resolved: don't discard mDNS queries with bad flags

Even though RFC 6762 specifies these bits MUST be zero, it also says they MUST
be ignored on reception.

(cherry picked from commit 2aaf3765974c9f340c0c3d705e9f0609073cf83c)

diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
index bcb292303b06c5601ba49a4d3d8af4173236173a..62cd6da5fb12d66437ce49367ce3380ec6edc230 100644 (file)
--- a/src/resolve/resolved-dns-packet.c
+++ b/src/resolve/resolved-dns-packet.c
@@ -294,13 +294,10 @@ int dns_packet_validate_query(DnsPacket *p) {
                 break;
 
         case DNS_PROTOCOL_MDNS:
-                /* RFC 6762, Section 18 */
-                if (DNS_PACKET_AA(p)    != 0 ||
-                    DNS_PACKET_RD(p)    != 0 ||
-                    DNS_PACKET_RA(p)    != 0 ||
-                    DNS_PACKET_AD(p)    != 0 ||
-                    DNS_PACKET_CD(p)    != 0 ||
-                    DNS_PACKET_RCODE(p) != 0)
+                /* RFC 6762, Section 18 specifies that messages with non-zero RCODE
+                 * must be silently ignored, and that we must ignore the values of
+                 * AA, RD, RA, AD, and CD bits. */
+                if (DNS_PACKET_RCODE(p) != 0)
                         return -EBADMSG;
 
                 break;