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nftables.go
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nftables.go
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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// TODO(#8502): add support for more architectures
//go:build linux && (arm64 || amd64)
package linuxfw
import (
"fmt"
"sort"
"strings"
"github.com/google/nftables"
"github.com/google/nftables/expr"
"github.com/google/nftables/xt"
"github.com/josharian/native"
"golang.org/x/sys/unix"
"tailscale.com/types/logger"
"tailscale.com/util/cmpx"
)
// DebugNetfilter prints debug information about netfilter rules to the
// provided log function.
func DebugNetfilter(logf logger.Logf) error {
conn, err := nftables.New()
if err != nil {
return err
}
chains, err := conn.ListChains()
if err != nil {
return fmt.Errorf("cannot list chains: %w", err)
}
if len(chains) == 0 {
logf("netfilter: no chains")
return nil
}
for _, chain := range chains {
logf("netfilter: table=%s chain=%s", chain.Table.Name, chain.Name)
rules, err := conn.GetRules(chain.Table, chain)
if err != nil {
continue
}
sort.Slice(rules, func(i, j int) bool {
return rules[i].Position < rules[j].Position
})
for i, rule := range rules {
logf("netfilter: rule[%d]: pos=%d flags=%d", i, rule.Position, rule.Flags)
for _, ex := range rule.Exprs {
switch v := ex.(type) {
case *expr.Meta:
key := cmpx.Or(metaKeyNames[v.Key], "UNKNOWN")
logf("netfilter: Meta: key=%s source_register=%v register=%d", key, v.SourceRegister, v.Register)
case *expr.Cmp:
op := cmpx.Or(cmpOpNames[v.Op], "UNKNOWN")
logf("netfilter: Cmp: op=%s register=%d data=%s", op, v.Register, formatMaybePrintable(v.Data))
case *expr.Counter:
// don't print
case *expr.Verdict:
kind := cmpx.Or(verdictNames[v.Kind], "UNKNOWN")
logf("netfilter: Verdict: kind=%s data=%s", kind, v.Chain)
case *expr.Target:
logf("netfilter: Target: name=%s info=%s", v.Name, printTargetInfo(v.Name, v.Info))
case *expr.Match:
logf("netfilter: Match: name=%s info=%+v", v.Name, printMatchInfo(v.Name, v.Info))
case *expr.Payload:
logf("netfilter: Payload: op=%s src=%d dst=%d base=%s offset=%d len=%d",
payloadOperationTypeNames[v.OperationType],
v.SourceRegister, v.DestRegister,
payloadBaseNames[v.Base],
v.Offset, v.Len)
// TODO(andrew): csum
case *expr.Bitwise:
var xor string
for _, b := range v.Xor {
if b != 0 {
xor = fmt.Sprintf(" xor=%v", v.Xor)
break
}
}
logf("netfilter: Bitwise: src=%d dst=%d len=%d mask=%v%s",
v.SourceRegister, v.DestRegister, v.Len, v.Mask, xor)
default:
logf("netfilter: unknown %T: %+v", v, v)
}
}
}
}
return nil
}
// detectNetfilter returns the number of nftables rules present in the system.
func detectNetfilter() (int, error) {
// Frist try creating a dummy postrouting chain. Emperically, we have
// noticed that on some devices there is partial nftables support and the
// kernel rejects some chains that are valid on other devices. This is a
// workaround to detect that case.
//
// This specifically allows us to run in on GKE nodes using COS images which
// have partial nftables support (as of 2023-10-18). When we try to create a
// dummy postrouting chain, we get an error like:
// add chain: conn.Receive: netlink receive: no such file or directory
nft, err := newNfTablesRunner(logger.Discard)
if err != nil {
return 0, FWModeNotSupportedError{
Mode: FirewallModeNfTables,
Err: fmt.Errorf("cannot create nftables runner: %w", err),
}
}
if err := nft.createDummyPostroutingChains(); err != nil {
return 0, FWModeNotSupportedError{
Mode: FirewallModeNfTables,
Err: err,
}
}
conn, err := nftables.New()
if err != nil {
return 0, FWModeNotSupportedError{
Mode: FirewallModeNfTables,
Err: err,
}
}
chains, err := conn.ListChains()
if err != nil {
return 0, FWModeNotSupportedError{
Mode: FirewallModeNfTables,
Err: fmt.Errorf("cannot list chains: %w", err),
}
}
var validRules int
for _, chain := range chains {
rules, err := conn.GetRules(chain.Table, chain)
if err != nil {
continue
}
validRules += len(rules)
}
return validRules, nil
}
func printMatchInfo(name string, info xt.InfoAny) string {
var sb strings.Builder
sb.WriteString(`{`)
var handled bool = true
switch v := info.(type) {
// TODO(andrew): we should support these common types
//case *xt.ConntrackMtinfo3:
//case *xt.ConntrackMtinfo2:
case *xt.Tcp:
fmt.Fprintf(&sb, "Src:%s Dst:%s", formatPortRange(v.SrcPorts), formatPortRange(v.DstPorts))
if v.Option != 0 {
fmt.Fprintf(&sb, " Option:%d", v.Option)
}
if v.FlagsMask != 0 {
fmt.Fprintf(&sb, " FlagsMask:%d", v.FlagsMask)
}
if v.FlagsCmp != 0 {
fmt.Fprintf(&sb, " FlagsCmp:%d", v.FlagsCmp)
}
if v.InvFlags != 0 {
fmt.Fprintf(&sb, " InvFlags:%d", v.InvFlags)
}
case *xt.Udp:
fmt.Fprintf(&sb, "Src:%s Dst:%s", formatPortRange(v.SrcPorts), formatPortRange(v.DstPorts))
if v.InvFlags != 0 {
fmt.Fprintf(&sb, " InvFlags:%d", v.InvFlags)
}
case *xt.AddrType:
var sprefix, dprefix string
if v.InvertSource {
sprefix = "!"
}
if v.InvertDest {
dprefix = "!"
}
// TODO(andrew): translate source/dest
fmt.Fprintf(&sb, "Source:%s%d Dest:%s%d", sprefix, v.Source, dprefix, v.Dest)
case *xt.AddrTypeV1:
// TODO(andrew): translate source/dest
fmt.Fprintf(&sb, "Source:%d Dest:%d", v.Source, v.Dest)
var flags []string
for flag, name := range addrTypeFlagNames {
if v.Flags&flag != 0 {
flags = append(flags, name)
}
}
if len(flags) > 0 {
sort.Strings(flags)
fmt.Fprintf(&sb, "Flags:%s", strings.Join(flags, ","))
}
default:
handled = false
}
if handled {
sb.WriteString(`}`)
return sb.String()
}
unknown, ok := info.(*xt.Unknown)
if !ok {
return fmt.Sprintf("(%T)%+v", info, info)
}
data := []byte(*unknown)
// Things where upstream has no type
handled = true
switch name {
case "pkttype":
if len(data) != 8 {
handled = false
break
}
pkttype := int(native.Endian.Uint32(data[0:4]))
invert := int(native.Endian.Uint32(data[4:8]))
var invertPrefix string
if invert != 0 {
invertPrefix = "!"
}
pkttypeName := packetTypeNames[pkttype]
if pkttypeName != "" {
fmt.Fprintf(&sb, "PktType:%s%s", invertPrefix, pkttypeName)
} else {
fmt.Fprintf(&sb, "PktType:%s%d", invertPrefix, pkttype)
}
default:
handled = true
}
if !handled {
return fmt.Sprintf("(%T)%+v", info, info)
}
sb.WriteString(`}`)
return sb.String()
}
func printTargetInfo(name string, info xt.InfoAny) string {
var sb strings.Builder
sb.WriteString(`{`)
unknown, ok := info.(*xt.Unknown)
if !ok {
return fmt.Sprintf("(%T)%+v", info, info)
}
data := []byte(*unknown)
// Things where upstream has no type
switch name {
case "LOG":
if len(data) != 32 {
fmt.Fprintf(&sb, `Error:"bad size; want 32, got %d"`, len(data))
break
}
level := data[0]
logflags := data[1]
prefix := unix.ByteSliceToString(data[2:])
fmt.Fprintf(&sb, "Level:%d LogFlags:%d Prefix:%q", level, logflags, prefix)
default:
return fmt.Sprintf("(%T)%+v", info, info)
}
sb.WriteString(`}`)
return sb.String()
}