From 7612760462e0de6b730c7bd9f70fa00398aec888 Mon Sep 17 00:00:00 2001 From: Tom D <40675700+twitchy-jsonp@users.noreply.github.com> Date: Thu, 17 Jan 2019 00:48:46 -0800 Subject: [PATCH] Implement verdict expression. (#7) --- expr/verdict.go | 89 +++++++++++++++++++++++++++++++++++++++++++ nftables_test.go | 98 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 187 insertions(+) create mode 100644 expr/verdict.go diff --git a/expr/verdict.go b/expr/verdict.go new file mode 100644 index 0000000..92cc98b --- /dev/null +++ b/expr/verdict.go @@ -0,0 +1,89 @@ +// 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 ( + "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 +} + +type VerdictKind uint64 + +// Verdicts, as per netfilter.h. +const ( + VerdictDrop VerdictKind = iota + 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 + // } + // } + // } + + codeData, err := netlink.MarshalAttributes([]netlink.Attribute{ + {Type: unix.NFTA_VERDICT_CODE, Data: binaryutil.BigEndian.PutUint32(uint32(e.Kind))}, + }) + 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 { + return fmt.Errorf("not yet implemented") +} diff --git a/nftables_test.go b/nftables_test.go index 1d26b4f..0b89675 100644 --- a/nftables_test.go +++ b/nftables_test.go @@ -731,3 +731,101 @@ func TestConfigureClamping(t *testing.T) { t.Fatal(err) } } + +func TestDropVerdict(t *testing.T) { + // The want byte sequences come from stracing nft(8), e.g.: + // strace -f -v -x -s 2048 -eraw=sendto nft add table ip nat + // + // The nft(8) command sequence was taken from: + // https://wiki.nftables.org/wiki-nftables/index.php/Mangle_TCP_options + want := [][]byte{ + // batch begin + []byte("\x00\x00\x00\x0a"), + // nft flush ruleset + []byte("\x00\x00\x00\x00"), + // nft add table ip filter + []byte("\x02\x00\x00\x00\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x08\x00\x02\x00\x00\x00\x00\x00"), + // nft add chain filter forward '{' type filter hook forward priority 0 \; '}' + []byte("\x02\x00\x00\x00\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0c\x00\x03\x00\x66\x6f\x72\x77\x61\x72\x64\x00\x14\x00\x04\x80\x08\x00\x01\x00\x00\x00\x00\x02\x08\x00\x02\x00\x00\x00\x00\x00\x0b\x00\x07\x00\x66\x69\x6c\x74\x65\x72\x00\x00"), + // nft add rule filter forward tcp dport 1234 drop + []byte("\x02\x00\x00\x00\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0c\x00\x02\x00\x66\x6f\x72\x77\x61\x72\x64\x00\xe4\x00\x04\x80\x24\x00\x01\x80\x09\x00\x01\x00\x6d\x65\x74\x61\x00\x00\x00\x00\x14\x00\x02\x80\x08\x00\x02\x00\x00\x00\x00\x10\x08\x00\x01\x00\x00\x00\x00\x01\x2c\x00\x01\x80\x08\x00\x01\x00\x63\x6d\x70\x00\x20\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x01\x08\x00\x02\x00\x00\x00\x00\x00\x0c\x00\x03\x80\x05\x00\x01\x00\x06\x00\x00\x00\x34\x00\x01\x80\x0c\x00\x01\x00\x70\x61\x79\x6c\x6f\x61\x64\x00\x24\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x01\x08\x00\x02\x00\x00\x00\x00\x02\x08\x00\x03\x00\x00\x00\x00\x02\x08\x00\x04\x00\x00\x00\x00\x02\x2c\x00\x01\x80\x08\x00\x01\x00\x63\x6d\x70\x00\x20\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x01\x08\x00\x02\x00\x00\x00\x00\x00\x0c\x00\x03\x80\x06\x00\x01\x00\x04\xd2\x00\x00\x30\x00\x01\x80\x0e\x00\x01\x00\x69\x6d\x6d\x65\x64\x69\x61\x74\x65\x00\x00\x00\x1c\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x00\x10\x00\x02\x80\x0c\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x00"), + // batch end + []byte("\x00\x00\x00\x0a"), + } + + c := &nftables.Conn{ + TestDial: func(req []netlink.Message) ([]netlink.Message, error) { + for idx, msg := range req { + b, err := msg.MarshalBinary() + if err != nil { + t.Fatal(err) + } + if len(b) < 16 { + continue + } + b = b[16:] + if len(want) == 0 { + t.Errorf("no want entry for message %d: %x", idx, b) + continue + } + if got, want := b, want[0]; !bytes.Equal(got, want) { + t.Errorf("message %d: %s", idx, linediff(nfdump(got), nfdump(want))) + } + want = want[1:] + } + return req, nil + }, + } + + c.FlushRuleset() + + filter := c.AddTable(&nftables.Table{ + Family: nftables.TableFamilyIPv4, + Name: "filter", + }) + + forward := c.AddChain(&nftables.Chain{ + Name: "forward", + Table: filter, + Type: nftables.ChainTypeFilter, + Hooknum: nftables.ChainHookForward, + Priority: nftables.ChainPriorityFilter, + }) + + c.AddRule(&nftables.Rule{ + Table: filter, + Chain: forward, + Exprs: []expr.Any{ + // [ meta load l4proto => reg 1 ] + &expr.Meta{Key: expr.MetaKeyL4PROTO, Register: 1}, + // [ cmp eq reg 1 0x00000006 ] + &expr.Cmp{ + Op: expr.CmpOpEq, + Register: 1, + Data: []byte{unix.IPPROTO_TCP}, + }, + + // [ payload load 2b @ transport header + 2 => reg 1 ] + &expr.Payload{ + DestRegister: 1, + Base: expr.PayloadBaseTransportHeader, + Offset: 2, + Len: 2, + }, + // [ cmp eq reg 1 0x0000d204 ] + &expr.Cmp{ + Op: expr.CmpOpEq, + Register: 1, + Data: []byte{0x04, 0xd2}, + }, + // [ immediate reg 0 drop ] + &expr.Verdict{ + Kind: expr.VerdictDrop, + }, + }, + }) + + if err := c.Flush(); err != nil { + t.Fatal(err) + } +}