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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 (
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/header"
)
// AcceptTarget accepts packets.
type AcceptTarget struct{}
// Action implements Target.Action.
func (AcceptTarget) Action(*PacketBuffer, *ConnTrack, Hook, *GSO, *Route, tcpip.Address) (RuleVerdict, int) {
return RuleAccept, 0
}
// DropTarget drops packets.
type DropTarget struct{}
// Action implements Target.Action.
func (DropTarget) Action(*PacketBuffer, *ConnTrack, Hook, *GSO, *Route, tcpip.Address) (RuleVerdict, int) {
return RuleDrop, 0
}
// ErrorTarget logs an error and drops the packet. It represents a target that
// should be unreachable.
type ErrorTarget struct{}
// Action implements Target.Action.
func (ErrorTarget) Action(*PacketBuffer, *ConnTrack, Hook, *GSO, *Route, tcpip.Address) (RuleVerdict, int) {
log.Debugf("ErrorTarget triggered.")
return RuleDrop, 0
}
// UserChainTarget marks a rule as the beginning of a user chain.
type UserChainTarget struct {
Name string
}
// Action implements Target.Action.
func (UserChainTarget) Action(*PacketBuffer, *ConnTrack, Hook, *GSO, *Route, tcpip.Address) (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{}
// Action implements Target.Action.
func (ReturnTarget) Action(*PacketBuffer, *ConnTrack, Hook, *GSO, *Route, tcpip.Address) (RuleVerdict, int) {
return RuleReturn, 0
}
// RedirectTarget redirects the packet by modifying the destination port/IP.
// Min and Max values for IP and Ports in the struct indicate the range of
// values which can be used to redirect.
type RedirectTarget struct {
// TODO(gvisor.dev/issue/170): Other flags need to be added after
// we support them.
// RangeProtoSpecified flag indicates single port is specified to
// redirect.
RangeProtoSpecified bool
// MinIP indicates address used to redirect.
MinIP tcpip.Address
// MaxIP indicates address used to redirect.
MaxIP tcpip.Address
// MinPort indicates port used to redirect.
MinPort uint16
// MaxPort indicates port used to redirect.
MaxPort uint16
}
// Action implements Target.Action.
// TODO(gvisor.dev/issue/170): Parse headers without copying. The current
// implementation only works for PREROUTING and calls pkt.Clone(), neither
// of which should be the case.
func (rt RedirectTarget) Action(pkt *PacketBuffer, ct *ConnTrack, hook Hook, gso *GSO, r *Route, address tcpip.Address) (RuleVerdict, int) {
// Packet is already manipulated.
if pkt.NatDone {
return RuleAccept, 0
}
// Drop the packet if network and transport header are not set.
if pkt.NetworkHeader().View().IsEmpty() || pkt.TransportHeader().View().IsEmpty() {
return RuleDrop, 0
}
// Change the address to localhost (127.0.0.1) in Output and
// to primary address of the incoming interface in Prerouting.
switch hook {
case Output:
rt.MinIP = tcpip.Address([]byte{127, 0, 0, 1})
rt.MaxIP = tcpip.Address([]byte{127, 0, 0, 1})
case Prerouting:
rt.MinIP = address
rt.MaxIP = address
default:
panic("redirect target is supported only on output and prerouting hooks")
}
// TODO(gvisor.dev/issue/170): Check Flags in RedirectTarget if
// we need to change dest address (for OUTPUT chain) or ports.
netHeader := header.IPv4(pkt.NetworkHeader().View())
switch protocol := netHeader.TransportProtocol(); protocol {
case header.UDPProtocolNumber:
udpHeader := header.UDP(pkt.TransportHeader().View())
udpHeader.SetDestinationPort(rt.MinPort)
// Calculate UDP checksum and set it.
if hook == Output {
udpHeader.SetChecksum(0)
length := uint16(pkt.Size()) - uint16(netHeader.HeaderLength())
// Only calculate the checksum if offloading isn't supported.
if r.Capabilities()&CapabilityTXChecksumOffload == 0 {
xsum := r.PseudoHeaderChecksum(protocol, length)
for _, v := range pkt.Data.Views() {
xsum = header.Checksum(v, xsum)
}
udpHeader.SetChecksum(0)
udpHeader.SetChecksum(^udpHeader.CalculateChecksum(xsum))
}
}
// Change destination address.
netHeader.SetDestinationAddress(rt.MinIP)
netHeader.SetChecksum(0)
netHeader.SetChecksum(^netHeader.CalculateChecksum())
pkt.NatDone = true
case header.TCPProtocolNumber:
if ct == nil {
return RuleAccept, 0
}
// Set up conection for matching NAT rule. Only the first
// packet of the connection comes here. Other packets will be
// manipulated in connection tracking.
if conn := ct.insertRedirectConn(pkt, hook, rt); conn != nil {
ct.handlePacket(pkt, hook, gso, r)
}
default:
return RuleDrop, 0
}
return RuleAccept, 0
}
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