Request both v4 and v6 dns when on secondary net

We can't easily tell the protocol family of the secondary network,
so try both and trust that the carrier has configured dns servers
according to the protocols supported on its network.

bug:5468224
Change-Id: If4f017573d313a6ad8354574076de6d63d43b444

1 files changed, 19 insertions, 8 deletions

diff --git a/libc/netbsd/net/getaddrinfo.c b/libc/netbsd/net/getaddrinfo.c
index ace8c1a..6ae6e3e 100644
--- a/libc/netbsd/net/getaddrinfo.c
+++ b/libc/netbsd/net/getaddrinfo.c
@@ -1867,6 +1867,19 @@ error:
 	free(elems);
 }
 
+static int _using_alt_dns()
+{
+	char propname[PROP_NAME_MAX];
+	char propvalue[PROP_VALUE_MAX];
+
+	propvalue[0] = 0;
+	snprintf(propname, sizeof(propname), "net.dns1.%d", getpid());
+	if (__system_property_get(propname, propvalue) > 0 ) {
+		return 1;
+	}
+	return 0;
+}
+
 /*ARGSUSED*/
 static int
 _dns_getaddrinfo(void *rv, void	*cb_data, va_list ap)
@@ -1909,14 +1922,12 @@ _dns_getaddrinfo(void *rv, void	*cb_data, va_list ap)
 		q.anslen = sizeof(buf->buf);
 		int query_ipv6 = 1, query_ipv4 = 1;
 		if (pai->ai_flags & AI_ADDRCONFIG) {
-			query_ipv6 = _have_ipv6();
-			query_ipv4 = _have_ipv4();
-			if (query_ipv6 == 0 && query_ipv4 == 0) {
-				// Both our IPv4 and IPv6 connectivity probes failed, which indicates
-				// that we have neither an IPv4 or an IPv6 default route (and thus no
-				// global IPv4 or IPv6 connectivity). We might be in a walled garden.
-				// Throw up our arms and ask for both A and AAAA.
-				query_ipv6 = query_ipv4 = 1;
+			// Only implement AI_ADDRCONFIG if the application is not
+			// using its own DNS servers, since our implementation
+			// only works on the default connection.
+			if (!_using_alt_dns()) {
+				query_ipv6 = _have_ipv6();
+				query_ipv4 = _have_ipv4();
 			}
 		}
 		if (query_ipv6) {