slirp: Send RDNSS in RA only if host has an IPv6 DNS server

Previously we would always send an RDNSS option in the RA, making the guest
try to resolve DNS through IPv6, even if the host does not actually have
and IPv6 DNS server available.

This makes the RDNSS option enabled only when an IPv6 DNS server is
available.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

diff --git a/slirp/ip6_icmp.c b/slirp/ip6_icmp.c
index d0f5cc1456ed492e1f7140c0be9ec3bcc14871b2..777eb574be057d4ee72ab43ea3db5212a6a82b2d 100644 (file)
--- a/slirp/ip6_icmp.c
+++ b/slirp/ip6_icmp.c
@@ -144,6 +144,9 @@ void ndp_send_ra(Slirp *slirp)
     struct mbuf *t = m_get(slirp);
     struct ip6 *rip = mtod(t, struct ip6 *);
     size_t pl_size = 0;
+    struct in6_addr addr;
+    uint32_t scope_id;
+
     rip->ip_src = (struct in6_addr)LINKLOCAL_ADDR;
     rip->ip_dst = (struct in6_addr)ALLNODES_MULTICAST;
     rip->ip_nh = IPPROTO_ICMPV6;
@@ -189,18 +192,18 @@ void ndp_send_ra(Slirp *slirp)
     t->m_data += NDPOPT_PREFIXINFO_LEN;
     pl_size += NDPOPT_PREFIXINFO_LEN;
 
-#ifndef _WIN32
     /* Prefix information (NDP option) */
-    /* disabled for windows for now, until get_dns6_addr is implemented */
-    struct ndpopt *opt3 = mtod(t, struct ndpopt *);
-    opt3->ndpopt_type = NDPOPT_RDNSS;
-    opt3->ndpopt_len = NDPOPT_RDNSS_LEN / 8;
-    opt3->ndpopt_rdnss.reserved = 0;
-    opt3->ndpopt_rdnss.lifetime = htonl(2 * NDP_MaxRtrAdvInterval);
-    opt3->ndpopt_rdnss.addr = slirp->vnameserver_addr6;
-    t->m_data += NDPOPT_RDNSS_LEN;
-    pl_size += NDPOPT_RDNSS_LEN;
-#endif
+    if (get_dns6_addr(&addr, &scope_id) >= 0) {
+        /* Host system does have an IPv6 DNS server, announce our proxy.  */
+        struct ndpopt *opt3 = mtod(t, struct ndpopt *);
+        opt3->ndpopt_type = NDPOPT_RDNSS;
+        opt3->ndpopt_len = NDPOPT_RDNSS_LEN / 8;
+        opt3->ndpopt_rdnss.reserved = 0;
+        opt3->ndpopt_rdnss.lifetime = htonl(2 * NDP_MaxRtrAdvInterval);
+        opt3->ndpopt_rdnss.addr = slirp->vnameserver_addr6;
+        t->m_data += NDPOPT_RDNSS_LEN;
+        pl_size += NDPOPT_RDNSS_LEN;
+    }
 
     rip->ip_pl = htons(pl_size);
     t->m_data -= sizeof(struct ip6) + pl_size;