We use stream objects in four different cases: let's track them.
This in particular allows us to make sure the limit on outgoing streams
cannot be exhausted by having incoming streams as this means we can
neatly separate the counters for all four types.
In all three cases, sd_event_loop() will return the exit code anyway.
If sd_event_loop() returns negative, failure is logged and results in an
immediate return. Otherwise, we don't care if sd_event_loop() returns 0
or positive, because the return value feeds into DEFINE_MAIN_FUNCTION(), which
doesn't make the distinction.
Previously, we'd use a link as "default" route depending on whether
there are route-only domains defined on it or not. (If there are, it
would not be used as default route, if there aren't it would.)
Let's make this explicit and add a link variable controlling this. The
variable is not changeable from the outside yet, but subsequent commits
are supposed to add that.
Note that making this configurable adds a certain amount of redundancy,
as there are now two ways to ensure a link does not receive "default"
lookup (i.e. DNS queries matching no configured route):
1. By ensuring that at least one other link configures a route on it
(for example by add "." to its search list)
2. By setting this new boolean to false.
But this is exactly what is intended with this patch: that there is an
explicit way to configure on the link itself whether it receives
'default' traffic, rather than require this to be configured on other
links.
The variable added is a tri-state: if true, the link is suitable for
recieving "default" traffic. If false, the link is not suitable for it.
If unset (i.e. negative) the original logic of "has this route-only
routes" is used, to ensure compatibility with the status quo ante.
The function dns_server_limited_domains() was very strange as it
enumerate the domains associated with a DnsScope object to determine
whether any "route-only" domains, but did so as a function associated
with a DnsServer object.
Let's clear this up, and replace it by a function associated with a
DnsScope instead. This makes more sense philosphically and allows us to
reduce the loops through which we need to jump to determine whether a
scope is suitable for default routing a bit.
Previously, we'd return DNS_SCOPE_MAYBE for all domain lookups matching
LLMNR or mDNS. Let's upgrade this to DNS_SCOPE_YES, to make the binding
stronger.
The effect of this is that even if "local" is defined as routing domain
on some iface, we'll still lookup domains in local via mDNS — if mDNS is
turned on. This should not be limiting, as people who don't want such
lookups should turn off mDNS altogether, as it is useless if nothing is
routed to it.
This also has the nice benefit that mDNS/LLMR continue to work if people
use "~." as routing domain on some interface.
Similar for LLMNR and single label names.
Similar also for the link local IPv4 and IPv6 reverse lookups.
Fixes: #10125
There's no value in authenticating SOA RRs that are neither answer to
our question nor parent of our question (the latter being relevant so
that we have a TTL from the SOA field for negative caching of the actual
query).
By being to eager here, and trying to authenticate too much we run the
risk of creating cyclic deps between our transactions which then causes
the over-all authentication to fail.
Fixes: #9771
This appears to be necessary for client software to ensure the reponse data
is validated with DNSSEC. For example, `ssh -v -o VerifyHostKeyDNS=yes -o
StrictHostKeyChecking=yes redpilllinpro01.ring.nlnog.net` fails if EDNS0 is
not enabled. The debugging output reveals that the `SSHFP` records were
found in DNS, but were considered insecure.
Note that the patch intentionally does *not* enable EDNS0 in the
`/run/systemd/resolve/resolv.conf` file (the one that contains `nameserver`
entries for the upstream DNS servers), as it is impossible to know for
certain that all the upstream DNS servers handles EDNS0 correctly.
Apparently people want more of these (as #11175 shows). Since this is
merely a safety limit for us, let's just bump all values substantially.
Fixes: #11175
RFC7766 section 4 states that in the absence of EDNS0, a response that
is too large for a 512-byte UDP packet will have the 'truncated' bit
set. The client is expected to retry the query over TCP.
Fixes#10264.
It would be very wrong if any of the specfier printf calls modified
any of the objects or data being printed. Let's mark all arguments as const
(primarily to make it easier for the reader to see where modifications cannot
occur).
https://tools.ietf.org/html/rfc1035#section-2.3.1 says (approximately)
that only letters, numbers, and non-leading non-trailing dashes are allowed
(for entries with A/AAAA records). We set no restrictions.
hosts(5) says:
> Host names may contain only alphanumeric characters, minus signs ("-"), and
> periods ("."). They must begin with an alphabetic character and end with an
> alphanumeric character.
nss-files follows those rules, and will ignore names in /etc/hosts that do not
follow this rule.
Let's follow the documented rules for /etc/hosts. In particular, this makes us
consitent with nss-files, reducing surprises for the user.
I'm pretty sure we should apply stricter filtering to names received over DNS
and LLMNR and MDNS, but it's a bigger project, because the rules differ
depepending on which level the label appears (rules for top-level names are
stricter), and this patch takes the minimalistic approach and only changes
behaviour for /etc/hosts.
Escape syntax is also disallowed in /etc/hosts, even if the resulting character
would be allowed. Other tools that parse /etc/hosts do not support this, and
there is no need to use it because no allowed characters benefit from escaping.
Do not treat various errors (missing hostname, invalid address) as fatal,
just warn and continue. /etc/hosts is written by humans and we should not
reject the whole file just because a singly entry is not to our liking.
Handle comments as described in hosts(5):
everything from the comment character until the end of the line should be
ignored.
Fixes#10779.
Add tests.
This adds a helper call for detaching a DnsServer from a DnsStream if
the latter is the "default" stream of the server.
Also, let's unref the stream in dns_stream_stop() rather than
dns_stream_free(): as soon as our stream is disconnected by stopping
there's really no need to keep it as default stream for the server
around.
Since dns_stream_free() calls dns_stream_stop() we can remove it from
the former.
DnsStream and DnsServer have a symbiotic relationship: one DnsStream is
the current "default" stream of the server (and thus reffed by it), but
each stream also refs the server it is connected to. This cyclic
dependency can result in weird situations: when one is
destroyed/unlinked/stopped it needs to unregister itself from the other,
but doing this will trigger unregistration of the other. Hence, let's
make sure we unregister the stream from the server before destroying it,
to break this cycle.
Most likely fixes: #10725
We register an on_packet() handler anyway, which is called first.
There's hence no need to check in on_stream_complete() again, as it is
already taken by that time.
Let's not name a variable of type ssize_t "r". We usually use "r" for
return values of API calls that return some kind of error as in int.
This creates a lot of confusion if used differently here, which actually
resulted in connect()'s return value being assigned to this mistyped "r"
by accident.
Let's rename the variable "m" hence, and not use it for connect() return
values.
