemd-resolved derives its query timeout entirely from
the RTT and does not consider the query timeout of the upstream
resolver. Therefore it often mistakenly degrades the feature set of its
upstream resolvers if it takes them longer than usual to answer a query.
It has been reported to be a considerable problem in practice, in
particular if DNSSEC=yes. So the query timeout systemd-resolved should
be derived from the timeout of the upstream resolved and the RTT to the
upstream resolver.
At the moment systemd-resolved measures the RTT as the time that it
takes the upstream resolver to answer a query. This clearly leads to
incorrect measurements. In order to correctly measure the RTT
systemd-resolved would have to measure RTT separately and continuously,
for example with a query with an empty question section or a query for
the SOA RR of the root zone so that the upstream resolver would be able
to answer to query without querying another server. However, this
requires significant changes to systemd-resolved. So it seems best to
postpone them until other issues have been addressed and to set the
resend timeout to a fixed value for now.
As mentioned, BIND seems to use a timeout of 10 s, so perhaps 12 s is a
reasonable value that also accounts for common RTT values. If we assume
that the we are going to retry, it could be less. So it should be enough
to set the resend timeout to DNS_TIMEOUT_MAX_USEC as
DNS_SERVER_FEATURE_RETRY_ATTEMPTS * DNS_TIMEOUT_MAX_USEC = 15 s.
However, this will not solve the incorrect feature set degradation and
should be seen as a temporary change until systemd-resolved does
probe the feature set of an upstream resolver independently from the
actual queries.
[1] https://www.knot-dns.cz/benchmark/
Let's always write "1 << 0", "1 << 1" and so on, except where we need
more than 31 flag bits, where we write "UINT64(1) << 0", and so on to force
64bit values.
This drops needless safety checks that ensure we only reference block
devices for blockio/io settings. The backing code was already able to
accept regular file system paths too, in which case the backing device
node of that file system would be used. Hence, let's drop the artificial
restrictions and open up this underlying functionality.
We document the rule that return values >= 0 of functions are supposed
to indicate success, and that in case of success all return parameters
should be initialized. Let's actually do so.
Just a tiny coding style fix-up.
../src/test/test-sizeof.c: In function ‘main’:
../src/test/test-sizeof.c:70:24: error: result of ‘1 << 31’ requires 33 bits to represent, but ‘int’ only has 32 bits [-Werror=shift-overflow=]
X = (1 << 31),
^~
cc1: some warnings being treated as errors
Follow-up for b05ecb8cad.
Jun 11 14:29:12 krowka systemd[1]: /etc/systemd/system/workingdir.service:6: = path is not normalizedWorkingDirectory: /../../etc
↓
Jun 11 14:32:12 krowka systemd[1]: /etc/systemd/system/workingdir.service:6: WorkingDirectory= path is not normalized: /../../etc
Since bb28e68477 parsing failures of
certain unit file settings will result in load failures of units. This
introduces a new load state "bad-setting" that is entered in precisely
this case.
With this addition error messages on bad settings should be a lot more
explicit, as we don't have to show some generic "errno" error in that
case, but can explicitly say that a bad setting is at fault.
Internally this unit load state is entered as soon as any configuration
loader call returns ENOEXEC. Hence: config parser calls should return
ENOEXEC now for such essential unit file settings. Turns out, they
generally already do.
Fixes: #9107
These states should never be visible to the outside, as they are used
only internally while loading unit. Hence let's drop them from the
documentation.
The load_error is only valid in some load_state cases, lets generate
prettier messages for other cases too, by reusing the
bus_unit_validate_load_state() call which does jus that.
Clients (such as systemctl) ignored LoadError unles LoadState was
"error" before. With this change they could even show LoadError in other
cases and it would show a useful name.
Let's use a switch() statement, cover more cases with pretty messages.
Also let's rename it to "validate", as that's more specific that
"check", as it implies checking for a "valid"/"good" state, which is
what this function does.
This makes two changes: first of all we will now explicitly check
whether a domain to test against an NSEC record is actually below the
signer's name. This is relevant for NSEC records that chain up the end
and the beginning of a zone: we shouldn't alow that NSEC record to match
against domains outside of the zone.
This also fixes how we handle NSEC checks for domains that are prefixes
of the NSEC RR domain itself, fixing #8164 which triggers this specific
case. The non-wildcard NSEC check is simplified for that, we can
directly make our between check, there's no need to find the "Next
Closer" first, as the between check should not be affected by additional
prefixes. For the wild card NSEC check we'll prepend the asterisk in
this case to the NSEC RR itself to make a correct check.
Fixes: #8164
oss-fuzz flags this as:
==1==WARNING: MemorySanitizer: use-of-uninitialized-value
0. 0x7fce77519ca5 in ascii_is_valid systemd/src/basic/utf8.c:252:9
1. 0x7fce774d203c in ellipsize_mem systemd/src/basic/string-util.c:544:13
2. 0x7fce7730a299 in print_multiline systemd/src/shared/logs-show.c:244:37
3. 0x7fce772ffdf3 in output_short systemd/src/shared/logs-show.c:495:25
4. 0x7fce772f5a27 in show_journal_entry systemd/src/shared/logs-show.c:1077:15
5. 0x7fce772f66ad in show_journal systemd/src/shared/logs-show.c:1164:29
6. 0x4a2fa0 in LLVMFuzzerTestOneInput systemd/src/fuzz/fuzz-journal-remote.c:64:21
...
I didn't reproduce the issue, but this looks like an obvious error: the length
is specified, so we shouldn't use the string with any functions for normal
C-strings.
