@ -50,13 +50,21 @@ const (
// Empirically, most of the documentation on packet marks on the
// internet gives the impression that the marks are 16 bits
// wide. Based on this, we theorize that the upper two bytes are
// relatively unused in the wild, and so we consume bits starting at
// th e 17th .
// relatively unused in the wild, and so we consume bits 16:23 (the
// th ird byte) .
//
// The constants are in the iptables/iproute2 string format for
// matching and setting the bits, so they can be directly embedded in
// commands.
const (
// The mask for reading/writing the 'firewall mask' bits on a packet.
// See the comment on the const block on why we only use the third byte.
//
// We claim bits 16:23 entirely. For now we only use the lower four
// bits, leaving the higher 4 bits for future use.
tailscaleFwmarkMask = "0xff0000"
tailscaleFwmarkMaskNum = 0xff0000
// Packet is from Tailscale and to a subnet route destination, so
// is allowed to be routed through this machine.
tailscaleSubnetRouteMark = "0x40000"
@ -104,6 +112,7 @@ type linuxRouter struct {
ipRuleAvailable bool // whether kernel was built with IP_MULTIPLE_TABLES
v6Available bool
v6NATAvailable bool
fwmaskWorks bool // whether we can use 'ip rule...fwmark <mark>/<mask>'
// ipPolicyPrefBase is the base priority at which ip rules are installed.
ipPolicyPrefBase int
@ -180,6 +189,20 @@ func newUserspaceRouterAdvanced(logf logger.Logf, tunname string, linkMon *monit
}
}
// To be a good denizen of the 4-byte 'fwmark' bitspace on every packet, we try to
// only use the third byte. However, support for masking to part of the fwmark bitspace
// was only added to busybox in 1.33.0. As such, we want to detect older versions and
// not issue such a stanza.
var err error
if r . fwmaskWorks , err = ipCmdSupportsFwmask ( ) ; err != nil {
r . logf ( "failed to determine ip command fwmask support: %v" , err )
}
if r . fwmaskWorks {
r . logf ( "[v1] ip command supports fwmark masks" )
} else {
r . logf ( "[v1] ip command does NOT support fwmark masks" )
}
// A common installation of OpenWRT involves use of the 'mwan3' package.
// This package installs ip-tables rules like:
// -A mwan3_fallback_policy -m mark --mark 0x0/0x3f00 -j MARK --set-xmark 0x100/0x3f00
@ -206,6 +229,86 @@ func newUserspaceRouterAdvanced(logf logger.Logf, tunname string, linkMon *monit
return r , nil
}
// ipCmdSupportsFwmask returns true if the system 'ip' binary supports using a
// fwmark stanza with a mask specified. To our knowledge, everything except busybox
// pre-1.33 supports this.
func ipCmdSupportsFwmask ( ) ( bool , error ) {
ipPath , err := exec . LookPath ( "ip" )
if err != nil {
return false , fmt . Errorf ( "lookpath: %v" , err )
}
stat , err := os . Lstat ( ipPath )
if err != nil {
return false , fmt . Errorf ( "lstat: %v" , err )
}
if stat . Mode ( ) & os . ModeSymlink == 0 {
// Not a symlink, so can't be busybox. Must be regular ip utility.
return true , nil
}
linkDest , err := os . Readlink ( ipPath )
if err != nil {
return false , err
}
if ! strings . Contains ( strings . ToLower ( linkDest ) , "busybox" ) {
// Not busybox, presumably supports fwmark masks.
return true , nil
}
// If we got this far, the ip utility is a busybox version with an
// unknown version.
// We run `ip --version` and look for the busybox banner (which
// is a stable 'BusyBox vX.Y.Z (<builddate>)' string) to determine
// the version.
out , err := exec . Command ( "ip" , "--version" ) . CombinedOutput ( )
if err != nil {
return false , err
}
major , minor , _ , err := busyboxParseVersion ( string ( out ) )
if err != nil {
return false , nil
}
// Support for masks added in 1.33.0.
switch {
case major > 1 :
return true , nil
case major == 1 && minor >= 33 :
return true , nil
default :
return false , nil
}
}
func busyboxParseVersion ( output string ) ( major , minor , patch int , err error ) {
bannerStart := strings . Index ( output , "BusyBox v" )
if bannerStart < 0 {
return 0 , 0 , 0 , errors . New ( "missing BusyBox banner" )
}
bannerEnd := bannerStart + len ( "BusyBox v" )
end := strings . Index ( output [ bannerEnd : ] , " " )
if end < 0 {
return 0 , 0 , 0 , errors . New ( "missing end delimiter" )
}
elements := strings . Split ( output [ bannerEnd : bannerEnd + end ] , "." )
if len ( elements ) < 3 {
return 0 , 0 , 0 , fmt . Errorf ( "expected 3 version elements, got %d" , len ( elements ) )
}
if major , err = strconv . Atoi ( elements [ 0 ] ) ; err != nil {
return 0 , 0 , 0 , fmt . Errorf ( "parsing major: %v" , err )
}
if minor , err = strconv . Atoi ( elements [ 1 ] ) ; err != nil {
return 0 , 0 , 0 , fmt . Errorf ( "parsing minor: %v" , err )
}
if patch , err = strconv . Atoi ( elements [ 2 ] ) ; err != nil {
return 0 , 0 , 0 , fmt . Errorf ( "parsing patch: %v" , err )
}
return major , minor , patch , nil
}
func useAmbientCaps ( ) bool {
if distro . Get ( ) != distro . Synology {
return false
@ -961,7 +1064,9 @@ func (r *linuxRouter) justAddIPRules() error {
for _ , ru := range ipRules {
// Note: r is a value type here; safe to mutate it.
ru . Family = family . netlinkInt ( )
ru . Mask = - 1
if ru . Mark != 0 {
ru . Mask = tailscaleFwmarkMaskNum
}
ru . Goto = - 1
ru . SuppressIfgroup = - 1
ru . SuppressPrefixlen = - 1
@ -992,7 +1097,11 @@ func (r *linuxRouter) addIPRulesWithIPCommand() error {
"pref" , strconv . Itoa ( rule . Priority + r . ipPolicyPrefBase ) ,
}
if rule . Mark != 0 {
args = append ( args , "fwmark" , fmt . Sprintf ( "0x%x" , rule . Mark ) )
if r . fwmaskWorks {
args = append ( args , "fwmark" , fmt . Sprintf ( "0x%x/%s" , rule . Mark , tailscaleFwmarkMask ) )
} else {
args = append ( args , "fwmark" , fmt . Sprintf ( "0x%x" , rule . Mark ) )
}
}
if rule . Table != 0 {
args = append ( args , "table" , mustRouteTable ( rule . Table ) . ipCmdArg ( ) )
@ -1042,6 +1151,7 @@ func (r *linuxRouter) delIPRules() error {
ru . Goto = - 1
ru . SuppressIfgroup = - 1
ru . SuppressPrefixlen = - 1
ru . Priority += r . ipPolicyPrefBase
err := netlink . RuleDel ( & ru )
if errors . Is ( err , errENOENT ) {
@ -1172,11 +1282,11 @@ func (r *linuxRouter) addNetfilterBase4() error {
// POSTROUTING. So instead, we match on the inbound interface in
// filter/FORWARD, and set a packet mark that nat/POSTROUTING can
// use to effectively run that same test again.
args = [ ] string { "-i" , r . tunname , "-j" , "MARK" , "--set-mark" , tailscaleSubnetRouteMark }
args = [ ] string { "-i" , r . tunname , "-j" , "MARK" , "--set-mark" , tailscaleSubnetRouteMark + "/" + tailscaleFwmarkMask }
if err := r . ipt4 . Append ( "filter" , "ts-forward" , args ... ) ; err != nil {
return fmt . Errorf ( "adding %v in v4/filter/ts-forward: %w" , args , err )
}
args = [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark , "-j" , "ACCEPT" }
args = [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark + "/" + tailscaleFwmarkMask , "-j" , "ACCEPT" }
if err := r . ipt4 . Append ( "filter" , "ts-forward" , args ... ) ; err != nil {
return fmt . Errorf ( "adding %v in v4/filter/ts-forward: %w" , args , err )
}
@ -1198,11 +1308,11 @@ func (r *linuxRouter) addNetfilterBase6() error {
// TODO: only allow traffic from Tailscale's ULA range to come
// from tailscale0.
args := [ ] string { "-i" , r . tunname , "-j" , "MARK" , "--set-mark" , tailscaleSubnetRouteMark }
args := [ ] string { "-i" , r . tunname , "-j" , "MARK" , "--set-mark" , tailscaleSubnetRouteMark + "/" + tailscaleFwmarkMask }
if err := r . ipt6 . Append ( "filter" , "ts-forward" , args ... ) ; err != nil {
return fmt . Errorf ( "adding %v in v6/filter/ts-forward: %w" , args , err )
}
args = [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark , "-j" , "ACCEPT" }
args = [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark + "/" + tailscaleFwmarkMask , "-j" , "ACCEPT" }
if err := r . ipt6 . Append ( "filter" , "ts-forward" , args ... ) ; err != nil {
return fmt . Errorf ( "adding %v in v6/filter/ts-forward: %w" , args , err )
}
@ -1374,7 +1484,7 @@ func (r *linuxRouter) addSNATRule() error {
return nil
}
args := [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark , "-j" , "MASQUERADE" }
args := [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark + "/" + tailscaleFwmarkMask , "-j" , "MASQUERADE" }
if err := r . ipt4 . Append ( "nat" , "ts-postrouting" , args ... ) ; err != nil {
return fmt . Errorf ( "adding %v in v4/nat/ts-postrouting: %w" , args , err )
}
@ -1393,7 +1503,7 @@ func (r *linuxRouter) delSNATRule() error {
return nil
}
args := [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark , "-j" , "MASQUERADE" }
args := [ ] string { "-m" , "mark" , "--mark" , tailscaleSubnetRouteMark + "/" + tailscaleFwmarkMask , "-j" , "MASQUERADE" }
if err := r . ipt4 . Delete ( "nat" , "ts-postrouting" , args ... ) ; err != nil {
return fmt . Errorf ( "deleting %v in v4/nat/ts-postrouting: %w" , args , err )
}
Tom DNetto
2 years ago
committed by