Merge pull request #3549 from poettering/resolved-more

resolved: more fixes, among them "systemctl-resolve --status" to see DNS configuration in effect, and a local DNS stub listener on 127.0.0.53

Makefile.am

@@ -125,6 +125,7 @@ dist_systemunit_DATA_busnames =
 dist_sysusers_DATA =
 check_PROGRAMS =
 check_DATA =
+dist_rootlibexec_DATA =
 tests=
 manual_tests =
 TEST_EXTENSIONS = .py
@@ -5147,7 +5148,7 @@ systemd_export_LDADD = \
 	$(ZLIB_LIBS) \
 	-lbz2
 
-dist_rootlibexec_DATA = \
+dist_rootlibexec_DATA += \
 	src/import/import-pubring.gpg
 
 nodist_systemunit_DATA += \
@@ -5259,6 +5260,8 @@ systemd_resolved_SOURCES = \
 	src/resolve/resolved-dns-stream.c \
 	src/resolve/resolved-dns-trust-anchor.h \
 	src/resolve/resolved-dns-trust-anchor.c \
+	src/resolve/resolved-dns-stub.h \
+	src/resolve/resolved-dns-stub.c \
 	src/resolve/resolved-etc-hosts.h \
 	src/resolve/resolved-etc-hosts.c \
 	src/shared/gcrypt-util.c \
@@ -5411,6 +5414,9 @@ EXTRA_DIST += \
 	units/systemd-resolved.service.m4.in \
 	src/resolve/resolved.conf.in
 
+dist_rootlibexec_DATA += \
+	src/resolve/resolv.conf
+
 # ------------------------------------------------------------------------------
 if ENABLE_NETWORKD
 rootlibexec_PROGRAMS += \

man/systemd-resolve.xml

@@ -294,8 +294,15 @@
         <listitem><para>Flushes all DNS resource record caches the service maintains locally.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>--status</option></term>
+
+        <listitem><para>Shows the global and per-link DNS settings in currently in effect.</para></listitem>
+      </varlistentry>
+
       <xi:include href="standard-options.xml" xpointer="help" />
       <xi:include href="standard-options.xml" xpointer="version" />
+      <xi:include href="standard-options.xml" xpointer="no-pager" />
     </variablelist>
   </refsect1>
 

man/systemd-resolved.service.xml

@@ -58,27 +58,45 @@
 
     <para><command>systemd-resolved</command> is a system service that provides network name resolution to local
     applications. It implements a caching and validating DNS/DNSSEC stub resolver, as well as an LLMNR resolver and
-    responder. In addition it maintains the <filename>/run/systemd/resolve/resolv.conf</filename> file for
-    compatibility with traditional Linux programs. This file may be symlinked from
-    <filename>/etc/resolv.conf</filename>.</para>
+    responder. Local applications may submit network name resolution requests via three interfaces:</para>
 
-    <para>The glibc NSS module
-    <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry> is required to
-    permit glibc's NSS resolver functions to resolve host names via <command>systemd-resolved</command>.</para>
+    <itemizedlist>
+      <listitem><para>The native, fully-featured API <command>systemd-resolved</command> exposes on the bus. See the
+      <ulink url="http://www.freedesktop.org/wiki/Software/systemd/resolved">API Documentation</ulink> for
+      details. Usage of this API is generally recommended to clients as it is asynchronous and fully featured (for
+      example, properly returns DNSSEC validation status and interface scope for addresses as necessary for supporting
+      link-local networking).</para></listitem>
 
-    <para>The DNS servers contacted are determined from the global
-    settings in <filename>/etc/systemd/resolved.conf</filename>, the
-    per-link static settings in <filename>/etc/systemd/network/*.network</filename> files,
-    and the per-link dynamic settings received over DHCP. See
-    <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
-    and
-    <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
-    for details. To improve compatibility,
-    <filename>/etc/resolv.conf</filename> is read in order to discover
-    configured system DNS servers, but only if it is not a symlink
-    to <filename>/run/systemd/resolve/resolv.conf</filename> (see above).</para>
+      <listitem><para>The glibc
+      <citerefentry><refentrytitle>getaddrinfo</refentrytitle><manvolnum>3</manvolnum></citerefentry> API (as defined
+      by <ulink url="https://tools.ietf.org/html/rfc3493">RFC3493</ulink>) and its related resolver functions,
+      including <citerefentry><refentrytitle>gethostbyname</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
+      API is widely supported, including beyond the Linux platform. In its current form it does not expose DNSSEC
+      validation status information however, and is synchronous only. This API is backed by the glibc Name Service
+      Switch (<citerefentry><refentrytitle>nss</refentrytitle><manvolnum>5</manvolnum></citerefentry>). Usage of the
+      glibc NSS module <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+      is required in order to allow glibc's NSS resolver functions to resolve host names via
+      <command>systemd-resolved</command>.</para></listitem>
 
-    <para><command>systemd-resolved</command> synthesizes DNS RRs for the following cases:</para>
+      <listitem><para>Additionally, <command>systemd-resolved</command> provides a local DNS stub listener on IP
+      address 127.0.0.53 on the local loopback interface. Programs issuing DNS requests directly, bypassing any local
+      API may be directed to this stub, in order to connect them <command>systemd-resolved</command>. Note however that
+      it is strongly recommended that local programs use the glibc NSS or bus APIs instead (as described above), as
+      various network resolution concepts (such as link-local addressing, or LLMNR Unicode domains) cannot be mapped to
+      the unicast DNS protocol.</para></listitem>
+    </itemizedlist>
+
+    <para>The DNS servers contacted are determined from the global settings in
+    <filename>/etc/systemd/resolved.conf</filename>, the per-link static settings in
+    <filename>/etc/systemd/network/*.network</filename> files, the per-link dynamic settings received over DHCP and any
+    DNS server information made available by other system services. See
+    <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> and
+    <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details
+    about systemd's own configuration files for DNS servers. To improve compatibility,
+    <filename>/etc/resolv.conf</filename> is read in order to discover configured system DNS servers, but only if it is
+    not a symlink to <filename>/run/systemd/resolve/resolv.conf</filename> (see below).</para>
+
+    <para><command>systemd-resolved</command> synthesizes DNS resource records (RRs) for the following cases:</para>
 
     <itemizedlist>
       <listitem><para>The local, configured hostname is resolved to
@@ -137,14 +155,45 @@
     per-interface domains are exclusively routed to the matching
     interfaces.</para>
 
-    <para>Note that <filename>/run/systemd/resolve/resolv.conf</filename> should not be used directly by applications,
-    but only through a symlink from <filename>/etc/resolv.conf</filename>.</para>
-
     <para>See the <ulink url="http://www.freedesktop.org/wiki/Software/systemd/resolved"> resolved D-Bus API
     Documentation</ulink> for information about the APIs <filename>systemd-resolved</filename> provides.</para>
 
   </refsect1>
 
+  <refsect1>
+    <title><filename>/etc/resolv.conf</filename></title>
+
+    <para>Three modes of handling <filename>/etc/resolv.conf</filename> (see
+    <citerefentry><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>) are
+    supported:</para>
+
+    <itemizedlist>
+      <listitem><para>A static file <filename>/usr/lib/systemd/resolv.conf</filename> is provided that lists
+      the 127.0.0.53 DNS stub (see above) as only DNS server. This file may be symlinked from
+      <filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs to
+      <command>systemd-resolved</command>. This mode of operation is recommended.</para></listitem>
+
+      <listitem><para><command>systemd-resolved</command> maintains the
+      <filename>/run/systemd/resolve/resolv.conf</filename> file for compatibility with traditional Linux
+      programs. This file may be symlinked from <filename>/etc/resolv.conf</filename> and is always kept up-to-date,
+      containing information about all known DNS servers. Note the file format's limitations: it does not know a
+      concept of per-interface DNS servers and hence only contains system-wide DNS server definitions. Note that
+      <filename>/run/systemd/resolve/resolv.conf</filename> should not be used directly by applications, but only
+      through a symlink from <filename>/etc/resolv.conf</filename>. If this mode of operation is used local clients
+      that bypass any local DNS API will also bypass <command>systemd-resolved</command> and will talk directly to the
+      known DNS servers.</para> </listitem>
+
+      <listitem><para>Alternatively, <filename>/etc/resolv.conf</filename> may be managed by other packages, in which
+      case <command>systemd-resolved</command> will read it for DNS configuration data. In this mode of operation
+      <command>systemd-resolved</command> is consumer rather than provider of this configuration
+      file. </para></listitem>
+    </itemizedlist>
+
+    <para>Note that the selected mode of operation for this file is detected fully automatically, depending on whether
+    <filename>/etc/resolv.conf</filename> is a symlink to <filename>/run/systemd/resolve/resolv.conf</filename> or
+    lists 127.0.0.53 as DNS server.</para>
+  </refsect1>
+
   <refsect1>
     <title>Signals</title>
 

src/basic/bitmap.c

@@ -50,6 +50,23 @@ Bitmap *bitmap_new(void) {
         return new0(Bitmap, 1);
 }
 
+Bitmap *bitmap_copy(Bitmap *b) {
+        Bitmap *ret;
+
+        ret = bitmap_new();
+        if (!ret)
+                return NULL;
+
+        ret->bitmaps = newdup(uint64_t, b->bitmaps, b->n_bitmaps);
+        if (!ret->bitmaps) {
+                free(ret);
+                return NULL;
+        }
+
+        ret->n_bitmaps = ret->bitmaps_allocated = b->n_bitmaps;
+        return ret;
+}
+
 void bitmap_free(Bitmap *b) {
         if (!b)
                 return;

src/basic/bitmap.h

@@ -27,10 +27,9 @@
 typedef struct Bitmap Bitmap;
 
 Bitmap *bitmap_new(void);
-
-void bitmap_free(Bitmap *b);
-
+Bitmap *bitmap_copy(Bitmap *b);
 int bitmap_ensure_allocated(Bitmap **b);
+void bitmap_free(Bitmap *b);
 
 int bitmap_set(Bitmap *b, unsigned n);
 void bitmap_unset(Bitmap *b, unsigned n);

src/basic/hashmap.c

@@ -1764,6 +1764,9 @@ void *ordered_hashmap_next(OrderedHashmap *h, const void *key) {
 int set_consume(Set *s, void *value) {
         int r;
 
+        assert(s);
+        assert(value);
+
         r = set_put(s, value);
         if (r <= 0)
                 free(value);
@@ -1791,6 +1794,8 @@ int set_put_strdupv(Set *s, char **l) {
         int n = 0, r;
         char **i;
 
+        assert(s);
+
         STRV_FOREACH(i, l) {
                 r = set_put_strdup(s, *i);
                 if (r < 0)
@@ -1801,3 +1806,23 @@ int set_put_strdupv(Set *s, char **l) {
 
         return n;
 }
+
+int set_put_strsplit(Set *s, const char *v, const char *separators, ExtractFlags flags) {
+        const char *p = v;
+        int r;
+
+        assert(s);
+        assert(v);
+
+        for (;;) {
+                char *word;
+
+                r = extract_first_word(&p, &word, separators, flags);
+                if (r <= 0)
+                        return r;
+
+                r = set_consume(s, word);
+                if (r < 0)
+                        return r;
+        }
+}

src/basic/process-util.c

@@ -553,7 +553,7 @@ int wait_for_terminate(pid_t pid, siginfo_t *status) {
                         if (errno == EINTR)
                                 continue;
 
-                        return -errno;
+                        return negative_errno();
                 }
 
                 return 0;

src/basic/set.h

@@ -19,6 +19,7 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include "extract-word.h"
 #include "hashmap.h"
 #include "macro.h"
 
@@ -122,6 +123,7 @@ static inline char **set_get_strv(Set *s) {
 int set_consume(Set *s, void *value);
 int set_put_strdup(Set *s, const char *p);
 int set_put_strdupv(Set *s, char **l);
+int set_put_strsplit(Set *s, const char *v, const char *separators, ExtractFlags flags);
 
 #define SET_FOREACH(e, s, i) \
         for ((i) = ITERATOR_FIRST; set_iterate((s), &(i), (void**)&(e)); )

src/basic/string-table.h

@@ -48,6 +48,8 @@ ssize_t string_table_lookup(const char * const *table, size_t len, const char *k
 #define _DEFINE_STRING_TABLE_LOOKUP_FROM_STRING_WITH_BOOLEAN(name,type,yes,scope) \
         scope type name##_from_string(const char *s) {                  \
                 int b;                                                  \
+                if (!s)                                                 \
+                        return -1;                                      \
                 b = parse_boolean(s);                                   \
                 if (b == 0)                                             \
                         return (type) 0;                                \

src/journal/mmap-cache.c

@@ -481,7 +481,7 @@ static int mmap_try_harder(MMapCache *m, void *addr, int fd, int prot, int flags
                 if (ptr != MAP_FAILED)
                         break;
                 if (errno != ENOMEM)
-                        return -errno;
+                        return negative_errno();
 
                 r = make_room(m);
                 if (r < 0)
@@ -571,7 +571,7 @@ static int add_mmap(
         return 1;
 
 outofmem:
-        munmap(d, wsize);
+        (void) munmap(d, wsize);
         return -ENOMEM;
 }
 

src/login/loginctl.c

@@ -290,7 +290,7 @@ typedef struct SessionStatusInfo {
         char *seat;
         char *tty;
         char *display;
-        bool remote;
+        int remote;
         char *remote_host;
         char *remote_user;
         char *service;
@@ -304,7 +304,7 @@ typedef struct SessionStatusInfo {
 
 typedef struct UserStatusInfo {
         uid_t uid;
-        bool linger;
+        int linger;
         char *name;
         struct dual_timestamp timestamp;
         char *state;

src/network/networkd-brvlan.c

@@ -58,7 +58,7 @@ static int append_vlan_info_data(Link *const link, sd_netlink_message *req, uint
         struct bridge_vlan_info br_vlan;
         int i, j, k, r, done, cnt;
         uint16_t begin, end;
-        bool untagged;
+        bool untagged = false;
 
         assert(link);
         assert(req);

src/network/networkd-network-gperf.gperf

@@ -52,7 +52,7 @@ Network.DNS,                            config_parse_strv,
 Network.LLMNR,                          config_parse_resolve_support,                   0,                             offsetof(Network, llmnr)
 Network.MulticastDNS,                   config_parse_resolve_support,                   0,                             offsetof(Network, mdns)
 Network.DNSSEC,                         config_parse_dnssec_mode,                       0,                             offsetof(Network, dnssec_mode)
-Network.DNSSECNegativeTrustAnchors,     config_parse_dnssec_negative_trust_anchors,     0,                             offsetof(Network, dnssec_negative_trust_anchors)
+Network.DNSSECNegativeTrustAnchors,     config_parse_dnssec_negative_trust_anchors,     0,                             0
 Network.NTP,                            config_parse_strv,                              0,                             offsetof(Network, ntp)
 Network.IPForward,                      config_parse_address_family_boolean_with_kernel,0,                             offsetof(Network, ip_forward)
 Network.IPMasquerade,                   config_parse_bool,                              0,                             offsetof(Network, ip_masquerade)

src/resolve/dns-type.c

@@ -96,6 +96,15 @@ bool dns_type_is_valid_query(uint16_t type) {
                        DNS_TYPE_RRSIG);
 }
 
+bool dns_type_is_zone_transer(uint16_t type) {
+
+        /* Zone transfers, either normal or incremental */
+
+        return IN_SET(type,
+                      DNS_TYPE_AXFR,
+                      DNS_TYPE_IXFR);
+}
+
 bool dns_type_is_valid_rr(uint16_t type) {
 
         /* The types valid as RR in packets (but not necessarily

src/resolve/dns-type.h

@@ -136,6 +136,7 @@ bool dns_type_is_obsolete(uint16_t type);
 bool dns_type_may_wildcard(uint16_t type);
 bool dns_type_apex_only(uint16_t type);
 bool dns_type_needs_authentication(uint16_t type);
+bool dns_type_is_zone_transer(uint16_t type);
 int dns_type_to_af(uint16_t type);
 
 bool dns_class_is_pseudo(uint16_t class);

src/resolve/resolv.conf

@@ -0,0 +1,11 @@
+# This is a static resolv.conf file for connecting local clients to
+# systemd-resolved via its DNS stub listener on 127.0.0.53.
+#
+# Third party programs must not access this file directly, but only through the
+# symlink at /etc/resolv.conf. To manage resolv.conf(5) in a different way,
+# replace this symlink by a static file or a different symlink.
+#
+# See systemd-resolved.service(8) for details about the supported modes of
+# operation for /etc/resolv.conf.
+
+nameserver 127.0.0.53

src/resolve/resolve-tool.c

@@ -21,17 +21,21 @@
 #include <net/if.h>
 
 #include "sd-bus.h"
+#include "sd-netlink.h"
 
 #include "af-list.h"
 #include "alloc-util.h"
 #include "bus-error.h"
 #include "bus-util.h"
 #include "escape.h"
-#include "in-addr-util.h"
 #include "gcrypt-util.h"
+#include "in-addr-util.h"
+#include "netlink-util.h"
+#include "pager.h"
 #include "parse-util.h"
 #include "resolved-def.h"
 #include "resolved-dns-packet.h"
+#include "strv.h"
 #include "terminal-util.h"
 
 #define DNS_CALL_TIMEOUT_USEC (45*USEC_PER_SEC)
@@ -42,6 +46,7 @@ static uint16_t arg_type = 0;
 static uint16_t arg_class = 0;
 static bool arg_legend = true;
 static uint64_t arg_flags = 0;
+static bool arg_no_pager = false;
 
 typedef enum ServiceFamily {
         SERVICE_FAMILY_TCP,
@@ -67,6 +72,7 @@ static enum {
         MODE_STATISTICS,
         MODE_RESET_STATISTICS,
         MODE_FLUSH_CACHES,
+        MODE_STATUS,
 } arg_mode = MODE_RESOLVE_HOST;
 
 static ServiceFamily service_family_from_string(const char *s) {
@@ -1031,6 +1037,472 @@ static int flush_caches(sd_bus *bus) {
         return 0;
 }
 
+static int map_link_dns_servers(sd_bus *bus, const char *member, sd_bus_message *m, sd_bus_error *error, void *userdata) {
+        char ***l = userdata;
+        int r;
+
+        assert(bus);
+        assert(member);
+        assert(m);
+        assert(l);
+
+        r = sd_bus_message_enter_container(m, 'a', "(iay)");
+        if (r < 0)
+                return r;
+
+        for (;;) {
+                const void *a;
+                char *pretty;
+                int family;
+                size_t sz;
+
+                r = sd_bus_message_enter_container(m, 'r', "iay");
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                r = sd_bus_message_read(m, "i", &family);
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_message_read_array(m, 'y', &a, &sz);
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_message_exit_container(m);
+                if (r < 0)
+                        return r;
+
+                if (!IN_SET(family, AF_INET, AF_INET6)) {
+                        log_debug("Unexpected family, ignoring.");
+                        continue;
+                }
+
+                if (sz != FAMILY_ADDRESS_SIZE(family)) {
+                        log_debug("Address size mismatch, ignoring.");
+                        continue;
+                }
+
+                r = in_addr_to_string(family, a, &pretty);
+                if (r < 0)
+                        return r;
+
+                r = strv_consume(l, pretty);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_bus_message_exit_container(m);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+static int map_link_domains(sd_bus *bus, const char *member, sd_bus_message *m, sd_bus_error *error, void *userdata) {
+        char ***l = userdata;
+        int r;
+
+        assert(bus);
+        assert(member);
+        assert(m);
+        assert(l);
+
+        r = sd_bus_message_enter_container(m, 'a', "(sb)");
+        if (r < 0)
+                return r;
+
+        for (;;) {
+                const char *domain;
+                int route_only;
+                char *pretty;
+
+                r = sd_bus_message_read(m, "(sb)", &domain, &route_only);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                if (route_only)
+                        pretty = strappend("~", domain);
+                else
+                        pretty = strdup(domain);
+                if (!pretty)
+                        return -ENOMEM;
+
+                r = strv_consume(l, pretty);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_bus_message_exit_container(m);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+static int status_ifindex(sd_bus *bus, int ifindex, const char *name, bool *empty_line) {
+
+        struct link_info {
+                uint64_t scopes_mask;
+                char *llmnr;
+                char *mdns;
+                char *dnssec;
+                char **dns;
+                char **domains;
+                char **ntas;
+                int dnssec_supported;
+        } link_info = {};
+
+        static const struct bus_properties_map property_map[] = {
+                { "ScopesMask",                 "t",      NULL,                 offsetof(struct link_info, scopes_mask)      },
+                { "DNS",                        "a(iay)", map_link_dns_servers, offsetof(struct link_info, dns)              },
+                { "Domains",                    "a(sb)",  map_link_domains,     offsetof(struct link_info, domains)          },
+                { "LLMNR",                      "s",      NULL,                 offsetof(struct link_info, llmnr)            },
+                { "MulticastDNS",               "s",      NULL,                 offsetof(struct link_info, mdns)             },
+                { "DNSSEC",                     "s",      NULL,                 offsetof(struct link_info, dnssec)           },
+                { "DNSSECNegativeTrustAnchors", "as",     NULL,                 offsetof(struct link_info, ntas)             },
+                { "DNSSECSupported",            "b",      NULL,                 offsetof(struct link_info, dnssec_supported) },
+                {}
+        };
+
+        _cleanup_free_ char *ifi = NULL, *p = NULL;
+        char ifname[IF_NAMESIZE] = "";
+        char **i;
+        int r;
+
+        assert(bus);
+        assert(ifindex > 0);
+        assert(empty_line);
+
+        if (!name) {
+                if (!if_indextoname(ifindex, ifname))
+                        return log_error_errno(errno, "Failed to resolve interface name for %i: %m", ifindex);
+
+                name = ifname;
+        }
+
+        if (asprintf(&ifi, "%i", ifindex) < 0)
+                return log_oom();
+
+        r = sd_bus_path_encode("/org/freedesktop/resolve1/link", ifi, &p);
+        if (r < 0)
+                return log_oom();
+
+        r = bus_map_all_properties(bus,
+                                   "org.freedesktop.resolve1",
+                                   p,
+                                   property_map,
+                                   &link_info);
+        if (r < 0) {
+                log_error_errno(r, "Failed to get link data for %i: %m", ifindex);
+                goto finish;
+        }
+
+        pager_open(arg_no_pager, false);
+
+        if (*empty_line)
+                fputc('\n', stdout);
+
+        printf("%sLink %i (%s)%s\n",
+               ansi_highlight(), ifindex, name, ansi_normal());
+
+        if (link_info.scopes_mask == 0)
+                printf("      Current Scopes: none\n");
+        else
+                printf("      Current Scopes:%s%s%s%s%s\n",
+                       link_info.scopes_mask & SD_RESOLVED_DNS ? " DNS" : "",
+                       link_info.scopes_mask & SD_RESOLVED_LLMNR_IPV4 ? " LLMNR/IPv4" : "",
+                       link_info.scopes_mask & SD_RESOLVED_LLMNR_IPV6 ? " LLMNR/IPv6" : "",
+                       link_info.scopes_mask & SD_RESOLVED_MDNS_IPV4 ? " mDNS/IPv4" : "",
+                       link_info.scopes_mask & SD_RESOLVED_MDNS_IPV6 ? " mDNS/IPv6" : "");
+
+        printf("       LLMNR setting: %s\n"
+               "MulticastDNS setting: %s\n"
+               "      DNSSEC setting: %s\n"
+               "    DNSSEC supported: %s\n",
+               strna(link_info.llmnr),
+               strna(link_info.mdns),
+               strna(link_info.dnssec),
+               yes_no(link_info.dnssec_supported));
+
+        STRV_FOREACH(i, link_info.dns) {
+                printf("          %s %s\n",
+                       i == link_info.dns ? "DNS Server:" : "           ",
+                       *i);
+        }
+
+        STRV_FOREACH(i, link_info.domains) {
+                printf("          %s %s\n",
+                       i == link_info.domains ? "DNS Domain:" : "           ",
+                       *i);
+        }
+
+        STRV_FOREACH(i, link_info.ntas) {
+                printf("          %s %s\n",
+                       i == link_info.ntas ? "DNSSEC NTA:" : "           ",
+                       *i);
+        }
+
+        *empty_line = true;
+
+        r = 0;
+
+finish:
+        strv_free(link_info.dns);
+        strv_free(link_info.domains);
+        free(link_info.llmnr);
+        free(link_info.mdns);
+        free(link_info.dnssec);
+        strv_free(link_info.ntas);
+        return r;
+}
+
+static int map_global_dns_servers(sd_bus *bus, const char *member, sd_bus_message *m, sd_bus_error *error, void *userdata) {
+        char ***l = userdata;
+        int r;
+
+        assert(bus);
+        assert(member);
+        assert(m);
+        assert(l);
+
+        r = sd_bus_message_enter_container(m, 'a', "(iiay)");
+        if (r < 0)
+                return r;
+
+        for (;;) {
+                const void *a;
+                char *pretty;
+                int family, ifindex;
+                size_t sz;
+
+                r = sd_bus_message_enter_container(m, 'r', "iiay");
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                r = sd_bus_message_read(m, "ii", &ifindex, &family);
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_message_read_array(m, 'y', &a, &sz);
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_message_exit_container(m);
+                if (r < 0)
+                        return r;
+
+                if (ifindex != 0) /* only show the global ones here */
+                        continue;
+
+                if (!IN_SET(family, AF_INET, AF_INET6)) {
+                        log_debug("Unexpected family, ignoring.");
+                        continue;
+                }
+
+                if (sz != FAMILY_ADDRESS_SIZE(family)) {
+                        log_debug("Address size mismatch, ignoring.");
+                        continue;
+                }
+
+                r = in_addr_to_string(family, a, &pretty);
+                if (r < 0)
+                        return r;
+
+                r = strv_consume(l, pretty);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_bus_message_exit_container(m);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+static int map_global_domains(sd_bus *bus, const char *member, sd_bus_message *m, sd_bus_error *error, void *userdata) {
+        char ***l = userdata;
+        int r;
+
+        assert(bus);
+        assert(member);
+        assert(m);
+        assert(l);
+
+        r = sd_bus_message_enter_container(m, 'a', "(isb)");
+        if (r < 0)
+                return r;
+
+        for (;;) {
+                const char *domain;
+                int route_only, ifindex;
+                char *pretty;
+
+                r = sd_bus_message_read(m, "(isb)", &ifindex, &domain, &route_only);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                if (ifindex != 0) /* only show the global ones here */
+                        continue;
+
+                if (route_only)
+                        pretty = strappend("~", domain);
+                else
+                        pretty = strdup(domain);
+                if (!pretty)
+                        return -ENOMEM;
+
+                r = strv_consume(l, pretty);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_bus_message_exit_container(m);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+static int status_global(sd_bus *bus, bool *empty_line) {
+
+        struct global_info {
+                char **dns;
+                char **domains;
+                char **ntas;
+        } global_info = {};
+
+        static const struct bus_properties_map property_map[] = {
+                { "DNS",                        "a(iiay)", map_global_dns_servers, offsetof(struct global_info, dns)     },
+                { "Domains",                    "a(isb)",  map_global_domains,     offsetof(struct global_info, domains) },
+                { "DNSSECNegativeTrustAnchors", "as",      NULL,                   offsetof(struct global_info, ntas)    },
+                {}
+        };
+
+        char **i;
+        int r;
+
+        assert(bus);
+        assert(empty_line);
+
+        r = bus_map_all_properties(bus,
+                                   "org.freedesktop.resolve1",
+                                   "/org/freedesktop/resolve1",
+                                   property_map,
+                                   &global_info);
+        if (r < 0) {
+                log_error_errno(r, "Failed to get global data: %m");
+                goto finish;
+        }
+
+        if (strv_isempty(global_info.dns) && strv_isempty(global_info.domains) && strv_isempty(global_info.ntas)) {
+                r = 0;
+                goto finish;
+        }
+
+        pager_open(arg_no_pager, false);
+
+        printf("%sGlobal%s\n", ansi_highlight(), ansi_normal());
+        STRV_FOREACH(i, global_info.dns) {
+                printf("          %s %s\n",
+                       i == global_info.dns ? "DNS Server:" : "           ",
+                       *i);
+        }
+
+        STRV_FOREACH(i, global_info.domains) {
+                printf("          %s %s\n",
+                       i == global_info.domains ? "DNS Domain:" : "           ",
+                       *i);
+        }
+
+        strv_sort(global_info.ntas);
+        STRV_FOREACH(i, global_info.ntas) {
+                printf("          %s %s\n",
+                       i == global_info.ntas ? "DNSSEC NTA:" : "           ",
+                       *i);
+        }
+
+        *empty_line = true;
+
+        r = 0;
+
+finish:
+        strv_free(global_info.dns);
+        strv_free(global_info.domains);
+        strv_free(global_info.ntas);
+
+        return r;
+}
+
+static int status_all(sd_bus *bus) {
+        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *req = NULL, *reply = NULL;
+        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
+        sd_netlink_message *i;
+        bool empty_line = true;
+        int r;
+
+        assert(bus);
+
+        r = status_global(bus, &empty_line);
+        if (r < 0)
+                return r;
+
+        r = sd_netlink_open(&rtnl);
+        if (r < 0)
+                return log_error_errno(r, "Failed to connect to netlink: %m");
+
+        r = sd_rtnl_message_new_link(rtnl, &req, RTM_GETLINK, 0);
+        if (r < 0)
+                return rtnl_log_create_error(r);
+
+        r = sd_netlink_message_request_dump(req, true);
+        if (r < 0)
+                return rtnl_log_create_error(r);
+
+        r = sd_netlink_call(rtnl, req, 0, &reply);
+        if (r < 0)
+                return log_error_errno(r, "Failed to enumerate links: %m");
+
+        r = 0;
+        for (i = reply; i; i = sd_netlink_message_next(i)) {
+                const char *name;
+                int ifindex, q;
+                uint16_t type;
+
+                q = sd_netlink_message_get_type(i, &type);
+                if (q < 0)
+                        return rtnl_log_parse_error(q);
+
+                if (type != RTM_NEWLINK)
+                        continue;
+
+                q = sd_rtnl_message_link_get_ifindex(i, &ifindex);
+                if (q < 0)
+                        return rtnl_log_parse_error(q);
+
+                if (ifindex == LOOPBACK_IFINDEX)
+                        continue;
+
+                q = sd_netlink_message_read_string(i, IFLA_IFNAME, &name);
+                if (q < 0)
+                        return rtnl_log_parse_error(q);
+
+                q = status_ifindex(bus, ifindex, name, &empty_line);
+                if (q < 0 && r >= 0)
+                        r = q;
+        }
+
+        return r;
+}
+
 static void help_protocol_types(void) {
         if (arg_legend)
                 puts("Known protocol types:");
@@ -1038,8 +1510,8 @@ static void help_protocol_types(void) {
 }
 
 static void help_dns_types(void) {
-        int i;
         const char *t;
+        int i;
 
         if (arg_legend)
                 puts("Known DNS RR types:");
@@ -1051,8 +1523,8 @@ static void help_dns_types(void) {
 }
 
 static void help_dns_classes(void) {
-        int i;
         const char *t;
+        int i;
 
         if (arg_legend)
                 puts("Known DNS RR classes:");
@@ -1073,6 +1545,7 @@ static void help(void) {
                "Resolve domain names, IPv4 and IPv6 addresses, DNS resource records, and services.\n\n"
                "  -h --help                 Show this help\n"
                "     --version              Show package version\n"
+               "     --no-pager             Do not pipe output into a pager\n"
                "  -4                        Resolve IPv4 addresses\n"
                "  -6                        Resolve IPv6 addresses\n"
                "  -i --interface=INTERFACE  Look on interface\n"
@@ -1091,6 +1564,7 @@ static void help(void) {
                "     --legend=BOOL          Print headers and additional info (default: yes)\n"
                "     --statistics           Show resolver statistics\n"
                "     --reset-statistics     Reset resolver statistics\n"
+               "     --status               Show link and server status\n"
                "     --flush-caches         Flush all local DNS caches\n"
                , program_invocation_short_name);
 }
@@ -1109,7 +1583,9 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_SEARCH,
                 ARG_STATISTICS,
                 ARG_RESET_STATISTICS,
+                ARG_STATUS,
                 ARG_FLUSH_CACHES,
+                ARG_NO_PAGER,
         };
 
         static const struct option options[] = {
@@ -1130,7 +1606,9 @@ static int parse_argv(int argc, char *argv[]) {
                 { "search",           required_argument, NULL, ARG_SEARCH           },
                 { "statistics",       no_argument,       NULL, ARG_STATISTICS,      },
                 { "reset-statistics", no_argument,       NULL, ARG_RESET_STATISTICS },
+                { "status",           no_argument,       NULL, ARG_STATUS           },
                 { "flush-caches",     no_argument,       NULL, ARG_FLUSH_CACHES     },
+                { "no-pager",         no_argument,       NULL, ARG_NO_PAGER         },
                 {}
         };
 
@@ -1308,6 +1786,14 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_mode = MODE_FLUSH_CACHES;
                         break;
 
+                case ARG_STATUS:
+                        arg_mode = MODE_STATUS;
+                        break;
+
+                case ARG_NO_PAGER:
+                        arg_no_pager = true;
+                        break;
+
                 case '?':
                         return -EINVAL;
 
@@ -1484,8 +1970,38 @@ int main(int argc, char **argv) {
 
                 r = flush_caches(bus);
                 break;
+
+        case MODE_STATUS:
+
+                if (argc > optind) {
+                        char **ifname;
+                        bool empty_line = false;
+
+                        r = 0;
+                        STRV_FOREACH(ifname, argv + optind) {
+                                int ifindex, q;
+
+                                q = parse_ifindex(argv[optind], &ifindex);
+                                if (q < 0) {
+                                        ifindex = if_nametoindex(argv[optind]);
+                                        if (ifindex <= 0) {
+                                                log_error_errno(errno, "Failed to resolve interface name: %s", argv[optind]);
+                                                continue;
+                                        }
+                                }
+
+                                q = status_ifindex(bus, ifindex, NULL, &empty_line);
+                                if (q < 0 && r >= 0)
+                                        r = q;
+                        }
+                } else
+                        r = status_all(bus);
+
+                break;
         }
 
 finish:
+        pager_close();
+
         return r == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }

src/resolve/resolved-bus.c

@@ -647,6 +647,8 @@ static int bus_method_resolve_record(sd_bus_message *message, void *userdata, sd
 
         if (!dns_type_is_valid_query(type))
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Specified resource record type %" PRIu16 " may not be used in a query.", type);
+        if (dns_type_is_zone_transer(type))
+                return sd_bus_error_setf(error, SD_BUS_ERROR_NOT_SUPPORTED, "Zone transfers not permitted via this programming interface.");
         if (dns_type_is_obsolete(type))
                 return sd_bus_error_setf(error, SD_BUS_ERROR_NOT_SUPPORTED, "Specified DNS resource record type %" PRIu16 " is obsolete.", type);
 
@@ -670,6 +672,10 @@ static int bus_method_resolve_record(sd_bus_message *message, void *userdata, sd
         if (r < 0)
                 return r;
 
+        /* Let's request that the TTL is fixed up for locally cached entries, after all we return it in the wire format
+         * blob */
+        q->clamp_ttl = true;
+
         q->request = sd_bus_message_ref(message);
         q->complete = bus_method_resolve_record_complete;
 
@@ -1414,6 +1420,36 @@ static int bus_property_get_dnssec_supported(
         return sd_bus_message_append(reply, "b", manager_dnssec_supported(m));
 }
 
+static int bus_property_get_ntas(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        Manager *m = userdata;
+        const char *domain;
+        Iterator i;
+        int r;
+
+        assert(reply);
+        assert(m);
+
+        r = sd_bus_message_open_container(reply, 'a', "s");
+        if (r < 0)
+                return r;
+
+        SET_FOREACH(domain, m->trust_anchor.negative_by_name, i) {
+                r = sd_bus_message_append(reply, "s", domain);
+                if (r < 0)
+                        return r;
+        }
+
+        return sd_bus_message_close_container(reply);
+}
+
 static int bus_method_reset_statistics(sd_bus_message *message, void *userdata, sd_bus_error *error) {
         Manager *m = userdata;
         DnsScope *s;
@@ -1540,6 +1576,7 @@ static const sd_bus_vtable resolve_vtable[] = {
         SD_BUS_PROPERTY("CacheStatistics", "(ttt)", bus_property_get_cache_statistics, 0, 0),
         SD_BUS_PROPERTY("DNSSECStatistics", "(tttt)", bus_property_get_dnssec_statistics, 0, 0),
         SD_BUS_PROPERTY("DNSSECSupported", "b", bus_property_get_dnssec_supported, 0, 0),
+        SD_BUS_PROPERTY("DNSSECNegativeTrustAnchors", "as", bus_property_get_ntas, 0, 0),
 
         SD_BUS_METHOD("ResolveHostname", "isit", "a(iiay)st", bus_method_resolve_hostname, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("ResolveAddress", "iiayt", "a(is)t", bus_method_resolve_address, SD_BUS_VTABLE_UNPRIVILEGED),

src/resolve/resolved-conf.c

@@ -37,6 +37,10 @@ int manager_add_dns_server_by_string(Manager *m, DnsServerType type, const char
         if (r < 0)
                 return r;
 
+        /* Silently filter out 0.0.0.0 and 127.0.0.53 (our own stub DNS listener) */
+        if (!dns_server_address_valid(family, &address))
+                return 0;
+
         /* Filter out duplicates */
         s = dns_server_find(manager_get_first_dns_server(m, type), family, &address, ifindex);
         if (s) {

src/resolve/resolved-dns-answer.h

@@ -87,6 +87,10 @@ static inline unsigned dns_answer_size(DnsAnswer *a) {
         return a ? a->n_rrs : 0;
 }
 
+static inline bool dns_answer_isempty(DnsAnswer *a) {
+        return dns_answer_size(a) <= 0;
+}
+
 void dns_answer_dump(DnsAnswer *answer, FILE *f);
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswer*, dns_answer_unref);

src/resolve/resolved-dns-cache.c

@@ -790,7 +790,7 @@ static DnsCacheItem *dns_cache_get_by_key_follow_cname_dname_nsec(DnsCache *c, D
         return NULL;
 }
 
-int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **ret, bool *authenticated) {
+int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcode, DnsAnswer **ret, bool *authenticated) {
         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
         char key_str[DNS_RESOURCE_KEY_STRING_MAX];
         unsigned n = 0;
@@ -798,6 +798,7 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **r
         bool nxdomain = false;
         DnsCacheItem *j, *first, *nsec = NULL;
         bool have_authenticated = false, have_non_authenticated = false;
+        usec_t current;
 
         assert(c);
         assert(key);
@@ -892,11 +893,24 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **r
         if (!answer)
                 return -ENOMEM;
 
+        if (clamp_ttl)
+                current = now(clock_boottime_or_monotonic());
+
         LIST_FOREACH(by_key, j, first) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
                 if (!j->rr)
                         continue;
 
-                r = dns_answer_add(answer, j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
+                if (clamp_ttl) {
+                        rr = dns_resource_record_ref(j->rr);
+
+                        r = dns_resource_record_clamp_ttl(&rr, LESS_BY(j->until, current) / USEC_PER_SEC);
+                        if (r < 0)
+                                return r;
+                }
+
+                r = dns_answer_add(answer, rr ?: j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
                 if (r < 0)
                         return r;
         }

src/resolve/resolved-dns-cache.h

@@ -40,7 +40,7 @@ void dns_cache_flush(DnsCache *c);
 void dns_cache_prune(DnsCache *c);
 
 int dns_cache_put(DnsCache *c, DnsResourceKey *key, int rcode, DnsAnswer *answer, bool authenticated, uint32_t nsec_ttl, usec_t timestamp, int owner_family, const union in_addr_union *owner_address);
-int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **answer, bool *authenticated);
+int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcode, DnsAnswer **answer, bool *authenticated);
 
 int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_family, const union in_addr_union *owner_address);
 

src/resolve/resolved-dns-packet.c

@@ -264,6 +264,7 @@ int dns_packet_validate_query(DnsPacket *p) {
         switch (p->protocol) {
 
         case DNS_PROTOCOL_LLMNR:
+        case DNS_PROTOCOL_DNS:
                 /* RFC 4795, Section 2.1.1. says to discard all queries with QDCOUNT != 1 */
                 if (DNS_PACKET_QDCOUNT(p) != 1)
                         return -EBADMSG;
@@ -676,13 +677,15 @@ fail:
 }
 
 /* Append the OPT pseudo-RR described in RFC6891 */
-int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, size_t *start) {
+int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, int rcode, size_t *start) {
         size_t saved_size;
         int r;
 
         assert(p);
         /* we must never advertise supported packet size smaller than the legacy max */
         assert(max_udp_size >= DNS_PACKET_UNICAST_SIZE_MAX);
+        assert(rcode >= 0);
+        assert(rcode <= _DNS_RCODE_MAX);
 
         if (p->opt_start != (size_t) -1)
                 return -EBUSY;
@@ -701,13 +704,13 @@ int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, si
         if (r < 0)
                 goto fail;
 
-        /* maximum udp packet that can be received */
+        /* class: maximum udp packet that can be received */
         r = dns_packet_append_uint16(p, max_udp_size, NULL);
         if (r < 0)
                 goto fail;
 
         /* extended RCODE and VERSION */
-        r = dns_packet_append_uint16(p, 0, NULL);
+        r = dns_packet_append_uint16(p, ((uint16_t) rcode & 0x0FF0) << 4, NULL);
         if (r < 0)
                 goto fail;
 
@@ -717,9 +720,8 @@ int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, si
                 goto fail;
 
         /* RDLENGTH */
-
-        if (edns0_do) {
-                /* If DO is on, also append RFC6975 Algorithm data */
+        if (edns0_do & !DNS_PACKET_QR(p)) {
+                /* If DO is on and this is not a reply, also append RFC6975 Algorithm data */
 
                 static const uint8_t rfc6975[] = {
 
@@ -750,7 +752,6 @@ int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, si
                 r = dns_packet_append_blob(p, rfc6975, sizeof(rfc6975), NULL);
         } else
                 r = dns_packet_append_uint16(p, 0, NULL);
-
         if (r < 0)
                 goto fail;
 
@@ -791,6 +792,7 @@ int dns_packet_truncate_opt(DnsPacket *p) {
 }
 
 int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *start, size_t *rdata_start) {
+
         size_t saved_size, rdlength_offset, end, rdlength, rds;
         int r;
 
@@ -1134,6 +1136,36 @@ fail:
         return r;
 }
 
+int dns_packet_append_question(DnsPacket *p, DnsQuestion *q) {
+        DnsResourceKey *key;
+        int r;
+
+        assert(p);
+
+        DNS_QUESTION_FOREACH(key, q) {
+                r = dns_packet_append_key(p, key, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int dns_packet_append_answer(DnsPacket *p, DnsAnswer *a) {
+        DnsResourceRecord *rr;
+        int r;
+
+        assert(p);
+
+        DNS_ANSWER_FOREACH(rr, a) {
+                r = dns_packet_append_rr(p, rr, NULL, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
 int dns_packet_read(DnsPacket *p, size_t sz, const void **ret, size_t *start) {
         assert(p);
 
@@ -2029,8 +2061,10 @@ static bool opt_is_good(DnsResourceRecord *rr, bool *rfc6975) {
         assert(rr->key->type == DNS_TYPE_OPT);
 
         /* Check that the version is 0 */
-        if (((rr->ttl >> 16) & UINT32_C(0xFF)) != 0)
-                return false;
+        if (((rr->ttl >> 16) & UINT32_C(0xFF)) != 0) {
+                *rfc6975 = false;
+                return true; /* if it's not version 0, it's OK, but we will ignore the OPT field contents */
+        }
 
         p = rr->opt.data;
         l = rr->opt.data_size;
@@ -2153,16 +2187,27 @@ int dns_packet_extract(DnsPacket *p) {
                                         continue;
                                 }
 
-                                if (has_rfc6975) {
-                                        /* If the OPT RR contains RFC6975 algorithm data, then this is indication that
-                                         * the server just copied the OPT it got from us (which contained that data)
-                                         * back into the reply. If so, then it doesn't properly support EDNS, as
-                                         * RFC6975 makes it very clear that the algorithm data should only be contained
-                                         * in questions, never in replies. Crappy Belkin routers copy the OPT data for
-                                         * example, hence let's detect this so that we downgrade early. */
-                                        log_debug("OPT RR contained RFC6975 data, ignoring.");
-                                        bad_opt = true;
-                                        continue;
+                                if (DNS_PACKET_QR(p)) {
+                                        /* Additional checks for responses */
+
+                                        if (!DNS_RESOURCE_RECORD_OPT_VERSION_SUPPORTED(rr)) {
+                                                /* If this is a reply and we don't know the EDNS version then something
+                                                 * is weird... */
+                                                log_debug("EDNS version newer that our request, bad server.");
+                                                return -EBADMSG;
+                                        }
+
+                                        if (has_rfc6975) {
+                                                /* If the OPT RR contains RFC6975 algorithm data, then this is indication that
+                                                 * the server just copied the OPT it got from us (which contained that data)
+                                                 * back into the reply. If so, then it doesn't properly support EDNS, as
+                                                 * RFC6975 makes it very clear that the algorithm data should only be contained
+                                                 * in questions, never in replies. Crappy Belkin routers copy the OPT data for
+                                                 * example, hence let's detect this so that we downgrade early. */
+                                                log_debug("OPT RR contained RFC6975 data, ignoring.");
+                                                bad_opt = true;
+                                                continue;
+                                        }
                                 }
 
                                 p->opt = dns_resource_record_ref(rr);

src/resolve/resolved-dns-packet.h

@@ -118,6 +118,8 @@ static inline uint8_t* DNS_PACKET_DATA(DnsPacket *p) {
 #define DNS_PACKET_AD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 5) & 1)
 #define DNS_PACKET_CD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 4) & 1)
 
+#define DNS_PACKET_FLAG_TC (UINT16_C(1) << 9)
+
 static inline uint16_t DNS_PACKET_RCODE(DnsPacket *p) {
         uint16_t rcode;
 
@@ -126,7 +128,34 @@ static inline uint16_t DNS_PACKET_RCODE(DnsPacket *p) {
         else
                 rcode = 0;
 
-        return rcode | (be16toh(DNS_PACKET_HEADER(p)->flags) & 15);
+        return rcode | (be16toh(DNS_PACKET_HEADER(p)->flags) & 0xF);
+}
+
+static inline uint16_t DNS_PACKET_PAYLOAD_SIZE_MAX(DnsPacket *p) {
+
+        /* Returns the advertised maximum datagram size for replies, or the DNS default if there's nothing defined. */
+
+        if (p->opt)
+                return MAX(DNS_PACKET_UNICAST_SIZE_MAX, p->opt->key->class);
+
+        return DNS_PACKET_UNICAST_SIZE_MAX;
+}
+
+static inline bool DNS_PACKET_DO(DnsPacket *p) {
+        if (!p->opt)
+                return false;
+
+        return !!(p->opt->ttl & (1U << 15));
+}
+
+static inline bool DNS_PACKET_VERSION_SUPPORTED(DnsPacket *p) {
+        /* Returns true if this packet is in a version we support. Which means either non-EDNS or EDNS(0), but not EDNS
+         * of any newer versions */
+
+        if (!p->opt)
+                return true;
+
+        return DNS_RESOURCE_RECORD_OPT_VERSION_SUPPORTED(p->opt);
 }
 
 /* LLMNR defines some bits differently */
@@ -182,7 +211,9 @@ int dns_packet_append_label(DnsPacket *p, const char *s, size_t l, bool canonica
 int dns_packet_append_name(DnsPacket *p, const char *name, bool allow_compression, bool canonical_candidate, size_t *start);
 int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *key, size_t *start);
 int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *start, size_t *rdata_start);
-int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, size_t *start);
+int dns_packet_append_opt(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, int rcode, size_t *start);
+int dns_packet_append_question(DnsPacket *p, DnsQuestion *q);
+int dns_packet_append_answer(DnsPacket *p, DnsAnswer *a);
 
 void dns_packet_truncate(DnsPacket *p, size_t sz);
 int dns_packet_truncate_opt(DnsPacket *p);
@@ -232,7 +263,8 @@ enum {
         DNS_RCODE_BADNAME = 20,
         DNS_RCODE_BADALG = 21,
         DNS_RCODE_BADTRUNC = 22,
-        _DNS_RCODE_MAX_DEFINED
+        _DNS_RCODE_MAX_DEFINED,
+        _DNS_RCODE_MAX = 4095 /* 4 bit rcode in the header plus 8 bit rcode in OPT, makes 12 bit */
 };
 
 const char* dns_rcode_to_string(int i) _const_;

src/resolve/resolved-dns-query.c

@@ -154,6 +154,7 @@ static int dns_query_candidate_add_transaction(DnsQueryCandidate *c, DnsResource
                 goto gc;
         }
 
+        t->clamp_ttl = c->query->clamp_ttl;
         return 1;
 
 gc:
@@ -403,6 +404,16 @@ DnsQuery *dns_query_free(DnsQuery *q) {
         sd_bus_message_unref(q->request);
         sd_bus_track_unref(q->bus_track);
 
+        dns_packet_unref(q->request_dns_packet);
+
+        if (q->request_dns_stream) {
+                /* Detach the stream from our query, in case something else keeps a reference to it. */
+                q->request_dns_stream->complete = NULL;
+                q->request_dns_stream->on_packet = NULL;
+                q->request_dns_stream->query = NULL;
+                dns_stream_unref(q->request_dns_stream);
+        }
+
         free(q->request_address_string);
 
         if (q->manager) {
@@ -420,7 +431,8 @@ int dns_query_new(
                 DnsQuery **ret,
                 DnsQuestion *question_utf8,
                 DnsQuestion *question_idna,
-                int ifindex, uint64_t flags) {
+                int ifindex,
+                uint64_t flags) {
 
         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
         DnsResourceKey *key;

src/resolve/resolved-dns-query.h

@@ -71,6 +71,10 @@ struct DnsQuery {
          * family */
         bool suppress_unroutable_family;
 
+
+        /* If true, the RR TTLs of the answer will be clamped by their current left validity in the cache */
+        bool clamp_ttl;
+
         DnsTransactionState state;
         unsigned n_cname_redirects;
 
@@ -95,6 +99,10 @@ struct DnsQuery {
         unsigned block_all_complete;
         char *request_address_string;
 
+        /* DNS stub information */
+        DnsPacket *request_dns_packet;
+        DnsStream *request_dns_stream;
+
         /* Completion callback */
         void (*complete)(DnsQuery* q);
         unsigned block_ready;

src/resolve/resolved-dns-question.h

@@ -56,6 +56,10 @@ static inline unsigned dns_question_size(DnsQuestion *q) {
         return q ? q->n_keys : 0;
 }
 
+static inline bool dns_question_isempty(DnsQuestion *q) {
+        return dns_question_size(q) <= 0;
+}
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsQuestion*, dns_question_unref);
 
 #define _DNS_QUESTION_FOREACH(u, key, q)                                \

src/resolve/resolved-dns-rr.c

@@ -1532,6 +1532,232 @@ const struct hash_ops dns_resource_record_hash_ops = {
         .compare = dns_resource_record_compare_func,
 };
 
+DnsResourceRecord *dns_resource_record_copy(DnsResourceRecord *rr) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *copy = NULL;
+        DnsResourceRecord *t;
+
+        assert(rr);
+
+        copy = dns_resource_record_new(rr->key);
+        if (!copy)
+                return NULL;
+
+        copy->ttl = rr->ttl;
+        copy->expiry = rr->expiry;
+        copy->n_skip_labels_signer = rr->n_skip_labels_signer;
+        copy->n_skip_labels_source = rr->n_skip_labels_source;
+        copy->unparseable = rr->unparseable;
+
+        switch (rr->unparseable ? _DNS_TYPE_INVALID : rr->key->type) {
+
+        case DNS_TYPE_SRV:
+                copy->srv.priority = rr->srv.priority;
+                copy->srv.weight = rr->srv.weight;
+                copy->srv.port = rr->srv.port;
+                copy->srv.name = strdup(rr->srv.name);
+                if (!copy->srv.name)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_PTR:
+        case DNS_TYPE_NS:
+        case DNS_TYPE_CNAME:
+        case DNS_TYPE_DNAME:
+                copy->ptr.name = strdup(rr->ptr.name);
+                if (!copy->ptr.name)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_HINFO:
+                copy->hinfo.cpu = strdup(rr->hinfo.cpu);
+                if (!copy->hinfo.cpu)
+                        return NULL;
+
+                copy->hinfo.os = strdup(rr->hinfo.os);
+                if(!copy->hinfo.os)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_TXT:
+        case DNS_TYPE_SPF:
+                copy->txt.items = dns_txt_item_copy(rr->txt.items);
+                if (!copy->txt.items)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_A:
+                copy->a = rr->a;
+                break;
+
+        case DNS_TYPE_AAAA:
+                copy->aaaa = rr->aaaa;
+                break;
+
+        case DNS_TYPE_SOA:
+                copy->soa.mname = strdup(rr->soa.mname);
+                if (!copy->soa.mname)
+                        return NULL;
+                copy->soa.rname = strdup(rr->soa.rname);
+                if (!copy->soa.rname)
+                        return NULL;
+                copy->soa.serial = rr->soa.serial;
+                copy->soa.refresh = rr->soa.refresh;
+                copy->soa.retry = rr->soa.retry;
+                copy->soa.expire = rr->soa.expire;
+                copy->soa.minimum = rr->soa.minimum;
+                break;
+
+        case DNS_TYPE_MX:
+                copy->mx.priority = rr->mx.priority;
+                copy->mx.exchange = strdup(rr->mx.exchange);
+                if (!copy->mx.exchange)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_LOC:
+                copy->loc = rr->loc;
+                break;
+
+        case DNS_TYPE_SSHFP:
+                copy->sshfp.algorithm = rr->sshfp.algorithm;
+                copy->sshfp.fptype = rr->sshfp.fptype;
+                copy->sshfp.fingerprint = memdup(rr->sshfp.fingerprint, rr->sshfp.fingerprint_size);
+                if (!copy->sshfp.fingerprint)
+                        return NULL;
+                copy->sshfp.fingerprint_size = rr->sshfp.fingerprint_size;
+                break;
+
+        case DNS_TYPE_DNSKEY:
+                copy->dnskey.flags = rr->dnskey.flags;
+                copy->dnskey.protocol = rr->dnskey.protocol;
+                copy->dnskey.algorithm = rr->dnskey.algorithm;
+                copy->dnskey.key = memdup(rr->dnskey.key, rr->dnskey.key_size);
+                if (!copy->dnskey.key)
+                        return NULL;
+                copy->dnskey.key_size = rr->dnskey.key_size;
+                break;
+
+        case DNS_TYPE_RRSIG:
+                copy->rrsig.type_covered = rr->rrsig.type_covered;
+                copy->rrsig.algorithm = rr->rrsig.algorithm;
+                copy->rrsig.labels = rr->rrsig.labels;
+                copy->rrsig.original_ttl = rr->rrsig.original_ttl;
+                copy->rrsig.expiration = rr->rrsig.expiration;
+                copy->rrsig.inception = rr->rrsig.inception;
+                copy->rrsig.key_tag = rr->rrsig.key_tag;
+                copy->rrsig.signer = strdup(rr->rrsig.signer);
+                if (!copy->rrsig.signer)
+                        return NULL;
+                copy->rrsig.signature = memdup(rr->rrsig.signature, rr->rrsig.signature_size);
+                if (!copy->rrsig.signature)
+                        return NULL;
+                copy->rrsig.signature_size = rr->rrsig.signature_size;
+                break;
+
+        case DNS_TYPE_NSEC:
+                copy->nsec.next_domain_name = strdup(rr->nsec.next_domain_name);
+                if (!copy->nsec.next_domain_name)
+                        return NULL;
+                copy->nsec.types = bitmap_copy(rr->nsec.types);
+                if (!copy->nsec.types)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_DS:
+                copy->ds.key_tag = rr->ds.key_tag;
+                copy->ds.algorithm = rr->ds.algorithm;
+                copy->ds.digest_type = rr->ds.digest_type;
+                copy->ds.digest = memdup(rr->ds.digest, rr->ds.digest_size);
+                if (!copy->ds.digest)
+                        return NULL;
+                copy->ds.digest_size = rr->ds.digest_size;
+                break;
+
+        case DNS_TYPE_NSEC3:
+                copy->nsec3.algorithm = rr->nsec3.algorithm;
+                copy->nsec3.flags = rr->nsec3.flags;
+                copy->nsec3.iterations = rr->nsec3.iterations;
+                copy->nsec3.salt = memdup(rr->nsec3.salt, rr->nsec3.salt_size);
+                if (!copy->nsec3.salt)
+                        return NULL;
+                copy->nsec3.salt_size = rr->nsec3.salt_size;
+                copy->nsec3.next_hashed_name = memdup(rr->nsec3.next_hashed_name, rr->nsec3.next_hashed_name_size);
+                if (!copy->nsec3.next_hashed_name_size)
+                        return NULL;
+                copy->nsec3.next_hashed_name_size = rr->nsec3.next_hashed_name_size;
+                copy->nsec3.types = bitmap_copy(rr->nsec3.types);
+                if (!copy->nsec3.types)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_TLSA:
+                copy->tlsa.cert_usage = rr->tlsa.cert_usage;
+                copy->tlsa.selector = rr->tlsa.selector;
+                copy->tlsa.matching_type = rr->tlsa.matching_type;
+                copy->tlsa.data = memdup(rr->tlsa.data, rr->tlsa.data_size);
+                if (!copy->tlsa.data)
+                        return NULL;
+                copy->tlsa.data_size = rr->tlsa.data_size;
+                break;
+
+        case DNS_TYPE_CAA:
+                copy->caa.flags = rr->caa.flags;
+                copy->caa.tag = strdup(rr->caa.tag);
+                if (!copy->caa.tag)
+                        return NULL;
+                copy->caa.value = memdup(rr->caa.value, rr->caa.value_size);
+                if (!copy->caa.value)
+                        return NULL;
+                copy->caa.value_size = rr->caa.value_size;
+                break;
+
+        case DNS_TYPE_OPT:
+        default:
+                copy->generic.data = memdup(rr->generic.data, rr->generic.data_size);
+                if (!copy->generic.data)
+                        return NULL;
+                copy->generic.data_size = rr->generic.data_size;
+                break;
+        }
+
+        t = copy;
+        copy = NULL;
+
+        return t;
+}
+
+int dns_resource_record_clamp_ttl(DnsResourceRecord **rr, uint32_t max_ttl) {
+        DnsResourceRecord *old_rr, *new_rr;
+        uint32_t new_ttl;
+
+        assert(rr);
+        old_rr = *rr;
+
+        if (old_rr->key->type == DNS_TYPE_OPT)
+                return -EINVAL;
+
+        new_ttl = MIN(old_rr->ttl, max_ttl);
+        if (new_ttl == old_rr->ttl)
+                return 0;
+
+        if (old_rr->n_ref == 1) {
+                /* Patch in place */
+                old_rr->ttl = new_ttl;
+                return 1;
+        }
+
+        new_rr = dns_resource_record_copy(old_rr);
+        if (!new_rr)
+                return -ENOMEM;
+
+        new_rr->ttl = new_ttl;
+
+        dns_resource_record_unref(*rr);
+        *rr = new_rr;
+
+        return 1;
+}
+
 DnsTxtItem *dns_txt_item_free_all(DnsTxtItem *i) {
         DnsTxtItem *n;
 
@@ -1564,6 +1790,25 @@ bool dns_txt_item_equal(DnsTxtItem *a, DnsTxtItem *b) {
         return dns_txt_item_equal(a->items_next, b->items_next);
 }
 
+DnsTxtItem *dns_txt_item_copy(DnsTxtItem *first) {
+        DnsTxtItem *i, *copy = NULL, *end = NULL;
+
+        LIST_FOREACH(items, i, first) {
+                DnsTxtItem *j;
+
+                j = memdup(i, offsetof(DnsTxtItem, data) + i->length + 1);
+                if (!j) {
+                        dns_txt_item_free_all(copy);
+                        return NULL;
+                }
+
+                LIST_INSERT_AFTER(items, copy, end, j);
+                end = j;
+        }
+
+        return copy;
+}
+
 static const char* const dnssec_algorithm_table[_DNSSEC_ALGORITHM_MAX_DEFINED] = {
         /* Mnemonics as listed on https://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml */
         [DNSSEC_ALGORITHM_RSAMD5]             = "RSAMD5",

src/resolve/resolved-dns-rr.h

@@ -282,6 +282,13 @@ static inline size_t DNS_RESOURCE_RECORD_RDATA_SIZE(DnsResourceRecord *rr) {
         return rr->wire_format_size - rr->wire_format_rdata_offset;
 }
 
+static inline uint8_t DNS_RESOURCE_RECORD_OPT_VERSION_SUPPORTED(DnsResourceRecord *rr) {
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_OPT);
+
+        return ((rr->ttl >> 16) & 0xFF) == 0;
+}
+
 DnsResourceKey* dns_resource_key_new(uint16_t class, uint16_t type, const char *name);
 DnsResourceKey* dns_resource_key_new_redirect(const DnsResourceKey *key, const DnsResourceRecord *cname);
 int dns_resource_key_new_append_suffix(DnsResourceKey **ret, DnsResourceKey *key, char *name);
@@ -318,6 +325,7 @@ int dns_resource_record_new_reverse(DnsResourceRecord **ret, int family, const u
 int dns_resource_record_new_address(DnsResourceRecord **ret, int family, const union in_addr_union *address, const char *name);
 int dns_resource_record_equal(const DnsResourceRecord *a, const DnsResourceRecord *b);
 const char* dns_resource_record_to_string(DnsResourceRecord *rr);
+DnsResourceRecord *dns_resource_record_copy(DnsResourceRecord *rr);
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsResourceRecord*, dns_resource_record_unref);
 
 int dns_resource_record_to_wire_format(DnsResourceRecord *rr, bool canonical);
@@ -327,8 +335,11 @@ int dns_resource_record_source(DnsResourceRecord *rr, const char **ret);
 int dns_resource_record_is_signer(DnsResourceRecord *rr, const char *zone);
 int dns_resource_record_is_synthetic(DnsResourceRecord *rr);
 
+int dns_resource_record_clamp_ttl(DnsResourceRecord **rr, uint32_t max_ttl);
+
 DnsTxtItem *dns_txt_item_free_all(DnsTxtItem *i);
 bool dns_txt_item_equal(DnsTxtItem *a, DnsTxtItem *b);
+DnsTxtItem *dns_txt_item_copy(DnsTxtItem *i);
 
 void dns_resource_record_hash_func(const void *i, struct siphash *state);
 

src/resolve/resolved-dns-scope.c

@@ -232,7 +232,7 @@ static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
                 if (fd < 0)
                         return fd;
 
-                r = manager_send(s->manager, fd, ifindex, family, &addr, LLMNR_PORT, p);
+                r = manager_send(s->manager, fd, ifindex, family, &addr, LLMNR_PORT, NULL, p);
                 if (r < 0)
                         return r;
 
@@ -257,7 +257,7 @@ static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
                 if (fd < 0)
                         return fd;
 
-                r = manager_send(s->manager, fd, ifindex, family, &addr, MDNS_PORT, p);
+                r = manager_send(s->manager, fd, ifindex, family, &addr, MDNS_PORT, NULL, p);
                 if (r < 0)
                         return r;
 
@@ -578,6 +578,7 @@ static int dns_scope_multicast_membership(DnsScope *s, bool b, struct in_addr in
 }
 
 int dns_scope_llmnr_membership(DnsScope *s, bool b) {
+        assert(s);
 
         if (s->protocol != DNS_PROTOCOL_LLMNR)
                 return 0;
@@ -586,6 +587,7 @@ int dns_scope_llmnr_membership(DnsScope *s, bool b) {
 }
 
 int dns_scope_mdns_membership(DnsScope *s, bool b) {
+        assert(s);
 
         if (s->protocol != DNS_PROTOCOL_MDNS)
                 return 0;
@@ -604,15 +606,14 @@ static int dns_scope_make_reply_packet(
                 DnsPacket **ret) {
 
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
-        unsigned i;
         int r;
 
         assert(s);
         assert(ret);
 
-        if ((!q || q->n_keys <= 0)
-            && (!answer || answer->n_rrs <= 0)
-            && (!soa || soa->n_rrs <= 0))
+        if (dns_question_isempty(q) &&
+            dns_answer_isempty(answer) &&
+            dns_answer_isempty(soa))
                 return -EINVAL;
 
         r = dns_packet_new(&p, s->protocol, 0);
@@ -631,35 +632,20 @@ static int dns_scope_make_reply_packet(
                                                               0 /* (cd) */,
                                                               rcode));
 
-        if (q) {
-                for (i = 0; i < q->n_keys; i++) {
-                        r = dns_packet_append_key(p, q->keys[i], NULL);
-                        if (r < 0)
-                                return r;
-                }
+        r = dns_packet_append_question(p, q);
+        if (r < 0)
+                return r;
+        DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q));
 
-                DNS_PACKET_HEADER(p)->qdcount = htobe16(q->n_keys);
-        }
+        r = dns_packet_append_answer(p, answer);
+        if (r < 0)
+                return r;
+        DNS_PACKET_HEADER(p)->ancount = htobe16(dns_answer_size(answer));
 
-        if (answer) {
-                for (i = 0; i < answer->n_rrs; i++) {
-                        r = dns_packet_append_rr(p, answer->items[i].rr, NULL, NULL);
-                        if (r < 0)
-                                return r;
-                }
-
-                DNS_PACKET_HEADER(p)->ancount = htobe16(answer->n_rrs);
-        }
-
-        if (soa) {
-                for (i = 0; i < soa->n_rrs; i++) {
-                        r = dns_packet_append_rr(p, soa->items[i].rr, NULL, NULL);
-                        if (r < 0)
-                                return r;
-                }
-
-                DNS_PACKET_HEADER(p)->arcount = htobe16(soa->n_rrs);
-        }
+        r = dns_packet_append_answer(p, soa);
+        if (r < 0)
+                return r;
+        DNS_PACKET_HEADER(p)->arcount = htobe16(dns_answer_size(soa));
 
         *ret = p;
         p = NULL;
@@ -668,25 +654,25 @@ static int dns_scope_make_reply_packet(
 }
 
 static void dns_scope_verify_conflicts(DnsScope *s, DnsPacket *p) {
-        unsigned n;
+        DnsResourceRecord *rr;
+        DnsResourceKey *key;
 
         assert(s);
         assert(p);
 
-        if (p->question)
-                for (n = 0; n < p->question->n_keys; n++)
-                        dns_zone_verify_conflicts(&s->zone, p->question->keys[n]);
-        if (p->answer)
-                for (n = 0; n < p->answer->n_rrs; n++)
-                        dns_zone_verify_conflicts(&s->zone, p->answer->items[n].rr->key);
+        DNS_QUESTION_FOREACH(key, p->question)
+                dns_zone_verify_conflicts(&s->zone, key);
+
+        DNS_ANSWER_FOREACH(rr, p->answer)
+                dns_zone_verify_conflicts(&s->zone, rr->key);
 }
 
 void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
-        _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL, *soa = NULL;
+        _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
         DnsResourceKey *key = NULL;
         bool tentative = false;
-        int r, fd;
+        int r;
 
         assert(s);
         assert(p);
@@ -708,7 +694,7 @@ void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
 
         r = dns_packet_extract(p);
         if (r < 0) {
-                log_debug_errno(r, "Failed to extract resources from incoming packet: %m");
+                log_debug_errno(r, "Failed to extract resource records from incoming packet: %m");
                 return;
         }
 
@@ -718,7 +704,7 @@ void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
                 return;
         }
 
-        assert(p->question->n_keys == 1);
+        assert(dns_question_size(p->question) == 1);
         key = p->question->keys[0];
 
         r = dns_zone_lookup(&s->zone, key, 0, &answer, &soa, &tentative);
@@ -738,9 +724,21 @@ void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
                 return;
         }
 
-        if (stream)
+        if (stream) {
                 r = dns_stream_write_packet(stream, reply);
-        else {
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to enqueue reply packet: %m");
+                        return;
+                }
+
+                /* Let's take an extra reference on this stream, so that it stays around after returning. The reference
+                 * will be dangling until the stream is disconnected, and the default completion handler of the stream
+                 * will then unref the stream and destroy it */
+                if (DNS_STREAM_QUEUED(stream))
+                        dns_stream_ref(stream);
+        } else {
+                int fd;
+
                 if (!ratelimit_test(&s->ratelimit))
                         return;
 
@@ -762,12 +760,11 @@ void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
                  * verified uniqueness for all records. Also see RFC
                  * 4795, Section 2.7 */
 
-                r = manager_send(s->manager, fd, p->ifindex, p->family, &p->sender, p->sender_port, reply);
-        }
-
-        if (r < 0) {
-                log_debug_errno(r, "Failed to send reply packet: %m");
-                return;
+                r = manager_send(s->manager, fd, p->ifindex, p->family, &p->sender, p->sender_port, NULL, reply);
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to send reply packet: %m");
+                        return;
+                }
         }
 }
 

src/resolve/resolved-dns-server.c

@@ -21,6 +21,7 @@
 
 #include "alloc-util.h"
 #include "resolved-dns-server.h"
+#include "resolved-dns-stub.h"
 #include "resolved-resolv-conf.h"
 #include "siphash24.h"
 #include "string-table.h"
@@ -517,7 +518,7 @@ int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeature
         else
                 packet_size = server->received_udp_packet_max;
 
-        return dns_packet_append_opt(packet, packet_size, edns_do, NULL);
+        return dns_packet_append_opt(packet, packet_size, edns_do, 0, NULL);
 }
 
 int dns_server_ifindex(const DnsServer *s) {
@@ -750,6 +751,19 @@ void manager_next_dns_server(Manager *m) {
                 manager_set_dns_server(m, m->dns_servers);
 }
 
+bool dns_server_address_valid(int family, const union in_addr_union *sa) {
+
+        /* Refuses the 0 IP addresses as well as 127.0.0.53 (which is our own DNS stub) */
+
+        if (in_addr_is_null(family, sa))
+                return false;
+
+        if (family == AF_INET && sa->in.s_addr == htobe32(INADDR_DNS_STUB))
+                return false;
+
+        return true;
+}
+
 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
         [DNS_SERVER_SYSTEM] = "system",
         [DNS_SERVER_FALLBACK] = "fallback",

src/resolve/resolved-dns-server.h

@@ -141,6 +141,8 @@ DnsServer *manager_set_dns_server(Manager *m, DnsServer *s);
 DnsServer *manager_get_dns_server(Manager *m);
 void manager_next_dns_server(Manager *m);
 
+bool dns_server_address_valid(int family, const union in_addr_union *sa);
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsServer*, dns_server_unref);
 
 extern const struct hash_ops dns_server_hash_ops;

src/resolve/resolved-dns-stream.c

@@ -56,8 +56,8 @@ static int dns_stream_complete(DnsStream *s, int error) {
 
         if (s->complete)
                 s->complete(s, error);
-        else
-                dns_stream_free(s);
+        else /* the default action if no completion function is set is to close the stream */
+                dns_stream_unref(s);
 
         return 0;
 }
@@ -323,10 +323,16 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
         return 0;
 }
 
-DnsStream *dns_stream_free(DnsStream *s) {
+DnsStream *dns_stream_unref(DnsStream *s) {
         if (!s)
                 return NULL;
 
+        assert(s->n_ref > 0);
+        s->n_ref--;
+
+        if (s->n_ref > 0)
+                return NULL;
+
         dns_stream_stop(s);
 
         if (s->manager) {
@@ -339,13 +345,23 @@ DnsStream *dns_stream_free(DnsStream *s) {
 
         free(s);
 
-        return 0;
+        return NULL;
 }
 
-DEFINE_TRIVIAL_CLEANUP_FUNC(DnsStream*, dns_stream_free);
+DEFINE_TRIVIAL_CLEANUP_FUNC(DnsStream*, dns_stream_unref);
+
+DnsStream *dns_stream_ref(DnsStream *s) {
+        if (!s)
+                return NULL;
+
+        assert(s->n_ref > 0);
+        s->n_ref++;
+
+        return s;
+}
 
 int dns_stream_new(Manager *m, DnsStream **ret, DnsProtocol protocol, int fd) {
-        _cleanup_(dns_stream_freep) DnsStream *s = NULL;
+        _cleanup_(dns_stream_unrefp) DnsStream *s = NULL;
         int r;
 
         assert(m);
@@ -358,6 +374,7 @@ int dns_stream_new(Manager *m, DnsStream **ret, DnsProtocol protocol, int fd) {
         if (!s)
                 return -ENOMEM;
 
+        s->n_ref = 1;
         s->fd = -1;
         s->protocol = protocol;
 

src/resolve/resolved-dns-stream.h

@@ -26,8 +26,16 @@ typedef struct DnsStream DnsStream;
 #include "resolved-dns-packet.h"
 #include "resolved-dns-transaction.h"
 
+/* Streams are used by three subsystems:
+ *
+ *   1. The normal transaction logic when doing a DNS or LLMNR lookup via TCP
+ *   2. The LLMNR logic when accepting a TCP-based lookup
+ *   3. The DNS stub logic when accepting a TCP-based lookup
+ */
+
 struct DnsStream {
         Manager *manager;
+        int n_ref;
 
         DnsProtocol protocol;
 
@@ -50,12 +58,23 @@ struct DnsStream {
         int (*on_packet)(DnsStream *s);
         int (*complete)(DnsStream *s, int error);
 
-        DnsTransaction *transaction;
+        DnsTransaction *transaction; /* when used by the transaction logic */
+        DnsQuery *query;             /* when used by the DNS stub logic */
 
         LIST_FIELDS(DnsStream, streams);
 };
 
 int dns_stream_new(Manager *m, DnsStream **s, DnsProtocol protocol, int fd);
-DnsStream *dns_stream_free(DnsStream *s);
+DnsStream *dns_stream_unref(DnsStream *s);
+DnsStream *dns_stream_ref(DnsStream *s);
 
 int dns_stream_write_packet(DnsStream *s, DnsPacket *p);
+
+static inline bool DNS_STREAM_QUEUED(DnsStream *s) {
+        assert(s);
+
+        if (s->fd < 0) /* already stopped? */
+                return false;
+
+        return !!s->write_packet;
+}

src/resolve/resolved-dns-stub.c

@@ -0,0 +1,572 @@
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "fd-util.h"
+#include "resolved-dns-stub.h"
+#include "socket-util.h"
+
+/* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
+ * IP and UDP header sizes */
+#define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
+
+static int dns_stub_make_reply_packet(
+                uint16_t id,
+                int rcode,
+                DnsQuestion *q,
+                DnsAnswer *answer,
+                bool add_opt,   /* add an OPT RR to this packet */
+                bool edns0_do,  /* set the EDNS0 DNSSEC OK bit */
+                bool ad,        /* set the DNSSEC authenticated data bit */
+                DnsPacket **ret) {
+
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        DnsResourceRecord *rr;
+        unsigned c = 0;
+        int r;
+
+        /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
+         * roundtrips aren't expensive. */
+
+        r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0);
+        if (r < 0)
+                return r;
+
+        /* If the client didn't do EDNS, clamp the rcode to 4 bit */
+        if (!add_opt && rcode > 0xF)
+                rcode = DNS_RCODE_SERVFAIL;
+
+        DNS_PACKET_HEADER(p)->id = id;
+        DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
+                                                              1 /* qr */,
+                                                              0 /* opcode */,
+                                                              0 /* aa */,
+                                                              0 /* tc */,
+                                                              1 /* rd */,
+                                                              1 /* ra */,
+                                                              ad /* ad */,
+                                                              0 /* cd */,
+                                                              rcode));
+
+        r = dns_packet_append_question(p, q);
+        if (r < 0)
+                return r;
+        DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q));
+
+        DNS_ANSWER_FOREACH(rr, answer) {
+                r = dns_question_matches_rr(q, rr, NULL);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        goto add;
+
+                r = dns_question_matches_cname_or_dname(q, rr, NULL);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        goto add;
+
+                continue;
+        add:
+                r = dns_packet_append_rr(p, rr, NULL, NULL);
+                if (r < 0)
+                        return r;
+
+                c++;
+        }
+        DNS_PACKET_HEADER(p)->ancount = htobe16(c);
+
+        if (add_opt) {
+                r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        *ret = p;
+        p = NULL;
+
+        return 0;
+}
+
+static void dns_stub_detach_stream(DnsStream *s) {
+        assert(s);
+
+        s->complete = NULL;
+        s->on_packet = NULL;
+        s->query = NULL;
+}
+
+static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *reply) {
+        int r;
+
+        assert(m);
+        assert(p);
+        assert(reply);
+
+        if (s)
+                r = dns_stream_write_packet(s, reply);
+        else {
+                int fd;
+
+                /* Truncate the message to the right size */
+                if (reply->size > DNS_PACKET_PAYLOAD_SIZE_MAX(p)) {
+                        dns_packet_truncate(reply, DNS_PACKET_UNICAST_SIZE_MAX);
+                        DNS_PACKET_HEADER(reply)->flags = htobe16(be16toh(DNS_PACKET_HEADER(reply)->flags) | DNS_PACKET_FLAG_TC);
+                }
+
+                fd = manager_dns_stub_udp_fd(m);
+                if (fd < 0)
+                        return log_debug_errno(fd, "Failed to get reply socket: %m");
+
+                /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
+                 * is because otherwise the kernel will choose it automatically based on the routing table and will
+                 * thus pick 127.0.0.1 rather than 127.0.0.53. */
+
+                r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
+        }
+        if (r < 0)
+                return log_debug_errno(r, "Failed to send reply packet: %m");
+
+        return 0;
+}
+
+static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
+        int r;
+
+        assert(m);
+        assert(p);
+
+        r = dns_stub_make_reply_packet(DNS_PACKET_ID(p), rcode, p->question, NULL, !!p->opt, DNS_PACKET_DO(p), false, &reply);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to build failure packet: %m");
+
+        return dns_stub_send(m, s, p, reply);
+}
+
+static void dns_stub_query_complete(DnsQuery *q) {
+        int r;
+
+        assert(q);
+        assert(q->request_dns_packet);
+
+        switch (q->state) {
+
+        case DNS_TRANSACTION_SUCCESS: {
+                _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
+
+                r = dns_stub_make_reply_packet(
+                                DNS_PACKET_ID(q->request_dns_packet),
+                                q->answer_rcode,
+                                q->question_idna,
+                                q->answer,
+                                !!q->request_dns_packet->opt,
+                                DNS_PACKET_DO(q->request_dns_packet),
+                                DNS_PACKET_DO(q->request_dns_packet) && q->answer_authenticated,
+                                &reply);
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to build reply packet: %m");
+                        break;
+                }
+
+                (void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, reply);
+                break;
+        }
+
+        case DNS_TRANSACTION_RCODE_FAILURE:
+                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode);
+                break;
+
+        case DNS_TRANSACTION_NOT_FOUND:
+                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN);
+                break;
+
+        case DNS_TRANSACTION_TIMEOUT:
+        case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
+                /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
+                break;
+
+        case DNS_TRANSACTION_NO_SERVERS:
+        case DNS_TRANSACTION_INVALID_REPLY:
+        case DNS_TRANSACTION_ERRNO:
+        case DNS_TRANSACTION_ABORTED:
+        case DNS_TRANSACTION_DNSSEC_FAILED:
+        case DNS_TRANSACTION_NO_TRUST_ANCHOR:
+        case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
+        case DNS_TRANSACTION_NETWORK_DOWN:
+                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL);
+                break;
+
+        case DNS_TRANSACTION_NULL:
+        case DNS_TRANSACTION_PENDING:
+        case DNS_TRANSACTION_VALIDATING:
+        default:
+                assert_not_reached("Impossible state");
+        }
+
+        /* If there's a packet to write set, let's leave the stream around */
+        if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {
+
+                /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
+                 * default completion action of the stream will drop the reference. */
+
+                dns_stub_detach_stream(q->request_dns_stream);
+                q->request_dns_stream = NULL;
+        }
+
+        dns_query_free(q);
+}
+
+static int dns_stub_stream_complete(DnsStream *s, int error) {
+        assert(s);
+
+        log_debug_errno(error, "DNS TCP connection terminated, destroying query: %m");
+
+        assert(s->query);
+        dns_query_free(s->query);
+
+        return 0;
+}
+
+static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
+        DnsQuery *q = NULL;
+        int r;
+
+        assert(m);
+        assert(p);
+        assert(p->protocol == DNS_PROTOCOL_DNS);
+
+        /* Takes ownership of the *s stream object */
+
+        if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
+            in_addr_is_localhost(p->family, &p->destination) <= 0) {
+                log_error("Got packet on unexpected IP range, refusing.");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
+                goto fail;
+        }
+
+        r = dns_packet_extract(p);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR);
+                goto fail;
+        }
+
+        if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
+                log_debug("Got EDNS OPT field with unsupported version number.");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS);
+                goto fail;
+        }
+
+        if (dns_type_is_obsolete(p->question->keys[0]->type)) {
+                log_debug("Got message with obsolete key type, refusing.");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
+                goto fail;
+        }
+
+        if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
+                log_debug("Got request for zone transfer, refusing.");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
+                goto fail;
+        }
+
+        if (!DNS_PACKET_RD(p))  {
+                /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
+                log_debug("Got request with recursion disabled, refusing.");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED);
+                goto fail;
+        }
+
+        if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
+                log_debug("Got request with DNSSEC CD bit set, refusing.");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
+                goto fail;
+        }
+
+        r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH|SD_RESOLVED_NO_CNAME);
+        if (r < 0) {
+                log_error_errno(r, "Failed to generate query object: %m");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
+                goto fail;
+        }
+
+        /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
+        q->clamp_ttl = true;
+
+        q->request_dns_packet = dns_packet_ref(p);
+        q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
+        q->complete = dns_stub_query_complete;
+
+        if (s) {
+                s->on_packet = NULL;
+                s->complete = dns_stub_stream_complete;
+                s->query = q;
+        }
+
+        r = dns_query_go(q);
+        if (r < 0) {
+                log_error_errno(r, "Failed to start query: %m");
+                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
+                goto fail;
+        }
+
+        log_info("Processing query...");
+        return;
+
+fail:
+        if (s && DNS_STREAM_QUEUED(s))
+                dns_stub_detach_stream(s);
+
+        dns_query_free(q);
+}
+
+static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        Manager *m = userdata;
+        int r;
+
+        r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
+        if (r <= 0)
+                return r;
+
+        if (dns_packet_validate_query(p) > 0) {
+                log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
+
+                dns_stub_process_query(m, NULL, p);
+        } else
+                log_debug("Invalid DNS stub UDP packet, ignoring.");
+
+        return 0;
+}
+
+int manager_dns_stub_udp_fd(Manager *m) {
+        static const int one = 1;
+
+        union sockaddr_union sa = {
+                .in.sin_family = AF_INET,
+                .in.sin_port = htobe16(53),
+                .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
+        };
+
+        int r;
+
+        if (m->dns_stub_udp_fd >= 0)
+                return m->dns_stub_udp_fd;
+
+        m->dns_stub_udp_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+        if (m->dns_stub_udp_fd < 0)
+                return -errno;
+
+        r = setsockopt(m->dns_stub_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = setsockopt(m->dns_stub_udp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = setsockopt(m->dns_stub_udp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        /* Make sure no traffic from outside the local host can leak to onto this socket */
+        r = setsockopt(m->dns_stub_udp_fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3);
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = bind(m->dns_stub_udp_fd, &sa.sa, sizeof(sa.in));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, m->dns_stub_udp_fd, EPOLLIN, on_dns_stub_packet, m);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
+
+        return m->dns_stub_udp_fd;
+
+fail:
+        m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
+        return r;
+}
+
+static int on_dns_stub_stream_packet(DnsStream *s) {
+        assert(s);
+        assert(s->read_packet);
+
+        if (dns_packet_validate_query(s->read_packet) > 0) {
+                log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
+
+                dns_stub_process_query(s->manager, s, s->read_packet);
+        } else
+                log_debug("Invalid DNS stub TCP packet, ignoring.");
+
+        /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
+         * or that didn't happen in which case we want to free the stream */
+        dns_stream_unref(s);
+
+        return 0;
+}
+
+static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        DnsStream *stream;
+        Manager *m = userdata;
+        int cfd, r;
+
+        cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
+        if (cfd < 0) {
+                if (errno == EAGAIN || errno == EINTR)
+                        return 0;
+
+                return -errno;
+        }
+
+        r = dns_stream_new(m, &stream, DNS_PROTOCOL_DNS, cfd);
+        if (r < 0) {
+                safe_close(cfd);
+                return r;
+        }
+
+        stream->on_packet = on_dns_stub_stream_packet;
+
+        /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
+         * of the stream, or by our packet callback, or when the manager is shut down. */
+
+        return 0;
+}
+
+int manager_dns_stub_tcp_fd(Manager *m) {
+        static const int one = 1;
+
+        union sockaddr_union sa = {
+                .in.sin_family = AF_INET,
+                .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
+                .in.sin_port = htobe16(53),
+        };
+
+        int r;
+
+        if (m->dns_stub_tcp_fd >= 0)
+                return m->dns_stub_tcp_fd;
+
+        m->dns_stub_tcp_fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+        if (m->dns_stub_tcp_fd < 0)
+                return -errno;
+
+        r = setsockopt(m->dns_stub_tcp_fd, IPPROTO_IP, IP_TTL, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = setsockopt(m->dns_stub_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = setsockopt(m->dns_stub_tcp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = setsockopt(m->dns_stub_tcp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        /* Make sure no traffic from outside the local host can leak to onto this socket */
+        r = setsockopt(m->dns_stub_tcp_fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3);
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = bind(m->dns_stub_tcp_fd, &sa.sa, sizeof(sa.in));
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = listen(m->dns_stub_tcp_fd, SOMAXCONN);
+        if (r < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, m->dns_stub_tcp_fd, EPOLLIN, on_dns_stub_stream, m);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");
+
+        return m->dns_stub_tcp_fd;
+
+fail:
+        m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
+        return r;
+}
+
+int manager_dns_stub_start(Manager *m) {
+        int r;
+
+        assert(m);
+
+        r = manager_dns_stub_udp_fd(m);
+        if (r == -EADDRINUSE)
+                goto eaddrinuse;
+        if (r < 0)
+                return r;
+
+        r = manager_dns_stub_tcp_fd(m);
+        if (r == -EADDRINUSE)
+                goto eaddrinuse;
+        if (r < 0)
+                return r;
+
+        return 0;
+
+eaddrinuse:
+        log_warning("Another process is already listening on 127.0.0.53:53. Turning off local DNS stub support.");
+        manager_dns_stub_stop(m);
+
+        return 0;
+}
+
+void manager_dns_stub_stop(Manager *m) {
+        assert(m);
+
+        m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source);
+        m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source);
+
+        m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
+        m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
+}

src/resolve/resolved-dns-stub.h

@@ -0,0 +1,31 @@
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "resolved-manager.h"
+
+/* 127.0.0.53 in native endian */
+#define INADDR_DNS_STUB ((in_addr_t) 0x7f000035U)
+
+int manager_dns_stub_udp_fd(Manager *m);
+int manager_dns_stub_tcp_fd(Manager *m);
+
+void manager_dns_stub_stop(Manager *m);
+int manager_dns_stub_start(Manager *m);

src/resolve/resolved-dns-transaction.c

@@ -60,7 +60,14 @@ static void dns_transaction_flush_dnssec_transactions(DnsTransaction *t) {
 static void dns_transaction_close_connection(DnsTransaction *t) {
         assert(t);
 
-        t->stream = dns_stream_free(t->stream);
+        if (t->stream) {
+                /* Let's detach the stream from our transaction, in case something else keeps a reference to it. */
+                t->stream->complete = NULL;
+                t->stream->on_packet = NULL;
+                t->stream->transaction = NULL;
+                t->stream = dns_stream_unref(t->stream);
+        }
+
         t->dns_udp_event_source = sd_event_source_unref(t->dns_udp_event_source);
         t->dns_udp_fd = safe_close(t->dns_udp_fd);
 }
@@ -444,7 +451,7 @@ static int on_stream_complete(DnsStream *s, int error) {
         t = s->transaction;
         p = dns_packet_ref(s->read_packet);
 
-        t->stream = dns_stream_free(t->stream);
+        dns_transaction_close_connection(t);
 
         if (ERRNO_IS_DISCONNECT(error)) {
                 usec_t usec;
@@ -556,7 +563,7 @@ static int dns_transaction_open_tcp(DnsTransaction *t) {
 
         r = dns_stream_write_packet(t->stream, t->sent);
         if (r < 0) {
-                t->stream = dns_stream_free(t->stream);
+                t->stream = dns_stream_unref(t->stream);
                 return r;
         }
 
@@ -1274,7 +1281,7 @@ static int dns_transaction_prepare(DnsTransaction *t, usec_t ts) {
                 /* Let's then prune all outdated entries */
                 dns_cache_prune(&t->scope->cache);
 
-                r = dns_cache_lookup(&t->scope->cache, t->key, &t->answer_rcode, &t->answer, &t->answer_authenticated);
+                r = dns_cache_lookup(&t->scope->cache, t->key, t->clamp_ttl, &t->answer_rcode, &t->answer, &t->answer_authenticated);
                 if (r < 0)
                         return r;
                 if (r > 0) {

src/resolve/resolved-dns-transaction.h

@@ -74,6 +74,8 @@ struct DnsTransaction {
         bool initial_jitter_scheduled:1;
         bool initial_jitter_elapsed:1;
 
+        bool clamp_ttl:1;
+
         DnsPacket *sent, *received;
 
         DnsAnswer *answer;

src/resolve/resolved-link-bus.c

@@ -28,7 +28,23 @@
 #include "strv.h"
 
 static BUS_DEFINE_PROPERTY_GET_ENUM(property_get_resolve_support, resolve_support, ResolveSupport);
-static BUS_DEFINE_PROPERTY_GET_ENUM(property_get_dnssec_mode, dnssec_mode, DnssecMode);
+
+static int property_get_dnssec_mode(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        Link *l = userdata;
+
+        assert(reply);
+        assert(l);
+
+        return sd_bus_message_append(reply, "s", dnssec_mode_to_string(link_get_dnssec_mode(l)));
+}
 
 static int property_get_dns(
                 sd_bus *bus,
@@ -214,6 +230,9 @@ int bus_link_method_set_dns_servers(sd_bus_message *message, void *userdata, sd_
                 if (sz != FAMILY_ADDRESS_SIZE(family))
                         return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid address size");
 
+                if (!dns_server_address_valid(family, d))
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid DNS server address");
+
                 r = sd_bus_message_exit_container(message);
                 if (r < 0)
                         return r;
@@ -249,6 +268,7 @@ int bus_link_method_set_dns_servers(sd_bus_message *message, void *userdata, sd_
         dns_server_unlink_marked(l->dns_servers);
         link_allocate_scopes(l);
 
+        (void) link_save_user(l);
         (void) manager_write_resolv_conf(l->manager);
 
         return sd_bus_reply_method_return(message, NULL);
@@ -330,6 +350,7 @@ int bus_link_method_set_domains(sd_bus_message *message, void *userdata, sd_bus_
 
         dns_search_domain_unlink_marked(l->search_domains);
 
+        (void) link_save_user(l);
         (void) manager_write_resolv_conf(l->manager);
 
         return sd_bus_reply_method_return(message, NULL);
@@ -368,6 +389,8 @@ int bus_link_method_set_llmnr(sd_bus_message *message, void *userdata, sd_bus_er
         link_allocate_scopes(l);
         link_add_rrs(l, false);
 
+        (void) link_save_user(l);
+
         return sd_bus_reply_method_return(message, NULL);
 }
 
@@ -400,6 +423,8 @@ int bus_link_method_set_mdns(sd_bus_message *message, void *userdata, sd_bus_err
         link_allocate_scopes(l);
         link_add_rrs(l, false);
 
+        (void) link_save_user(l);
+
         return sd_bus_reply_method_return(message, NULL);
 }
 
@@ -430,6 +455,8 @@ int bus_link_method_set_dnssec(sd_bus_message *message, void *userdata, sd_bus_e
 
         link_set_dnssec_mode(l, mode);
 
+        (void) link_save_user(l);
+
         return sd_bus_reply_method_return(message, NULL);
 }
 
@@ -473,6 +500,8 @@ int bus_link_method_set_dnssec_negative_trust_anchors(sd_bus_message *message, v
         l->dnssec_negative_trust_anchors = ns;
         ns = NULL;
 
+        (void) link_save_user(l);
+
         return sd_bus_reply_method_return(message, NULL);
 }
 
@@ -491,6 +520,7 @@ int bus_link_method_revert(sd_bus_message *message, void *userdata, sd_bus_error
         link_allocate_scopes(l);
         link_add_rrs(l, false);
 
+        (void) link_save_user(l);
         (void) manager_write_resolv_conf(l->manager);
 
         return sd_bus_reply_method_return(message, NULL);
@@ -504,7 +534,7 @@ const sd_bus_vtable link_vtable[] = {
         SD_BUS_PROPERTY("Domains", "a(sb)", property_get_domains, 0, 0),
         SD_BUS_PROPERTY("LLMNR", "s", property_get_resolve_support, offsetof(Link, llmnr_support), 0),
         SD_BUS_PROPERTY("MulticastDNS", "s", property_get_resolve_support, offsetof(Link, mdns_support), 0),
-        SD_BUS_PROPERTY("DNSSEC", "s", property_get_dnssec_mode, offsetof(Link, dnssec_mode), 0),
+        SD_BUS_PROPERTY("DNSSEC", "s", property_get_dnssec_mode, 0, 0),
         SD_BUS_PROPERTY("DNSSECNegativeTrustAnchors", "as", property_get_ntas, 0, 0),
         SD_BUS_PROPERTY("DNSSECSupported", "b", property_get_dnssec_supported, 0, 0),
 

src/resolve/resolved-link.c

@@ -22,7 +22,10 @@
 #include "sd-network.h"
 
 #include "alloc-util.h"
+#include "fd-util.h"
+#include "fileio.h"
 #include "missing.h"
+#include "mkdir.h"
 #include "parse-util.h"
 #include "resolved-link.h"
 #include "string-util.h"
@@ -49,6 +52,9 @@ int link_new(Manager *m, Link **ret, int ifindex) {
         l->dnssec_mode = _DNSSEC_MODE_INVALID;
         l->operstate = IF_OPER_UNKNOWN;
 
+        if (asprintf(&l->state_file, "/run/systemd/resolve/netif/%i", ifindex) < 0)
+                return -ENOMEM;
+
         r = hashmap_put(m->links, INT_TO_PTR(ifindex), l);
         if (r < 0)
                 return r;
@@ -93,6 +99,8 @@ Link *link_free(Link *l) {
         dns_scope_free(l->mdns_ipv4_scope);
         dns_scope_free(l->mdns_ipv6_scope);
 
+        free(l->state_file);
+
         free(l);
         return NULL;
 }
@@ -165,7 +173,7 @@ void link_add_rrs(Link *l, bool force_remove) {
                 link_address_add_rrs(a, force_remove);
 }
 
-int link_update_rtnl(Link *l, sd_netlink_message *m) {
+int link_process_rtnl(Link *l, sd_netlink_message *m) {
         const char *n = NULL;
         int r;
 
@@ -190,6 +198,27 @@ int link_update_rtnl(Link *l, sd_netlink_message *m) {
         return 0;
 }
 
+static int link_update_dns_server_one(Link *l, const char *name) {
+        union in_addr_union a;
+        DnsServer *s;
+        int family, r;
+
+        assert(l);
+        assert(name);
+
+        r = in_addr_from_string_auto(name, &family, &a);
+        if (r < 0)
+                return r;
+
+        s = dns_server_find(l->dns_servers, family, &a, 0);
+        if (s) {
+                dns_server_move_back_and_unmark(s);
+                return 0;
+        }
+
+        return dns_server_new(l->manager, NULL, DNS_SERVER_LINK, l, family, &a, 0);
+}
+
 static int link_update_dns_servers(Link *l) {
         _cleanup_strv_free_ char **nameservers = NULL;
         char **nameserver;
@@ -208,22 +237,9 @@ static int link_update_dns_servers(Link *l) {
         dns_server_mark_all(l->dns_servers);
 
         STRV_FOREACH(nameserver, nameservers) {
-                union in_addr_union a;
-                DnsServer *s;
-                int family;
-
-                r = in_addr_from_string_auto(*nameserver, &family, &a);
+                r = link_update_dns_server_one(l, *nameserver);
                 if (r < 0)
                         goto clear;
-
-                s = dns_server_find(l->dns_servers, family, &a, 0);
-                if (s)
-                        dns_server_move_back_and_unmark(s);
-                else {
-                        r = dns_server_new(l->manager, NULL, DNS_SERVER_LINK, l, family, &a, 0);
-                        if (r < 0)
-                                goto clear;
-                }
         }
 
         dns_server_unlink_marked(l->dns_servers);
@@ -341,7 +357,6 @@ clear:
 static int link_update_dnssec_negative_trust_anchors(Link *l) {
         _cleanup_strv_free_ char **ntas = NULL;
         _cleanup_set_free_free_ Set *ns = NULL;
-        char **i;
         int r;
 
         assert(l);
@@ -358,11 +373,9 @@ static int link_update_dnssec_negative_trust_anchors(Link *l) {
         if (!ns)
                 return -ENOMEM;
 
-        STRV_FOREACH(i, ntas) {
-                r = set_put_strdup(ns, *i);
-                if (r < 0)
-                        return r;
-        }
+        r = set_put_strdupv(ns, ntas);
+        if (r < 0)
+                return r;
 
         set_free_free(l->dnssec_negative_trust_anchors);
         l->dnssec_negative_trust_anchors = ns;
@@ -379,6 +392,9 @@ static int link_update_search_domain_one(Link *l, const char *name, bool route_o
         DnsSearchDomain *d;
         int r;
 
+        assert(l);
+        assert(name);
+
         r = dns_search_domain_find(l->search_domains, name, &d);
         if (r < 0)
                 return r;
@@ -439,7 +455,7 @@ clear:
         return r;
 }
 
-static int link_is_unmanaged(Link *l) {
+static int link_is_managed(Link *l) {
         _cleanup_free_ char *state = NULL;
         int r;
 
@@ -447,11 +463,11 @@ static int link_is_unmanaged(Link *l) {
 
         r = sd_network_link_get_setup_state(l->ifindex, &state);
         if (r == -ENODATA)
-                return 1;
+                return 0;
         if (r < 0)
                 return r;
 
-        return STR_IN_SET(state, "pending", "unmanaged");
+        return !STR_IN_SET(state, "pending", "unmanaged");
 }
 
 static void link_read_settings(Link *l) {
@@ -461,12 +477,12 @@ static void link_read_settings(Link *l) {
 
         /* Read settings from networkd, except when networkd is not managing this interface. */
 
-        r = link_is_unmanaged(l);
+        r = link_is_managed(l);
         if (r < 0) {
                 log_warning_errno(r, "Failed to determine whether interface %s is managed: %m", l->name);
                 return;
         }
-        if (r > 0) {
+        if (r == 0) {
 
                 /* If this link used to be managed, but is now unmanaged, flush all our settings — but only once. */
                 if (l->is_managed)
@@ -503,10 +519,11 @@ static void link_read_settings(Link *l) {
                 log_warning_errno(r, "Failed to read search domains for interface %s, ignoring: %m", l->name);
 }
 
-int link_update_monitor(Link *l) {
+int link_update(Link *l) {
         assert(l);
 
         link_read_settings(l);
+        link_load_user(l);
         link_allocate_scopes(l);
         link_add_rrs(l, false);
 
@@ -838,3 +855,261 @@ bool link_address_relevant(LinkAddress *a, bool local_multicast) {
 
         return true;
 }
+
+static bool link_needs_save(Link *l) {
+        assert(l);
+
+        /* Returns true if any of the settings where set different from the default */
+
+        if (l->is_managed)
+                return false;
+
+        if (l->llmnr_support != RESOLVE_SUPPORT_YES ||
+            l->mdns_support != RESOLVE_SUPPORT_NO ||
+            l->dnssec_mode != _DNSSEC_MODE_INVALID)
+                return true;
+
+        if (l->dns_servers ||
+            l->search_domains)
+                return true;
+
+        if (!set_isempty(l->dnssec_negative_trust_anchors))
+                return true;
+
+        return false;
+}
+
+int link_save_user(Link *l) {
+        _cleanup_free_ char *temp_path = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        const char *v;
+        int r;
+
+        assert(l);
+        assert(l->state_file);
+
+        if (!link_needs_save(l)) {
+                (void) unlink(l->state_file);
+                return 0;
+        }
+
+        r = mkdir_parents(l->state_file, 0700);
+        if (r < 0)
+                goto fail;
+
+        r = fopen_temporary(l->state_file, &f, &temp_path);
+        if (r < 0)
+                goto fail;
+
+        fputs("# This is private data. Do not parse.\n", f);
+
+        v = resolve_support_to_string(l->llmnr_support);
+        if (v)
+                fprintf(f, "LLMNR=%s\n", v);
+
+        v = resolve_support_to_string(l->mdns_support);
+        if (v)
+                fprintf(f, "MDNS=%s\n", v);
+
+        v = dnssec_mode_to_string(l->dnssec_mode);
+        if (v)
+                fprintf(f, "DNSSEC=%s\n", v);
+
+        if (l->dns_servers) {
+                DnsServer *server;
+
+                fputs("SERVERS=", f);
+                LIST_FOREACH(servers, server, l->dns_servers) {
+
+                        if (server != l->dns_servers)
+                                fputc(' ', f);
+
+                        v = dns_server_string(server);
+                        if (!v) {
+                                r = -ENOMEM;
+                                goto fail;
+                        }
+
+                        fputs(v, f);
+                }
+                fputc('\n', f);
+        }
+
+        if (l->search_domains) {
+                DnsSearchDomain *domain;
+
+                fputs("DOMAINS=", f);
+                LIST_FOREACH(domains, domain, l->search_domains) {
+
+                        if (domain != l->search_domains)
+                                fputc(' ', f);
+
+                        if (domain->route_only)
+                                fputc('~', f);
+
+                        fputs(DNS_SEARCH_DOMAIN_NAME(domain), f);
+                }
+                fputc('\n', f);
+        }
+
+        if (!set_isempty(l->dnssec_negative_trust_anchors)) {
+                bool space = false;
+                Iterator i;
+                char *nta;
+
+                fputs("NTAS=", f);
+                SET_FOREACH(nta, l->dnssec_negative_trust_anchors, i) {
+
+                        if (space)
+                                fputc(' ', f);
+
+                        fputs(nta, f);
+                        space = true;
+                }
+                fputc('\n', f);
+        }
+
+        r = fflush_and_check(f);
+        if (r < 0)
+                goto fail;
+
+        if (rename(temp_path, l->state_file) < 0) {
+                r = -errno;
+                goto fail;
+        }
+
+        return 0;
+
+fail:
+        (void) unlink(l->state_file);
+
+        if (temp_path)
+                (void) unlink(temp_path);
+
+        return log_error_errno(r, "Failed to save link data %s: %m", l->state_file);
+}
+
+int link_load_user(Link *l) {
+        _cleanup_free_ char
+                *llmnr = NULL,
+                *mdns = NULL,
+                *dnssec = NULL,
+                *servers = NULL,
+                *domains = NULL,
+                *ntas = NULL;
+
+        ResolveSupport s;
+        int r;
+
+        assert(l);
+        assert(l->state_file);
+
+        /* Try to load only a single time */
+        if (l->loaded)
+                return 0;
+        l->loaded = true;
+
+        if (l->is_managed)
+                return 0; /* if the device is managed, then networkd is our configuration source, not the bus API */
+
+        r = parse_env_file(l->state_file, NEWLINE,
+                           "LLMNR", &llmnr,
+                           "MDNS", &mdns,
+                           "DNSSEC", &dnssec,
+                           "SERVERS", &servers,
+                           "DOMAINS", &domains,
+                           "NTAS", &ntas,
+                           NULL);
+        if (r == -ENOENT)
+                return 0;
+        if (r < 0)
+                goto fail;
+
+        link_flush_settings(l);
+
+        /* If we can't recognize the LLMNR or MDNS setting we don't override the default */
+        s = resolve_support_from_string(llmnr);
+        if (s >= 0)
+                l->llmnr_support = s;
+
+        s = resolve_support_from_string(mdns);
+        if (s >= 0)
+                l->mdns_support = s;
+
+        /* If we can't recognize the DNSSEC setting, then set it to invalid, so that the daemon default is used. */
+        l->dnssec_mode = dnssec_mode_from_string(dnssec);
+
+        if (servers) {
+                const char *p = servers;
+
+                for (;;) {
+                        _cleanup_free_ char *word = NULL;
+
+                        r = extract_first_word(&p, &word, NULL, 0);
+                        if (r < 0)
+                                goto fail;
+                        if (r == 0)
+                                break;
+
+                        r = link_update_dns_server_one(l, word);
+                        if (r < 0) {
+                                log_debug_errno(r, "Failed to load DNS server '%s', ignoring: %m", word);
+                                continue;
+                        }
+                }
+        }
+
+        if (domains) {
+                const char *p = domains;
+
+                for (;;) {
+                        _cleanup_free_ char *word = NULL;
+                        const char *n;
+                        bool is_route;
+
+                        r = extract_first_word(&p, &word, NULL, 0);
+                        if (r < 0)
+                                goto fail;
+                        if (r == 0)
+                                break;
+
+                        is_route = word[0] == '~';
+                        n = is_route ? word + 1 : word;
+
+                        r = link_update_search_domain_one(l, n, is_route);
+                        if (r < 0) {
+                                log_debug_errno(r, "Failed to load search domain '%s', ignoring: %m", word);
+                                continue;
+                        }
+                }
+        }
+
+        if (ntas) {
+                _cleanup_set_free_free_ Set *ns = NULL;
+
+                ns = set_new(&dns_name_hash_ops);
+                if (!ns) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+
+                r = set_put_strsplit(ns, ntas, NULL, 0);
+                if (r < 0)
+                        goto fail;
+
+                l->dnssec_negative_trust_anchors = ns;
+                ns = NULL;
+        }
+
+        return 0;
+
+fail:
+        return log_error_errno(r, "Failed to load link data %s: %m", l->state_file);
+}
+
+void link_remove_user(Link *l) {
+        assert(l);
+        assert(l->state_file);
+
+        (void) unlink(l->state_file);
+}

src/resolve/resolved-link.h

@@ -81,12 +81,15 @@ struct Link {
         char name[IF_NAMESIZE];
         uint32_t mtu;
         uint8_t operstate;
+
+        bool loaded;
+        char *state_file;
 };
 
 int link_new(Manager *m, Link **ret, int ifindex);
 Link *link_free(Link *l);
-int link_update_rtnl(Link *l, sd_netlink_message *m);
-int link_update_monitor(Link *l);
+int link_process_rtnl(Link *l, sd_netlink_message *m);
+int link_update(Link *l);
 bool link_relevant(Link *l, int family, bool local_multicast);
 LinkAddress* link_find_address(Link *l, int family, const union in_addr_union *in_addr);
 void link_add_rrs(Link *l, bool force_remove);
@@ -102,6 +105,10 @@ void link_next_dns_server(Link *l);
 DnssecMode link_get_dnssec_mode(Link *l);
 bool link_dnssec_supported(Link *l);
 
+int link_save_user(Link *l);
+int link_load_user(Link *l);
+void link_remove_user(Link *l);
+
 int link_address_new(Link *l, LinkAddress **ret, int family, const union in_addr_union *in_addr);
 LinkAddress *link_address_free(LinkAddress *a);
 int link_address_update_rtnl(LinkAddress *a, sd_netlink_message *m);

src/resolve/resolved-llmnr.c

@@ -91,18 +91,19 @@ static int on_llmnr_packet(sd_event_source *s, int fd, uint32_t revents, void *u
         DnsScope *scope;
         int r;
 
+        assert(s);
+        assert(fd >= 0);
+        assert(m);
+
         r = manager_recv(m, fd, DNS_PROTOCOL_LLMNR, &p);
         if (r <= 0)
                 return r;
 
         scope = manager_find_scope(m, p);
-        if (!scope) {
+        if (!scope)
                 log_warning("Got LLMNR UDP packet on unknown scope. Ignoring.");
-                return 0;
-        }
-
-        if (dns_packet_validate_reply(p) > 0) {
-                log_debug("Got LLMNR reply packet for id %u", DNS_PACKET_ID(p));
+        else if (dns_packet_validate_reply(p) > 0) {
+                log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
 
                 dns_scope_check_conflicts(scope, p);
 
@@ -111,7 +112,7 @@ static int on_llmnr_packet(sd_event_source *s, int fd, uint32_t revents, void *u
                         dns_transaction_process_reply(t, p);
 
         } else if (dns_packet_validate_query(p) > 0)  {
-                log_debug("Got LLMNR query packet for id %u", DNS_PACKET_ID(p));
+                log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
 
                 dns_scope_process_query(scope, NULL, p);
         } else
@@ -283,25 +284,19 @@ static int on_llmnr_stream_packet(DnsStream *s) {
         DnsScope *scope;
 
         assert(s);
+        assert(s->read_packet);
 
         scope = manager_find_scope(s->manager, s->read_packet);
-        if (!scope) {
+        if (!scope)
                 log_warning("Got LLMNR TCP packet on unknown scope. Ignoring.");
-                return 0;
-        }
-
-        if (dns_packet_validate_query(s->read_packet) > 0) {
-                log_debug("Got query packet for id %u", DNS_PACKET_ID(s->read_packet));
+        else if (dns_packet_validate_query(s->read_packet) > 0) {
+                log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 
                 dns_scope_process_query(scope, s, s->read_packet);
-
-                /* If no reply packet was set, we free the stream */
-                if (s->write_packet)
-                        return 0;
         } else
-                log_debug("Invalid LLMNR TCP packet.");
+                log_debug("Invalid LLMNR TCP packet, ignoring.");
 
-        dns_stream_free(s);
+        dns_stream_unref(s);
         return 0;
 }
 

src/resolve/resolved-manager.c

@@ -23,6 +23,7 @@
 
 #include "af-list.h"
 #include "alloc-util.h"
+#include "dirent-util.h"
 #include "dns-domain.h"
 #include "fd-util.h"
 #include "fileio-label.h"
@@ -35,6 +36,7 @@
 #include "random-util.h"
 #include "resolved-bus.h"
 #include "resolved-conf.h"
+#include "resolved-dns-stub.h"
 #include "resolved-etc-hosts.h"
 #include "resolved-llmnr.h"
 #include "resolved-manager.h"
@@ -78,11 +80,11 @@ static int manager_process_link(sd_netlink *rtnl, sd_netlink_message *mm, void *
                                 goto fail;
                 }
 
-                r = link_update_rtnl(l, mm);
+                r = link_process_rtnl(l, mm);
                 if (r < 0)
                         goto fail;
 
-                r = link_update_monitor(l);
+                r = link_update(l);
                 if (r < 0)
                         goto fail;
 
@@ -95,6 +97,7 @@ static int manager_process_link(sd_netlink *rtnl, sd_netlink_message *mm, void *
         case RTM_DELLINK:
                 if (l) {
                         log_debug("Removing link %i/%s", l->ifindex, l->name);
+                        link_remove_user(l);
                         link_free(l);
                 }
 
@@ -279,7 +282,7 @@ static int on_network_event(sd_event_source *s, int fd, uint32_t revents, void *
         sd_network_monitor_flush(m->network_monitor);
 
         HASHMAP_FOREACH(l, m->links, i) {
-                r = link_update_monitor(l);
+                r = link_update(l);
                 if (r < 0)
                         log_warning_errno(r, "Failed to update monitor information for %i: %m", l->ifindex);
         }
@@ -491,6 +494,7 @@ int manager_new(Manager **ret) {
         m->llmnr_ipv4_udp_fd = m->llmnr_ipv6_udp_fd = -1;
         m->llmnr_ipv4_tcp_fd = m->llmnr_ipv6_tcp_fd = -1;
         m->mdns_ipv4_fd = m->mdns_ipv6_fd = -1;
+        m->dns_stub_udp_fd = m->dns_stub_tcp_fd = -1;
         m->hostname_fd = -1;
 
         m->llmnr_support = RESOLVE_SUPPORT_YES;
@@ -540,6 +544,8 @@ int manager_new(Manager **ret) {
         (void) sd_event_add_signal(m->event, &m->sigusr1_event_source, SIGUSR1, manager_sigusr1, m);
         (void) sd_event_add_signal(m->event, &m->sigusr2_event_source, SIGUSR2, manager_sigusr2, m);
 
+        manager_cleanup_saved_user(m);
+
         *ret = m;
         m = NULL;
 
@@ -551,6 +557,10 @@ int manager_start(Manager *m) {
 
         assert(m);
 
+        r = manager_dns_stub_start(m);
+        if (r < 0)
+                return r;
+
         r = manager_llmnr_start(m);
         if (r < 0)
                 return r;
@@ -580,6 +590,11 @@ Manager *manager_free(Manager *m) {
 
         dns_scope_free(m->unicast_scope);
 
+        /* At this point only orphaned streams should remain. All others should have been freed already by their
+         * owners */
+        while (m->dns_streams)
+                dns_stream_unref(m->dns_streams);
+
         hashmap_free(m->links);
         hashmap_free(m->dns_transactions);
 
@@ -591,6 +606,7 @@ Manager *manager_free(Manager *m) {
 
         manager_llmnr_stop(m);
         manager_mdns_stop(m);
+        manager_dns_stub_stop(m);
 
         sd_bus_slot_unref(m->prepare_for_sleep_slot);
         sd_event_source_unref(m->bus_retry_event_source);
@@ -805,7 +821,14 @@ int manager_write(Manager *m, int fd, DnsPacket *p) {
         return 0;
 }
 
-static int manager_ipv4_send(Manager *m, int fd, int ifindex, const struct in_addr *addr, uint16_t port, DnsPacket *p) {
+static int manager_ipv4_send(
+                Manager *m,
+                int fd,
+                int ifindex,
+                const struct in_addr *destination,
+                uint16_t port,
+                const struct in_addr *source,
+                DnsPacket *p) {
         union sockaddr_union sa = {
                 .in.sin_family = AF_INET,
         };
@@ -818,14 +841,14 @@ static int manager_ipv4_send(Manager *m, int fd, int ifindex, const struct in_ad
 
         assert(m);
         assert(fd >= 0);
-        assert(addr);
+        assert(destination);
         assert(port > 0);
         assert(p);
 
         iov.iov_base = DNS_PACKET_DATA(p);
         iov.iov_len = p->size;
 
-        sa.in.sin_addr = *addr;
+        sa.in.sin_addr = *destination;
         sa.in.sin_port = htobe16(port),
 
         mh.msg_iov = &iov;
@@ -849,12 +872,23 @@ static int manager_ipv4_send(Manager *m, int fd, int ifindex, const struct in_ad
 
                 pi = (struct in_pktinfo*) CMSG_DATA(cmsg);
                 pi->ipi_ifindex = ifindex;
+
+                if (source)
+                        pi->ipi_spec_dst = *source;
         }
 
         return sendmsg_loop(fd, &mh, 0);
 }
 
-static int manager_ipv6_send(Manager *m, int fd, int ifindex, const struct in6_addr *addr, uint16_t port, DnsPacket *p) {
+static int manager_ipv6_send(
+                Manager *m,
+                int fd,
+                int ifindex,
+                const struct in6_addr *destination,
+                uint16_t port,
+                const struct in6_addr *source,
+                DnsPacket *p) {
+
         union sockaddr_union sa = {
                 .in6.sin6_family = AF_INET6,
         };
@@ -867,14 +901,14 @@ static int manager_ipv6_send(Manager *m, int fd, int ifindex, const struct in6_a
 
         assert(m);
         assert(fd >= 0);
-        assert(addr);
+        assert(destination);
         assert(port > 0);
         assert(p);
 
         iov.iov_base = DNS_PACKET_DATA(p);
         iov.iov_len = p->size;
 
-        sa.in6.sin6_addr = *addr;
+        sa.in6.sin6_addr = *destination;
         sa.in6.sin6_port = htobe16(port),
         sa.in6.sin6_scope_id = ifindex;
 
@@ -899,24 +933,36 @@ static int manager_ipv6_send(Manager *m, int fd, int ifindex, const struct in6_a
 
                 pi = (struct in6_pktinfo*) CMSG_DATA(cmsg);
                 pi->ipi6_ifindex = ifindex;
+
+                if (source)
+                        pi->ipi6_addr = *source;
         }
 
         return sendmsg_loop(fd, &mh, 0);
 }
 
-int manager_send(Manager *m, int fd, int ifindex, int family, const union in_addr_union *addr, uint16_t port, DnsPacket *p) {
+int manager_send(
+                Manager *m,
+                int fd,
+                int ifindex,
+                int family,
+                const union in_addr_union *destination,
+                uint16_t port,
+                const union in_addr_union *source,
+                DnsPacket *p) {
+
         assert(m);
         assert(fd >= 0);
-        assert(addr);
+        assert(destination);
         assert(port > 0);
         assert(p);
 
         log_debug("Sending %s packet with id %" PRIu16 " on interface %i/%s.", DNS_PACKET_QR(p) ? "response" : "query", DNS_PACKET_ID(p), ifindex, af_to_name(family));
 
         if (family == AF_INET)
-                return manager_ipv4_send(m, fd, ifindex, &addr->in, port, p);
+                return manager_ipv4_send(m, fd, ifindex, &destination->in, port, &source->in, p);
         if (family == AF_INET6)
-                return manager_ipv6_send(m, fd, ifindex, &addr->in6, port, p);
+                return manager_ipv6_send(m, fd, ifindex, &destination->in6, port, &source->in6, p);
 
         return -EAFNOSUPPORT;
 }
@@ -1153,7 +1199,7 @@ int manager_compile_dns_servers(Manager *m, OrderedSet **dns) {
         return 0;
 }
 
-int manager_compile_search_domains(Manager *m, OrderedSet **domains) {
+int manager_compile_search_domains(Manager *m, OrderedSet **domains, int filter_route) {
         DnsSearchDomain *d;
         Iterator i;
         Link *l;
@@ -1167,6 +1213,11 @@ int manager_compile_search_domains(Manager *m, OrderedSet **domains) {
                 return r;
 
         LIST_FOREACH(domains, d, m->search_domains) {
+
+                if (filter_route >= 0 &&
+                    d->route_only != !!filter_route)
+                        continue;
+
                 r = ordered_set_put(*domains, d->name);
                 if (r == -EEXIST)
                         continue;
@@ -1177,6 +1228,11 @@ int manager_compile_search_domains(Manager *m, OrderedSet **domains) {
         HASHMAP_FOREACH(l, m->links, i) {
 
                 LIST_FOREACH(domains, d, l->search_domains) {
+
+                        if (filter_route >= 0 &&
+                            d->route_only != !!filter_route)
+                                continue;
+
                         r = ordered_set_put(*domains, d->name);
                         if (r == -EEXIST)
                                 continue;
@@ -1259,3 +1315,58 @@ void manager_flush_caches(Manager *m) {
 
         log_info("Flushed all caches.");
 }
+
+void manager_cleanup_saved_user(Manager *m) {
+        _cleanup_closedir_ DIR *d = NULL;
+        struct dirent *de;
+        int r;
+
+        assert(m);
+
+        /* Clean up all saved per-link files in /run/systemd/resolve/netif/ that don't have a matching interface
+         * anymore. These files are created to persist settings pushed in by the user via the bus, so that resolved can
+         * be restarted without losing this data. */
+
+        d = opendir("/run/systemd/resolve/netif/");
+        if (!d) {
+                if (errno == ENOENT)
+                        return;
+
+                log_warning_errno(errno, "Failed to open interface directory: %m");
+                return;
+        }
+
+        FOREACH_DIRENT_ALL(de, d, log_error_errno(errno, "Failed to read interface directory: %m")) {
+                _cleanup_free_ char *p = NULL;
+                int ifindex;
+                Link *l;
+
+                if (!IN_SET(de->d_type, DT_UNKNOWN, DT_REG))
+                        continue;
+
+                if (STR_IN_SET(de->d_name, ".", ".."))
+                        continue;
+
+                r = parse_ifindex(de->d_name, &ifindex);
+                if (r < 0) /* Probably some temporary file from a previous run. Delete it */
+                        goto rm;
+
+                l = hashmap_get(m->links, INT_TO_PTR(ifindex));
+                if (!l) /* link vanished */
+                        goto rm;
+
+                if (l->is_managed) /* now managed by networkd, hence the bus settings are useless */
+                        goto rm;
+
+                continue;
+
+        rm:
+                p = strappend("/run/systemd/resolve/netif/", de->d_name);
+                if (!p) {
+                        log_oom();
+                        return;
+                }
+
+                (void) unlink(p);
+        }
+}

src/resolve/resolved-manager.h

@@ -72,7 +72,6 @@ struct Manager {
 
         LIST_HEAD(DnsSearchDomain, search_domains);
         unsigned n_search_domains;
-        bool permit_domain_search;
 
         bool need_builtin_fallbacks:1;
 
@@ -129,6 +128,13 @@ struct Manager {
         Set* etc_hosts_by_address;
         Hashmap* etc_hosts_by_name;
         usec_t etc_hosts_last, etc_hosts_mtime;
+
+        /* Local DNS stub on 127.0.0.53:53 */
+        int dns_stub_udp_fd;
+        int dns_stub_tcp_fd;
+
+        sd_event_source *dns_stub_udp_event_source;
+        sd_event_source *dns_stub_tcp_event_source;
 };
 
 /* Manager */
@@ -141,7 +147,7 @@ int manager_start(Manager *m);
 uint32_t manager_find_mtu(Manager *m);
 
 int manager_write(Manager *m, int fd, DnsPacket *p);
-int manager_send(Manager *m, int fd, int ifindex, int family, const union in_addr_union *addr, uint16_t port, DnsPacket *p);
+int manager_send(Manager *m, int fd, int ifindex, int family, const union in_addr_union *destination, uint16_t port, const union in_addr_union *source, DnsPacket *p);
 int manager_recv(Manager *m, int fd, DnsProtocol protocol, DnsPacket **ret);
 
 int manager_find_ifindex(Manager *m, int family, const union in_addr_union *in_addr);
@@ -162,7 +168,7 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);
 int manager_is_own_hostname(Manager *m, const char *name);
 
 int manager_compile_dns_servers(Manager *m, OrderedSet **servers);
-int manager_compile_search_domains(Manager *m, OrderedSet **domains);
+int manager_compile_search_domains(Manager *m, OrderedSet **domains, int filter_route);
 
 DnssecMode manager_get_dnssec_mode(Manager *m);
 bool manager_dnssec_supported(Manager *m);
@@ -172,3 +178,5 @@ void manager_dnssec_verdict(Manager *m, DnssecVerdict verdict, const DnsResource
 bool manager_routable(Manager *m, int family);
 
 void manager_flush_caches(Manager *m);
+
+void manager_cleanup_saved_user(Manager *m);

src/resolve/resolved-resolv-conf.c

@@ -194,10 +194,13 @@ static int write_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *doma
         Iterator i;
 
         fputs("# This file is managed by systemd-resolved(8). Do not edit.\n#\n"
-              "# Third party programs must not access this file directly, but\n"
-              "# only through the symlink at /etc/resolv.conf. To manage\n"
-              "# resolv.conf(5) in a different way, replace the symlink by a\n"
-              "# static file or a different symlink.\n\n", f);
+              "# This is a dynamic resolv.conf file for connecting local clients directly to\n"
+              "# all known DNS servers.\n#\n"
+              "# Third party programs must not access this file directly, but only through the\n"
+              "# symlink at /etc/resolv.conf. To manage resolv.conf(5) in a different way,\n"
+              "# replace this symlink by a static file or a different symlink.\n#\n"
+              "# See systemd-resolved.service(8) for details about the supported modes of\n"
+              "# operation for /etc/resolv.conf.\n\n", f);
 
         if (ordered_set_isempty(dns))
                 fputs("# No DNS servers known.\n", f);
@@ -232,7 +235,7 @@ int manager_write_resolv_conf(Manager *m) {
         if (r < 0)
                 return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
 
-        r = manager_compile_search_domains(m, &domains);
+        r = manager_compile_search_domains(m, &domains, false);
         if (r < 0)
                 return log_warning_errno(r, "Failed to compile list of search domains: %m");
 

src/resolve/resolved.c

@@ -67,7 +67,11 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
-        r = drop_privileges(uid, gid, 0);
+        /* Drop privileges, but keep three caps. Note that we drop those too, later on (see below) */
+        r = drop_privileges(uid, gid,
+                            (UINT64_C(1) << CAP_NET_RAW)|          /* needed for SO_BINDTODEVICE */
+                            (UINT64_C(1) << CAP_NET_BIND_SERVICE)| /* needed to bind on port 53 */
+                            (UINT64_C(1) << CAP_SETPCAP)           /* needed in order to drop the caps later */);
         if (r < 0)
                 goto finish;
 
@@ -88,6 +92,13 @@ int main(int argc, char *argv[]) {
         /* Write finish default resolv.conf to avoid a dangling symlink */
         (void) manager_write_resolv_conf(m);
 
+        /* Let's drop the remaining caps now */
+        r = capability_bounding_set_drop(0, true);
+        if (r < 0) {
+                log_error_errno(r, "Failed to drop remaining caps: %m");
+                goto finish;
+        }
+
         sd_notify(false,
                   "READY=1\n"
                   "STATUS=Processing requests...");

src/resolve/test-dns-packet.c

@@ -33,6 +33,19 @@
 
 #define HASH_KEY SD_ID128_MAKE(d3,1e,48,90,4b,fa,4c,fe,af,9d,d5,a1,d7,2e,8a,b1)
 
+static void verify_rr_copy(DnsResourceRecord *rr) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *copy = NULL;
+        const char *a, *b;
+
+        assert_se(copy = dns_resource_record_copy(rr));
+        assert_se(dns_resource_record_equal(copy, rr) > 0);
+
+        assert_se(a = dns_resource_record_to_string(rr));
+        assert_se(b = dns_resource_record_to_string(copy));
+
+        assert_se(streq(a, b));
+}
+
 static uint64_t hash(DnsResourceRecord *rr) {
         struct siphash state;
 
@@ -66,6 +79,8 @@ static void test_packet_from_file(const char* filename, bool canonical) {
                 assert_se(dns_packet_append_blob(p, data + offset + 8, packet_size, NULL) >= 0);
                 assert_se(dns_packet_read_rr(p, &rr, NULL, NULL) >= 0);
 
+                verify_rr_copy(rr);
+
                 s = dns_resource_record_to_string(rr);
                 assert_se(s);
                 puts(s);
@@ -78,6 +93,8 @@ static void test_packet_from_file(const char* filename, bool canonical) {
                 assert_se(dns_packet_append_blob(p2, rr->wire_format, rr->wire_format_size, NULL) >= 0);
                 assert_se(dns_packet_read_rr(p2, &rr2, NULL, NULL) >= 0);
 
+                verify_rr_copy(rr);
+
                 s2 = dns_resource_record_to_string(rr);
                 assert_se(s2);
                 assert_se(streq(s, s2));

src/shared/bus-util.c

@@ -1048,7 +1048,7 @@ static int map_basic(sd_bus *bus, const char *member, sd_bus_message *m, sd_bus_
 
         case SD_BUS_TYPE_BOOLEAN: {
                 unsigned b;
-                bool *p = userdata;
+                int *p = userdata;
 
                 r = sd_bus_message_read_basic(m, type, &b);
                 if (r < 0)

src/timedate/timedatectl.c

@@ -57,11 +57,11 @@ typedef struct StatusInfo {
         char *timezone;
 
         usec_t rtc_time;
-        bool rtc_local;
+        int rtc_local;
 
-        bool ntp_enabled;
-        bool ntp_capable;
-        bool ntp_synced;
+        int ntp_enabled;
+        int ntp_capable;
+        int ntp_synced;
 } StatusInfo;
 
 static void status_info_clear(StatusInfo *info) {

src/tmpfiles/tmpfiles.c

@@ -2178,7 +2178,7 @@ static int read_config_file(const char *fn, bool ignore_enoent) {
         Iterator iterator;
         unsigned v = 0;
         Item *i;
-        int r;
+        int r = 0;
 
         assert(fn);
 

tmpfiles.d/etc.conf.m4

@@ -14,7 +14,7 @@ m4_ifdef(`HAVE_SMACK_RUN_LABEL',
 t /etc/mtab - - - - security.SMACK64=_
 )m4_dnl
 m4_ifdef(`ENABLE_RESOLVED',
-L! /etc/resolv.conf - - - - ../run/systemd/resolve/resolv.conf
+L! /etc/resolv.conf - - - - ../usr/lib/systemd/resolv.conf
 )m4_dnl
 C /etc/nsswitch.conf - - - -
 m4_ifdef(`HAVE_PAM',

units/systemd-resolved.service.m4.in

@@ -23,7 +23,7 @@ Type=notify
 Restart=always
 RestartSec=0
 ExecStart=@rootlibexecdir@/systemd-resolved
-CapabilityBoundingSet=CAP_SETUID CAP_SETGID CAP_SETPCAP CAP_CHOWN CAP_DAC_OVERRIDE CAP_FOWNER
+CapabilityBoundingSet=CAP_SETUID CAP_SETGID CAP_SETPCAP CAP_CHOWN CAP_DAC_OVERRIDE CAP_FOWNER CAP_NET_RAW CAP_NET_BIND_SERVICE
 ProtectSystem=full
 ProtectHome=yes
 WatchdogSec=3min