daemon: overlay2: Write layer metadata atomically

mike-sul · mike-sul · commit de2447c2abc7 · 2023-09-13T15:07:32.000+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 &lt;path&gt;:
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 &lt;mike.sul@foundries.io&gt;
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"
@@ -383,7 +384,7 @@ 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), 0o644); err != nil {
+	if err := ioutils.AtomicWriteFile(path.Join(dir, "link"), []byte(lid), 0o644); err != nil {
 		return err
 	}
 
@@ -396,7 +397,7 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return err
 	}
 
-	if err := os.WriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {
+	if err := ioutils.AtomicWriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {
 		return err
 	}
 
@@ -405,7 +406,7 @@ 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), 0o666); 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"`
`@@ -383,7 +384,7 @@ func (d Driver) create(id, parent string, opts graphdriver.CreateOpts) (retErr`
`383`	`384`	`}`
`384`	`385`
`385`	`386`	`// Write link id to link file`
`386`		`- if err := os.WriteFile(path.Join(dir, "link"), []byte(lid), 0o644); err != nil {`
	`387`	`+ if err := ioutils.AtomicWriteFile(path.Join(dir, "link"), []byte(lid), 0o644); err != nil {`
`387`	`388`	`return err`
`388`	`389`	`}`
`389`	`390`
`@@ -396,7 +397,7 @@ func (d Driver) create(id, parent string, opts graphdriver.CreateOpts) (retErr`
`396`	`397`	`return err`
`397`	`398`	`}`
`398`	`399`
`399`		`- if err := os.WriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {`
	`400`	`+ if err := ioutils.AtomicWriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {`
`400`	`401`	`return err`
`401`	`402`	`}`
`402`	`403`
`@@ -405,7 +406,7 @@ func (d Driver) create(id, parent string, opts graphdriver.CreateOpts) (retErr`
`405`	`406`	`return err`
`406`	`407`	`}`
`407`	`408`	`if lower != "" {`
`408`		`- if err := os.WriteFile(path.Join(dir, lowerFile), []byte(lower), 0o666); err != nil {`
	`409`	`+ if err := ioutils.AtomicWriteFile(path.Join(dir, lowerFile), []byte(lower), 0o666); err != nil {`
`409`	`410`	`return err`
`410`	`411`	`}`
`411`	`412`	`}`