1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
|
// 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.
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
}
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
}
|
