package iptables import ( "errors" "strconv" ) const ( // Chain to intercept inbound traffic ProxyInboundChain = "CONSUL_PROXY_INBOUND" // Chain to redirect inbound traffic to the proxy ProxyInboundRedirectChain = "CONSUL_PROXY_IN_REDIRECT" // Chain to intercept outbound traffic ProxyOutputChain = "CONSUL_PROXY_OUTPUT" // Chain to redirect outbound traffic to the proxy ProxyOutputRedirectChain = "CONSUL_PROXY_REDIRECT" DefaultTProxyOutboundPort = 15001 ) // Config is used to configure which traffic interception and redirection // rules should be applied with the iptables commands. type Config struct { // ProxyUserID is the user ID of the proxy process. ProxyUserID string // ProxyInboundPort is the port of the proxy's inbound listener. ProxyInboundPort int // ProxyInboundPort is the port of the proxy's outbound listener. ProxyOutboundPort int // IptablesProvider is the Provider that will apply iptables rules. IptablesProvider Provider } // Provider is an interface for executing iptables rules. type Provider interface { // AddRule adds a rule without executing it. AddRule(name string, args ...string) // ApplyRules executes rules that have been added via AddRule. // This operation is currently not atomic, and if there's an error applying rules, // you may be left in a state where partial rules were applied. ApplyRules() error // Rules returns the list of rules that have been added but not applied yet. Rules() []string } // Setup will set up iptables interception and redirection rules // based on the configuration provided in cfg. // This implementation was inspired by // https://github.com/openservicemesh/osm/blob/650a1a1dcf081ae90825f3b5dba6f30a0e532725/pkg/injector/iptables.go func Setup(cfg Config) error { if cfg.IptablesProvider == nil { cfg.IptablesProvider = &iptablesExecutor{} } err := validateConfig(cfg) if err != nil { return err } // Set the default outbound port if it's not already set. if cfg.ProxyOutboundPort == 0 { cfg.ProxyOutboundPort = DefaultTProxyOutboundPort } // Create chains we will use for redirection. chains := []string{ProxyInboundChain, ProxyInboundRedirectChain, ProxyOutputChain, ProxyOutputRedirectChain} for _, chain := range chains { cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-N", chain) } // Configure outbound rules. { // Redirects outbound TCP traffic hitting PROXY_REDIRECT chain to Envoy's outbound listener port. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyOutputRedirectChain, "-p", "tcp", "-j", "REDIRECT", "--to-port", strconv.Itoa(cfg.ProxyOutboundPort)) // For outbound TCP traffic jump from OUTPUT chain to PROXY_OUTPUT chain. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", "OUTPUT", "-p", "tcp", "-j", ProxyOutputChain) // Don't redirect proxy traffic back to itself, return it to the next chain for processing. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyOutputChain, "-m", "owner", "--uid-owner", cfg.ProxyUserID, "-j", "RETURN") // Skip localhost traffic, doesn't need to be routed via the proxy. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyOutputChain, "-d", "127.0.0.1/32", "-j", "RETURN") // Redirect remaining outbound traffic to Envoy. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyOutputChain, "-j", ProxyOutputRedirectChain) } // Configure inbound rules. { // Redirects inbound TCP traffic hitting the PROXY_IN_REDIRECT chain to Envoy's inbound listener port. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyInboundRedirectChain, "-p", "tcp", "-j", "REDIRECT", "--to-port", strconv.Itoa(cfg.ProxyInboundPort)) // For inbound traffic jump from PREROUTING chain to PROXY_INBOUND chain. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", "PREROUTING", "-p", "tcp", "-j", ProxyInboundChain) // Redirect remaining inbound traffic to Envoy. cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyInboundChain, "-p", "tcp", "-j", ProxyInboundRedirectChain) } return cfg.IptablesProvider.ApplyRules() } func validateConfig(cfg Config) error { if cfg.ProxyUserID == "" { return errors.New("ProxyUserID is required to set up traffic redirection") } if cfg.ProxyInboundPort == 0 { return errors.New("ProxyInboundPort is required to set up traffic redirection") } return nil }