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verdict.go
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verdict.go
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// Copyright 2018 Google LLC. All Rights Reserved.
//
// 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 expr
import (
"bytes"
"encoding/binary"
"fmt"
"github.com/google/nftables/binaryutil"
"github.com/mdlayher/netlink"
"golang.org/x/sys/unix"
)
// This code assembles the verdict structure, as expected by the
// nftables netlink API.
// For further information, consult:
// - netfilter.h (Linux kernel)
// - net/netfilter/nf_tables_api.c (Linux kernel)
// - src/expr/data_reg.c (linbnftnl)
type Verdict struct {
Kind VerdictKind
Chain string
}
type VerdictKind int64
// Verdicts, as per netfilter.h and netfilter/nf_tables.h.
const (
VerdictReturn VerdictKind = iota - 5
VerdictGoto
VerdictJump
VerdictBreak
VerdictContinue
VerdictDrop
VerdictAccept
VerdictStolen
VerdictQueue
VerdictRepeat
VerdictStop
)
func (e *Verdict) marshal() ([]byte, error) {
// A verdict is a tree of netlink attributes structured as follows:
// NFTA_LIST_ELEM | NLA_F_NESTED {
// NFTA_EXPR_NAME { "immediate\x00" }
// NFTA_EXPR_DATA | NLA_F_NESTED {
// NFTA_IMMEDIATE_DREG { NFT_REG_VERDICT }
// NFTA_IMMEDIATE_DATA | NLA_F_NESTED {
// the verdict code
// }
// }
// }
attrs := []netlink.Attribute{
{Type: unix.NFTA_VERDICT_CODE, Data: binaryutil.BigEndian.PutUint32(uint32(e.Kind))},
}
if e.Chain != "" {
attrs = append(attrs, netlink.Attribute{Type: unix.NFTA_VERDICT_CHAIN, Data: []byte(e.Chain + "\x00")})
}
codeData, err := netlink.MarshalAttributes(attrs)
if err != nil {
return nil, err
}
immData, err := netlink.MarshalAttributes([]netlink.Attribute{
{Type: unix.NLA_F_NESTED | unix.NFTA_DATA_VERDICT, Data: codeData},
})
if err != nil {
return nil, err
}
data, err := netlink.MarshalAttributes([]netlink.Attribute{
{Type: unix.NFTA_IMMEDIATE_DREG, Data: binaryutil.BigEndian.PutUint32(unix.NFT_REG_VERDICT)},
{Type: unix.NLA_F_NESTED | unix.NFTA_IMMEDIATE_DATA, Data: immData},
})
if err != nil {
return nil, err
}
return netlink.MarshalAttributes([]netlink.Attribute{
{Type: unix.NFTA_EXPR_NAME, Data: []byte("immediate\x00")},
{Type: unix.NLA_F_NESTED | unix.NFTA_EXPR_DATA, Data: data},
})
}
func (e *Verdict) unmarshal(data []byte) error {
ad, err := netlink.NewAttributeDecoder(data)
if err != nil {
return err
}
ad.ByteOrder = binary.BigEndian
for ad.Next() {
switch ad.Type() {
case unix.NFTA_IMMEDIATE_DATA:
nestedAD, err := netlink.NewAttributeDecoder(ad.Bytes())
if err != nil {
return fmt.Errorf("nested NewAttributeDecoder() failed: %v", err)
}
for nestedAD.Next() {
switch nestedAD.Type() {
case unix.NFTA_DATA_VERDICT:
e.Kind = VerdictKind(int32(binaryutil.BigEndian.Uint32(nestedAD.Bytes()[4:8])))
if len(nestedAD.Bytes()) > 12 {
e.Chain = string(bytes.Trim(nestedAD.Bytes()[12:], "\x00"))
}
}
}
if nestedAD.Err() != nil {
return fmt.Errorf("decoding immediate: %v", nestedAD.Err())
}
}
}
return ad.Err()
}