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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 iptables supports packet filtering and manipulation via the iptables
// tool.
package iptables
import (
"fmt"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/header"
)
// Table names.
const (
TablenameNat = "nat"
TablenameMangle = "mangle"
TablenameFilter = "filter"
)
// Chain names as defined by net/ipv4/netfilter/ip_tables.c.
const (
ChainNamePrerouting = "PREROUTING"
ChainNameInput = "INPUT"
ChainNameForward = "FORWARD"
ChainNameOutput = "OUTPUT"
ChainNamePostrouting = "POSTROUTING"
)
// HookUnset indicates that there is no hook set for an entrypoint or
// underflow.
const HookUnset = -1
// DefaultTables returns a default set of tables. Each chain is set to accept
// all packets.
func DefaultTables() IPTables {
// TODO(gvisor.dev/issue/170): We may be able to swap out some strings for
// iotas.
return IPTables{
Tables: map[string]Table{
TablenameNat: Table{
Rules: []Rule{
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: ErrorTarget{}},
},
BuiltinChains: map[Hook]int{
Prerouting: 0,
Input: 1,
Output: 2,
Postrouting: 3,
},
Underflows: map[Hook]int{
Prerouting: 0,
Input: 1,
Output: 2,
Postrouting: 3,
},
UserChains: map[string]int{},
},
TablenameMangle: Table{
Rules: []Rule{
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: ErrorTarget{}},
},
BuiltinChains: map[Hook]int{
Prerouting: 0,
Output: 1,
},
Underflows: map[Hook]int{
Prerouting: 0,
Output: 1,
},
UserChains: map[string]int{},
},
TablenameFilter: Table{
Rules: []Rule{
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: UnconditionalAcceptTarget{}},
Rule{Target: ErrorTarget{}},
},
BuiltinChains: map[Hook]int{
Input: 0,
Forward: 1,
Output: 2,
},
Underflows: map[Hook]int{
Input: 0,
Forward: 1,
Output: 2,
},
UserChains: map[string]int{},
},
},
Priorities: map[Hook][]string{
Input: []string{TablenameNat, TablenameFilter},
Prerouting: []string{TablenameMangle, TablenameNat},
Output: []string{TablenameMangle, TablenameNat, TablenameFilter},
},
}
}
// EmptyFilterTable returns a Table with no rules and the filter table chains
// mapped to HookUnset.
func EmptyFilterTable() Table {
return Table{
Rules: []Rule{},
BuiltinChains: map[Hook]int{
Input: HookUnset,
Forward: HookUnset,
Output: HookUnset,
},
Underflows: map[Hook]int{
Input: HookUnset,
Forward: HookUnset,
Output: HookUnset,
},
UserChains: map[string]int{},
}
}
// Check runs pkt through the rules for hook. It returns true when the packet
// should continue traversing the network stack and false when it should be
// dropped.
//
// Precondition: pkt.NetworkHeader is set.
func (it *IPTables) Check(hook Hook, pkt tcpip.PacketBuffer) bool {
// TODO(gvisor.dev/issue/170): A lot of this is uncomplicated because
// we're missing features. Jumps, the call stack, etc. aren't checked
// for yet because we're yet to support them.
// Go through each table containing the hook.
for _, tablename := range it.Priorities[hook] {
switch verdict := it.checkTable(hook, pkt, tablename); verdict {
// If the table returns Accept, move on to the next table.
case Accept:
continue
// The Drop verdict is final.
case Drop:
return false
case Stolen, Queue, Repeat, None, Jump, Return, Continue:
panic(fmt.Sprintf("Unimplemented verdict %v.", verdict))
default:
panic(fmt.Sprintf("Unknown verdict %v.", verdict))
}
}
// Every table returned Accept.
return true
}
// Precondition: pkt.NetworkHeader is set.
func (it *IPTables) checkTable(hook Hook, pkt tcpip.PacketBuffer, tablename string) Verdict {
// Start from ruleIdx and walk the list of rules until a rule gives us
// a verdict.
table := it.Tables[tablename]
for ruleIdx := table.BuiltinChains[hook]; ruleIdx < len(table.Rules); ruleIdx++ {
switch verdict := it.checkRule(hook, pkt, table, ruleIdx); verdict {
// In either of these cases, this table is done with the packet.
case Accept, Drop:
return verdict
// Continue traversing the rules of the table.
case Continue:
continue
case Stolen, Queue, Repeat, None, Jump, Return:
panic(fmt.Sprintf("Unimplemented verdict %v.", verdict))
default:
panic(fmt.Sprintf("Unknown verdict %v.", verdict))
}
}
panic(fmt.Sprintf("Traversed past the entire list of iptables rules in table %q.", tablename))
}
// Precondition: pk.NetworkHeader is set.
func (it *IPTables) checkRule(hook Hook, pkt tcpip.PacketBuffer, table Table, ruleIdx int) Verdict {
rule := table.Rules[ruleIdx]
// First check whether the packet matches the IP header filter.
// TODO(gvisor.dev/issue/170): Support other fields of the filter.
if rule.Filter.Protocol != 0 && rule.Filter.Protocol != header.IPv4(pkt.NetworkHeader).TransportProtocol() {
return Continue
}
// Go through each rule matcher. If they all match, run
// the rule target.
for _, matcher := range rule.Matchers {
matches, hotdrop := matcher.Match(hook, pkt, "")
if hotdrop {
return Drop
}
if !matches {
return Continue
}
}
// All the matchers matched, so run the target.
verdict, _ := rule.Target.Action(pkt)
return verdict
}
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