fix application bug

vendor/golang.org/x/net/ipv4/helper.go

@@ -8,6 +8,8 @@ import (
 	"errors"
 	"net"
 	"runtime"
+
+	"golang.org/x/net/internal/socket"
 )
 
 var (
@@ -22,10 +24,22 @@ var (
 	errNoSuchMulticastInterface = errors.New("no such multicast interface")
 	errNotImplemented           = errors.New("not implemented on " + runtime.GOOS + "/" + runtime.GOARCH)
 
-	// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
-	freebsdVersion uint32
+	// See https://www.freebsd.org/doc/en/books/porters-handbook/versions.html.
+	freebsdVersion  uint32
+	compatFreeBSD32 bool // 386 emulation on amd64
 )
 
+// See golang.org/issue/30899.
+func adjustFreeBSD32(m *socket.Message) {
+	// FreeBSD 12.0-RELEASE is affected by https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236737
+	if 1200086 <= freebsdVersion && freebsdVersion < 1201000 {
+		l := (m.NN + 4 - 1) &^ (4 - 1)
+		if m.NN < l && l <= len(m.OOB) {
+			m.NN = l
+		}
+	}
+}
+
 func boolint(b bool) int {
 	if b {
 		return 1