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control/controlknobs,net/{batching,tstun},wgengine: add nodecaps to disable UDP & TUN GRO/GSO

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Add four control-plane node attributes that let us disable UDP GSO/GRO
on the magicsock UDP socket and UDP/TCP GRO on the Tailscale TUN
device.

These complement the pre-existing TS_DEBUG_DISABLE_UDP_{GRO,GSO} and
TS_TUN_DISABLE_{UDP,TCP}_GRO envknobs. They exist so we can mitigate
upstream Linux kernel regressions on a deployed fleet without
requiring a client release, after two incidents (#13041, #19777) where
buggy kernel patches landed upstream and the fix took an excessively
long time to reach downstream distros.

Knob changes are reacted to in setNetworkMapInternal / SetNetworkMap via
a comparison against a cached "last applied" value and only an actual
transition triggers work: magicsock Rebind()+ReSTUN for UDP,
ApplyGROKnobs for TUN. The TUN side is gated by buildfeatures.HasGRO and
is one-way (wireguard-go GRO disablement is sticky); re-enabling
requires a client restart.

Updates #13041
Updates #19777

Change-Id: I802993070afa659cc06809bb0bfbb7f8a0cdb273
Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
James Tucker
2026-05-27 17:10:14 -07:00
committed by James Tucker
parent 94af1b00fb
commit 25b8ed8d9e
13 changed files with 212 additions and 30 deletions
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net/tstun/wrap_linux.go
+34 -5
View File
@@ -15,22 +15,26 @@ import (
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/checksum"
"gvisor.dev/gvisor/pkg/tcpip/header"
"tailscale.com/control/controlknobs"
"tailscale.com/envknob"
"tailscale.com/net/tsaddr"
)
// SetLinkFeaturesPostUp configures link features on t based on select TS_TUN_
// environment variables and OS feature tests. Callers should ensure t is
// up prior to calling, otherwise OS feature tests may be inconclusive.
func (t *Wrapper) SetLinkFeaturesPostUp() {
// environment variables, control-plane node attributes (via knobs, which may be
// nil), and OS feature tests. Callers should ensure t is up prior to calling,
// otherwise OS feature tests may be inconclusive.
func (t *Wrapper) SetLinkFeaturesPostUp(knobs *controlknobs.Knobs) {
if t.isTAP || runtime.GOOS == "android" {
return
}
if groDev, ok := t.tdev.(tun.GRODevice); ok {
if envknob.Bool("TS_TUN_DISABLE_UDP_GRO") {
if envknob.Bool("TS_TUN_DISABLE_UDP_GRO") ||
(knobs != nil && knobs.DisableTUNUDPGRO.Load()) {
groDev.DisableUDPGRO()
}
if envknob.Bool("TS_TUN_DISABLE_TCP_GRO") {
if envknob.Bool("TS_TUN_DISABLE_TCP_GRO") ||
(knobs != nil && knobs.DisableTUNTCPGRO.Load()) {
groDev.DisableTCPGRO()
}
err := probeTCPGRO(groDev)
@@ -42,6 +46,31 @@ func (t *Wrapper) SetLinkFeaturesPostUp() {
}
}
// ApplyGROKnobs applies the [tailcfg.NodeAttrDisableTUNUDPGRO] and
// [tailcfg.NodeAttrDisableTUNTCPGRO] knob values (via knobs, which must be
// non-nil) to t's underlying device. It is intended to be called when a
// control-plane node attribute change is detected after [SetLinkFeaturesPostUp]
// has already run.
//
// Note: wireguard-go's GRO disablement is one-way (sticky); ApplyGROKnobs can
// move TUN UDP/TCP GRO from enabled to disabled, but the reverse requires a
// client restart.
func (t *Wrapper) ApplyGROKnobs(knobs *controlknobs.Knobs) {
if t.isTAP || runtime.GOOS == "android" || knobs == nil {
return
}
groDev, ok := t.tdev.(tun.GRODevice)
if !ok {
return
}
if knobs.DisableTUNUDPGRO.Load() {
groDev.DisableUDPGRO()
}
if knobs.DisableTUNTCPGRO.Load() {
groDev.DisableTCPGRO()
}
}
func probeTCPGRO(dev tun.GRODevice) error {
ipPort := netip.MustParseAddrPort(tsaddr.TailscaleServiceIPString + ":0")
fingerprint := []byte("tailscale-probe-tun-gro")