Set AI_ADDRCONFIG when making getaddrinfo(3) calls for outgoing conns (#7295)

When making an outgoing TCP or UDP connection, set AI_ADDRCONFIG in the
hints we send to getaddrinfo(3) (if supported). This will prompt the
resolver to _NOT_ issue A or AAAA queries if the system does not
actually have an IPv4 or IPv6 address (respectively).

This makes outgoing connections marginally more efficient on
non-dual-stack systems, since we don't have to try connecting to an
address which can't possibly work.

More importantly, however, this works around a race condition present
in some older versions of glibc on aarch64 where it could accidently
send the two outgoing DNS queries with the same DNS txnid, and get
confused when receiving the responses. This manifests as outgoing
connections sometimes taking 5 seconds (the DNS timeout before retry) to
be made.

Fixes #19144

1 files changed, 8 insertions, 1 deletions

diff --git a/ext/socket/udpsocket.c b/ext/socket/udpsocket.c
index 5224e48a96..cf3eb6ab9a 100644
--- a/ext/socket/udpsocket.c
+++ b/ext/socket/udpsocket.c
@@ -88,9 +88,16 @@ udp_connect(VALUE sock, VALUE host, VALUE port)
 {
     struct udp_arg arg;
     VALUE ret;
+    int addrinfo_hints = 0;
 
     GetOpenFile(sock, arg.fptr);
-    arg.res = rsock_addrinfo(host, port, rsock_fd_family(arg.fptr->fd), SOCK_DGRAM, 0);
+
+#ifdef HAVE_CONST_AI_ADDRCONFIG
+    addrinfo_hints |= AI_ADDRCONFIG;
+#endif
+
+    arg.res = rsock_addrinfo(host, port, rsock_fd_family(arg.fptr->fd), SOCK_DGRAM,
+                             addrinfo_hints);
     ret = rb_ensure(udp_connect_internal, (VALUE)&arg,
                     rsock_freeaddrinfo, (VALUE)arg.res);
     if (!ret) rsock_sys_fail_host_port("connect(2)", host, port);