129 lines
3.4 KiB
Go
129 lines
3.4 KiB
Go
// Copyright 2018 Google LLC. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package expr
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"github.com/google/nftables/binaryutil"
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"github.com/mdlayher/netlink"
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"golang.org/x/sys/unix"
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)
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// This code assembles the verdict structure, as expected by the
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// nftables netlink API.
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// For further information, consult:
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// - netfilter.h (Linux kernel)
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// - net/netfilter/nf_tables_api.c (Linux kernel)
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// - src/expr/data_reg.c (linbnftnl)
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type Verdict struct {
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Kind VerdictKind
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Chain string
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}
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type VerdictKind int64
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// Verdicts, as per netfilter.h and netfilter/nf_tables.h.
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const (
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VerdictReturn VerdictKind = iota - 5
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VerdictGoto
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VerdictJump
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VerdictBreak
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VerdictContinue
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VerdictDrop
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VerdictAccept
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VerdictStolen
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VerdictQueue
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VerdictRepeat
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VerdictStop
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)
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func (e *Verdict) marshal() ([]byte, error) {
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// A verdict is a tree of netlink attributes structured as follows:
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// NFTA_LIST_ELEM | NLA_F_NESTED {
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// NFTA_EXPR_NAME { "immediate\x00" }
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// NFTA_EXPR_DATA | NLA_F_NESTED {
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// NFTA_IMMEDIATE_DREG { NFT_REG_VERDICT }
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// NFTA_IMMEDIATE_DATA | NLA_F_NESTED {
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// the verdict code
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// }
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// }
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// }
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attrs := []netlink.Attribute{
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{Type: unix.NFTA_VERDICT_CODE, Data: binaryutil.BigEndian.PutUint32(uint32(e.Kind))},
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}
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if e.Chain != "" {
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attrs = append(attrs, netlink.Attribute{Type: unix.NFTA_VERDICT_CHAIN, Data: []byte(e.Chain + "\x00")})
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}
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codeData, err := netlink.MarshalAttributes(attrs)
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if err != nil {
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return nil, err
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}
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immData, err := netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NLA_F_NESTED | unix.NFTA_DATA_VERDICT, Data: codeData},
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})
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if err != nil {
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return nil, err
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}
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data, err := netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NFTA_IMMEDIATE_DREG, Data: binaryutil.BigEndian.PutUint32(unix.NFT_REG_VERDICT)},
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{Type: unix.NLA_F_NESTED | unix.NFTA_IMMEDIATE_DATA, Data: immData},
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})
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if err != nil {
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return nil, err
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}
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return netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NFTA_EXPR_NAME, Data: []byte("immediate\x00")},
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{Type: unix.NLA_F_NESTED | unix.NFTA_EXPR_DATA, Data: data},
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})
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}
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func (e *Verdict) unmarshal(data []byte) error {
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ad, err := netlink.NewAttributeDecoder(data)
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if err != nil {
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return err
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}
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ad.ByteOrder = binary.BigEndian
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for ad.Next() {
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switch ad.Type() {
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case unix.NFTA_IMMEDIATE_DATA:
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nestedAD, err := netlink.NewAttributeDecoder(ad.Bytes())
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if err != nil {
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return fmt.Errorf("nested NewAttributeDecoder() failed: %v", err)
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}
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for nestedAD.Next() {
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switch nestedAD.Type() {
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case unix.NFTA_DATA_VERDICT:
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e.Kind = VerdictKind(int32(binaryutil.BigEndian.Uint32(nestedAD.Bytes()[4:8])))
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if len(nestedAD.Bytes()) > 12 {
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e.Chain = string(bytes.Trim(nestedAD.Bytes()[12:], "\x00"))
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}
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}
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}
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if nestedAD.Err() != nil {
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return fmt.Errorf("decoding immediate: %v", nestedAD.Err())
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}
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}
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}
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return ad.Err()
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}
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