net/tstun: implement env var for disabling UDP GRO on Linux

Certain device drivers (e.g. vxlan, geneve) do not properly handle
coalesced UDP packets later in the stack, resulting in packet loss.

Updates #11026

Signed-off-by: Jordan Whited <jordan@tailscale.com>

go.mod

@@ -77,7 +77,7 @@ require (
 	github.com/tailscale/peercred v0.0.0-20240214030740-b535050b2aa4
 	github.com/tailscale/web-client-prebuilt v0.0.0-20240226180453-5db17b287bf1
 	github.com/tailscale/wf v0.0.0-20240214030419-6fbb0a674ee6
-	github.com/tailscale/wireguard-go v0.0.0-20240413175505-64040e66467d
+	github.com/tailscale/wireguard-go v0.0.0-20240429185444-03c5a0ccf754
 	github.com/tailscale/xnet v0.0.0-20240117122442-62b9a7c569f9
 	github.com/tc-hib/winres v0.2.1
 	github.com/tcnksm/go-httpstat v0.2.0

go.sum

@@ -889,8 +889,8 @@ github.com/tailscale/web-client-prebuilt v0.0.0-20240226180453-5db17b287bf1 h1:t
 github.com/tailscale/web-client-prebuilt v0.0.0-20240226180453-5db17b287bf1/go.mod h1:agQPE6y6ldqCOui2gkIh7ZMztTkIQKH049tv8siLuNQ=
 github.com/tailscale/wf v0.0.0-20240214030419-6fbb0a674ee6 h1:l10Gi6w9jxvinoiq15g8OToDdASBni4CyJOdHY1Hr8M=
 github.com/tailscale/wf v0.0.0-20240214030419-6fbb0a674ee6/go.mod h1:ZXRML051h7o4OcI0d3AaILDIad/Xw0IkXaHM17dic1Y=
-github.com/tailscale/wireguard-go v0.0.0-20240413175505-64040e66467d h1:IREg0cn4nDyMjnqTgPacjgl66qDYmoOnt1k/vb96ius=
-github.com/tailscale/wireguard-go v0.0.0-20240413175505-64040e66467d/go.mod h1:BOm5fXUBFM+m9woLNBoxI9TaBXXhGNP50LX/TGIvGb4=
+github.com/tailscale/wireguard-go v0.0.0-20240429185444-03c5a0ccf754 h1:iazWjqVHE6CbNam7WXRhi33Qad5o7a8LVYgVoILpZdI=
+github.com/tailscale/wireguard-go v0.0.0-20240429185444-03c5a0ccf754/go.mod h1:BOm5fXUBFM+m9woLNBoxI9TaBXXhGNP50LX/TGIvGb4=
 github.com/tailscale/xnet v0.0.0-20240117122442-62b9a7c569f9 h1:81P7rjnikHKTJ75EkjppvbwUfKHDHYk6LJpO5PZy8pA=
 github.com/tailscale/xnet v0.0.0-20240117122442-62b9a7c569f9/go.mod h1:orPd6JZXXRyuDusYilywte7k094d7dycXXU5YnWsrwg=
 github.com/tc-hib/winres v0.2.1 h1:YDE0FiP0VmtRaDn7+aaChp1KiF4owBiJa5l964l5ujA=

net/tstun/tun.go

@@ -53,6 +53,9 @@ func New(logf logger.Logf, tunName string) (tun.Device, string, error) {
 		dev.Close()
 		return nil, "", err
 	}
+	if err := setLinkFeatures(dev); err != nil {
+		logf("setting link features: %v", err)
+	}
 	if err := setLinkAttrs(dev); err != nil {
 		logf("setting link attributes: %v", err)
 	}

net/tstun/tun_features_linux.go

@@ -0,0 +1,22 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package tstun
+
+import (
+	"os"
+	"strings"
+
+	"github.com/tailscale/wireguard-go/tun"
+)
+
+func setLinkFeatures(dev tun.Device) error {
+	val := os.Getenv("TS_TUN_DISABLE_UDP_GRO")
+	if strings.ToLower(val) == "true" || val == "1" {
+		linuxDev, ok := dev.(tun.LinuxDevice)
+		if ok {
+			linuxDev.DisableUDPGRO()
+		}
+	}
+	return nil
+}

net/tstun/tun_features_notlinux.go

@@ -0,0 +1,14 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !linux
+
+package tstun
+
+import (
+	"github.com/tailscale/wireguard-go/tun"
+)
+
+func setLinkFeatures(dev tun.Device) error {
+	return nil
+}