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net/dns: avoid using NetworkManager as much as possible. (#1945)

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Addresses #1699 as best as possible.

Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
Dave Anderson 2021-06-10 07:46:08 -07:00 committed by GitHub
parent f944614c5c
commit 144c68b80b
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 24 additions and 74 deletions
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98
net/dns/manager_linux.go
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@ -5,7 +5,6 @@
package dns
import (
"bytes"
"context"
"errors"
"fmt"
@ -79,6 +78,18 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
// "unmanaged" interfaces - meaning NM 1.26.6 and later
// actively ignore DNS configuration we give it. So, for those
// NM versions, we can and must use resolved directly.
//
// In a perfect world, we'd avoid this by replacing
// configuration out from under NM entirely (e.g. using
// directManager to overwrite resolv.conf), but in a world
// where resolved runs, we need to get correct configuration
// into resolved regardless of what's in resolv.conf (because
// resolved can also be queried over dbus, or via an NSS
// module that bypasses /etc/resolv.conf). Given that we must
// get correct configuration into resolved, we have no choice
// but to use NM, and accept the loss of IPv6 configuration
// that comes with it (see
// https://github.com/tailscale/tailscale/issues/1699)
old, err := nmVersionOlderThan("1.26.6")
if err != nil {
// Failed to figure out NM's version, can't make a correct
@ -93,26 +104,6 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
return newResolvedManager(logf, interfaceName)
case "resolvconf":
dbg("rc", "resolvconf")
if err := resolvconfSourceIsNM(bs); err == nil {
dbg("src-is-nm", "yes")
if err := dbusPing("org.freedesktop.NetworkManager", "/org/freedesktop/NetworkManager/DnsManager"); err == nil {
dbg("nm", "yes")
old, err := nmVersionOlderThan("1.26.6")
if err != nil {
return nil, fmt.Errorf("checking NetworkManager version: %v", err)
}
if old {
dbg("nm-old", "yes")
return newNMManager(interfaceName)
} else {
dbg("nm-old", "no")
}
} else {
dbg("nm", "no")
}
} else {
dbg("src-is-nm", "no")
}
if _, err := exec.LookPath("resolvconf"); err != nil {
dbg("resolvconf", "no")
return newDirectManager()
@ -120,21 +111,19 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
dbg("resolvconf", "yes")
return newResolvconfManager(logf)
case "NetworkManager":
// You'd think we would use newNMManager somewhere in
// here. However, as explained in
// https://github.com/tailscale/tailscale/issues/1699 , using
// NetworkManager for DNS configuration carries with it the
// cost of losing IPv6 configuration on the Tailscale network
// interface. So, when we can avoid it, we bypass
// NetworkManager by replacing resolv.conf directly.
//
// If you ever try to put NMManager back here, keep in mind
// that versions >=1.26.6 will ignore DNS configuration
// anyway, so you still need a fallback path that uses
// directManager.
dbg("rc", "nm")
if err := dbusPing("org.freedesktop.NetworkManager", "/org/freedesktop/NetworkManager/DnsManager"); err != nil {
dbg("nm", "no")
return newDirectManager()
}
dbg("nm", "yes")
old, err := nmVersionOlderThan("1.26.6")
if err != nil {
return nil, fmt.Errorf("checking NetworkManager version: %v", err)
}
if old {
dbg("nm-old", "yes")
return newNMManager(interfaceName)
}
dbg("nm-old", "no")
return newDirectManager()
default:
dbg("rc", "unknown")
@ -142,45 +131,6 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
}
}
func resolvconfSourceIsNM(resolvDotConf []byte) error {
b := bytes.NewBuffer(resolvDotConf)
cfg, err := readResolv(b)
if err != nil {
return fmt.Errorf("parsing /etc/resolv.conf: %w", err)
}
var (
paths = []string{
"/etc/resolvconf/run/interface/NetworkManager",
"/run/resolvconf/interface/NetworkManager",
"/var/run/resolvconf/interface/NetworkManager",
"/run/resolvconf/interfaces/NetworkManager",
"/var/run/resolvconf/interfaces/NetworkManager",
}
nmCfg OSConfig
found bool
)
for _, path := range paths {
nmCfg, err = readResolvFile(path)
if os.IsNotExist(err) {
continue
} else if err != nil {
return err
}
found = true
break
}
if !found {
return errors.New("NetworkManager resolvconf snippet not found")
}
if !nmCfg.Equal(cfg) {
return errors.New("NetworkManager config not applied by resolvconf")
}
return nil
}
func nmVersionOlderThan(want string) (bool, error) {
conn, err := dbus.SystemBus()
if err != nil {