disable GSO and ECN on kernels older than version 5 (#4456)

quic_suite_linux_test.go

@@ -0,0 +1,12 @@
+//go:build linux
+
+package quic
+
+import (
+	"fmt"
+)
+
+func init() {
+	major, minor := kernelVersion()
+	fmt.Printf("Kernel Version: %d.%d\n\n", major, minor)
+}

sys_conn_helper_darwin.go

@@ -33,4 +33,6 @@ func parseIPv4PktInfo(body []byte) (ip netip.Addr, ifIndex uint32, ok bool) {
 	return netip.AddrFrom4(*(*[4]byte)(body[8:12])), binary.LittleEndian.Uint32(body), true
 }
 
-func isGSOSupported(syscall.RawConn) bool { return false }
+func isGSOEnabled(syscall.RawConn) bool { return false }
+
+func isECNEnabled() bool { return !isECNDisabledUsingEnv() }

sys_conn_helper_freebsd.go

@@ -28,4 +28,6 @@ func parseIPv4PktInfo(body []byte) (ip netip.Addr, _ uint32, ok bool) {
 	return netip.AddrFrom4(*(*[4]byte)(body)), 0, true
 }
 
-func isGSOSupported(syscall.RawConn) bool { return false }
+func isGSOEnabled(syscall.RawConn) bool { return false }
+
+func isECNEnabled() bool { return !isECNDisabledUsingEnv() }

sys_conn_helper_linux.go

@@ -23,6 +23,12 @@ const ecnIPv4DataLen = 1
 
 const batchSize = 8 // needs to smaller than MaxUint8 (otherwise the type of oobConn.readPos has to be changed)
 
+var kernelVersionMajor int
+
+func init() {
+	kernelVersionMajor, _ = kernelVersion()
+}
+
 func forceSetReceiveBuffer(c syscall.RawConn, bytes int) error {
 	var serr error
 	if err := c.Control(func(fd uintptr) {
@@ -55,9 +61,12 @@ func parseIPv4PktInfo(body []byte) (ip netip.Addr, ifIndex uint32, ok bool) {
 	return netip.AddrFrom4(*(*[4]byte)(body[8:12])), binary.LittleEndian.Uint32(body), true
 }
 
-// isGSOSupported tests if the kernel supports GSO.
+// isGSOEnabled tests if the kernel supports GSO.
 // Sending with GSO might still fail later on, if the interface doesn't support it (see isGSOError).
-func isGSOSupported(conn syscall.RawConn) bool {
+func isGSOEnabled(conn syscall.RawConn) bool {
+	if kernelVersionMajor < 5 {
+		return false
+	}
 	disabled, err := strconv.ParseBool(os.Getenv("QUIC_GO_DISABLE_GSO"))
 	if err == nil && disabled {
 		return false
@@ -108,3 +117,40 @@ func isPermissionError(err error) bool {
 	}
 	return false
 }
+
+func isECNEnabled() bool {
+	return kernelVersionMajor >= 5 && !isECNDisabledUsingEnv()
+}
+
+// kernelVersion returns major and minor kernel version numbers, parsed from
+// the syscall.Uname's Release field, or 0, 0 if the version can't be obtained
+// or parsed.
+//
+// copied from the standard library's internal/syscall/unix/kernel_version_linux.go
+func kernelVersion() (major, minor int) {
+	var uname syscall.Utsname
+	if err := syscall.Uname(&uname); err != nil {
+		return
+	}
+
+	var (
+		values    [2]int
+		value, vi int
+	)
+	for _, c := range uname.Release {
+		if '0' <= c && c <= '9' {
+			value = (value * 10) + int(c-'0')
+		} else {
+			// Note that we're assuming N.N.N here.
+			// If we see anything else, we are likely to mis-parse it.
+			values[vi] = value
+			vi++
+			if vi >= len(values) {
+				break
+			}
+			value = 0
+		}
+	}
+
+	return values[0], values[1]
+}

sys_conn_oob.go

@@ -59,7 +59,7 @@ func inspectWriteBuffer(c syscall.RawConn) (int, error) {
 	return size, serr
 }
 
-func isECNDisabled() bool {
+func isECNDisabledUsingEnv() bool {
 	disabled, err := strconv.ParseBool(os.Getenv("QUIC_GO_DISABLE_ECN"))
 	return err == nil && disabled
 }
@@ -147,8 +147,8 @@ func newConn(c OOBCapablePacketConn, supportsDF bool) (*oobConn, error) {
 		readPos:              batchSize,
 		cap: connCapabilities{
 			DF:  supportsDF,
-			GSO: isGSOSupported(rawConn),
-			ECN: !isECNDisabled(),
+			GSO: isGSOEnabled(rawConn),
+			ECN: isECNEnabled(),
 		},
 	}
 	for i := 0; i < batchSize; i++ {
@@ -247,7 +247,7 @@ func (c *oobConn) WritePacket(b []byte, addr net.Addr, packetInfoOOB []byte, gso
 	}
 	if ecn != protocol.ECNUnsupported {
 		if !c.capabilities().ECN {
-			panic("tried to send a ECN-marked packet although ECN is disabled")
+			panic("tried to send an ECN-marked packet although ECN is disabled")
 		}
 		if remoteUDPAddr, ok := addr.(*net.UDPAddr); ok {
 			if remoteUDPAddr.IP.To4() != nil {