slirp: Send RDNSS in RA only if host has an IPv6 DNS serverv2.9.0-rc5v2.9.0-rc4v2.9.0-rc3v2.9.0

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>

1 files changed, 14 insertions, 11 deletions

diff --git a/ip6_icmp.c b/ip6_icmp.c
index c177b6d..f48fd0c 100644
--- a/ip6_icmp.c
+++ b/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;