daemon: overlay2: Write layer metadata atomically

mike-sul · thaJeztah · commit 57bd38858262 · 2023-10-23T20:15:21.000+02:00
When the daemon process or the host running it is abruptly terminated, the layer metadata file can become inconsistent on the file system. Specifically, `link` and `lower` files may exist but be empty, leading to overlay mounting errors during layer extraction, such as: "failed to register layer: error creating overlay mount to <path>: too many levels of symbolic links." This commit introduces the use of `AtomicWriteFile` to ensure that the layer metadata files contain correct data when they exist on the file system. Signed-off-by: Mike <mike.sul@foundries.io> (cherry picked from commit de2447c) Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
diff --git a/daemon/graphdriver/overlay2/overlay.go b/daemon/graphdriver/overlay2/overlay.go
@@ -23,6 +23,7 @@ import (
 	"github.com/docker/docker/pkg/containerfs"
 	"github.com/docker/docker/pkg/directory"
 	"github.com/docker/docker/pkg/idtools"
+	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/parsers"
 	"github.com/docker/docker/quota"
 	units "github.com/docker/go-units"
@@ -386,7 +387,7 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 	}
 
 	// Write link id to link file
-	if err := os.WriteFile(path.Join(dir, "link"), []byte(lid), 0644); err != nil {
+	if err := ioutils.AtomicWriteFile(path.Join(dir, "link"), []byte(lid), 0o644); err != nil {
 		return err
 	}
 
@@ -399,7 +400,7 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return err
 	}
 
-	if err := os.WriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0600); err != nil {
+	if err := ioutils.AtomicWriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {
 		return err
 	}
 
@@ -408,7 +409,7 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return err
 	}
 	if lower != "" {
-		if err := os.WriteFile(path.Join(dir, lowerFile), []byte(lower), 0666); err != nil {
+		if err := ioutils.AtomicWriteFile(path.Join(dir, lowerFile), []byte(lower), 0o666); err != nil {
 			return err
 		}
 	}

Original file line number	Diff line number	Diff line change
`@@ -23,6 +23,7 @@ import (`
`23`	`23`	`"github.com/docker/docker/pkg/containerfs"`
`24`	`24`	`"github.com/docker/docker/pkg/directory"`
`25`	`25`	`"github.com/docker/docker/pkg/idtools"`
	`26`	`+ "github.com/docker/docker/pkg/ioutils"`
`26`	`27`	`"github.com/docker/docker/pkg/parsers"`
`27`	`28`	`"github.com/docker/docker/quota"`
`28`	`29`	`units "github.com/docker/go-units"`
`@@ -386,7 +387,7 @@ func (d Driver) create(id, parent string, opts graphdriver.CreateOpts) (retErr`
`386`	`387`	`}`
`387`	`388`
`388`	`389`	`// Write link id to link file`
`389`		`- if err := os.WriteFile(path.Join(dir, "link"), []byte(lid), 0644); err != nil {`
	`390`	`+ if err := ioutils.AtomicWriteFile(path.Join(dir, "link"), []byte(lid), 0o644); err != nil {`
`390`	`391`	`return err`
`391`	`392`	`}`
`392`	`393`
`@@ -399,7 +400,7 @@ func (d Driver) create(id, parent string, opts graphdriver.CreateOpts) (retErr`
`399`	`400`	`return err`
`400`	`401`	`}`
`401`	`402`
`402`		`- if err := os.WriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0600); err != nil {`
	`403`	`+ if err := ioutils.AtomicWriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {`
`403`	`404`	`return err`
`404`	`405`	`}`
`405`	`406`
`@@ -408,7 +409,7 @@ func (d Driver) create(id, parent string, opts graphdriver.CreateOpts) (retErr`
`408`	`409`	`return err`
`409`	`410`	`}`
`410`	`411`	`if lower != "" {`
`411`		`- if err := os.WriteFile(path.Join(dir, lowerFile), []byte(lower), 0666); err != nil {`
	`412`	`+ if err := ioutils.AtomicWriteFile(path.Join(dir, lowerFile), []byte(lower), 0o666); err != nil {`
`412`	`413`	`return err`
`413`	`414`	`}`
`414`	`415`	`}`