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package libnetwork
import (
"context"
"errors"
"fmt"
"os"
"github.com/containerd/log"
"github.com/docker/docker/libnetwork/internal/nftables"
"github.com/docker/docker/libnetwork/iptables"
)
const userChain = "DOCKER-USER"
func (c *Controller) selectFirewallBackend() {
// Only try to use nftables if explicitly enabled by env-var.
// TODO(robmry) - command line options?
if os.Getenv("DOCKER_FIREWALL_BACKEND") == "nftables" {
_ = nftables.Enable()
}
}
// Sets up the DOCKER-USER chain for each iptables version (IPv4, IPv6) that's
// enabled in the controller's configuration.
func (c *Controller) setupUserChains() {
// There's no equivalent to DOCKER-USER in the nftables implementation.
if nftables.Enabled() {
return
}
setup := func() error {
var errs []error
for _, ipVersion := range c.enabledIptablesVersions() {
errs = append(errs, setupUserChain(ipVersion))
}
return errors.Join(errs...)
}
if err := setup(); err != nil {
log.G(context.Background()).WithError(err).Warn("configuring " + userChain)
}
iptables.OnReloaded(func() {
if err := setup(); err != nil {
log.G(context.Background()).WithError(err).Warn("configuring " + userChain + " on firewall reload")
}
})
}
// setupUserChain sets up the DOCKER-USER chain for the given [iptables.IPVersion].
//
// This chain allows users to configure firewall policies in a way that
// persist daemon operations/restarts. The daemon does not delete or modify
// any pre-existing rules from the DOCKER-USER filter chain.
//
// Once the DOCKER-USER chain is created, the daemon does not remove it when
// IPTableForwarding is disabled, because it contains rules configured by user
// that are beyond the daemon's control.
func setupUserChain(ipVersion iptables.IPVersion) error {
ipt := iptables.GetIptable(ipVersion)
if _, err := ipt.NewChain(userChain, iptables.Filter); err != nil {
return fmt.Errorf("failed to create %s %v chain: %v", userChain, ipVersion, err)
}
if err := ipt.EnsureJumpRule("FORWARD", userChain); err != nil {
return fmt.Errorf("failed to ensure the jump rule for %s %v: %w", userChain, ipVersion, err)
}
return nil
}
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