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net/dns: split resolvconfManager into a debian and an openresolv manager.

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Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
David Anderson
2021-04-10 18:55:05 -07:00
parent 5480189313
commit 58760f7b82
4 changed files with 86 additions and 69 deletions
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80
net/dns/resolvconf.go
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@@ -86,62 +86,21 @@ func isResolvconfActive() bool {
return false
}
// resolvconfImpl enumerates supported implementations of the resolvconf CLI.
type resolvconfImpl uint8
const (
// resolvconfOpenresolv is the implementation packaged as "openresolv" on Ubuntu.
// It supports exclusive mode and interface metrics.
resolvconfOpenresolv resolvconfImpl = iota
// resolvconfLegacy is the implementation by Thomas Hood packaged as "resolvconf" on Ubuntu.
// It does not support exclusive mode or interface metrics.
resolvconfLegacy
)
func (impl resolvconfImpl) String() string {
switch impl {
case resolvconfOpenresolv:
return "openresolv"
case resolvconfLegacy:
return "legacy"
default:
return "unknown"
}
}
// getResolvconfImpl returns the implementation of resolvconf that appears to be in use.
func getResolvconfImpl() resolvconfImpl {
err := exec.Command("resolvconf", "-v").Run()
if err != nil {
if exitErr, ok := err.(*exec.ExitError); ok {
// Thomas Hood's resolvconf has a minimal flag set
// and exits with code 99 when passed an unknown flag.
if exitErr.ExitCode() == 99 {
return resolvconfLegacy
}
}
}
return resolvconfOpenresolv
}
// resolvconfManager manages DNS configuration using the Debian
// implementation of the `resolvconf` program, written by Thomas Hood.
type resolvconfManager struct {
logf logger.Logf
impl resolvconfImpl
workaroundApplied bool // libc update script has been installed.
logf logger.Logf
scriptInstalled bool // libc update script has been installed
}
func newResolvconfManager(logf logger.Logf) *resolvconfManager {
impl := getResolvconfImpl()
logf("resolvconf implementation is %s", impl)
return &resolvconfManager{
logf: logf,
impl: impl,
}
}
func (m *resolvconfManager) SetDNS(config OSConfig) error {
if m.impl == resolvconfLegacy && !m.workaroundApplied {
if !m.scriptInstalled {
m.logf("injecting resolvconf workaround script")
if err := os.MkdirAll(resolvconfLibcHookPath, 0755); err != nil {
return err
@@ -149,22 +108,17 @@ func (m *resolvconfManager) SetDNS(config OSConfig) error {
if err := atomicfile.WriteFile(resolvconfHookPath, legacyResolvconfScript, 0755); err != nil {
return err
}
m.workaroundApplied = true
m.scriptInstalled = true
}
stdin := new(bytes.Buffer)
writeResolvConf(stdin, config.Nameservers, config.SearchDomains) // dns_direct.go
var cmd *exec.Cmd
switch m.impl {
case resolvconfOpenresolv:
// Request maximal priority (metric 0) and exclusive mode.
cmd = exec.Command("resolvconf", "-m", "0", "-x", "-a", resolvconfConfigName)
case resolvconfLegacy:
// This does not quite give us the desired behavior (queries leak),
// but there is nothing else we can do without messing with other interfaces' settings.
cmd = exec.Command("resolvconf", "-a", resolvconfConfigName)
}
// This resolvconf implementation doesn't support exclusive mode
// or interface priorities, so it will end up blending our
// configuration with other sources. However, this will get fixed
// up by the script we injected above.
cmd := exec.Command("resolvconf", "-a", resolvconfConfigName)
cmd.Stdin = stdin
out, err := cmd.CombinedOutput()
if err != nil {
@@ -183,21 +137,13 @@ func (m *resolvconfManager) GetBaseConfig() (OSConfig, error) {
}
func (m *resolvconfManager) Close() error {
var cmd *exec.Cmd
switch m.impl {
case resolvconfOpenresolv:
cmd = exec.Command("resolvconf", "-f", "-d", resolvconfConfigName)
case resolvconfLegacy:
// resolvconfLegacy lacks the -f flag.
// Instead, it succeeds even when the config does not exist.
cmd = exec.Command("resolvconf", "-d", resolvconfConfigName)
}
cmd := exec.Command("resolvconf", "-d", resolvconfConfigName)
out, err := cmd.CombinedOutput()
if err != nil {
return fmt.Errorf("running %s: %s", cmd, out)
}
if m.workaroundApplied {
if m.scriptInstalled {
m.logf("removing resolvconf workaround script")
os.Remove(resolvconfHookPath) // Best-effort
}