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-rw-r--r--src/resolve/resolved-dns-synthesize.c484
1 files changed, 484 insertions, 0 deletions
diff --git a/src/resolve/resolved-dns-synthesize.c b/src/resolve/resolved-dns-synthesize.c
new file mode 100644
index 0000000..b3442ad
--- /dev/null
+++ b/src/resolve/resolved-dns-synthesize.c
@@ -0,0 +1,484 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "alloc-util.h"
+#include "env-util.h"
+#include "hostname-util.h"
+#include "local-addresses.h"
+#include "missing_network.h"
+#include "resolved-dns-synthesize.h"
+
+int dns_synthesize_ifindex(int ifindex) {
+
+ /* When the caller asked for resolving on a specific
+ * interface, we synthesize the answer for that
+ * interface. However, if nothing specific was claimed and we
+ * only return localhost RRs, we synthesize the answer for
+ * localhost. */
+
+ if (ifindex > 0)
+ return ifindex;
+
+ return LOOPBACK_IFINDEX;
+}
+
+int dns_synthesize_family(uint64_t flags) {
+
+ /* Picks an address family depending on set flags. This is
+ * purely for synthesized answers, where the family we return
+ * for the reply should match what was requested in the
+ * question, even though we are synthesizing the answer
+ * here. */
+
+ if (!(flags & SD_RESOLVED_DNS)) {
+ if (flags & (SD_RESOLVED_LLMNR_IPV4|SD_RESOLVED_MDNS_IPV4))
+ return AF_INET;
+ if (flags & (SD_RESOLVED_LLMNR_IPV6|SD_RESOLVED_MDNS_IPV6))
+ return AF_INET6;
+ }
+
+ return AF_UNSPEC;
+}
+
+DnsProtocol dns_synthesize_protocol(uint64_t flags) {
+
+ /* Similar as dns_synthesize_family() but does this for the
+ * protocol. If resolving via DNS was requested, we claim it
+ * was DNS. Similar, if nothing specific was
+ * requested. However, if only resolving via LLMNR was
+ * requested we return that. */
+
+ if (flags & SD_RESOLVED_DNS)
+ return DNS_PROTOCOL_DNS;
+ if (flags & SD_RESOLVED_LLMNR)
+ return DNS_PROTOCOL_LLMNR;
+ if (flags & SD_RESOLVED_MDNS)
+ return DNS_PROTOCOL_MDNS;
+
+ return DNS_PROTOCOL_DNS;
+}
+
+static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+ int r;
+
+ assert(m);
+ assert(key);
+ assert(answer);
+
+ r = dns_answer_reserve(answer, 2);
+ if (r < 0)
+ return r;
+
+ if (IN_SET(key->type, DNS_TYPE_A, DNS_TYPE_ANY)) {
+ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+ 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(INADDR_LOOPBACK);
+
+ r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
+ if (r < 0)
+ return r;
+ }
+
+ if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY) && socket_ipv6_is_enabled()) {
+ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+ rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_AAAA, dns_resource_key_name(key));
+ if (!rr)
+ return -ENOMEM;
+
+ rr->aaaa.in6_addr = in6addr_loopback;
+
+ r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
+ if (r < 0)
+ return r;
+ }
+
+ return 0;
+}
+
+static int answer_add_ptr(DnsAnswer **answer, const char *from, const char *to, int ifindex, DnsAnswerFlags flags) {
+ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+ rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_PTR, from);
+ if (!rr)
+ return -ENOMEM;
+
+ rr->ptr.name = strdup(to);
+ if (!rr->ptr.name)
+ return -ENOMEM;
+
+ return dns_answer_add(*answer, rr, ifindex, flags, NULL);
+}
+
+static int synthesize_localhost_ptr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+ int r;
+
+ assert(m);
+ assert(key);
+ assert(answer);
+
+ if (IN_SET(key->type, DNS_TYPE_PTR, DNS_TYPE_ANY)) {
+ r = dns_answer_reserve(answer, 1);
+ if (r < 0)
+ return r;
+
+ r = answer_add_ptr(answer, dns_resource_key_name(key), "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+ if (r < 0)
+ return r;
+ }
+
+ return 0;
+}
+
+static int answer_add_addresses_rr(
+ DnsAnswer **answer,
+ const char *name,
+ struct local_address *addresses,
+ unsigned n_addresses) {
+
+ unsigned j;
+ int r;
+
+ assert(answer);
+ assert(name);
+
+ r = dns_answer_reserve(answer, n_addresses);
+ if (r < 0)
+ return r;
+
+ for (j = 0; j < n_addresses; j++) {
+ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+ r = dns_resource_record_new_address(&rr, addresses[j].family, &addresses[j].address, name);
+ if (r < 0)
+ return r;
+
+ r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
+ if (r < 0)
+ return r;
+ }
+
+ return 0;
+}
+
+static int answer_add_addresses_ptr(
+ DnsAnswer **answer,
+ const char *name,
+ struct local_address *addresses,
+ unsigned n_addresses,
+ int af, const union in_addr_union *match) {
+
+ bool added = false;
+ unsigned j;
+ int r;
+
+ assert(answer);
+ assert(name);
+
+ for (j = 0; j < n_addresses; j++) {
+ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+ if (af != AF_UNSPEC) {
+
+ if (addresses[j].family != af)
+ continue;
+
+ if (match && !in_addr_equal(af, match, &addresses[j].address))
+ continue;
+ }
+
+ r = dns_answer_reserve(answer, 1);
+ if (r < 0)
+ return r;
+
+ r = dns_resource_record_new_reverse(&rr, addresses[j].family, &addresses[j].address, name);
+ if (r < 0)
+ return r;
+
+ r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
+ if (r < 0)
+ return r;
+
+ added = true;
+ }
+
+ return added;
+}
+
+static int synthesize_system_hostname_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+ _cleanup_free_ struct local_address *addresses = NULL;
+ int n = 0, af;
+
+ assert(m);
+ assert(key);
+ assert(answer);
+
+ af = dns_type_to_af(key->type);
+ if (af >= 0) {
+ n = local_addresses(m->rtnl, ifindex, af, &addresses);
+ if (n < 0)
+ return n;
+
+ if (n == 0) {
+ struct local_address buffer[2];
+
+ /* If we have no local addresses then use ::1
+ * and 127.0.0.2 as local ones. */
+
+ if (IN_SET(af, AF_INET, AF_UNSPEC))
+ buffer[n++] = (struct local_address) {
+ .family = AF_INET,
+ .ifindex = dns_synthesize_ifindex(ifindex),
+ .address.in.s_addr = htobe32(0x7F000002),
+ };
+
+ if (IN_SET(af, AF_INET6, AF_UNSPEC) && socket_ipv6_is_enabled())
+ buffer[n++] = (struct local_address) {
+ .family = AF_INET6,
+ .ifindex = dns_synthesize_ifindex(ifindex),
+ .address.in6 = in6addr_loopback,
+ };
+
+ return answer_add_addresses_rr(answer,
+ dns_resource_key_name(key),
+ buffer, n);
+ }
+ }
+
+ return answer_add_addresses_rr(answer, dns_resource_key_name(key), addresses, n);
+}
+
+static int synthesize_system_hostname_ptr(Manager *m, int af, const union in_addr_union *address, int ifindex, DnsAnswer **answer) {
+ _cleanup_free_ struct local_address *addresses = NULL;
+ bool added = false;
+ int n, r;
+
+ assert(m);
+ assert(address);
+ assert(answer);
+
+ if (af == AF_INET && address->in.s_addr == htobe32(0x7F000002)) {
+
+ /* Always map the IPv4 address 127.0.0.2 to the local hostname, in addition to "localhost": */
+
+ r = dns_answer_reserve(answer, 4);
+ if (r < 0)
+ return r;
+
+ r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->full_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+ if (r < 0)
+ return r;
+
+ r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->llmnr_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+ if (r < 0)
+ return r;
+
+ r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->mdns_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+ if (r < 0)
+ return r;
+
+ r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+ if (r < 0)
+ return r;
+
+ return 1;
+ }
+
+ n = local_addresses(m->rtnl, ifindex, af, &addresses);
+ if (n <= 0)
+ return n;
+
+ r = answer_add_addresses_ptr(answer, m->full_hostname, addresses, n, af, address);
+ if (r < 0)
+ return r;
+ if (r > 0)
+ added = true;
+
+ r = answer_add_addresses_ptr(answer, m->llmnr_hostname, addresses, n, af, address);
+ if (r < 0)
+ return r;
+ if (r > 0)
+ added = true;
+
+ r = answer_add_addresses_ptr(answer, m->mdns_hostname, addresses, n, af, address);
+ if (r < 0)
+ return r;
+ if (r > 0)
+ added = true;
+
+ return added;
+}
+
+static int synthesize_gateway_rr(
+ Manager *m,
+ const DnsResourceKey *key,
+ int ifindex,
+ int (*lookup)(sd_netlink *context, int ifindex, int af, struct local_address **ret), /* either local_gateways() or local_outbound() */
+ DnsAnswer **answer) {
+ _cleanup_free_ struct local_address *addresses = NULL;
+ int n = 0, af, r;
+
+ assert(m);
+ assert(key);
+ assert(lookup);
+ assert(answer);
+
+ af = dns_type_to_af(key->type);
+ if (af >= 0) {
+ n = lookup(m->rtnl, ifindex, af, &addresses);
+ if (n < 0) /* < 0 means: error */
+ return n;
+
+ if (n == 0) { /* == 0 means we have no gateway */
+ /* See if there's a gateway on the other protocol */
+ if (af == AF_INET)
+ n = lookup(m->rtnl, ifindex, AF_INET6, NULL);
+ else {
+ assert(af == AF_INET6);
+ n = lookup(m->rtnl, ifindex, AF_INET, NULL);
+ }
+ if (n <= 0) /* error (if < 0) or really no gateway at all (if == 0) */
+ return n;
+
+ /* We have a gateway on the other protocol. Let's return > 0 without adding any RR to
+ * the answer, i.e. synthesize NODATA (and not NXDOMAIN!) */
+ return 1;
+ }
+ }
+
+ r = answer_add_addresses_rr(answer, dns_resource_key_name(key), addresses, n);
+ if (r < 0)
+ return r;
+
+ 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) {
+ _cleanup_free_ struct local_address *addresses = NULL;
+ int n;
+
+ assert(m);
+ assert(address);
+ assert(answer);
+
+ n = local_gateways(m->rtnl, ifindex, af, &addresses);
+ if (n <= 0)
+ return n;
+
+ return answer_add_addresses_ptr(answer, "_gateway", addresses, n, af, address);
+}
+
+int dns_synthesize_answer(
+ Manager *m,
+ DnsQuestion *q,
+ int ifindex,
+ DnsAnswer **ret) {
+
+ _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+ DnsResourceKey *key;
+ bool found = false, nxdomain = false;
+ int r;
+
+ assert(m);
+ assert(q);
+
+ DNS_QUESTION_FOREACH(key, q) {
+ union in_addr_union address;
+ const char *name;
+ int af;
+
+ if (!IN_SET(key->class, DNS_CLASS_IN, DNS_CLASS_ANY))
+ continue;
+
+ name = dns_resource_key_name(key);
+
+ if (dns_name_is_empty(name)) {
+ /* Do nothing. */
+
+ } else if (dns_name_dont_resolve(name)) {
+ /* Synthesize NXDOMAIN for some of the domains in RFC6303 + RFC6761 */
+ nxdomain = true;
+ continue;
+
+ } else if (is_localhost(name)) {
+
+ r = synthesize_localhost_rr(m, key, ifindex, &answer);
+ if (r < 0)
+ return log_error_errno(r, "Failed to synthesize localhost RRs: %m");
+
+ } else if (manager_is_own_hostname(m, name)) {
+
+ if (getenv_bool("SYSTEMD_RESOLVED_SYNTHESIZE_HOSTNAME") == 0)
+ continue;
+ r = synthesize_system_hostname_rr(m, key, ifindex, &answer);
+ if (r < 0)
+ return log_error_errno(r, "Failed to synthesize system hostname RRs: %m");
+
+ } else if (is_gateway_hostname(name)) {
+
+ r = synthesize_gateway_rr(m, key, ifindex, local_gateways, &answer);
+ if (r < 0)
+ return log_error_errno(r, "Failed to synthesize gateway RRs: %m");
+ if (r == 0) { /* if we have no gateway return NXDOMAIN */
+ nxdomain = true;
+ continue;
+ }
+
+ } else if (is_outbound_hostname(name)) {
+
+ r = synthesize_gateway_rr(m, key, ifindex, local_outbounds, &answer);
+ if (r < 0)
+ return log_error_errno(r, "Failed to synthesize outbound RRs: %m");
+ if (r == 0) { /* if we have no gateway return NXDOMAIN */
+ nxdomain = true;
+ continue;
+ }
+
+ } 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, "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, ifindex, &answer);
+ if (r < 0)
+ return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");
+
+ } else if (dns_name_address(name, &af, &address) > 0) {
+ int v, w;
+
+ if (getenv_bool("SYSTEMD_RESOLVED_SYNTHESIZE_HOSTNAME") == 0)
+ continue;
+
+ v = synthesize_system_hostname_ptr(m, af, &address, ifindex, &answer);
+ if (v < 0)
+ return log_error_errno(v, "Failed to synthesize system hostname PTR RR: %m");
+
+ w = synthesize_gateway_ptr(m, af, &address, ifindex, &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 */
+ continue;
+
+ /* Note that we never synthesize reverse PTR for _outbound, since those are local
+ * addresses and thus mapped to the local hostname anyway, hence they already have a
+ * mapping. */
+
+ } else
+ continue;
+
+ found = true;
+ }
+
+ if (found) {
+
+ if (ret)
+ *ret = TAKE_PTR(answer);
+
+ return 1;
+ } else if (nxdomain)
+ return -ENXIO;
+
+ return 0;
+}
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