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Revert "libnet: setupDNS: don't overwrite user-modified resolv.conf"

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This reverts commit 7639e193ff.

Signed-off-by: Albin Kerouanton <albin.kerouanton@docker.com>
This commit is contained in:
Albin Kerouanton
2025-11-28 09:47:01 +01:00
parent 710302ecf2
commit 14a955db2f
3 changed files with 2 additions and 111 deletions
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11
daemon/libnetwork/sandbox_dns_unix.go
View File

@@ -264,17 +264,8 @@ func (sb *Sandbox) loadResolvConf(path string) (*resolvconf.ResolvConf, error) {
// be a copy of the host's file, with overrides for nameservers, options and search
// domains applied.
func (sb *Sandbox) setupDNS() error {
sb.restoreResolvConfPath()
// When the container is restarted, a new Sandbox is created but the same resolv.conf is re-used. If it was
// user-modified, do not attempt to overwrite it.
if !sb.config.useDefaultSandBox {
if mod, err := resolvconf.UserModified(sb.config.resolvConfPath, sb.config.resolvConfHashFile); err != nil || mod {
return err
}
}
// Make sure the directory exists.
sb.restoreResolvConfPath()
dir, _ := filepath.Split(sb.config.resolvConfPath)
if err := createBasePath(dir); err != nil {
return err

64
daemon/libnetwork/sandbox_dns_unix_test.go
View File

@@ -14,17 +14,12 @@ import (
is "gotest.tools/v3/assert/cmp"
)
func getResolvConf(t *testing.T, rcPath string) resolvconf.ResolvConf {
func getResolvConfOptions(t *testing.T, rcPath string) []string {
t.Helper()
resolv, err := os.ReadFile(rcPath)
assert.NilError(t, err)
rc, err := resolvconf.Parse(bytes.NewBuffer(resolv), "")
assert.NilError(t, err)
return rc
}
func getResolvConfOptions(t *testing.T, rcPath string) []string {
rc := getResolvConf(t, rcPath)
return rc.Options()
}
@@ -95,60 +90,3 @@ func TestDNSOptions(t *testing.T) {
dnsOptionsList = getResolvConfOptions(t, sb2.config.resolvConfPath)
assert.Check(t, is.DeepEqual([]string{"ndots:0"}, dnsOptionsList))
}
func TestNonHostNetDNSRestart(t *testing.T) {
c, err := New(context.Background(), config.OptionDataDir(t.TempDir()))
assert.NilError(t, err)
// Step 1: Create initial sandbox (simulating first container start)
sb, err := c.NewSandbox(context.Background(), "cnt1")
assert.NilError(t, err)
defer func() {
_ = sb.Delete(context.Background())
}()
sb.startResolver(false)
err = sb.setupDNS()
assert.NilError(t, err)
err = sb.rebuildDNS()
assert.NilError(t, err)
// Step 2: Simulate user manually overwriting the container's resolv.conf
resolvConfPath := sb.config.resolvConfPath
modifiedContent := []byte(`nameserver 1.1.1.1`)
err = os.WriteFile(resolvConfPath, modifiedContent, 0644)
assert.NilError(t, err)
// Step 3: Delete the sandbox (simulating container stop)
err = sb.Delete(context.Background())
assert.NilError(t, err)
// Step 4: Create a new sandbox (simulating container restart)
sbRestart, err := c.NewSandbox(context.Background(), "cnt1",
OptionResolvConfPath(resolvConfPath),
)
assert.NilError(t, err)
defer func() {
if err := sbRestart.Delete(context.Background()); err != nil {
t.Error(err)
}
}()
sbRestart.startResolver(false)
// Step 5: Call setupDNS on restart - should preserve user modifications
err = sbRestart.setupDNS()
assert.NilError(t, err)
rc := getResolvConf(t, sbRestart.config.resolvConfPath)
assert.Check(t, is.Equal("1.1.1.1", rc.NameServers()[0].String()))
// Step 6: Call rebuildDNS on restart - should preserve user modifications
err = sbRestart.rebuildDNS()
assert.NilError(t, err)
rc = getResolvConf(t, sbRestart.config.resolvConfPath)
assert.Check(t, is.Equal("1.1.1.1", rc.NameServers()[0].String()))
}

38
integration/networking/resolvconf_test.go
View File

@@ -212,41 +212,3 @@ func TestNslookupWindows(t *testing.T) {
// can only be changed in daemon.json using feature flag "windows-dns-proxy".
assert.Check(t, is.Contains(res.Stdout.String(), "Addresses:"))
}
// TestResolvConfPreservedOnRestart verifies that external modifications to
// /etc/resolv.conf are preserved when a non-host network container is restarted.
// Regression test for https://github.com/moby/moby/issues/51490
func TestResolvConfPreservedOnRestart(t *testing.T) {
skip.If(t, testEnv.DaemonInfo.OSType == "windows", "No /etc/resolv.conf on Windows")
ctx := setupTest(t)
d := daemon.New(t, daemon.WithResolvConf(network.GenResolvConf("8.8.8.8")))
d.StartWithBusybox(ctx, t)
defer d.Stop(t)
c := d.NewClientT(t)
defer c.Close()
const ctrName = "test-resolvconf-preserved-on-restart"
id := container.Run(ctx, t, c, container.WithName(ctrName))
defer c.ContainerRemove(ctx, id, client.ContainerRemoveOptions{Force: true})
appendContent := `# hello`
res, err := container.Exec(ctx, c, ctrName, []string{
"sh", "-c",
"echo '" + appendContent + "' >> /etc/resolv.conf",
})
assert.NilError(t, err)
assert.Check(t, is.Equal(res.ExitCode, 0))
// Restart the container.
_, err = c.ContainerRestart(ctx, ctrName, client.ContainerRestartOptions{})
assert.Assert(t, is.Nil(err))
// Verify the modification was preserved
res, err = container.Exec(ctx, c, ctrName, []string{"tail", "-n", "1", "/etc/resolv.conf"})
assert.NilError(t, err)
assert.Check(t, is.Equal(res.ExitCode, 0))
assert.Check(t, is.Contains(res.Stdout(), appendContent))
}