wgengine/filter: support subnet mask rules, not just /32 IPs.

This depends on improved support from the control server, to send the
new subnet width (Bits) fields. If these are missing, we fall back to
assuming their value is /32.

Conversely, if the server sends Bits fields to an older client, it will
interpret them as /32 addresses. Since the only rules we allow are
"accept" rules, this will be narrower or equal to the intended rule, so
older clients will simply reject hosts on the wider subnet (fail
closed).

With this change, the internal filter.Matches format has diverged
from the wire format used by controlclient, so move the wire format
into tailcfg and convert it to filter.Matches in controlclient.

Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>

control/controlclient/direct.go

@@ -593,7 +593,7 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 			DNS:          resp.DNS,
 			DNSDomains:   resp.SearchPaths,
 			Hostinfo:     resp.Node.Hostinfo,
-			PacketFilter: resp.PacketFilter,
+			PacketFilter: c.parsePacketFilter(resp.PacketFilter),
 		}
 		for _, profile := range resp.UserProfiles {
 			nm.UserProfiles[profile.ID] = profile

control/controlclient/filter.go

@@ -0,0 +1,80 @@
+package controlclient
+
+import (
+	"fmt"
+	"net"
+	"tailscale.com/tailcfg"
+	"tailscale.com/wgengine/filter"
+)
+
+func parseIP(host string, defaultBits int) (filter.Net, error) {
+	ip := net.ParseIP(host)
+	if ip != nil && ip.IsUnspecified() {
+		// For clarity, reject 0.0.0.0 as an input
+		return filter.NetNone, fmt.Errorf("ports=%#v: to allow all IP addresses, use *:port, not 0.0.0.0:port", host)
+	} else if ip == nil && host == "*" {
+		// User explicitly requested wildcard dst ip
+		return filter.NetAny, nil
+	} else {
+		if ip != nil {
+			ip = ip.To4()
+		}
+		if ip == nil || len(ip) != 4 {
+			return filter.NetNone, fmt.Errorf("ports=%#v: invalid IPv4 address", host)
+		}
+		return filter.Net{
+			IP:   filter.NewIP(ip),
+			Mask: filter.Netmask(defaultBits),
+		}, nil
+	}
+}
+
+// Parse a backward-compatible FilterRule used by control's wire format,
+// producing the most current filter.Matches format.
+func (c *Direct) parsePacketFilter(pf []tailcfg.FilterRule) filter.Matches {
+	mm := make([]filter.Match, 0, len(pf))
+	var erracc error
+
+	for _, r := range pf {
+		m := filter.Match{}
+
+		for i, s := range r.SrcIPs {
+			bits := 32
+			if len(r.SrcBits) > i {
+				bits = r.SrcBits[i]
+			}
+			net, err := parseIP(s, bits)
+			if err != nil && erracc == nil {
+				erracc = err
+				continue
+			}
+			m.Srcs = append(m.Srcs, net)
+		}
+
+		for _, d := range r.DstPorts {
+			bits := 32
+			if d.Bits != nil {
+				bits = *d.Bits
+			}
+			net, err := parseIP(d.IP, bits)
+			if err != nil && erracc == nil {
+				erracc = err
+				continue
+			}
+			m.Dsts = append(m.Dsts, filter.NetPortRange{
+				Net: net,
+				Ports: filter.PortRange{
+					First: d.Ports.First,
+					Last:  d.Ports.Last,
+				},
+			})
+		}
+
+		mm = append(mm, m)
+	}
+
+	if erracc != nil {
+		c.logf("parsePacketFilter: %s\n", erracc)
+	}
+	return mm
+}

tailcfg/tailcfg.go

@@ -15,7 +15,6 @@ import (
 	"github.com/tailscale/wireguard-go/wgcfg"
 	"golang.org/x/oauth2"
 	"tailscale.com/types/opt"
-	"tailscale.com/wgengine/filter"
 )
 
 type ID int64
@@ -404,6 +403,40 @@ type MapRequest struct {
 	Hostinfo    *Hostinfo
 }
 
+// PortRange represents a range of UDP or TCP port numbers.
+type PortRange struct {
+	First uint16
+	Last  uint16
+}
+
+var PortRangeAny = PortRange{0, 65535}
+
+// NetPortRange represents a single subnet:portrange.
+type NetPortRange struct {
+	IP    string
+	Bits  *int // backward compatibility: if missing, means "all" bits
+	Ports PortRange
+}
+
+// FilterRule represents one rule in a packet filter.
+type FilterRule struct {
+	SrcIPs   []string
+	SrcBits  []int
+	DstPorts []NetPortRange
+}
+
+var FilterAllowAll = []FilterRule{
+	FilterRule{
+		SrcIPs:  []string{"*"},
+		SrcBits: nil,
+		DstPorts: []NetPortRange{NetPortRange{
+			IP:    "*",
+			Bits:  nil,
+			Ports: PortRange{0, 65535},
+		}},
+	},
+}
+
 type MapResponse struct {
 	KeepAlive bool // if set, all other fields are ignored
 
@@ -415,7 +448,7 @@ type MapResponse struct {
 
 	// ACLs
 	Domain       string
-	PacketFilter filter.Matches
+	PacketFilter []FilterRule
 	UserProfiles []UserProfile
 	Roles        []Role
 	// TODO: Groups       []Group

wgengine/filter/filter.go

@@ -71,7 +71,7 @@ const lruMax = 512 // max entries in UDP LRU cache
 
 // MatchAllowAll matches all packets.
 var MatchAllowAll = Matches{
-	Match{[]IPPortRange{IPPortRangeAny}, []IP{IPAny}},
+	Match{[]NetPortRange{NetPortRangeAny}, []Net{NetAny}},
 }
 
 // NewAllowAll returns a packet filter that accepts everything.

wgengine/filter/filter_test.go

@@ -21,23 +21,37 @@ var TCP = packet.TCP
 var UDP = packet.UDP
 var Fragment = packet.Fragment
 
-func ippr(ip IP, start, end uint16) []IPPortRange {
-	return []IPPortRange{
-		IPPortRange{ip, PortRange{start, end}},
+func nets(ips []IP) []Net {
+	out := make([]Net, 0, len(ips))
+	for _, ip := range ips {
+		out = append(out, Net{ip, Netmask(32)})
+	}
+	return out
+}
+
+func ippr(ip IP, start, end uint16) []NetPortRange {
+	return []NetPortRange{
+		NetPortRange{Net{ip, Netmask(32)}, PortRange{start, end}},
+	}
+}
+
+func netpr(ip IP, bits int, start, end uint16) []NetPortRange {
+	return []NetPortRange{
+		NetPortRange{Net{ip, Netmask(bits)}, PortRange{start, end}},
 	}
 }
 
 func TestFilter(t *testing.T) {
 	mm := Matches{
-		{SrcIPs: []IP{0x08010101, 0x08020202}, DstPorts: []IPPortRange{
-			IPPortRange{0x01020304, PortRange{22, 22}},
-			IPPortRange{0x05060708, PortRange{23, 24}},
+		{Srcs: nets([]IP{0x08010101, 0x08020202}), Dsts: []NetPortRange{
+			NetPortRange{Net{0x01020304, Netmask(32)}, PortRange{22, 22}},
+			NetPortRange{Net{0x05060708, Netmask(32)}, PortRange{23, 24}},
 		}},
-		{SrcIPs: []IP{0x08010101, 0x08020202}, DstPorts: ippr(0x05060708, 27, 28)},
-		{SrcIPs: []IP{0x02020202}, DstPorts: ippr(0x08010101, 22, 22)},
-		{SrcIPs: []IP{0}, DstPorts: ippr(0x647a6232, 0, 65535)},
-		{SrcIPs: []IP{0}, DstPorts: ippr(0, 443, 443)},
-		{SrcIPs: []IP{0x99010101, 0x99010102, 0x99030303}, DstPorts: ippr(0x01020304, 999, 999)},
+		{Srcs: nets([]IP{0x08010101, 0x08020202}), Dsts: ippr(0x05060708, 27, 28)},
+		{Srcs: nets([]IP{0x02020202}), Dsts: ippr(0x08010101, 22, 22)},
+		{Srcs: []Net{NetAny}, Dsts: ippr(0x647a6232, 0, 65535)},
+		{Srcs: []Net{NetAny}, Dsts: netpr(0, 0, 443, 443)},
+		{Srcs: nets([]IP{0x99010101, 0x99010102, 0x99030303}), Dsts: ippr(0x01020304, 999, 999)},
 	}
 	acl := New(mm, nil)
 

wgengine/filter/match.go

@@ -6,6 +6,8 @@ package filter
 
 import (
 	"fmt"
+	"math/bits"
+	"net"
 	"strings"
 
 	"tailscale.com/wgengine/packet"
@@ -13,9 +15,42 @@ import (
 
 type IP = packet.IP
 
-const IPAny = IP(0)
+func NewIP(ip net.IP) IP {
+	return packet.NewIP(ip)
+}
+
+type Net struct {
+	IP   IP
+	Mask IP
+}
+
+func (n Net) Includes(ip IP) bool {
+	return (n.IP & n.Mask) == (ip & n.Mask)
+}
+
+func (n Net) Bits() int {
+	return 32 - bits.TrailingZeros32(uint32(n.Mask))
+}
 
-var NewIP = packet.NewIP
+func (n Net) String() string {
+	b := n.Bits()
+	if b == 32 {
+		return n.IP.String()
+	} else if b == 0 {
+		return "*"
+	} else {
+		return fmt.Sprintf("%s/%d", n.IP, b)
+	}
+}
+
+var NetAny = Net{0, 0}
+var NetNone = Net{^IP(0), ^IP(0)}
+
+func Netmask(bits int) IP {
+	var b uint32
+	b = ^uint32((1 << (32 - bits)) - 1)
+	return IP(b)
+}
 
 type PortRange struct {
 	First, Last uint16
@@ -33,39 +68,39 @@ func (pr PortRange) String() string {
 	}
 }
 
-type IPPortRange struct {
-	IP    IP
+type NetPortRange struct {
+	Net   Net
 	Ports PortRange
 }
 
-var IPPortRangeAny = IPPortRange{IPAny, PortRangeAny}
+var NetPortRangeAny = NetPortRange{NetAny, PortRangeAny}
 
-func (ipr IPPortRange) String() string {
-	return fmt.Sprintf("%v:%v", ipr.IP, ipr.Ports)
+func (ipr NetPortRange) String() string {
+	return fmt.Sprintf("%v:%v", ipr.Net, ipr.Ports)
 }
 
 type Match struct {
-	DstPorts []IPPortRange
-	SrcIPs   []IP
+	Dsts []NetPortRange
+	Srcs []Net
 }
 
 func (m Match) Clone() (res Match) {
-	if m.DstPorts != nil {
-		res.DstPorts = append([]IPPortRange{}, m.DstPorts...)
+	if m.Dsts != nil {
+		res.Dsts = append([]NetPortRange{}, m.Dsts...)
 	}
-	if m.SrcIPs != nil {
-		res.SrcIPs = append([]IP{}, m.SrcIPs...)
+	if m.Srcs != nil {
+		res.Srcs = append([]Net{}, m.Srcs...)
 	}
 	return res
 }
 
 func (m Match) String() string {
 	srcs := []string{}
-	for _, srcip := range m.SrcIPs {
-		srcs = append(srcs, srcip.String())
+	for _, src := range m.Srcs {
+		srcs = append(srcs, src.String())
 	}
 	dsts := []string{}
-	for _, dst := range m.DstPorts {
+	for _, dst := range m.Dsts {
 		dsts = append(dsts, dst.String())
 	}
 
@@ -92,9 +127,9 @@ func (m Matches) Clone() (res Matches) {
 	return res
 }
 
-func ipInList(ip IP, iplist []IP) bool {
-	for _, ipp := range iplist {
-		if ipp == IPAny || ipp == ip {
+func ipInList(ip IP, netlist []Net) bool {
+	for _, net := range netlist {
+		if net.Includes(ip) {
 			return true
 		}
 	}
@@ -103,14 +138,14 @@ func ipInList(ip IP, iplist []IP) bool {
 
 func matchIPPorts(mm Matches, q *packet.QDecode) bool {
 	for _, acl := range mm {
-		for _, dst := range acl.DstPorts {
-			if dst.IP != IPAny && dst.IP != q.DstIP {
+		for _, dst := range acl.Dsts {
+			if !dst.Net.Includes(q.DstIP) {
 				continue
 			}
 			if q.DstPort < dst.Ports.First || q.DstPort > dst.Ports.Last {
 				continue
 			}
-			if !ipInList(q.SrcIP, acl.SrcIPs) {
+			if !ipInList(q.SrcIP, acl.Srcs) {
 				// Skip other dests in this acl, since
 				// the src will never match.
 				break
@@ -123,11 +158,11 @@ func matchIPPorts(mm Matches, q *packet.QDecode) bool {
 
 func matchIPWithoutPorts(mm Matches, q *packet.QDecode) bool {
 	for _, acl := range mm {
-		for _, dst := range acl.DstPorts {
-			if dst.IP != IPAny && dst.IP != q.DstIP {
+		for _, dst := range acl.Dsts {
+			if !dst.Net.Includes(q.DstIP) {
 				continue
 			}
-			if !ipInList(q.SrcIP, acl.SrcIPs) {
+			if !ipInList(q.SrcIP, acl.Srcs) {
 				// Skip other dests in this acl, since
 				// the src will never match.
 				break

wgengine/packet/packet.go

@@ -6,7 +6,6 @@ package packet
 
 import (
 	"encoding/binary"
-	"encoding/json"
 	"fmt"
 	"log"
 	"net"
@@ -43,8 +42,6 @@ func (p IPProto) String() string {
 
 type IP uint32
 
-const IPAny = IP(0)
-
 func NewIP(b net.IP) IP {
 	b4 := b.To4()
 	if b4 == nil {
@@ -54,45 +51,11 @@ func NewIP(b net.IP) IP {
 }
 
 func (ip IP) String() string {
-	if ip == 0 {
-		return "*"
-	}
 	b := make([]byte, 4)
 	binary.BigEndian.PutUint32(b, uint32(ip))
 	return fmt.Sprintf("%d.%d.%d.%d", b[0], b[1], b[2], b[3])
 }
 
-func (ipp *IP) MarshalJSON() ([]byte, error) {
-	s := "\"" + (*ipp).String() + "\""
-	return []byte(s), nil
-}
-
-func (ipp *IP) UnmarshalJSON(b []byte) error {
-	var hostp *string
-	err := json.Unmarshal(b, &hostp)
-	if err != nil {
-		return err
-	}
-	host := *hostp
-	ip := net.ParseIP(host)
-	if ip != nil && ip.IsUnspecified() {
-		// For clarity, reject 0.0.0.0 as an input
-		return fmt.Errorf("ports=%#v: to allow all IP addresses, use *:port, not 0.0.0.0:port", host)
-	} else if ip == nil && host == "*" {
-		// User explicitly requested wildcard dst ip
-		*ipp = IPAny
-	} else {
-		if ip != nil {
-			ip = ip.To4()
-		}
-		if ip == nil || len(ip) != 4 {
-			return fmt.Errorf("ports=%#v: invalid IPv4 address", host)
-		}
-		*ipp = NewIP(ip)
-	}
-	return nil
-}
-
 const (
 	EchoReply    uint8 = 0x00
 	EchoRequest  uint8 = 0x08