119 lines
3.5 KiB
Go
119 lines
3.5 KiB
Go
// Copyright 2024 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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"encoding/binary"
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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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type SynProxy struct {
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Mss uint16
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Wscale uint8
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Timestamp bool
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SackPerm bool
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// Probably not expected to be set by users
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// https://github.com/torvalds/linux/blob/521b1e7f4cf0b05a47995b103596978224b380a8/net/netfilter/nft_synproxy.c#L30-L31
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Ecn bool
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// True when Mss is set to a value or if 0 is an intended value of Mss
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MssValueSet bool
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// True when Wscale is set to a value or if 0 is an intended value of Wscale
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WscaleValueSet bool
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}
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// From https://git.netfilter.org/libnftnl/tree/include/linux/netfilter/nf_tables.h?id=be0bae0ad31b0adb506f96de083f52a2bd0d4fbf#n1723
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// Currently not available in golang.org/x/sys/unix
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const (
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NFTA_SYNPROXY_MSS = 0x01
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NFTA_SYNPROXY_WSCALE = 0x02
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NFTA_SYNPROXY_FLAGS = 0x03
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)
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// From https://github.com/torvalds/linux/blob/521b1e7f4cf0b05a47995b103596978224b380a8/include/uapi/linux/netfilter/nf_synproxy.h#L7-L15
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// Currently not available in golang.org/x/sys/unix
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const (
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NF_SYNPROXY_OPT_MSS = 0x01
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NF_SYNPROXY_OPT_WSCALE = 0x02
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NF_SYNPROXY_OPT_SACK_PERM = 0x04
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NF_SYNPROXY_OPT_TIMESTAMP = 0x08
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NF_SYNPROXY_OPT_ECN = 0x10
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)
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func (e *SynProxy) marshal(fam byte) ([]byte, error) {
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data, err := e.marshalData(fam)
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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("synproxy\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 *SynProxy) marshalData(fam byte) ([]byte, error) {
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var flags uint32
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if e.Mss != 0 || e.MssValueSet {
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flags |= NF_SYNPROXY_OPT_MSS
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}
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if e.Wscale != 0 || e.WscaleValueSet {
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flags |= NF_SYNPROXY_OPT_WSCALE
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}
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if e.SackPerm {
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flags |= NF_SYNPROXY_OPT_SACK_PERM
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}
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if e.Timestamp {
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flags |= NF_SYNPROXY_OPT_TIMESTAMP
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}
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if e.Ecn {
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flags |= NF_SYNPROXY_OPT_ECN
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}
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attrs := []netlink.Attribute{
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{Type: NFTA_SYNPROXY_MSS, Data: binaryutil.BigEndian.PutUint16(e.Mss)},
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{Type: NFTA_SYNPROXY_WSCALE, Data: []byte{e.Wscale}},
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{Type: NFTA_SYNPROXY_FLAGS, Data: binaryutil.BigEndian.PutUint32(flags)},
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}
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return netlink.MarshalAttributes(attrs)
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}
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func (e *SynProxy) unmarshal(fam byte, 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 NFTA_SYNPROXY_MSS:
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e.Mss = ad.Uint16()
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case NFTA_SYNPROXY_WSCALE:
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e.Wscale = ad.Uint8()
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case NFTA_SYNPROXY_FLAGS:
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flags := ad.Uint32()
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checkFlag := func(flag uint32) bool {
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return (flags & flag) == flag
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}
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e.MssValueSet = checkFlag(NF_SYNPROXY_OPT_MSS)
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e.WscaleValueSet = checkFlag(NF_SYNPROXY_OPT_WSCALE)
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e.SackPerm = checkFlag(NF_SYNPROXY_OPT_SACK_PERM)
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e.Timestamp = checkFlag(NF_SYNPROXY_OPT_TIMESTAMP)
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e.Ecn = checkFlag(NF_SYNPROXY_OPT_ECN)
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}
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}
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return ad.Err()
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}
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