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net/netmon: move TailscaleInterfaceIndex out of netmon.State (#18428)

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fixes tailscale/tailscale#18418

Both Serve and PeerAPI broke when we moved the TailscaleInterfaceName
into State, which is updated asynchronously and may not be
available when we configure the listeners.

This extracts the explicit interface name property from netmon.State
and adds as a static struct with getters that have proper error
handling.

The bug is only found in sandboxed Darwin clients, where we
need to know the Tailscale interface details in order to set up the
listeners correctly (they must bind to our interface explicitly to escape
the network sandboxing that is applied by NECP).

Currently set only sandboxed macOS and Plan9 set this but it will
also be useful on Windows to simplify interface filtering in netns.

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>
This commit is contained in:
Jonathan Nobels
2026-01-16 14:53:23 -05:00
committed by GitHub
parent 1478028591
commit 643e91f2eb
9 changed files with 184 additions and 60 deletions
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net/netmon/netmon.go
+15 -34
View File
@@ -78,8 +78,7 @@ type Monitor struct {
goroutines sync.WaitGroup
wallTimer *time.Timer // nil until Started; re-armed AfterFunc per tick
lastWall time.Time
timeJumped bool // whether we need to send a changed=true after a big time jump
tsIfName string // tailscale interface name, if known/set ("tailscale0", "utun3", ...)
timeJumped bool // whether we need to send a changed=true after a big time jump
}
// ChangeFunc is a callback function registered with Monitor that's called when the
@@ -103,10 +102,6 @@ type ChangeDelta struct {
// come out of sleep.
TimeJumped bool
// The tailscale interface name, e.g. "tailscale0", "utun3", etc. Not all
// platforms know this or set it. Copied from netmon.Monitor.tsIfName.
TailscaleIfaceName string
DefaultRouteInterface string
// Computed Fields
@@ -134,12 +129,11 @@ func (cd *ChangeDelta) CurrentState() *State {
// NewChangeDelta builds a ChangeDelta and eagerly computes the cached fields.
// forceViability, if true, forces DefaultInterfaceMaybeViable to be true regardless of the
// actual state of the default interface. This is useful in testing.
func NewChangeDelta(old, new *State, timeJumped bool, tsIfName string, forceViability bool) (*ChangeDelta, error) {
func NewChangeDelta(old, new *State, timeJumped bool, forceViability bool) (*ChangeDelta, error) {
cd := ChangeDelta{
old: old,
new: new,
TimeJumped: timeJumped,
TailscaleIfaceName: tsIfName,
old: old,
new: new,
TimeJumped: timeJumped,
}
if cd.new == nil {
@@ -162,8 +156,10 @@ func NewChangeDelta(old, new *State, timeJumped bool, tsIfName string, forceViab
cd.DefaultRouteInterface = new.DefaultRouteInterface
defIf := new.Interface[cd.DefaultRouteInterface]
tsIfName, err := TailscaleInterfaceName()
// The default interface is not viable if it is down or it is the Tailscale interface itself.
if !forceViability && (!defIf.IsUp() || cd.DefaultRouteInterface == tsIfName) {
if !forceViability && (!defIf.IsUp() || (err == nil && cd.DefaultRouteInterface == tsIfName)) {
cd.DefaultInterfaceMaybeViable = false
} else {
cd.DefaultInterfaceMaybeViable = true
@@ -223,10 +219,11 @@ func (cd *ChangeDelta) isInterestingInterfaceChange() bool {
}
// Compare interfaces in both directions. Old to new and new to old.
tsIfName, ifNameErr := TailscaleInterfaceName()
for iname, oldInterface := range cd.old.Interface {
if iname == cd.TailscaleIfaceName {
// Ignore changes in the Tailscale interface itself.
if ifNameErr == nil && iname == tsIfName {
// Ignore changes in the Tailscale interface itself
continue
}
oldIps := filterRoutableIPs(cd.old.InterfaceIPs[iname])
@@ -259,7 +256,8 @@ func (cd *ChangeDelta) isInterestingInterfaceChange() bool {
}
for iname, newInterface := range cd.new.Interface {
if iname == cd.TailscaleIfaceName {
if ifNameErr == nil && iname == tsIfName {
// Ignore changes in the Tailscale interface itself
continue
}
newIps := filterRoutableIPs(cd.new.InterfaceIPs[iname])
@@ -360,24 +358,7 @@ func (m *Monitor) InterfaceState() *State {
}
func (m *Monitor) interfaceStateUncached() (*State, error) {
return getState(m.tsIfName)
}
// SetTailscaleInterfaceName sets the name of the Tailscale interface. For
// example, "tailscale0", "tun0", "utun3", etc.
//
// This must be called only early in tailscaled startup before the monitor is
// used.
func (m *Monitor) SetTailscaleInterfaceName(ifName string) {
m.mu.Lock()
defer m.mu.Unlock()
m.tsIfName = ifName
}
func (m *Monitor) TailscaleInterfaceName() string {
m.mu.Lock()
defer m.mu.Unlock()
return m.tsIfName
return getState(tsIfProps.tsIfName())
}
// GatewayAndSelfIP returns the current network's default gateway, and
@@ -598,7 +579,7 @@ func (m *Monitor) handlePotentialChange(newState *State, forceCallbacks bool) {
return
}
delta, err := NewChangeDelta(oldState, newState, timeJumped, m.tsIfName, false)
delta, err := NewChangeDelta(oldState, newState, timeJumped, false)
if err != nil {
m.logf("[unexpected] error creating ChangeDelta: %v", err)
return