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-rw-r--r--pkg/tcpip/stack/iptables.go311
1 files changed, 311 insertions, 0 deletions
diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.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"
+
+ "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: AcceptTarget{}},
+ Rule{Target: AcceptTarget{}},
+ Rule{Target: AcceptTarget{}},
+ Rule{Target: AcceptTarget{}},
+ 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: AcceptTarget{}},
+ Rule{Target: AcceptTarget{}},
+ 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: AcceptTarget{}},
+ Rule{Target: AcceptTarget{}},
+ Rule{Target: AcceptTarget{}},
+ 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{},
+ }
+}
+
+// EmptyNatTable returns a Table with no rules and the filter table chains
+// mapped to HookUnset.
+func EmptyNatTable() Table {
+ return Table{
+ Rules: []Rule{},
+ BuiltinChains: map[Hook]int{
+ Prerouting: HookUnset,
+ Input: HookUnset,
+ Output: HookUnset,
+ Postrouting: HookUnset,
+ },
+ Underflows: map[Hook]int{
+ Prerouting: HookUnset,
+ Input: HookUnset,
+ Output: HookUnset,
+ Postrouting: HookUnset,
+ },
+ UserChains: map[string]int{},
+ }
+}
+
+// A chainVerdict is what a table decides should be done with a packet.
+type chainVerdict int
+
+const (
+ // chainAccept indicates the packet should continue through netstack.
+ chainAccept chainVerdict = iota
+
+ // chainAccept indicates the packet should be dropped.
+ chainDrop
+
+ // chainReturn indicates the packet should return to the calling chain
+ // or the underflow rule of a builtin chain.
+ chainReturn
+)
+
+// 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 PacketBuffer) bool {
+ // Go through each table containing the hook.
+ for _, tablename := range it.Priorities[hook] {
+ table := it.Tables[tablename]
+ ruleIdx := table.BuiltinChains[hook]
+ switch verdict := it.checkChain(hook, pkt, table, ruleIdx); verdict {
+ // If the table returns Accept, move on to the next table.
+ case chainAccept:
+ continue
+ // The Drop verdict is final.
+ case chainDrop:
+ return false
+ case chainReturn:
+ // Any Return from a built-in chain means we have to
+ // call the underflow.
+ underflow := table.Rules[table.Underflows[hook]]
+ switch v, _ := underflow.Target.Action(pkt); v {
+ case RuleAccept:
+ continue
+ case RuleDrop:
+ return false
+ case RuleJump, RuleReturn:
+ panic("Underflows should only return RuleAccept or RuleDrop.")
+ default:
+ panic(fmt.Sprintf("Unknown verdict: %d", v))
+ }
+
+ default:
+ panic(fmt.Sprintf("Unknown verdict %v.", verdict))
+ }
+ }
+
+ // Every table returned Accept.
+ return true
+}
+
+// Precondition: pkt.NetworkHeader is set.
+func (it *IPTables) checkChain(hook Hook, pkt PacketBuffer, table Table, ruleIdx int) chainVerdict {
+ // Start from ruleIdx and walk the list of rules until a rule gives us
+ // a verdict.
+ for ruleIdx < len(table.Rules) {
+ switch verdict, jumpTo := it.checkRule(hook, pkt, table, ruleIdx); verdict {
+ case RuleAccept:
+ return chainAccept
+
+ case RuleDrop:
+ return chainDrop
+
+ case RuleReturn:
+ return chainReturn
+
+ case RuleJump:
+ // "Jumping" to the next rule just means we're
+ // continuing on down the list.
+ if jumpTo == ruleIdx+1 {
+ ruleIdx++
+ continue
+ }
+ switch verdict := it.checkChain(hook, pkt, table, jumpTo); verdict {
+ case chainAccept:
+ return chainAccept
+ case chainDrop:
+ return chainDrop
+ case chainReturn:
+ ruleIdx++
+ continue
+ default:
+ panic(fmt.Sprintf("Unknown verdict: %d", verdict))
+ }
+
+ default:
+ panic(fmt.Sprintf("Unknown verdict: %d", verdict))
+ }
+
+ }
+
+ // We got through the entire table without a decision. Default to DROP
+ // for safety.
+ return chainDrop
+}
+
+// Precondition: pk.NetworkHeader is set.
+func (it *IPTables) checkRule(hook Hook, pkt PacketBuffer, table Table, ruleIdx int) (RuleVerdict, int) {
+ rule := table.Rules[ruleIdx]
+
+ // If pkt.NetworkHeader hasn't been set yet, it will be contained in
+ // pkt.Data.First().
+ if pkt.NetworkHeader == nil {
+ pkt.NetworkHeader = pkt.Data.First()
+ }
+
+ // Check whether the packet matches the IP header filter.
+ if !filterMatch(rule.Filter, header.IPv4(pkt.NetworkHeader)) {
+ // Continue on to the next rule.
+ return RuleJump, ruleIdx + 1
+ }
+
+ // 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 RuleDrop, 0
+ }
+ if !matches {
+ // Continue on to the next rule.
+ return RuleJump, ruleIdx + 1
+ }
+ }
+
+ // All the matchers matched, so run the target.
+ return rule.Target.Action(pkt)
+}
+
+func filterMatch(filter IPHeaderFilter, hdr header.IPv4) bool {
+ // TODO(gvisor.dev/issue/170): Support other fields of the filter.
+ // Check the transport protocol.
+ if filter.Protocol != 0 && filter.Protocol != hdr.TransportProtocol() {
+ return false
+ }
+
+ // Check the destination IP.
+ dest := hdr.DestinationAddress()
+ matches := true
+ for i := range filter.Dst {
+ if dest[i]&filter.DstMask[i] != filter.Dst[i] {
+ matches = false
+ break
+ }
+ }
+ if matches == filter.DstInvert {
+ return false
+ }
+
+ return true
+}
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