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overlay[2] graphdriver: Fix/improve overlayfs support check for rootless #40194

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merged 2 commits into from
Nov 15, 2019
Merged

overlay[2] graphdriver: Fix/improve overlayfs support check for rootless #40194

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d568707
overlay: move supportsMultipleLowerDir to utils
kolyshkin Nov 7, 2019
649e4c8
Fix/improve overlay support check
kolyshkin Nov 7, 2019
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37 changes: 5 additions & 32 deletions daemon/graphdriver/overlay/overlay.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
package overlay // import "github.com/docker/docker/daemon/graphdriver/overlay"

import (
"bufio"
"fmt"
"io"
"io/ioutil"
Expand Down Expand Up @@ -123,10 +122,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
return nil, err
}

if err := supportsOverlay(); err != nil {
return nil, graphdriver.ErrNotSupported
}

// Perform feature detection on /var/lib/docker/overlay if it's an existing directory.
// This covers situations where /var/lib/docker/overlay is a mount, and on a different
// filesystem than /var/lib/docker.
Expand All @@ -136,6 +131,11 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
testdir = filepath.Dir(testdir)
}

if err := overlayutils.SupportsOverlay(testdir, false); err != nil {
logrus.WithField("storage-driver", "overlay").Error(err)
return nil, graphdriver.ErrNotSupported
}

fsMagic, err := graphdriver.GetFSMagic(testdir)
if err != nil {
return nil, err
Expand Down Expand Up @@ -199,33 +199,6 @@ func parseOptions(options []string) (*overlayOptions, error) {
return o, nil
}

func supportsOverlay() error {
// Access overlay filesystem so that Linux loads it (if possible).
mountTarget, err := ioutil.TempDir("", "supportsOverlay")
if err != nil {
logrus.WithError(err).WithField("storage-driver", "overlay2").Error("could not create temporary directory, so assuming that 'overlay' is not supported")
return graphdriver.ErrNotSupported
}
/* The mounting will fail--after the module has been loaded.*/
defer os.RemoveAll(mountTarget)
unix.Mount("overlay", mountTarget, "overlay", 0, "")

f, err := os.Open("/proc/filesystems")
if err != nil {
return err
}
defer f.Close()

s := bufio.NewScanner(f)
for s.Scan() {
if s.Text() == "nodev\toverlay" {
return nil
}
}
logrus.WithField("storage-driver", "overlay").Error("'overlay' not found as a supported filesystem on this host. Please ensure kernel is new enough and has overlay support loaded.")
return graphdriver.ErrNotSupported
}

func (d *Driver) String() string {
return "overlay"
}
Expand Down
32 changes: 0 additions & 32 deletions daemon/graphdriver/overlay2/check.go
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Original file line number Diff line number Diff line change
Expand Up @@ -99,35 +99,3 @@ func doesSupportNativeDiff(d string) error {

return nil
}

// supportsMultipleLowerDir checks if the system supports multiple lowerdirs,
// which is required for the overlay2 driver. On 4.x kernels, multiple lowerdirs
// are always available (so this check isn't needed), and backported to RHEL and
// CentOS 3.x kernels (3.10.0-693.el7.x86_64 and up). This function is to detect
// support on those kernels, without doing a kernel version compare.
func supportsMultipleLowerDir(d string) error {
td, err := ioutil.TempDir(d, "multiple-lowerdir-check")
if err != nil {
return err
}
defer func() {
if err := os.RemoveAll(td); err != nil {
logger.Warnf("Failed to remove check directory %v: %v", td, err)
}
}()

for _, dir := range []string{"lower1", "lower2", "upper", workDirName, mergedDirName} {
if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
return err
}
}

opts := fmt.Sprintf("lowerdir=%s:%s,upperdir=%s,workdir=%s", path.Join(td, "lower2"), path.Join(td, "lower1"), path.Join(td, "upper"), path.Join(td, workDirName))
if err := unix.Mount("overlay", filepath.Join(td, mergedDirName), "overlay", 0, opts); err != nil {
return errors.Wrap(err, "failed to mount overlay")
}
if err := unix.Unmount(filepath.Join(td, mergedDirName), 0); err != nil {
logger.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, mergedDirName), err)
}
return nil
}
47 changes: 5 additions & 42 deletions daemon/graphdriver/overlay2/overlay.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
package overlay2 // import "github.com/docker/docker/daemon/graphdriver/overlay2"

import (
"bufio"
"context"
"errors"
"fmt"
Expand Down Expand Up @@ -133,10 +132,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
return nil, err
}

if err := supportsOverlay(); err != nil {
return nil, graphdriver.ErrNotSupported
}

// require kernel 4.0.0 to ensure multiple lower dirs are supported
v, err := kernel.GetKernelVersion()
if err != nil {
Expand All @@ -152,6 +147,11 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
testdir = filepath.Dir(testdir)
}

if err := overlayutils.SupportsOverlay(testdir, true); err != nil {
logger.Error(err)
return nil, graphdriver.ErrNotSupported
}

fsMagic, err := graphdriver.GetFSMagic(testdir)
if err != nil {
return nil, err
Expand All @@ -176,16 +176,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
}
}

if kernel.CompareKernelVersion(*v, kernel.VersionInfo{Kernel: 4, Major: 0, Minor: 0}) < 0 {
if opts.overrideKernelCheck {
logger.Warn("Using pre-4.0.0 kernel for overlay2, mount failures may require kernel update")
} else {
if err := supportsMultipleLowerDir(testdir); err != nil {
logger.Debugf("Multiple lower dirs not supported: %v", err)
return nil, graphdriver.ErrNotSupported
}
}
}
supportsDType, err := fsutils.SupportsDType(testdir)
if err != nil {
return nil, err
Expand Down Expand Up @@ -274,33 +264,6 @@ func parseOptions(options []string) (*overlayOptions, error) {
return o, nil
}

func supportsOverlay() error {
// Access overlay filesystem so that Linux loads it (if possible).
mountTarget, err := ioutil.TempDir("", "supportsOverlay2")
if err != nil {
logrus.WithError(err).WithField("storage-driver", "overlay2").Error("could not create temporary directory, so assuming that 'overlay' is not supported")
return graphdriver.ErrNotSupported
}
/* The mounting will fail--after the module has been loaded.*/
defer os.RemoveAll(mountTarget)
unix.Mount("overlay", mountTarget, "overlay", 0, "")

f, err := os.Open("/proc/filesystems")
if err != nil {
return err
}
defer f.Close()

s := bufio.NewScanner(f)
for s.Scan() {
if s.Text() == "nodev\toverlay" {
return nil
}
}
logger.Error("'overlay' not found as a supported filesystem on this host. Please ensure kernel is new enough and has overlay support loaded.")
return graphdriver.ErrNotSupported
}

func useNaiveDiff(home string) bool {
useNaiveDiffLock.Do(func() {
if err := doesSupportNativeDiff(home); err != nil {
Expand Down
44 changes: 44 additions & 0 deletions daemon/graphdriver/overlayutils/overlayutils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,15 @@ package overlayutils // import "github.com/docker/docker/daemon/graphdriver/over

import (
"fmt"
"io/ioutil"
"os"
"path"
"path/filepath"

"github.com/docker/docker/daemon/graphdriver"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)

// ErrDTypeNotSupported denotes that the backing filesystem doesn't support d_type.
Expand All @@ -23,3 +30,40 @@ func ErrDTypeNotSupported(driver, backingFs string) error {

return graphdriver.NotSupportedError(msg)
}

// SupportsOverlay checks if the system supports overlay filesystem
// by performing an actual overlay mount.
//
// checkMultipleLowers parameter enables check for multiple lowerdirs,
// which is required for the overlay2 driver.
func SupportsOverlay(d string, checkMultipleLowers bool) error {
td, err := ioutil.TempDir(d, "check-overlayfs-support")
if err != nil {
return err
}
defer func() {
if err := os.RemoveAll(td); err != nil {
logrus.Warnf("Failed to remove check directory %v: %v", td, err)
}
}()

for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
return err
}
}

mnt := filepath.Join(td, "merged")
lowerDir := path.Join(td, "lower2")
if checkMultipleLowers {
lowerDir += ":" + path.Join(td, "lower1")
}
opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, path.Join(td, "upper"), path.Join(td, "work"))
if err := unix.Mount("overlay", mnt, "overlay", 0, opts); err != nil {
return errors.Wrap(err, "failed to mount overlay")
}
if err := unix.Unmount(mnt, 0); err != nil {
logrus.Warnf("Failed to unmount check directory %v: %v", mnt, err)
}
return nil
}