+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)
+ log_debug("Failed to invoke IP_UNICAST_IF: %m");
+ } else if (s->local.sa.sa_family == AF_INET6) {
+ r = setsockopt(s->fd, IPPROTO_IPV6, IPV6_UNICAST_IF, &ifindex, sizeof(ifindex));
+ if (r < 0)
+ log_debug("Failed to invoke IPV6_UNICAST_IF: %m");
+ }
+ }
+
+ s->identified = true;
+
+ return 0;
+}
+