Change how DNS resolver handle no default iface

We used to just try any iface we'd been told about as a
fallback, but that will end up mistakenly using a secondary
network's dns when we really don't have a default connection.

It also messed up our detection of whether we were doing the
lookup on the default or not (we'd get back our secondary net
iface as the default, do the compare and think we were on default).

Remove the lies and let dns fail if we don't have an iface for it.

bug:10132565
Change-Id: I5f0f2abacaaaaf23c5292b20fba9d8dcb6fb10c5

2 files changed, 10 insertions, 12 deletions

diff --git a/libc/netbsd/net/getaddrinfo.c b/libc/netbsd/net/getaddrinfo.c
index c4766e4..0d1949d 100644
--- a/libc/netbsd/net/getaddrinfo.c
+++ b/libc/netbsd/net/getaddrinfo.c
@@ -1874,10 +1874,10 @@ static bool _using_default_dns(const char *iface)
 	if (iface == NULL || *iface == '\0') return true;
 
 	if_len = _resolv_get_default_iface(buf, sizeof(buf));
-	if (if_len + 1 <= sizeof(buf)) {
-		if (strcmp(buf, iface) != 0) return false;
+	if (if_len != 0 && if_len + 1 <= sizeof(buf)) {
+		if (strcmp(buf, iface) == 0) return true;
 	}
-	return true;
+	return false;
 }
 
 /*ARGSUSED*/
diff --git a/libc/netbsd/resolv/res_cache.c b/libc/netbsd/resolv/res_cache.c
index 829bf10..7e367ad 100644
--- a/libc/netbsd/resolv/res_cache.c
+++ b/libc/netbsd/resolv/res_cache.c
@@ -2426,18 +2426,16 @@ _resolv_get_default_iface(char* buff, int buffLen)
 
     ifname = _get_default_iface_locked(); // never null, but may be empty
 
-    // if default interface not set. Get first cache with an interface
+    // if default interface not set give up.
     if (ifname[0] == '\0') {
-        ifname = _find_any_iface_name_locked(); // may be null
+        pthread_mutex_unlock(&_res_cache_list_lock);
+        return 0;
     }
 
-    // if we got the default iface or if (no-default) the find_any call gave an answer
-    if (ifname) {
-        len = strlen(ifname);
-        if (len < buffLen) {
-            strncpy(buff, ifname, len);
-            buff[len] = '\0';
-        }
+    len = strlen(ifname);
+    if (len < buffLen) {
+        strncpy(buff, ifname, len);
+        buff[len] = '\0';
     } else {
         buff[0] = '\0';
     }