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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build !android
package monitor
import (
"net"
"time"
"github.com/jsimonetti/rtnetlink"
"github.com/mdlayher/netlink"
"golang.org/x/sys/unix"
"inet.af/netaddr"
"tailscale.com/net/tsaddr"
"tailscale.com/types/logger"
)
// unspecifiedMessage is a minimal message implementation that should not
// be ignored. In general, OS-specific implementations should use better
// types and avoid this if they can.
type unspecifiedMessage struct{}
func (unspecifiedMessage) ignore() bool { return false }
// nlConn wraps a *netlink.Conn and returns a monitor.Message
// instead of a netlink.Message. Currently, messages are discarded,
// but down the line, when messages trigger different logic depending
// on the type of event, this provides the capability of handling
// each architecture-specific message in a generic fashion.
type nlConn struct {
logf logger.Logf
conn *netlink.Conn
buffered []netlink.Message
}
func newOSMon(logf logger.Logf, m *Mon) (osMon, error) {
conn, err := netlink.Dial(unix.NETLINK_ROUTE, &netlink.Config{
// Routes get us most of the events of interest, but we need
// address as well to cover things like DHCP deciding to give
// us a new address upon renewal - routing wouldn't change,
// but all reachability would.
Groups: unix.RTMGRP_IPV4_IFADDR | unix.RTMGRP_IPV6_IFADDR |
unix.RTMGRP_IPV4_ROUTE | unix.RTMGRP_IPV6_ROUTE |
unix.RTMGRP_IPV4_RULE, // no IPV6_RULE in x/sys/unix
})
if err != nil {
// Google Cloud Run does not implement NETLINK_ROUTE RTMGRP support
logf("monitor_linux: AF_NETLINK RTMGRP failed, falling back to polling")
return newPollingMon(logf, m)
}
return &nlConn{logf: logf, conn: conn}, nil
}
func (c *nlConn) Close() error { return c.conn.Close() }
func (c *nlConn) Receive() (message, error) {
if len(c.buffered) == 0 {
var err error
c.buffered, err = c.conn.Receive()
if err != nil {
return nil, err
}
if len(c.buffered) == 0 {
// Unexpected. Not seen in wild, but sleep defensively.
time.Sleep(time.Second)
return ignoreMessage{}, nil
}
}
msg := c.buffered[0]
c.buffered = c.buffered[1:]
// See https://github.com/torvalds/linux/blob/master/include/uapi/linux/rtnetlink.h
// And https://man7.org/linux/man-pages/man7/rtnetlink.7.html
switch msg.Header.Type {
case unix.RTM_NEWADDR, unix.RTM_DELADDR:
var rmsg rtnetlink.AddressMessage
if err := rmsg.UnmarshalBinary(msg.Data); err != nil {
c.logf("failed to parse type %v: %v", msg.Header.Type, err)
return unspecifiedMessage{}, nil
}
return &newAddrMessage{
Label: rmsg.Attributes.Label,
Addr: netaddrIP(rmsg.Attributes.Local),
Delete: msg.Header.Type == unix.RTM_DELADDR,
}, nil
case unix.RTM_NEWROUTE, unix.RTM_DELROUTE:
typeStr := "RTM_NEWROUTE"
if msg.Header.Type == unix.RTM_DELROUTE {
typeStr = "RTM_DELROUTE"
}
var rmsg rtnetlink.RouteMessage
if err := rmsg.UnmarshalBinary(msg.Data); err != nil {
c.logf("%s: failed to parse: %v", typeStr, err)
return unspecifiedMessage{}, nil
}
src := netaddrIPPrefix(rmsg.Attributes.Src, rmsg.SrcLength)
dst := netaddrIPPrefix(rmsg.Attributes.Dst, rmsg.DstLength)
gw := netaddrIP(rmsg.Attributes.Gateway)
if rmsg.Table == tsTable && dst.IsSingleIP() {
// Don't log. Spammy and normal to see a bunch of these on start-up,
// which we make ourselves.
} else {
c.logf("%s: src=%v, dst=%v, gw=%v, outif=%v, table=%v", typeStr,
condNetAddrPrefix(src), condNetAddrPrefix(dst), condNetAddrIP(gw),
rmsg.Attributes.OutIface, rmsg.Attributes.Table)
}
if msg.Header.Type == unix.RTM_DELROUTE {
// Just logging it for now.
// (Debugging https://github.com/tailscale/tailscale/issues/643)
return unspecifiedMessage{}, nil
}
return &newRouteMessage{
Table: rmsg.Table,
Src: src,
Dst: dst,
Gateway: gw,
}, nil
case unix.RTM_NEWRULE:
// Probably ourselves adding it.
return ignoreMessage{}, nil
case unix.RTM_DELRULE:
// For https://github.com/tailscale/tailscale/issues/1591 where
// systemd-networkd deletes our rules.
var rmsg rtnetlink.RouteMessage
err := rmsg.UnmarshalBinary(msg.Data)
if err != nil {
c.logf("ip rule deleted; failed to parse netlink message: %v", err)
} else {
c.logf("ip rule deleted: %+v", rmsg)
// On `ip -4 rule del pref 5210 table main`, logs:
// monitor: ip rule deleted: {Family:2 DstLength:0 SrcLength:0 Tos:0 Table:254 Protocol:0 Scope:0 Type:1 Flags:0 Attributes:{Dst:<nil> Src:<nil> Gateway:<nil> OutIface:0 Priority:5210 Table:254 Mark:4294967295 Expires:<nil> Metrics:<nil> Multipath:[]}}
}
return ipRuleDeletedMessage{
table: rmsg.Table,
priority: rmsg.Attributes.Priority,
}, nil
default:
c.logf("unhandled netlink msg type %+v, %q", msg.Header, msg.Data)
return unspecifiedMessage{}, nil
}
}
func netaddrIP(std net.IP) netaddr.IP {
ip, _ := netaddr.FromStdIP(std)
return ip
}
func netaddrIPPrefix(std net.IP, bits uint8) netaddr.IPPrefix {
ip, _ := netaddr.FromStdIP(std)
return netaddr.IPPrefixFrom(ip, bits)
}
func condNetAddrPrefix(ipp netaddr.IPPrefix) string {
if ipp.IP().IsZero() {
return ""
}
return ipp.String()
}
func condNetAddrIP(ip netaddr.IP) string {
if ip.IsZero() {
return ""
}
return ip.String()
}
// newRouteMessage is a message for a new route being added.
type newRouteMessage struct {
Src, Dst netaddr.IPPrefix
Gateway netaddr.IP
Table uint8
}
const tsTable = 52
func (m *newRouteMessage) ignore() bool {
return m.Table == tsTable || tsaddr.IsTailscaleIP(m.Dst.IP())
}
// newAddrMessage is a message for a new address being added.
type newAddrMessage struct {
Delete bool
Addr netaddr.IP
Label string // netlink Label attribute (e.g. "tailscale0")
}
func (m *newAddrMessage) ignore() bool {
return tsaddr.IsTailscaleIP(m.Addr)
}
type ignoreMessage struct{}
func (ignoreMessage) ignore() bool { return true }
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