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firewall_iptables_linux.go
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firewall_iptables_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 (
"fmt"
"log/slog"
"os/exec"
"strings"
"github.com/webmeshproj/webmesh/pkg/context"
)
// newIPTablesFirewall returns a new iptables firewall manager. This firewall manager
// is technically not safe for use with multiple interfaces. The Close method may restore
// rules from another interface. But documentation should push people to use nftables instead.
// This is just a fallback.
func newIPTablesFirewall(ctx context.Context, _ *Options) (Firewall, error) {
fw := &iptablesFirewall{
log: context.LoggerFrom(ctx).With(slog.String("component", "iptables-firewall")),
}
var initialRules []string
rules, err := fw.execOutput(context.Background(), "-S")
if err != nil {
return nil, fmt.Errorf("iptables -S: %v", err)
}
initialRules = append(initialRules, strings.Split(string(rules), "\n")...)
fw.initialRules = initialRules
return fw, nil
}
type iptablesFirewall struct {
log *slog.Logger
initialRules []string
}
// AddWireguardForwarding should configure the firewall to allow forwarding traffic on the wireguard interface.
func (fw *iptablesFirewall) AddWireguardForwarding(ctx context.Context, ifaceName string) error {
return fw.exec(ctx, "-A", "FORWARD", "-i", ifaceName, "-j", "ACCEPT")
}
// AddMasquerade should configure the firewall to masquerade outbound traffic on the wireguard interface.
func (fw *iptablesFirewall) AddMasquerade(ctx context.Context, ifaceName string) error {
return fw.exec(ctx, "-t", "nat", "-A", "POSTROUTING", "-o", ifaceName, "-j", "MASQUERADE")
}
// Clear should clear any changes made to the firewall.
func (fw *iptablesFirewall) Clear(ctx context.Context) error {
err := fw.exec(ctx, "-F")
if err != nil {
return err
}
// Restore initial rules
for _, rule := range fw.initialRules {
if strings.HasPrefix(rule, "#") {
// Comment, skip
continue
}
err = fw.exec(ctx, strings.Fields(rule)...)
if err != nil {
return err
}
}
return nil
}
// Close should close any resources used by the firewall. It should also perform a Clear.
func (fw *iptablesFirewall) Close(ctx context.Context) error {
return fw.Clear(ctx)
}
func (fw *iptablesFirewall) exec(ctx context.Context, args ...string) error {
cmd := exec.CommandContext(ctx, "iptables", args...)
fw.log.Debug("iptables", slog.String("args", strings.Join(args, " ")))
if out, err := cmd.CombinedOutput(); err != nil {
return fmt.Errorf("iptables %v: %v: %s", args, err, out)
}
return nil
}
func (rw *iptablesFirewall) execOutput(ctx context.Context, args ...string) ([]byte, error) {
cmd := exec.CommandContext(ctx, "iptables", args...)
rw.log.Debug("iptables", slog.String("args", strings.Join(args, " ")))
return cmd.CombinedOutput()
}