From a47ce618bda7829be5ee829fb762026bda8acf88 Mon Sep 17 00:00:00 2001
From: Jordan Whited <jordan@tailscale.com>
Date: Tue, 30 Apr 2024 09:14:02 -0700
Subject: [PATCH] net/tstun: implement env var for disabling UDP GRO on Linux
 (#11924)

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                             |  2 +-
 go.sum                             |  4 ++--
 net/tstun/tun.go                   |  3 +++
 net/tstun/tun_features_linux.go    | 19 +++++++++++++++++++
 net/tstun/tun_features_notlinux.go | 14 ++++++++++++++
 5 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 net/tstun/tun_features_linux.go
 create mode 100644 net/tstun/tun_features_notlinux.go

diff --git a/go.mod b/go.mod
index c35d1057d..67b2dd8fd 100644
--- a/go.mod
+++ b/go.mod
@@ -76,7 +76,7 @@ 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
diff --git a/go.sum b/go.sum
index 3c8428556..c6502c08d 100644
--- a/go.sum
+++ b/go.sum
@@ -886,8 +886,8 @@ 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=
diff --git a/net/tstun/tun.go b/net/tstun/tun.go
index 66e209d1a..f2c034fc3 100644
--- a/net/tstun/tun.go
+++ b/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)
 	}
diff --git a/net/tstun/tun_features_linux.go b/net/tstun/tun_features_linux.go
new file mode 100644
index 000000000..424088115
--- /dev/null
+++ b/net/tstun/tun_features_linux.go
@@ -0,0 +1,19 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package tstun
+
+import (
+	"github.com/tailscale/wireguard-go/tun"
+	"tailscale.com/envknob"
+)
+
+func setLinkFeatures(dev tun.Device) error {
+	if envknob.Bool("TS_TUN_DISABLE_UDP_GRO") {
+		linuxDev, ok := dev.(tun.LinuxDevice)
+		if ok {
+			linuxDev.DisableUDPGRO()
+		}
+	}
+	return nil
+}
diff --git a/net/tstun/tun_features_notlinux.go b/net/tstun/tun_features_notlinux.go
new file mode 100644
index 000000000..85285fd05
--- /dev/null
+++ b/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
+}