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firewall_nftables_linux.go
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firewall_nftables_linux.go
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/*
Copyright 2023 Avi Zimmerman <avi.zimmerman@gmail.com>
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 firewall
import (
"context"
"fmt"
"strings"
"github.com/google/nftables"
"github.com/google/nftables/expr"
"github.com/sbezverk/nftableslib"
)
// firewall is a firewall manager that uses nftables.
type firewall struct {
opts *Options
conn *nftables.Conn
// nftables interfaces
ti nftableslib.TableFuncs
natchains nftableslib.ChainFuncs
filterchains nftableslib.ChainFuncs
rawchains nftableslib.ChainFuncs
// nat chains
prerouting nftableslib.RulesInterface
postrouting nftableslib.RulesInterface
output nftableslib.RulesInterface
// filter chains
input nftableslib.RulesInterface
forward nftableslib.RulesInterface
// raw chains
rawprerouting nftableslib.RulesInterface
// Maps of rule handles to nat options
dnats map[uint64][]byte
}
// newFirewall returns a new nftables firewall manager.
func newFirewall(opts *Options) (Firewall, error) {
// Initialize a long lasting connection to the nftables library
conn := nftableslib.InitConn()
// Initialize tables
fw := &firewall{
opts: opts,
conn: conn,
dnats: make(map[uint64][]byte),
}
err := fw.initialize(opts)
if err != nil {
if strings.Contains(err.Error(), "not supported") || strings.Contains(err.Error(), "no such file") {
// Try to fallback to iptables
return newIPTablesFirewall(opts)
}
return nil, err
}
return fw, nil
}
// AddWireguardForwarding should configure the firewall to allow forwarding traffic on the wireguard interface.
func (fw *firewall) AddWireguardForwarding(ctx context.Context, ifaceName string) error {
accept, err := nftableslib.SetVerdict(nftableslib.NFT_ACCEPT)
if err != nil {
return fmt.Errorf("failed to create accept verdict: %w", err)
}
_, err = fw.forward.Rules().CreateImm(&nftableslib.Rule{
Meta: &nftableslib.Meta{
Expr: []nftableslib.MetaExpr{
{
Key: uint32(expr.MetaKeyOIFNAME),
Value: []byte(ifaceName),
},
},
},
Action: accept,
UserData: nftableslib.MakeRuleComment("Allow forwarding traffic on the wireguard interface"),
})
return err
}
// AddMasquerade should configure the firewall to masquerade outbound traffic on the wireguard interface.
func (fw *firewall) AddMasquerade(ctx context.Context, ifaceName string) error {
// Masquearade outbound traffic from the wireguard interface
masq, err := nftableslib.SetMasq(false, false, false)
if err != nil {
return fmt.Errorf("failed to create masquerade verdict: %w", err)
}
_, err = fw.postrouting.Rules().CreateImm(&nftableslib.Rule{
Meta: &nftableslib.Meta{
Expr: []nftableslib.MetaExpr{
{
Key: uint32(expr.MetaKeyOIFNAME),
Value: []byte(ifaceName),
},
},
},
Action: masq,
UserData: nftableslib.MakeRuleComment("Masquerade outbound traffic from the wireguard interface"),
})
if err != nil {
return fmt.Errorf("failed to create wireguard masquerade rule: %w", err)
}
return fw.conn.Flush()
}
// Clear should clear any changes made to the firewall.
func (fw *firewall) Clear(ctx context.Context) error {
for _, table := range []string{inetNatTable, inetFilterTable, inetRawTable} {
err := fw.ti.DeleteImm(table, nftables.TableFamilyINet)
if err != nil {
return fmt.Errorf("failed to delete inet %s table: %w", table, err)
}
}
return fw.conn.Flush()
}
// Close should close any resources used by the firewall. It should also
// call Clear.
func (fw *firewall) Close(ctx context.Context) error {
err := fw.Clear(ctx)
if err != nil {
return fmt.Errorf("failed to clear firewall: %w", err)
}
return fw.conn.CloseLasting()
}