Add basic iptables structures to netstack.

Change-Id: Ib589906175a59dae315405a28f2d7f525ff8877f

4 files changed, 342 insertions, 0 deletions

diff --git a/pkg/tcpip/iptables/BUILD b/pkg/tcpip/iptables/BUILD
new file mode 100644
index 000000000..173f148da
--- /dev/null
+++ b/pkg/tcpip/iptables/BUILD
@@ -0,0 +1,20 @@
+package(licenses = ["notice"])
+
+load("//tools/go_stateify:defs.bzl", "go_library", "go_test")
+
+go_library(
+    name = "iptables",
+    srcs = [
+        "iptables.go",
+        "targets.go",
+        "types.go",
+    ],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/tcpip/iptables",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/state",
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/header",
+    ],
+)
diff --git a/pkg/tcpip/iptables/iptables.go b/pkg/tcpip/iptables/iptables.go
new file mode 100644
index 000000000..ee1ed4666
--- /dev/null
+++ b/pkg/tcpip/iptables/iptables.go
@@ -0,0 +1,97 @@
+// 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
+
+const (
+	tablenameNat    = "nat"
+	tablenameMangle = "mangle"
+)
+
+// Chain names as defined by net/ipv4/netfilter/ip_tables.c.
+const (
+	chainNamePrerouting  = "PREROUTING"
+	chainNameInput       = "INPUT"
+	chainNameForward     = "FORWARD"
+	chainNameOutput      = "OUTPUT"
+	chainNamePostrouting = "POSTROUTING"
+)
+
+// DefaultTables returns a default set of tables. Each chain is set to accept
+// all packets.
+func DefaultTables() *IPTables {
+	tables := IPTables{
+		Tables: map[string]*Table{
+			tablenameNat: &Table{
+				BuiltinChains: map[Hook]*Chain{
+					Prerouting:  unconditionalAcceptChain(chainNamePrerouting),
+					Input:       unconditionalAcceptChain(chainNameInput),
+					Output:      unconditionalAcceptChain(chainNameOutput),
+					Postrouting: unconditionalAcceptChain(chainNamePostrouting),
+				},
+				DefaultTargets: map[Hook]Target{
+					Prerouting:  UnconditionalAcceptTarget{},
+					Input:       UnconditionalAcceptTarget{},
+					Output:      UnconditionalAcceptTarget{},
+					Postrouting: UnconditionalAcceptTarget{},
+				},
+				UserChains: map[string]*Chain{},
+			},
+			tablenameMangle: &Table{
+				BuiltinChains: map[Hook]*Chain{
+					Prerouting: unconditionalAcceptChain(chainNamePrerouting),
+					Output:     unconditionalAcceptChain(chainNameOutput),
+				},
+				DefaultTargets: map[Hook]Target{
+					Prerouting: UnconditionalAcceptTarget{},
+					Output:     UnconditionalAcceptTarget{},
+				},
+				UserChains: map[string]*Chain{},
+			},
+		},
+		Priorities: map[Hook][]string{
+			Prerouting: []string{tablenameMangle, tablenameNat},
+			Output:     []string{tablenameMangle, tablenameNat},
+		},
+	}
+
+	// Initialize each table's Chains field.
+	tables.Tables[tablenameNat].Chains = map[string]*Chain{
+		chainNamePrerouting:  tables.Tables[tablenameNat].BuiltinChains[Prerouting],
+		chainNameInput:       tables.Tables[tablenameNat].BuiltinChains[Input],
+		chainNameOutput:      tables.Tables[tablenameNat].BuiltinChains[Output],
+		chainNamePostrouting: tables.Tables[tablenameNat].BuiltinChains[Postrouting],
+	}
+	tables.Tables[tablenameMangle].Chains = map[string]*Chain{
+		chainNamePrerouting:  tables.Tables[tablenameMangle].BuiltinChains[Prerouting],
+		chainNameInput:       tables.Tables[tablenameMangle].BuiltinChains[Input],
+		chainNameOutput:      tables.Tables[tablenameMangle].BuiltinChains[Output],
+		chainNamePostrouting: tables.Tables[tablenameMangle].BuiltinChains[Postrouting],
+	}
+
+	return &tables
+}
+
+func unconditionalAcceptChain(name string) *Chain {
+	return &Chain{
+		Name: name,
+		Rules: []*Rule{
+			&Rule{
+				Target: UnconditionalAcceptTarget{},
+			},
+		},
+	}
+}
diff --git a/pkg/tcpip/iptables/targets.go b/pkg/tcpip/iptables/targets.go
new file mode 100644
index 000000000..028978e3a
--- /dev/null
+++ b/pkg/tcpip/iptables/targets.go
@@ -0,0 +1,35 @@
+// 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
+
+import "gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
+
+// This file contains various Targets.
+
+// UnconditionalAcceptTarget accepts all packets.
+type UnconditionalAcceptTarget struct{}
+
+// Action implements Target.Action.
+func (_ UnconditionalAcceptTarget) Action(packet buffer.VectorisedView) (Verdict, string) {
+	return Accept, ""
+}
+
+// UnconditionalDropTarget denies all packets.
+type UnconditionalDropTarget struct{}
+
+// Action implements Target.Action.
+func (_ UnconditionalDropTarget) Action(packet buffer.VectorisedView) (Verdict, string) {
+	return Drop, ""
+}
diff --git a/pkg/tcpip/iptables/types.go b/pkg/tcpip/iptables/types.go
new file mode 100644
index 000000000..65bfc7b1d
--- /dev/null
+++ b/pkg/tcpip/iptables/types.go
@@ -0,0 +1,190 @@
+// 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
+
+import (
+	"sync"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
+)
+
+// Hook specifies one of the hooks built into the network stack.
+//
+//                      Userspace app          Userspace app
+//                            ^                      |
+//                            |                      v
+//                         [Input]               [Output]
+//                            ^                      |
+//                            |                      v
+//                            |                   routing
+//                            |                      |
+//                            |                      v
+// ----->[Prerouting]----->routing----->[Forward]---------[Postrouting]----->
+type Hook uint
+
+// These values correspond to values in include/uapi/linux/netfilter.h.
+const (
+	// Prerouting happens before a packet is routed to applications or to
+	// be forwarded.
+	Prerouting Hook = iota
+
+	// Input happens before a packet reaches an application.
+	Input
+
+	// Forward happens once it's decided that a packet should be forwarded
+	// to another host.
+	Forward
+
+	// Output happens after a packet is written by an application to be
+	// sent out.
+	Output
+
+	// Postrouting happens just before a packet goes out on the wire.
+	Postrouting
+
+	// The total number of hooks.
+	NumHooks
+)
+
+// Verdict is returned by a rule's target to indicate how traversal of rules
+// should (or should not) continue.
+type Verdict int
+
+const (
+	// Accept indicates the packet should continue traversing netstack as
+	// normal.
+	Accept Verdict = iota
+
+	// Drop inicates the packet should be dropped, stopping traversing
+	// netstack.
+	Drop
+
+	// Stolen indicates the packet was co-opted by the target and should
+	// stop traversing netstack.
+	Stolen
+
+	// Queue indicates the packet should be queued for userspace processing.
+	Queue
+
+	// Repeat indicates the packet should re-traverse the chains for the
+	// current hook.
+	Repeat
+
+	// None indicates no verdict was reached.
+	None
+
+	// Jump indicates a jump to another chain.
+	Jump
+
+	// Continue indicates that traversal should continue at the next rule.
+	Continue
+
+	// Return indicates that traversal should return to the calling chain.
+	Return
+)
+
+// IPTables holds all the tables for a netstack.
+type IPTables struct {
+	// mu protects the entire struct.
+	mu sync.RWMutex
+
+	// Tables maps table names to tables. User tables have arbitrary names.
+	Tables map[string]*Table
+
+	// Priorities maps each hook to a list of table names. The order of the
+	// list is the order in which each table should be visited for that
+	// hook.
+	Priorities map[Hook][]string
+}
+
+// Table defines a set of chains and hooks into the network stack. The
+// currently supported tables are:
+//   * nat
+//   * mangle
+type Table struct {
+	// BuiltinChains holds the un-deletable chains built into netstack. If
+	// a hook isn't present in the map, this table doesn't utilize that
+	// hook.
+	BuiltinChains map[Hook]*Chain
+
+	// DefaultTargets holds a target for each hook that will be executed if
+	// chain traversal doesn't yield a verdict.
+	DefaultTargets map[Hook]Target
+
+	// UserChains holds user-defined chains for the keyed by name. Users
+	// can give their chains arbitrary names.
+	UserChains map[string]*Chain
+
+	// Chains maps names to chains for both builtin and user-defined chains.
+	// Its entries point to Chains already either in BuiltinChains and
+	// UserChains, and its purpose is to make looking up tables by name
+	// fast.
+	Chains map[string]*Chain
+}
+
+// ValidHooks returns a bitmap of the builtin hooks for the given table.
+//
+// Precondition: IPTables.mu must be locked for reading.
+func (table *Table) ValidHooks() (uint32, *tcpip.Error) {
+	hooks := uint32(0)
+	for hook, _ := range table.BuiltinChains {
+		hooks |= 1 << hook
+	}
+	return hooks, nil
+}
+
+// Chain defines a list of rules for packet processing. When a packet traverses
+// a chain, it is checked against each rule until either a rule returns a
+// verdict or the chain ends.
+//
+// By convention, builtin chains end with a rule that matches everything and
+// returns either Accept or Drop. User-defined chains end with Return. These
+// aren't strictly necessary here, but the iptables tool writes tables this way.
+type Chain struct {
+	// Name is the chain name.
+	Name string
+
+	// Rules is the list of rules to traverse.
+	Rules []*Rule
+}
+
+// Rule is a packet processing rule. It consists of two pieces. First it
+// contains zero or more matchers, each of which is a specification of which
+// packets this rule applies to. If there are no matchers in the rule, it
+// applies to any packet.
+type Rule struct {
+	// Matchers is the list of matchers for this rule.
+	Matchers []Matcher
+
+	// Target is the action to invoke if all the matchers match the packet.
+	Target Target
+}
+
+// Matcher is the interface for matching packets.
+type Matcher interface {
+	// Match returns whether the packet matches and whether the packet
+	// should be "hotdropped", i.e. dropped immediately. This is usually
+	// used for suspicious packets.
+	Match(hook Hook, packet buffer.VectorisedView, interfaceName string) (matches bool, hotdrop bool)
+}
+
+// Target is the interface for taking an action for a packet.
+type Target interface {
+	// Action takes an action on the packet and returns a verdict on how
+	// traversal should (or should not) continue. If the return value is
+	// Jump, it also returns the name of the chain to jump to.
+	Action(packet buffer.VectorisedView) (Verdict, string)
+}