/
iptables_targets.go
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/
iptables_targets.go
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// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package stack
import (
"fmt"
"math"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/header"
)
// AcceptTarget accepts packets.
type AcceptTarget struct {
// NetworkProtocol is the network protocol the target is used with.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (*AcceptTarget) Action(*PacketBuffer, Hook, *Route, AddressableEndpoint) (RuleVerdict, int) {
return RuleAccept, 0
}
// DropTarget drops packets.
type DropTarget struct {
// NetworkProtocol is the network protocol the target is used with.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (*DropTarget) Action(*PacketBuffer, Hook, *Route, AddressableEndpoint) (RuleVerdict, int) {
return RuleDrop, 0
}
// RejectIPv4WithHandler handles rejecting a packet.
type RejectIPv4WithHandler interface {
// SendRejectionError sends an error packet in response to the packet.
SendRejectionError(pkt *PacketBuffer, rejectWith RejectIPv4WithICMPType, inputHook bool) tcpip.Error
}
// RejectIPv4WithICMPType indicates the type of ICMP error that should be sent.
type RejectIPv4WithICMPType int
// The types of errors that may be returned when rejecting IPv4 packets.
const (
_ RejectIPv4WithICMPType = iota
RejectIPv4WithICMPNetUnreachable
RejectIPv4WithICMPHostUnreachable
RejectIPv4WithICMPPortUnreachable
RejectIPv4WithICMPNetProhibited
RejectIPv4WithICMPHostProhibited
RejectIPv4WithICMPAdminProhibited
)
// RejectIPv4Target drops packets and sends back an error packet in response to the
// matched packet.
type RejectIPv4Target struct {
Handler RejectIPv4WithHandler
RejectWith RejectIPv4WithICMPType
}
// Action implements Target.Action.
func (rt *RejectIPv4Target) Action(pkt *PacketBuffer, hook Hook, _ *Route, _ AddressableEndpoint) (RuleVerdict, int) {
switch hook {
case Input, Forward, Output:
// There is nothing reasonable for us to do in response to an error here;
// we already drop the packet.
_ = rt.Handler.SendRejectionError(pkt, rt.RejectWith, hook == Input)
return RuleDrop, 0
case Prerouting, Postrouting:
panic(fmt.Sprintf("%s hook not supported for REDIRECT", hook))
default:
panic(fmt.Sprintf("unhandled hook = %s", hook))
}
}
// RejectIPv6WithHandler handles rejecting a packet.
type RejectIPv6WithHandler interface {
// SendRejectionError sends an error packet in response to the packet.
SendRejectionError(pkt *PacketBuffer, rejectWith RejectIPv6WithICMPType, forwardingHook bool) tcpip.Error
}
// RejectIPv6WithICMPType indicates the type of ICMP error that should be sent.
type RejectIPv6WithICMPType int
// The types of errors that may be returned when rejecting IPv6 packets.
const (
_ RejectIPv6WithICMPType = iota
RejectIPv6WithICMPNoRoute
RejectIPv6WithICMPAddrUnreachable
RejectIPv6WithICMPPortUnreachable
RejectIPv6WithICMPAdminProhibited
)
// RejectIPv6Target drops packets and sends back an error packet in response to the
// matched packet.
type RejectIPv6Target struct {
Handler RejectIPv6WithHandler
RejectWith RejectIPv6WithICMPType
}
// Action implements Target.Action.
func (rt *RejectIPv6Target) Action(pkt *PacketBuffer, hook Hook, _ *Route, _ AddressableEndpoint) (RuleVerdict, int) {
switch hook {
case Input, Forward, Output:
// There is nothing reasonable for us to do in response to an error here;
// we already drop the packet.
_ = rt.Handler.SendRejectionError(pkt, rt.RejectWith, hook == Input)
return RuleDrop, 0
case Prerouting, Postrouting:
panic(fmt.Sprintf("%s hook not supported for REDIRECT", hook))
default:
panic(fmt.Sprintf("unhandled hook = %s", hook))
}
}
// ErrorTarget logs an error and drops the packet. It represents a target that
// should be unreachable.
type ErrorTarget struct {
// NetworkProtocol is the network protocol the target is used with.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (*ErrorTarget) Action(*PacketBuffer, Hook, *Route, AddressableEndpoint) (RuleVerdict, int) {
log.Debugf("ErrorTarget triggered.")
return RuleDrop, 0
}
// UserChainTarget marks a rule as the beginning of a user chain.
type UserChainTarget struct {
// Name is the chain name.
Name string
// NetworkProtocol is the network protocol the target is used with.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (*UserChainTarget) Action(*PacketBuffer, Hook, *Route, AddressableEndpoint) (RuleVerdict, int) {
panic("UserChainTarget should never be called.")
}
// ReturnTarget returns from the current chain. If the chain is a built-in, the
// hook's underflow should be called.
type ReturnTarget struct {
// NetworkProtocol is the network protocol the target is used with.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (*ReturnTarget) Action(*PacketBuffer, Hook, *Route, AddressableEndpoint) (RuleVerdict, int) {
return RuleReturn, 0
}
// DNATTarget modifies the destination port/IP of packets.
type DNATTarget struct {
// The new destination address for packets.
//
// Immutable.
Addr tcpip.Address
// The new destination port for packets.
//
// Immutable.
Port uint16
// NetworkProtocol is the network protocol the target is used with.
//
// Immutable.
NetworkProtocol tcpip.NetworkProtocolNumber
// ChangeAddress indicates whether we should check addresses.
//
// Immutable.
ChangeAddress bool
// ChangePort indicates whether we should check ports.
//
// Immutable.
ChangePort bool
}
// Action implements Target.Action.
func (rt *DNATTarget) Action(pkt *PacketBuffer, hook Hook, r *Route, addressEP AddressableEndpoint) (RuleVerdict, int) {
// Sanity check.
if rt.NetworkProtocol != pkt.NetworkProtocolNumber {
panic(fmt.Sprintf(
"DNATTarget.Action with NetworkProtocol %d called on packet with NetworkProtocolNumber %d",
rt.NetworkProtocol, pkt.NetworkProtocolNumber))
}
switch hook {
case Prerouting, Output:
case Input, Forward, Postrouting:
panic(fmt.Sprintf("%s not supported for DNAT", hook))
default:
panic(fmt.Sprintf("%s unrecognized", hook))
}
return dnatAction(pkt, hook, r, rt.Port, rt.Addr, rt.ChangePort, rt.ChangeAddress)
}
// RedirectTarget redirects the packet to this machine by modifying the
// destination port/IP. Outgoing packets are redirected to the loopback device,
// and incoming packets are redirected to the incoming interface (rather than
// forwarded).
type RedirectTarget struct {
// Port indicates port used to redirect. It is immutable.
Port uint16
// NetworkProtocol is the network protocol the target is used with. It
// is immutable.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (rt *RedirectTarget) Action(pkt *PacketBuffer, hook Hook, r *Route, addressEP AddressableEndpoint) (RuleVerdict, int) {
// Sanity check.
if rt.NetworkProtocol != pkt.NetworkProtocolNumber {
panic(fmt.Sprintf(
"RedirectTarget.Action with NetworkProtocol %d called on packet with NetworkProtocolNumber %d",
rt.NetworkProtocol, pkt.NetworkProtocolNumber))
}
// Change the address to loopback (127.0.0.1 or ::1) in Output and to
// the primary address of the incoming interface in Prerouting.
var address tcpip.Address
switch hook {
case Output:
if pkt.NetworkProtocolNumber == header.IPv4ProtocolNumber {
address = tcpip.AddrFrom4([4]byte{127, 0, 0, 1})
} else {
address = header.IPv6Loopback
}
case Prerouting:
// addressEP is expected to be set for the prerouting hook.
address = addressEP.MainAddress().Address
default:
panic("redirect target is supported only on output and prerouting hooks")
}
return dnatAction(pkt, hook, r, rt.Port, address, true /* changePort */, true /* changeAddress */)
}
// SNATTarget modifies the source port/IP in the outgoing packets.
type SNATTarget struct {
Addr tcpip.Address
Port uint16
// NetworkProtocol is the network protocol the target is used with. It
// is immutable.
NetworkProtocol tcpip.NetworkProtocolNumber
// ChangeAddress indicates whether we should check addresses.
//
// Immutable.
ChangeAddress bool
// ChangePort indicates whether we should check ports.
//
// Immutable.
ChangePort bool
}
func dnatAction(pkt *PacketBuffer, hook Hook, r *Route, port uint16, address tcpip.Address, changePort, changeAddress bool) (RuleVerdict, int) {
return natAction(pkt, hook, r, portOrIdentRange{start: port, size: 1}, address, true /* dnat */, changePort, changeAddress)
}
func targetPortRangeForTCPAndUDP(originalSrcPort uint16) portOrIdentRange {
// As per iptables(8),
//
// If no port range is specified, then source ports below 512 will be
// mapped to other ports below 512: those between 512 and 1023 inclusive
// will be mapped to ports below 1024, and other ports will be mapped to
// 1024 or above.
switch {
case originalSrcPort < 512:
return portOrIdentRange{start: 1, size: 511}
case originalSrcPort < 1024:
return portOrIdentRange{start: 1, size: 1023}
default:
return portOrIdentRange{start: 1024, size: math.MaxUint16 - 1023}
}
}
func snatAction(pkt *PacketBuffer, hook Hook, r *Route, port uint16, address tcpip.Address, changePort, changeAddress bool) (RuleVerdict, int) {
portsOrIdents := portOrIdentRange{start: port, size: 1}
switch pkt.TransportProtocolNumber {
case header.UDPProtocolNumber:
if port == 0 {
portsOrIdents = targetPortRangeForTCPAndUDP(header.UDP(pkt.TransportHeader().Slice()).SourcePort())
}
case header.TCPProtocolNumber:
if port == 0 {
portsOrIdents = targetPortRangeForTCPAndUDP(header.TCP(pkt.TransportHeader().Slice()).SourcePort())
}
case header.ICMPv4ProtocolNumber, header.ICMPv6ProtocolNumber:
// Allow NAT-ing to any 16-bit value for ICMP's Ident field to match Linux
// behaviour.
//
// https://github.com/torvalds/linux/blob/58e1100fdc5990b0cc0d4beaf2562a92e621ac7d/net/netfilter/nf_nat_core.c#L391
portsOrIdents = portOrIdentRange{start: 0, size: math.MaxUint16 + 1}
}
return natAction(pkt, hook, r, portsOrIdents, address, false /* dnat */, changePort, changeAddress)
}
func natAction(pkt *PacketBuffer, hook Hook, r *Route, portsOrIdents portOrIdentRange, address tcpip.Address, dnat, changePort, changeAddress bool) (RuleVerdict, int) {
// Drop the packet if network and transport header are not set.
if len(pkt.NetworkHeader().Slice()) == 0 || len(pkt.TransportHeader().Slice()) == 0 {
return RuleDrop, 0
}
if t := pkt.tuple; t != nil {
t.conn.performNAT(pkt, hook, r, portsOrIdents, address, dnat, changePort, changeAddress)
return RuleAccept, 0
}
return RuleDrop, 0
}
// Action implements Target.Action.
func (st *SNATTarget) Action(pkt *PacketBuffer, hook Hook, r *Route, _ AddressableEndpoint) (RuleVerdict, int) {
// Sanity check.
if st.NetworkProtocol != pkt.NetworkProtocolNumber {
panic(fmt.Sprintf(
"SNATTarget.Action with NetworkProtocol %d called on packet with NetworkProtocolNumber %d",
st.NetworkProtocol, pkt.NetworkProtocolNumber))
}
switch hook {
case Postrouting, Input:
case Prerouting, Output, Forward:
panic(fmt.Sprintf("%s not supported", hook))
default:
panic(fmt.Sprintf("%s unrecognized", hook))
}
return snatAction(pkt, hook, r, st.Port, st.Addr, st.ChangePort, st.ChangeAddress)
}
// MasqueradeTarget modifies the source port/IP in the outgoing packets.
type MasqueradeTarget struct {
// NetworkProtocol is the network protocol the target is used with. It
// is immutable.
NetworkProtocol tcpip.NetworkProtocolNumber
}
// Action implements Target.Action.
func (mt *MasqueradeTarget) Action(pkt *PacketBuffer, hook Hook, r *Route, addressEP AddressableEndpoint) (RuleVerdict, int) {
// Sanity check.
if mt.NetworkProtocol != pkt.NetworkProtocolNumber {
panic(fmt.Sprintf(
"MasqueradeTarget.Action with NetworkProtocol %d called on packet with NetworkProtocolNumber %d",
mt.NetworkProtocol, pkt.NetworkProtocolNumber))
}
switch hook {
case Postrouting:
case Prerouting, Input, Forward, Output:
panic(fmt.Sprintf("masquerade target is supported only on postrouting hook; hook = %d", hook))
default:
panic(fmt.Sprintf("%s unrecognized", hook))
}
// addressEP is expected to be set for the postrouting hook.
ep := addressEP.AcquireOutgoingPrimaryAddress(pkt.Network().DestinationAddress(), tcpip.Address{} /* srcHint */, false /* allowExpired */)
if ep == nil {
// No address exists that we can use as a source address.
return RuleDrop, 0
}
address := ep.AddressWithPrefix().Address
ep.DecRef()
return snatAction(pkt, hook, r, 0 /* port */, address, true /* changePort */, true /* changeAddress */)
}
func rewritePacket(n header.Network, t header.Transport, updateSRCFields, fullChecksum, updatePseudoHeader bool, newPortOrIdent uint16, newAddr tcpip.Address) {
switch t := t.(type) {
case header.ChecksummableTransport:
if updateSRCFields {
if fullChecksum {
t.SetSourcePortWithChecksumUpdate(newPortOrIdent)
} else {
t.SetSourcePort(newPortOrIdent)
}
} else {
if fullChecksum {
t.SetDestinationPortWithChecksumUpdate(newPortOrIdent)
} else {
t.SetDestinationPort(newPortOrIdent)
}
}
if updatePseudoHeader {
var oldAddr tcpip.Address
if updateSRCFields {
oldAddr = n.SourceAddress()
} else {
oldAddr = n.DestinationAddress()
}
t.UpdateChecksumPseudoHeaderAddress(oldAddr, newAddr, fullChecksum)
}
case header.ICMPv4:
switch icmpType := t.Type(); icmpType {
case header.ICMPv4Echo:
if updateSRCFields {
t.SetIdentWithChecksumUpdate(newPortOrIdent)
}
case header.ICMPv4EchoReply:
if !updateSRCFields {
t.SetIdentWithChecksumUpdate(newPortOrIdent)
}
default:
panic(fmt.Sprintf("unexpected ICMPv4 type = %d", icmpType))
}
case header.ICMPv6:
switch icmpType := t.Type(); icmpType {
case header.ICMPv6EchoRequest:
if updateSRCFields {
t.SetIdentWithChecksumUpdate(newPortOrIdent)
}
case header.ICMPv6EchoReply:
if !updateSRCFields {
t.SetIdentWithChecksumUpdate(newPortOrIdent)
}
default:
panic(fmt.Sprintf("unexpected ICMPv4 type = %d", icmpType))
}
var oldAddr tcpip.Address
if updateSRCFields {
oldAddr = n.SourceAddress()
} else {
oldAddr = n.DestinationAddress()
}
t.UpdateChecksumPseudoHeaderAddress(oldAddr, newAddr)
default:
panic(fmt.Sprintf("unhandled transport = %#v", t))
}
if checksummableNetHeader, ok := n.(header.ChecksummableNetwork); ok {
if updateSRCFields {
checksummableNetHeader.SetSourceAddressWithChecksumUpdate(newAddr)
} else {
checksummableNetHeader.SetDestinationAddressWithChecksumUpdate(newAddr)
}
} else if updateSRCFields {
n.SetSourceAddress(newAddr)
} else {
n.SetDestinationAddress(newAddr)
}
}