Merge pull request #35467 from kolyshkin/dup-mnt

Fix "duplicate mount point" when --tmpfs /dev/shm is used

container/container_unix.go

@@ -65,12 +65,11 @@ func (container *Container) NetworkMounts() []Mount {
 		if _, err := os.Stat(container.ResolvConfPath); err != nil {
 			logrus.Warnf("ResolvConfPath set to %q, but can't stat this filename (err = %v); skipping", container.ResolvConfPath, err)
 		} else {
-			if !container.HasMountFor("/etc/resolv.conf") {
-				label.Relabel(container.ResolvConfPath, container.MountLabel, shared)
-			}
 			writable := !container.HostConfig.ReadonlyRootfs
 			if m, exists := container.MountPoints["/etc/resolv.conf"]; exists {
 				writable = m.RW
+			} else {
+				label.Relabel(container.ResolvConfPath, container.MountLabel, shared)
 			}
 			mounts = append(mounts, Mount{
 				Source:      container.ResolvConfPath,
@@ -84,12 +83,11 @@ func (container *Container) NetworkMounts() []Mount {
 		if _, err := os.Stat(container.HostnamePath); err != nil {
 			logrus.Warnf("HostnamePath set to %q, but can't stat this filename (err = %v); skipping", container.HostnamePath, err)
 		} else {
-			if !container.HasMountFor("/etc/hostname") {
-				label.Relabel(container.HostnamePath, container.MountLabel, shared)
-			}
 			writable := !container.HostConfig.ReadonlyRootfs
 			if m, exists := container.MountPoints["/etc/hostname"]; exists {
 				writable = m.RW
+			} else {
+				label.Relabel(container.HostnamePath, container.MountLabel, shared)
 			}
 			mounts = append(mounts, Mount{
 				Source:      container.HostnamePath,
@@ -103,12 +101,11 @@ func (container *Container) NetworkMounts() []Mount {
 		if _, err := os.Stat(container.HostsPath); err != nil {
 			logrus.Warnf("HostsPath set to %q, but can't stat this filename (err = %v); skipping", container.HostsPath, err)
 		} else {
-			if !container.HasMountFor("/etc/hosts") {
-				label.Relabel(container.HostsPath, container.MountLabel, shared)
-			}
 			writable := !container.HostConfig.ReadonlyRootfs
 			if m, exists := container.MountPoints["/etc/hosts"]; exists {
 				writable = m.RW
+			} else {
+				label.Relabel(container.HostsPath, container.MountLabel, shared)
 			}
 			mounts = append(mounts, Mount{
 				Source:      container.HostsPath,
@@ -160,7 +157,18 @@ func (container *Container) ShmResourcePath() (string, error) {
 // HasMountFor checks if path is a mountpoint
 func (container *Container) HasMountFor(path string) bool {
 	_, exists := container.MountPoints[path]
-	return exists
+	if exists {
+		return true
+	}
+
+	// Also search among the tmpfs mounts
+	for dest := range container.HostConfig.Tmpfs {
+		if dest == path {
+			return true
+		}
+	}
+
+	return false
 }
 
 // UnmountIpcMount uses the provided unmount function to unmount shm if it was mounted

daemon/oci_linux_test.go

@@ -0,0 +1,50 @@
+package daemon
+
+import (
+	"testing"
+
+	containertypes "github.com/docker/docker/api/types/container"
+	"github.com/docker/docker/container"
+	"github.com/docker/docker/daemon/config"
+	"github.com/docker/docker/oci"
+	"github.com/docker/docker/pkg/idtools"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestTmpfsDevShmNoDupMount checks that a user-specified /dev/shm tmpfs
+// mount (as in "docker run --tmpfs /dev/shm:rw,size=NNN") does not result
+// in "Duplicate mount point" error from the engine.
+// https://github.com/moby/moby/issues/35455
+func TestTmpfsDevShmNoDupMount(t *testing.T) {
+	d := Daemon{
+		// some empty structs to avoid getting a panic
+		// caused by a null pointer dereference
+		idMappings:  &idtools.IDMappings{},
+		configStore: &config.Config{},
+	}
+	c := &container.Container{
+		ShmPath: "foobar", // non-empty, for c.IpcMounts() to work
+		HostConfig: &containertypes.HostConfig{
+			IpcMode: containertypes.IpcMode("shareable"), // default mode
+			// --tmpfs /dev/shm:rw,exec,size=NNN
+			Tmpfs: map[string]string{
+				"/dev/shm": "rw,exec,size=1g",
+			},
+		},
+	}
+
+	// Mimick the code flow of daemon.createSpec(), enough to reproduce the issue
+	ms, err := d.setupMounts(c)
+	assert.NoError(t, err)
+
+	ms = append(ms, c.IpcMounts()...)
+
+	tmpfsMounts, err := c.TmpfsMounts()
+	assert.NoError(t, err)
+	ms = append(ms, tmpfsMounts...)
+
+	s := oci.DefaultSpec()
+	err = setMounts(&d, &s, c, ms)
+	assert.NoError(t, err)
+}