resolved: when resolving an address PTR record via llmnr, make a tcp connection by default

9 files changed, 332 insertions, 132 deletions

diff --git a/src/resolve/resolved-dns-domain.c b/src/resolve/resolved-dns-domain.c
index eea73f6d54..f3e7df7a1e 100644
--- a/src/resolve/resolved-dns-domain.c
+++ b/src/resolve/resolved-dns-domain.c
@@ -360,6 +360,93 @@ int dns_name_reverse(int family, const union in_addr_union *a, char **ret) {
         return 0;
 }
 
+int dns_name_address(const char *p, int *family, union in_addr_union *address) {
+        int r;
+
+        assert(p);
+        assert(family);
+        assert(address);
+
+        r = dns_name_endswith(p, "in-addr.arpa");
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                uint8_t a[4];
+                unsigned i;
+
+                for (i = 0; i < ELEMENTSOF(a); i++) {
+                        char label[DNS_LABEL_MAX+1];
+
+                        r = dns_label_unescape(&p, label, sizeof(label));
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                return -EINVAL;
+                        if (r > 3)
+                                return -EINVAL;
+
+                        r = safe_atou8(label, &a[i]);
+                        if (r < 0)
+                                return r;
+                }
+
+                r = dns_name_equal(p, "in-addr.arpa");
+                if (r <= 0)
+                        return r;
+
+                *family = AF_INET;
+                address->in.s_addr = htobe32(((uint32_t) a[3] << 24) |
+                                             ((uint32_t) a[2] << 16) |
+                                             ((uint32_t) a[1] << 8) |
+                                              (uint32_t) a[0]);
+
+                return 1;
+        }
+
+        r = dns_name_endswith(p, "ip6.arpa");
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                struct in6_addr a;
+                unsigned i;
+
+                for (i = 0; i < ELEMENTSOF(a.s6_addr); i++) {
+                        char label[DNS_LABEL_MAX+1];
+                        int x, y;
+
+                        r = dns_label_unescape(&p, label, sizeof(label));
+                        if (r <= 0)
+                                return r;
+                        if (r != 1)
+                                return -EINVAL;
+                        x = unhexchar(label[0]);
+                        if (x < 0)
+                                return -EINVAL;
+
+                        r = dns_label_unescape(&p, label, sizeof(label));
+                        if (r <= 0)
+                                return r;
+                        if (r != 1)
+                                return -EINVAL;
+                        y = unhexchar(label[0]);
+                        if (y < 0)
+                                return -EINVAL;
+
+                        a.s6_addr[ELEMENTSOF(a.s6_addr) - i - 1] = (uint8_t) y << 4 | (uint8_t) x;
+                }
+
+                r = dns_name_equal(p, "ip6.arpa");
+                if (r <= 0)
+                        return r;
+
+                *family = AF_INET6;
+                address->in6 = a;
+                return 1;
+        }
+
+        return 0;
+}
+
 int dns_name_root(const char *name) {
         char label[DNS_LABEL_MAX+1];
         int r;
@@ -382,7 +469,6 @@ int dns_name_single_label(const char *name) {
         r = dns_label_unescape(&name, label, sizeof(label));
         if (r < 0)
                 return r;
-
         if (r == 0)
                 return 0;
 
diff --git a/src/resolve/resolved-dns-domain.h b/src/resolve/resolved-dns-domain.h
index 809c4daacc..16372fd940 100644
--- a/src/resolve/resolved-dns-domain.h
+++ b/src/resolve/resolved-dns-domain.h
@@ -39,6 +39,7 @@ int dns_name_equal(const char *x, const char *y);
 int dns_name_endswith(const char *name, const char *suffix);
 
 int dns_name_reverse(int family, const union in_addr_union *a, char **ret);
+int dns_name_address(const char *p, int *family, union in_addr_union *a);
 
 int dns_name_root(const char *name);
 int dns_name_single_label(const char *name);
diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c
index 32448c5822..42f4f23cb9 100644
--- a/src/resolve/resolved-dns-query.c
+++ b/src/resolve/resolved-dns-query.c
@@ -165,7 +165,14 @@ static int on_stream_complete(DnsStream *s, int error) {
                 return 0;
         }
 
+        t->block_gc++;
         dns_query_transaction_process_reply(t, p);
+        t->block_gc--;
+
+        /* If the response wasn't useful, then complete the transition now */
+        if (t->state == DNS_QUERY_PENDING)
+                dns_query_transaction_complete(t, DNS_QUERY_INVALID_REPLY);
+
         return 0;
 }
 
@@ -181,10 +188,25 @@ static int dns_query_transaction_open_tcp(DnsQueryTransaction *t) {
         if (t->scope->protocol == DNS_PROTOCOL_DNS)
                 fd = dns_scope_tcp_socket(t->scope, AF_UNSPEC, NULL, 53);
         else if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
-                if (!t->received)
-                        return -EINVAL;
 
-                fd = dns_scope_tcp_socket(t->scope, t->received->family, &t->received->sender, t->received->sender_port);
+                /* When we already received a query to this (but it was truncated), send to its sender address */
+                if (t->received)
+                        fd = dns_scope_tcp_socket(t->scope, t->received->family, &t->received->sender, t->received->sender_port);
+                else {
+                        union in_addr_union address;
+                        int family;
+
+                        /* Otherwise, try to talk to the owner of a
+                         * the IP address, in case this is a reverse
+                         * PTR lookup */
+                        r = dns_question_extract_reverse_address(t->question, &family, &address);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                return -EINVAL;
+
+                        fd = dns_scope_tcp_socket(t->scope, family, &address, 5355);
+                }
         } else
                 return -EAFNOSUPPORT;
 
@@ -205,6 +227,13 @@ static int dns_query_transaction_open_tcp(DnsQueryTransaction *t) {
 
         t->received = dns_packet_unref(t->received);
         t->stream->complete = on_stream_complete;
+        t->stream->transaction = t;
+
+        /* The interface index is difficult to determine if we are
+         * connecting to the local host, hence fill this in right away
+         * instead of determining it from the socket */
+        if (t->scope->link)
+                t->stream->ifindex = t->scope->link->ifindex;
 
         return 0;
 }
@@ -416,10 +445,19 @@ static int dns_query_transaction_go(DnsQueryTransaction *t) {
         if (r < 0)
                 return r;
 
-        /* Try via UDP, and if that fails due to large size try via TCP */
-        r = dns_scope_send(t->scope, t->sent);
-        if (r == -EMSGSIZE)
+        if (t->scope->protocol == DNS_PROTOCOL_LLMNR &&
+            (dns_question_endswith(t->question, "in-addr.arpa") > 0 ||
+             dns_question_endswith(t->question, "ip6.arpa") > 0)) {
+
+                /* RFC 4795, Section 2.4. says reverse lookups shall
+                 * always be made via TCP on LLMNR */
                 r = dns_query_transaction_open_tcp(t);
+        } else {
+                /* Try via UDP, and if that fails due to large size try via TCP */
+                r = dns_scope_send(t->scope, t->sent);
+                if (r == -EMSGSIZE)
+                        r = dns_query_transaction_open_tcp(t);
+        }
         if (r == -ESRCH) {
                 /* No servers to send this to? */
                 dns_query_transaction_complete(t, DNS_QUERY_NO_SERVERS);
diff --git a/src/resolve/resolved-dns-question.c b/src/resolve/resolved-dns-question.c
index 056bd6eb64..66017e82cd 100644
--- a/src/resolve/resolved-dns-question.c
+++ b/src/resolve/resolved-dns-question.c
@@ -235,3 +235,38 @@ int dns_question_cname_redirect(DnsQuestion *q, const char *name, DnsQuestion **
 
         return 1;
 }
+
+int dns_question_endswith(DnsQuestion *q, const char *suffix) {
+        unsigned i;
+
+        assert(q);
+        assert(suffix);
+
+        for (i = 0; i < q->n_keys; i++) {
+                int k;
+
+                k = dns_name_endswith(DNS_RESOURCE_KEY_NAME(q->keys[i]), suffix);
+                if (k <= 0)
+                        return k;
+        }
+
+        return 1;
+}
+
+int dns_question_extract_reverse_address(DnsQuestion *q, int *family, union in_addr_union *address) {
+        unsigned i;
+
+        assert(q);
+        assert(family);
+        assert(address);
+
+        for (i = 0; i < q->n_keys; i++) {
+                int k;
+
+                k = dns_name_address(DNS_RESOURCE_KEY_NAME(q->keys[i]), family, address);
+                if (k != 0)
+                        return k;
+        }
+
+        return 0;
+}
diff --git a/src/resolve/resolved-dns-question.h b/src/resolve/resolved-dns-question.h
index 7da627fdca..4ba2fe9f0e 100644
--- a/src/resolve/resolved-dns-question.h
+++ b/src/resolve/resolved-dns-question.h
@@ -46,4 +46,7 @@ int dns_question_is_superset(DnsQuestion *q, DnsQuestion *other);
 
 int dns_question_cname_redirect(DnsQuestion *q, const char *name, DnsQuestion **ret);
 
+int dns_question_endswith(DnsQuestion *q, const char *suffix);
+int dns_question_extract_reverse_address(DnsQuestion *q, int *family, union in_addr_union *address);
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsQuestion*, dns_question_unref);
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index 9a636b179c..5d2edbae47 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -312,8 +312,8 @@ DnsScopeMatch dns_scope_good_domain(DnsScope *s, const char *domain) {
         }
 
         if (s->protocol == DNS_PROTOCOL_LLMNR) {
-                if (dns_name_endswith(domain, "254.169.in-addr.arpa") > 0 ||
-                    dns_name_endswith(domain, "0.8.e.f.ip6.arpa") > 0 ||
+                if (dns_name_endswith(domain, "in-addr.arpa") > 0 ||
+                    dns_name_endswith(domain, "ip6.arpa") > 0 ||
                     dns_name_single_label(domain) > 0)
                         return DNS_SCOPE_MAYBE;
 
diff --git a/src/resolve/resolved-dns-stream.c b/src/resolve/resolved-dns-stream.c
index 24a2288428..47130c4231 100644
--- a/src/resolve/resolved-dns-stream.c
+++ b/src/resolve/resolved-dns-stream.c
@@ -48,7 +48,7 @@ static int dns_stream_update_io(DnsStream *s) {
         return sd_event_source_set_io_events(s->io_event_source, f);
 }
 
-static int stream_complete(DnsStream *s, int error) {
+static int dns_stream_complete(DnsStream *s, int error) {
         assert(s);
 
         dns_stream_stop(s);
@@ -61,12 +61,136 @@ static int stream_complete(DnsStream *s, int error) {
         return 0;
 }
 
+static int dns_stream_identify(DnsStream *s) {
+        union {
+                struct cmsghdr header; /* For alignment */
+                uint8_t buffer[CMSG_SPACE(MAX(sizeof(struct in_pktinfo), sizeof(struct in6_pktinfo)))
+                               + EXTRA_CMSG_SPACE /* kernel appears to require extra space */];
+        } control;
+        struct msghdr mh = {};
+        struct cmsghdr *cmsg;
+        socklen_t sl;
+        int r;
+
+        assert(s);
+
+        if (s->identified)
+                return 0;
+
+        /* Query the local side */
+        s->local_salen = sizeof(s->local);
+        r = getsockname(s->fd, &s->local.sa, &s->local_salen);
+        if (r < 0)
+                return -errno;
+        if (s->local.sa.sa_family == AF_INET6 && s->ifindex <= 0)
+                s->ifindex = s->local.in6.sin6_scope_id;
+
+        /* Query the remote side */
+        s->peer_salen = sizeof(s->peer);
+        r = getpeername(s->fd, &s->peer.sa, &s->peer_salen);
+        if (r < 0)
+                return -errno;
+        if (s->peer.sa.sa_family == AF_INET6 && s->ifindex <= 0)
+                s->ifindex = s->peer.in6.sin6_scope_id;
+
+        /* Check consistency */
+        assert(s->peer.sa.sa_family == s->local.sa.sa_family);
+        assert(IN_SET(s->peer.sa.sa_family, AF_INET, AF_INET6));
+
+        /* Query connection meta information */
+        sl = sizeof(control);
+        if (s->peer.sa.sa_family == AF_INET) {
+                r = getsockopt(s->fd, IPPROTO_IP, IP_PKTOPTIONS, &control, &sl);
+                if (r < 0)
+                        return -errno;
+        } else if (s->peer.sa.sa_family == AF_INET6) {
+
+                r = getsockopt(s->fd, IPPROTO_IPV6, IPV6_2292PKTOPTIONS, &control, &sl);
+                if (r < 0)
+                        return -errno;
+        } else
+                return -EAFNOSUPPORT;
+
+        mh.msg_control = &control;
+        mh.msg_controllen = sl;
+        for (cmsg = CMSG_FIRSTHDR(&mh); cmsg; cmsg = CMSG_NXTHDR(&mh, cmsg)) {
+
+                if (cmsg->cmsg_level == IPPROTO_IPV6) {
+                        assert(s->peer.sa.sa_family == AF_INET6);
+
+                        switch (cmsg->cmsg_type) {
+
+                        case IPV6_PKTINFO: {
+                                struct in6_pktinfo *i = (struct in6_pktinfo*) CMSG_DATA(cmsg);
+
+                                if (s->ifindex <= 0)
+                                        s->ifindex = i->ipi6_ifindex;
+                                break;
+                        }
+
+                        case IPV6_HOPLIMIT:
+                                s->ttl = *(int *) CMSG_DATA(cmsg);
+                                break;
+                        }
+
+                } else if (cmsg->cmsg_level == IPPROTO_IP) {
+                        assert(s->peer.sa.sa_family == AF_INET);
+
+                        switch (cmsg->cmsg_type) {
+
+                        case IP_PKTINFO: {
+                                struct in_pktinfo *i = (struct in_pktinfo*) CMSG_DATA(cmsg);
+
+                                if (s->ifindex <= 0)
+                                        s->ifindex = i->ipi_ifindex;
+                                break;
+                        }
+
+                        case IP_TTL:
+                                s->ttl = *(int *) CMSG_DATA(cmsg);
+                                break;
+                        }
+                }
+        }
+
+        /* The Linux kernel sets the interface index to the loopback
+         * device if the connection came from the local host since it
+         * avoids the routing table in such a case. Let's unset the
+         * interface index in such a case. */
+        if (s->ifindex > 0 && manager_ifindex_is_loopback(s->manager, s->ifindex) != 0)
+                s->ifindex = 0;
+
+        /* If we don't know the interface index still, we look for the
+         * first local interface with a matching address. Yuck! */
+        if (s->ifindex <= 0)
+                s->ifindex = manager_find_ifindex(s->manager, s->local.sa.sa_family, s->local.sa.sa_family == AF_INET ? (union in_addr_union*) &s->local.in.sin_addr : (union in_addr_union*)  &s->local.in6.sin6_addr);
+
+        if (s->protocol == DNS_PROTOCOL_LLMNR && s->ifindex > 0) {
+                uint32_t ifindex = htobe32(s->ifindex);
+
+                /* Make sure all packets for this connection are sent on the same interface */
+                if (s->local.sa.sa_family == AF_INET) {
+                        r = setsockopt(s->fd, IPPROTO_IP, IP_UNICAST_IF, &ifindex, sizeof(ifindex));
+                        if (r < 0)
+                                return -errno;
+                } else if (s->local.sa.sa_family == AF_INET6) {
+                        r = setsockopt(s->fd, IPPROTO_IPV6, IPV6_UNICAST_IF, &ifindex, sizeof(ifindex));
+                        if (r < 0)
+                                return -errno;
+                }
+        }
+
+        s->identified = true;
+
+        return 0;
+}
+
 static int on_stream_timeout(sd_event_source *es, usec_t usec, void *userdata) {
         DnsStream *s = userdata;
 
         assert(s);
 
-        return stream_complete(s, ETIMEDOUT);
+        return dns_stream_complete(s, ETIMEDOUT);
 }
 
 static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *userdata) {
@@ -75,6 +199,10 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
 
         assert(s);
 
+        r = dns_stream_identify(s);
+        if (r < 0)
+                return dns_stream_complete(s, -r);
+
         if ((revents & EPOLLOUT) &&
             s->write_packet &&
             s->n_written < sizeof(s->write_size) + s->write_packet->size) {
@@ -92,7 +220,7 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                 ss = writev(fd, iov, 2);
                 if (ss < 0) {
                         if (errno != EINTR && errno != EAGAIN)
-                                return stream_complete(s, errno);
+                                return dns_stream_complete(s, errno);
                 } else
                         s->n_written += ss;
 
@@ -100,7 +228,7 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                 if (s->n_written >= sizeof(s->write_size) + s->write_packet->size) {
                         r = dns_stream_update_io(s);
                         if (r < 0)
-                                return stream_complete(s, -r);
+                                return dns_stream_complete(s, -r);
                 }
         }
 
@@ -114,9 +242,9 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                         ss = read(fd, (uint8_t*) &s->read_size + s->n_read, sizeof(s->read_size) - s->n_read);
                         if (ss < 0) {
                                 if (errno != EINTR && errno != EAGAIN)
-                                        return stream_complete(s, errno);
+                                        return dns_stream_complete(s, errno);
                         } else if (ss == 0)
-                                return stream_complete(s, ECONNRESET);
+                                return dns_stream_complete(s, ECONNRESET);
                         else
                                 s->n_read += ss;
                 }
@@ -124,7 +252,7 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                 if (s->n_read >= sizeof(s->read_size)) {
 
                         if (be16toh(s->read_size) < DNS_PACKET_HEADER_SIZE)
-                                return stream_complete(s, EBADMSG);
+                                return dns_stream_complete(s, EBADMSG);
 
                         if (s->n_read < sizeof(s->read_size) + be16toh(s->read_size)) {
                                 ssize_t ss;
@@ -132,7 +260,7 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                                 if (!s->read_packet) {
                                         r = dns_packet_new(&s->read_packet, s->protocol, be16toh(s->read_size));
                                         if (r < 0)
-                                                return stream_complete(s, -r);
+                                                return dns_stream_complete(s, -r);
 
                                         s->read_packet->size = be16toh(s->read_size);
                                         s->read_packet->ipproto = IPPROTO_TCP;
@@ -164,9 +292,9 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                                           sizeof(s->read_size) + be16toh(s->read_size) - s->n_read);
                                 if (ss < 0) {
                                         if (errno != EINTR && errno != EAGAIN)
-                                                return stream_complete(s, errno);
+                                                return dns_stream_complete(s, errno);
                                 } else if (ss == 0)
-                                        return stream_complete(s, ECONNRESET);
+                                        return dns_stream_complete(s, ECONNRESET);
                                 else
                                         s->n_read += ss;
                         }
@@ -175,7 +303,7 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                         if (s->n_read >= sizeof(s->read_size) + be16toh(s->read_size)) {
                                 r = dns_stream_update_io(s);
                                 if (r < 0)
-                                        return stream_complete(s, -r);
+                                        return dns_stream_complete(s, -r);
 
                                 /* If there's a packet handler
                                  * installed, call that. Note that
@@ -188,7 +316,7 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
 
         if ((s->write_packet && s->n_written >= sizeof(s->write_size) + s->write_packet->size) &&
             (s->read_packet && s->n_read >= sizeof(s->read_size) + s->read_packet->size))
-                return stream_complete(s, 0);
+                return dns_stream_complete(s, 0);
 
         return 0;
 }
@@ -216,15 +344,7 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(DnsStream*, dns_stream_free);
 
 int dns_stream_new(Manager *m, DnsStream **ret, DnsProtocol protocol, int fd) {
         static const int one = 1;
-        union {
-                struct cmsghdr header; /* For alignment */
-                uint8_t buffer[CMSG_SPACE(MAX(sizeof(struct in_pktinfo), sizeof(struct in6_pktinfo)))
-                               + EXTRA_CMSG_SPACE /* kernel appears to require extra space */];
-        } control;
-        struct msghdr mh = {};
-        struct cmsghdr *cmsg;
         _cleanup_(dns_stream_freep) DnsStream *s = NULL;
-        socklen_t sl;
         int r;
 
         assert(m);
@@ -240,113 +360,10 @@ int dns_stream_new(Manager *m, DnsStream **ret, DnsProtocol protocol, int fd) {
         s->fd = -1;
         s->protocol = protocol;
 
-        /* Query the remote side */
-        s->peer_salen = sizeof(s->peer);
-        r = getpeername(fd, &s->peer.sa, &s->peer_salen);
-        if (r < 0)
-                return -errno;
-        if (s->peer.sa.sa_family == AF_INET6)
-                s->ifindex = s->peer.in6.sin6_scope_id;
-
-        /* Query the local side */
-        s->local_salen = sizeof(s->local);
-        r = getsockname(fd, &s->local.sa, &s->local_salen);
-        if (r < 0)
-                return -errno;
-        if (s->local.sa.sa_family == AF_INET6 && s->ifindex <= 0)
-                s->ifindex = s->local.in6.sin6_scope_id;
-
-        /* Check consistency */
-        assert(s->peer.sa.sa_family == s->local.sa.sa_family);
-        assert(IN_SET(s->peer.sa.sa_family, AF_INET, AF_INET6));
-
-        /* Query connection meta information */
-        sl = sizeof(control);
-        if (s->peer.sa.sa_family == AF_INET) {
-                r = getsockopt(fd, IPPROTO_IP, IP_PKTOPTIONS, &control, &sl);
-                if (r < 0)
-                        return -errno;
-        } else {
-                assert(s->peer.sa.sa_family == AF_INET6);
-
-                r = getsockopt(fd, IPPROTO_IPV6, IPV6_2292PKTOPTIONS, &control, &sl);
-                if (r < 0)
-                        return -errno;
-        }
-
-        mh.msg_control = &control;
-        mh.msg_controllen = sl;
-        for (cmsg = CMSG_FIRSTHDR(&mh); cmsg; cmsg = CMSG_NXTHDR(&mh, cmsg)) {
-
-                if (cmsg->cmsg_level == IPPROTO_IPV6) {
-                        assert(s->peer.sa.sa_family == AF_INET6);
-
-                        switch (cmsg->cmsg_type) {
-
-                        case IPV6_PKTINFO: {
-                                struct in6_pktinfo *i = (struct in6_pktinfo*) CMSG_DATA(cmsg);
-
-                                if (s->ifindex <= 0)
-                                        s->ifindex = i->ipi6_ifindex;
-                                break;
-                        }
-
-                        case IPV6_HOPLIMIT:
-                                s->ttl = *(int *) CMSG_DATA(cmsg);
-                                break;
-                        }
-
-                } else if (cmsg->cmsg_level == IPPROTO_IP) {
-                        assert(s->peer.sa.sa_family == AF_INET);
-
-                        switch (cmsg->cmsg_type) {
-
-                        case IP_PKTINFO: {
-                                struct in_pktinfo *i = (struct in_pktinfo*) CMSG_DATA(cmsg);
-
-                                if (s->ifindex <= 0)
-                                        s->ifindex = i->ipi_ifindex;
-                                break;
-                        }
-
-                        case IP_TTL:
-                                s->ttl = *(int *) CMSG_DATA(cmsg);
-                                break;
-                        }
-                }
-        }
-
-        /* The Linux kernel sets the interface index to the loopback
-         * device if the connection came from the local host since it
-         * avoids the routing table in such a case. Let's unset the
-         * interface index in such a case. */
-        if (s->ifindex > 0 && manager_ifindex_is_loopback(m, s->ifindex) != 0)
-                s->ifindex = 0;
-
-        /* If we don't know the interface index still, we look for the
-         * first local interface with a matching address. Yuck! */
-        if (s->ifindex <= 0)
-                s->ifindex = manager_find_ifindex(m, s->local.sa.sa_family, s->local.sa.sa_family == AF_INET ? (union in_addr_union*) &s->local.in.sin_addr : (union in_addr_union*)  &s->local.in6.sin6_addr);
-
         r = setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &one, sizeof(one));
         if (r < 0)
                 return -errno;
 
-        if (s->protocol == DNS_PROTOCOL_LLMNR && s->ifindex > 0) {
-                uint32_t ifindex = htobe32(s->ifindex);
-
-                /* Make sure all packets for this connection are sent on the same interface */
-                if (s->local.sa.sa_family == AF_INET) {
-                        r = setsockopt(fd, IPPROTO_IP, IP_UNICAST_IF, &ifindex, sizeof(ifindex));
-                        if (r < 0)
-                                return -errno;
-                } else if (s->local.sa.sa_family == AF_INET6) {
-                        r = setsockopt(fd, IPPROTO_IPV6, IPV6_UNICAST_IF, &ifindex, sizeof(ifindex));
-                        if (r < 0)
-                                return -errno;
-                }
-        }
-
         r = sd_event_add_io(m->event, &s->io_event_source, fd, EPOLLIN, on_stream_io, s);
         if (r < 0)
                 return r;
diff --git a/src/resolve/resolved-dns-stream.h b/src/resolve/resolved-dns-stream.h
index db456580cb..5509f7528b 100644
--- a/src/resolve/resolved-dns-stream.h
+++ b/src/resolve/resolved-dns-stream.h
@@ -39,6 +39,7 @@ struct DnsStream {
         socklen_t local_salen;
         int ifindex;
         uint32_t ttl;
+        bool identified;
 
         sd_event_source *io_event_source;
         sd_event_source *timeout_event_source;
diff --git a/src/resolve/test-dns-domain.c b/src/resolve/test-dns-domain.c
index bd53402be8..dfe2a44eae 100644
--- a/src/resolve/test-dns-domain.c
+++ b/src/resolve/test-dns-domain.c
@@ -159,6 +159,24 @@ static void test_dns_name_single_label(void) {
         assert_se(dns_name_single_label("xx.yy") == false);
 }
 
+static void test_dns_name_reverse_one(const char *address, const char *name) {
+        _cleanup_free_ char *p = NULL;
+        union in_addr_union a, b;
+        int familya, familyb;
+
+        assert_se(in_addr_from_string_auto(address, &familya, &a) >= 0);
+        assert_se(dns_name_reverse(familya, &a, &p) >= 0);
+        assert_se(streq(p, name));
+        assert_se(dns_name_address(p, &familyb, &b) > 0);
+        assert_se(familya == familyb);
+        assert_se(in_addr_equal(familya, &a, &b));
+}
+
+static void test_dns_name_reverse(void) {
+        test_dns_name_reverse_one("47.11.8.15", "15.8.11.47.in-addr.arpa");
+        test_dns_name_reverse_one("fe80::47", "7.4.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa");
+}
+
 int main(int argc, char *argv[]) {
 
         test_dns_label_unescape();
@@ -168,6 +186,7 @@ int main(int argc, char *argv[]) {
         test_dns_name_endswith();
         test_dns_name_root();
         test_dns_name_single_label();
+        test_dns_name_reverse();
 
         return 0;
 }