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resolved: introduce the _localdnsstub and _localdnsproxy special hostnames for 127.0.0.54 + 127.0.0.53

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Let's give these special IP addresses names. After all name resolution
is our job here.

Fixes: #23623
This commit is contained in:
Lennart Poettering 2022-11-25 12:15:56 +01:00
parent 68d449997f
commit 17f244e8f9
7 changed files with 147 additions and 12 deletions
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11
man/resolvectl.xml
View File

@ -323,11 +323,12 @@
<listitem><para>Takes a boolean parameter; used in conjunction with <command>query</command>. If true
(the default), select domains are resolved on the local system, among them
<literal>localhost</literal>, <literal>_gateway</literal> and <literal>_outbound</literal>, or
entries from <filename>/etc/hosts</filename>. If false these domains are not resolved locally, and
either fail (in case of <literal>localhost</literal>, <literal>_gateway</literal> or
<literal>_outbound</literal> and suchlike) or go to the network via regular DNS/mDNS/LLMNR lookups
(in case of <filename>/etc/hosts</filename> entries).</para></listitem>
<literal>localhost</literal>, <literal>_gateway</literal>, <literal>_outbound</literal>,
<literal>_localdnsstub</literal> and <literal>_localdnsproxy</literal> or entries from
<filename>/etc/hosts</filename>. If false these domains are not resolved locally, and either fail (in
case of <literal>localhost</literal>, <literal>_gateway</literal> or <literal>_outbound</literal> and
suchlike) or go to the network via regular DNS/mDNS/LLMNR lookups (in case of
<filename>/etc/hosts</filename> entries).</para></listitem>
</varlistentry>
<varlistentry>

6
man/systemd-resolved.service.xml
View File

@ -118,6 +118,12 @@
local default gateway configured. This assigns a stable hostname to the local outbound IP addresses,
useful for referencing them independently of the current network configuration state.</para></listitem>
<listitem><para>The hostname <literal>_localdnsstub</literal> is resolved to the IP address 127.0.0.53,
i.e. the address the local DNS stub (see above) is listening on.</para></listitem>
<listitem><para>The hostname <literal>_localdnsproxy</literal> is resolved to the IP address 127.0.0.54,
i.e. the address the local DNS proxy (see above) is listening on.</para></listitem>
<listitem><para>The mappings defined in <filename>/etc/hosts</filename> are resolved to their
configured addresses and back, but they will not affect lookups for non-address types (like MX).
Support for <filename>/etc/hosts</filename> may be disabled with <varname>ReadEtcHosts=no</varname>,

8
src/basic/hostname-util.h
View File

@ -60,4 +60,12 @@ static inline bool is_outbound_hostname(const char *hostname) {
return STRCASE_IN_SET(hostname, "_outbound", "_outbound.");
}
static inline bool is_dns_stub_hostname(const char *hostname) {
return STRCASE_IN_SET(hostname, "_localdnsstub", "_localdnsstub.");
}
static inline bool is_dns_proxy_stub_hostname(const char *hostname) {
return STRCASE_IN_SET(hostname, "_localdnsproxy", "_localdnsproxy.");
}
int get_pretty_hostname(char **ret);

6
src/resolve/resolvectl.c
View File

@ -480,7 +480,11 @@ static bool single_label_nonsynthetic(const char *name) {
if (!dns_name_is_single_label(name))
return false;
if (is_localhost(name) || is_gateway_hostname(name))
if (is_localhost(name) ||
is_gateway_hostname(name) ||
is_outbound_hostname(name) ||
is_dns_stub_hostname(name) ||
is_dns_proxy_stub_hostname(name))
return false;
r = resolve_system_hostname(NULL, &first_label);

7
src/resolve/resolved-dns-scope.c
View File

@ -635,8 +635,11 @@ DnsScopeMatch dns_scope_good_domain(
if (dns_name_dont_resolve(domain))
return DNS_SCOPE_NO;
/* Never go to network for the _gateway or _outbound domain — they're something special, synthesized locally. */
if (is_gateway_hostname(domain) || is_outbound_hostname(domain))
/* Never go to network for the _gateway, _outbound, _localdnsstub, _localdnsproxy domain — they're something special, synthesized locally. */
if (is_gateway_hostname(domain) ||
is_outbound_hostname(domain) ||
is_dns_stub_hostname(domain) ||
is_dns_proxy_stub_hostname(domain))
return DNS_SCOPE_NO;
switch (s->protocol) {

110
src/resolve/resolved-dns-synthesize.c
View File

@ -341,7 +341,90 @@ static int synthesize_gateway_rr(
return 1; /* > 0 means: we have some gateway */
}
static int synthesize_gateway_ptr(Manager *m, int af, const union in_addr_union *address, int ifindex, DnsAnswer **answer) {
static int synthesize_dns_stub_rr(
Manager *m,
const DnsResourceKey *key,
in_addr_t addr,
DnsAnswer **answer) {
_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
int r;
assert(m);
assert(key);
assert(answer);
if (!IN_SET(key->type, DNS_TYPE_A, DNS_TYPE_ANY))
return 1; /* we still consider ourselves the owner of this name */
r = dns_answer_reserve(answer, 1);
if (r < 0)
return r;
rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, dns_resource_key_name(key));
if (!rr)
return -ENOMEM;
rr->a.in_addr.s_addr = htobe32(addr);
r = dns_answer_add(*answer, rr, LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED, NULL);
if (r < 0)
return r;
return 1;
}
static int synthesize_dns_stub_ptr(
Manager *m,
int af,
const union in_addr_union *address,
DnsAnswer **answer) {
int r;
assert(m);
assert(address);
assert(answer);
if (af != AF_INET)
return 0;
if (address->in.s_addr == htobe32(INADDR_DNS_STUB)) {
r = dns_answer_reserve(answer, 1);
if (r < 0)
return r;
r = answer_add_ptr(answer, "53.0.0.127.in-addr.arpa", "_localdnsstub", LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
if (r < 0)
return r;
return 1;
}
if (address->in.s_addr == htobe32(INADDR_DNS_PROXY_STUB)) {
r = dns_answer_reserve(answer, 1);
if (r < 0)
return r;
r = answer_add_ptr(answer, "54.0.0.127.in-addr.arpa", "_localdnsproxy", LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
if (r < 0)
return r;
return 1;
}
return 0;
}
static int synthesize_gateway_ptr(
Manager *m,
int af,
const union in_addr_union *address,
int ifindex,
DnsAnswer **answer) {
_cleanup_free_ struct local_address *addresses = NULL;
int n;
@ -422,7 +505,22 @@ int dns_synthesize_answer(
continue;
}
} else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 && dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0) ||
} else if (is_dns_stub_hostname(name)) {
r = synthesize_dns_stub_rr(m, key, INADDR_DNS_STUB, &answer);
if (r < 0)
return log_error_errno(r, "Failed to synthesize local DNS stub RRs: %m");
} else if (is_dns_proxy_stub_hostname(name)) {
r = synthesize_dns_stub_rr(m, key, INADDR_DNS_PROXY_STUB, &answer);
if (r < 0)
return log_error_errno(r, "Failed to synthesize local DNS stub RRs: %m");
} else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 &&
dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0 &&
dns_name_equal(name, "53.0.0.127.in-addr.arpa") == 0 &&
dns_name_equal(name, "54.0.0.127.in-addr.arpa") == 0) ||
dns_name_equal(name, "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa") > 0) {
r = synthesize_localhost_ptr(m, key, &answer);
@ -430,7 +528,7 @@ int dns_synthesize_answer(
return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");
} else if (dns_name_address(name, &af, &address) > 0) {
int v, w;
int v, w, u;
if (getenv_bool("SYSTEMD_RESOLVED_SYNTHESIZE_HOSTNAME") == 0)
continue;
@ -443,7 +541,11 @@ int dns_synthesize_answer(
if (w < 0)
return log_error_errno(w, "Failed to synthesize gateway hostname PTR RR: %m");
if (v == 0 && w == 0) /* This IP address is neither a local one nor a gateway */
u = synthesize_dns_stub_ptr(m, af, &address, &answer);
if (u < 0)
return log_error_errno(u, "Failed to synthesize local stub hostname PTR PR: %m");
if (v == 0 && w == 0 && u == 0) /* This IP address is neither a local one, nor a gateway, nor a stub address */
continue;
/* Note that we never synthesize reverse PTR for _outbound, since those are local

11
test/units/testsuite-75.sh
View File

@ -56,6 +56,17 @@ echo nameserver 10.0.3.3 10.0.3.4 | "$RESOLVCONF" -a hoge.foo.dhcp
assert_in '10.0.3.1 10.0.3.2' "$(resolvectl dns hoge)"
assert_in '10.0.3.3 10.0.3.4' "$(resolvectl dns hoge.foo)"
# Tests for _localdnsstub and _localdnsproxy
assert_in '127.0.0.53' "$(resolvectl query _localdnsstub)"
assert_in '_localdnsstub' "$(resolvectl query 127.0.0.53)"
assert_in '127.0.0.54' "$(resolvectl query _localdnsproxy)"
assert_in '_localdnsproxy' "$(resolvectl query 127.0.0.54)"
assert_in '127.0.0.53' "$(dig @127.0.0.53 _localdnsstub)"
assert_in '_localdnsstub' "$(dig @127.0.0.53 -x 127.0.0.53)"
assert_in '127.0.0.54' "$(dig @127.0.0.53 _localdnsproxy)"
assert_in '_localdnsproxy' "$(dig @127.0.0.53 -x 127.0.0.54)"
# Tests for mDNS and LLMNR settings
mkdir -p /run/systemd/resolved.conf.d
{