7 files changed, 26 insertions, 5 deletions

diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
index 49c36e38f3..cb713f1f85 100644
--- a/src/resolve/resolved-dns-packet.c
+++ b/src/resolve/resolved-dns-packet.c
@@ -267,7 +267,7 @@ static int dns_packet_extend(DnsPacket *p, size_t add, void **ret, size_t *start
         return 0;
 }
 
-static void dns_packet_truncate(DnsPacket *p, size_t sz) {
+void dns_packet_truncate(DnsPacket *p, size_t sz) {
         Iterator i;
         char *s;
         void *n;
diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h
index ca94a208ba..385a8af796 100644
--- a/src/resolve/resolved-dns-packet.h
+++ b/src/resolve/resolved-dns-packet.h
@@ -162,6 +162,8 @@ 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);
 int dns_packet_append_opt_rr(DnsPacket *p, uint16_t max_udp_size, size_t *start);
 
+void dns_packet_truncate(DnsPacket *p, size_t sz);
+
 int dns_packet_read(DnsPacket *p, size_t sz, const void **ret, size_t *start);
 int dns_packet_read_blob(DnsPacket *p, void *d, size_t sz, size_t *start);
 int dns_packet_read_uint8(DnsPacket *p, uint8_t *ret, size_t *start);
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index a8c0ae1569..42478e41e2 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -158,12 +158,13 @@ void dns_scope_packet_lost(DnsScope *s, usec_t usec) {
                 s->resend_timeout = MIN(s->resend_timeout * 2, MULTICAST_RESEND_TIMEOUT_MAX_USEC);
 }
 
-int dns_scope_emit(DnsScope *s, int fd, DnsPacket *p) {
+int dns_scope_emit(DnsScope *s, int fd, DnsServer *server, DnsPacket *p) {
         union in_addr_union addr;
         int ifindex = 0, r;
         int family;
         uint16_t port;
         uint32_t mtu;
+        size_t saved_size = 0;
 
         assert(s);
         assert(p);
@@ -178,9 +179,19 @@ int dns_scope_emit(DnsScope *s, int fd, DnsPacket *p) {
 
         switch (s->protocol) {
         case DNS_PROTOCOL_DNS:
+                assert(server);
+
                 if (DNS_PACKET_QDCOUNT(p) > 1)
                         return -EOPNOTSUPP;
 
+                if (server->possible_features >= DNS_SERVER_FEATURE_LEVEL_EDNS0) {
+                        r = dns_packet_append_opt_rr(p, DNS_PACKET_UNICAST_SIZE_MAX, &saved_size);
+                        if (r < 0)
+                                return r;
+
+                        DNS_PACKET_HEADER(p)->arcount = htobe16(be16toh(DNS_PACKET_HEADER(p)->arcount) + 1);
+                }
+
                 if (p->size > DNS_PACKET_UNICAST_SIZE_MAX)
                         return -EMSGSIZE;
 
@@ -191,6 +202,12 @@ int dns_scope_emit(DnsScope *s, int fd, DnsPacket *p) {
                 if (r < 0)
                         return r;
 
+                if (saved_size > 0) {
+                        dns_packet_truncate(p, saved_size);
+
+                        DNS_PACKET_HEADER(p)->arcount = htobe16(be16toh(DNS_PACKET_HEADER(p)->arcount) - 1);
+                }
+
                 break;
 
         case DNS_PROTOCOL_LLMNR:
@@ -739,7 +756,7 @@ static int on_conflict_dispatch(sd_event_source *es, usec_t usec, void *userdata
                         return 0;
                 }
 
-                r = dns_scope_emit(scope, -1, p);
+                r = dns_scope_emit(scope, -1, NULL, p);
                 if (r < 0)
                         log_debug_errno(r, "Failed to send conflict packet: %m");
         }
diff --git a/src/resolve/resolved-dns-scope.h b/src/resolve/resolved-dns-scope.h
index 7876410b7d..0480f702f8 100644
--- a/src/resolve/resolved-dns-scope.h
+++ b/src/resolve/resolved-dns-scope.h
@@ -80,7 +80,7 @@ DnsScope* dns_scope_free(DnsScope *s);
 void dns_scope_packet_received(DnsScope *s, usec_t rtt);
 void dns_scope_packet_lost(DnsScope *s, usec_t usec);
 
-int dns_scope_emit(DnsScope *s, int fd, DnsPacket *p);
+int dns_scope_emit(DnsScope *s, int fd, DnsServer *server, DnsPacket *p);
 int dns_scope_tcp_socket(DnsScope *s, int family, const union in_addr_union *address, uint16_t port, DnsServer **server);
 int dns_scope_udp_dns_socket(DnsScope *s, DnsServer **server);
 
diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c
index c5396a03c8..f8c921e4c8 100644
--- a/src/resolve/resolved-dns-server.c
+++ b/src/resolve/resolved-dns-server.c
@@ -478,5 +478,6 @@ void manager_next_dns_server(Manager *m) {
 static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVEL_MAX] = {
         [DNS_SERVER_FEATURE_LEVEL_TCP] = "TCP",
         [DNS_SERVER_FEATURE_LEVEL_UDP] = "UDP",
+        [DNS_SERVER_FEATURE_LEVEL_EDNS0] = "UDP+EDNS0",
 };
 DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel);
diff --git a/src/resolve/resolved-dns-server.h b/src/resolve/resolved-dns-server.h
index a3e8cbcc52..e9b425430f 100644
--- a/src/resolve/resolved-dns-server.h
+++ b/src/resolve/resolved-dns-server.h
@@ -34,6 +34,7 @@ typedef enum DnsServerType {
 typedef enum DnsServerFeatureLevel {
         DNS_SERVER_FEATURE_LEVEL_TCP,
         DNS_SERVER_FEATURE_LEVEL_UDP,
+        DNS_SERVER_FEATURE_LEVEL_EDNS0,
         _DNS_SERVER_FEATURE_LEVEL_MAX,
         _DNS_SERVER_FEATURE_LEVEL_INVALID = -1
 } DnsServerFeatureLevel;
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index 4398c2cb99..f81461a4fe 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -545,7 +545,7 @@ static int dns_transaction_emit(DnsTransaction *t) {
                 t->server = dns_server_ref(server);
         }
 
-        r = dns_scope_emit(t->scope, t->dns_udp_fd, t->sent);
+        r = dns_scope_emit(t->scope, t->dns_udp_fd, t->server, t->sent);
         if (r < 0)
                 return r;