Merge pull request #3255 from rn/repeat

Initial support for reproducible builds

README.md

@@ -10,6 +10,7 @@ LinuxKit, a toolkit for building custom minimal, immutable Linux distributions.
 - Completely stateless, but persistent storage can be attached
 - Easy tooling, with easy iteration
 - Built with containers, for running containers
+- Designed to create [reproducible builds](./docs/reproducible-builds.md) [WIP]
 - Designed for building and running clustered applications, including but not limited to container orchestration such as Docker or Kubernetes
 - Designed from the experience of building Docker Editions, but redesigned as a general-purpose toolkit
 - Designed to be managed by external tooling, such as [Infrakit](https://github.com/docker/infrakit) or similar tools
@@ -155,7 +156,7 @@ This is an open project without fixed judgements, open to the community to set t
 
 ## Development reports
 
-There are weekly [development reports](reports/) summarizing work carried out in the week.
+There are monthly [development reports](reports/) summarising the work carried out each month.
 
 ## Adopters
 

docs/reproducible-builds.md

@@ -0,0 +1,71 @@
+# Reproducible builds
+
+We aim to make the outputs of `linuxkit build` reproducible, i.e. the
+build artefacts should be bit-by-bit identical copies if invoked with
+the same inputs and run with the same version of the `linuxkit`
+command. See [this
+document](https://reproducible-builds.org/docs/buy-in/) on why this
+matters.
+
+_Note, we do not (yet) aim to make `linuxkit pkg build` builds
+reproducible._
+
+
+## Current status
+
+Currently, the following output formats provide reproducible builds:
+- `tar` (Tested as part of the CI)
+- `tar-kernel-initrd`
+- `docker`
+- `kernel+initrd` (Tested as part of the CI)
+
+
+## Details
+
+In general, `linuxkit build` lends itself for reproducible
+builds. LinuxKit packages, used during `linuxkit build`, are (signed)
+docker images. Packages are tagged with the content hash of the source
+code (and optionally release version) and are typically only updated
+if the source of the package changed (in which case the tag
+changes). For all intents and purposes, when pulled by tag, the
+contents of a packages should be bit-by-bit identical. Alternatively,
+the digest of the package, in which case, the pulled image will always
+be the same.
+
+The first phase of the `linuxkit build` mostly untars and retars the
+images of the packages to produce an tar file of the root filesystem.
+This then serves as input for other output formats. During this first
+phase, there are a number of things to watch out for to generate
+reproducible builds:
+
+- Timestamps of generated files. The `docker export` command, as well
+  as `linuxkit build` itself, creates a small number of files. The
+  `ModTime` for these files needs to be clamped to a fixed date
+  (otherwise the current time is used). Use the `defaultModTime`
+  variable to set the `ModTime` of created files to a specific time.
+- Generated JSON files. `linuxkit build` generates a number of JSON
+  files by marshalling Go `struct` variables. Examples are the OCI
+  specification `config.json` and `runtime.json` files for
+  containers. The default Go `json.Marshal()` function seems to do a
+  reasonable good job in generating reproducible output from internal
+  structures, including for JSON objects. However, during `linuxkit
+  build` some of the OCI runtime spec fields are generated/modified
+  and care must be taken to ensure consistent ordering. For JSON
+  arrays (Go slices) it is best to sort them before Marshalling them.
+
+Reproducible builds for the first phase of `linuxkit build` can be
+tested using `-output tar` and comparing the output of subsequent
+builds with tools like `diff` or the excellent
+[`diffoscope`](https://diffoscope.org/).
+
+The second phase of `linuxkit build` converts the intermediary `tar`
+format into the desired output format. Making this phase reproducible
+depends on the tools used to generate the output.
+
+Builds, which produce ISO formats should probably be converted to use
+[`go-diskfs`](https://github.com/diskfs/go-diskfs) before attempting
+to make them reproducible.
+
+For ideas on how to make the builds for other output formats
+reproducible, see [this
+page](https://reproducible-builds.org/docs/system-images/).

src/cmd/linuxkit/moby/build.go

@@ -51,10 +51,11 @@ var additions = map[string]addFun{
 	"docker": func(tw *tar.Writer) error {
 		log.Infof("  Adding Dockerfile")
 		hdr := &tar.Header{
-			Name:   "Dockerfile",
-			Mode:   0644,
-			Size:   int64(len(dockerfile)),
-			Format: tar.FormatPAX,
+			Name:    "Dockerfile",
+			Mode:    0644,
+			Size:    int64(len(dockerfile)),
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
 			return err
@@ -368,6 +369,7 @@ func (k *kernelFilter) WriteHeader(hdr *tar.Header) error {
 				Name:     "boot",
 				Mode:     0755,
 				Typeflag: tar.TypeDir,
+				ModTime:  defaultModTime,
 				Format:   tar.FormatPAX,
 			}
 			if err := tw.WriteHeader(whdr); err != nil {
@@ -376,10 +378,11 @@ func (k *kernelFilter) WriteHeader(hdr *tar.Header) error {
 		}
 		// add the cmdline in /boot/cmdline
 		whdr := &tar.Header{
-			Name:   "boot/cmdline",
-			Mode:   0644,
-			Size:   int64(len(k.cmdline)),
-			Format: tar.FormatPAX,
+			Name:    "boot/cmdline",
+			Mode:    0644,
+			Size:    int64(len(k.cmdline)),
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(whdr); err != nil {
 			return err
@@ -391,10 +394,11 @@ func (k *kernelFilter) WriteHeader(hdr *tar.Header) error {
 		}
 		// Stash the kernel header and prime the buffer for the kernel
 		k.hdr = &tar.Header{
-			Name:   "boot/kernel",
-			Mode:   hdr.Mode,
-			Size:   hdr.Size,
-			Format: tar.FormatPAX,
+			Name:    "boot/kernel",
+			Mode:    hdr.Mode,
+			Size:    hdr.Size,
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		k.buffer = new(bytes.Buffer)
 	case k.tar:
@@ -410,6 +414,7 @@ func (k *kernelFilter) WriteHeader(hdr *tar.Header) error {
 				Name:     "boot",
 				Mode:     0755,
 				Typeflag: tar.TypeDir,
+				ModTime:  defaultModTime,
 				Format:   tar.FormatPAX,
 			}
 			if err := tw.WriteHeader(whdr); err != nil {
@@ -417,10 +422,11 @@ func (k *kernelFilter) WriteHeader(hdr *tar.Header) error {
 			}
 		}
 		whdr := &tar.Header{
-			Name:   "boot/ucode.cpio",
-			Mode:   hdr.Mode,
-			Size:   hdr.Size,
-			Format: tar.FormatPAX,
+			Name:    "boot/ucode.cpio",
+			Mode:    hdr.Mode,
+			Size:    hdr.Size,
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(whdr); err != nil {
 			return err
@@ -653,6 +659,7 @@ func filesystem(m Moby, tw *tar.Writer, idMap map[string]uint32) error {
 					Name:     root,
 					Typeflag: tar.TypeDir,
 					Mode:     dirMode,
+					ModTime:  defaultModTime,
 					Uid:      int(uid),
 					Gid:      int(gid),
 					Format:   tar.FormatPAX,
@@ -666,11 +673,12 @@ func filesystem(m Moby, tw *tar.Writer, idMap map[string]uint32) error {
 		}
 		addedFiles[f.Path] = true
 		hdr := &tar.Header{
-			Name:   f.Path,
-			Mode:   mode,
-			Uid:    int(uid),
-			Gid:    int(gid),
-			Format: tar.FormatPAX,
+			Name:    f.Path,
+			Mode:    mode,
+			ModTime: defaultModTime,
+			Uid:     int(uid),
+			Gid:     int(gid),
+			Format:  tar.FormatPAX,
 		}
 		if f.Directory {
 			if f.Contents != nil {

src/cmd/linuxkit/moby/config.go

@@ -2,8 +2,6 @@ package moby
 
 import (
 	"fmt"
-	"os"
-	"path/filepath"
 	"sort"
 	"strconv"
 	"strings"
@@ -416,22 +414,6 @@ func defaultMountpoint(tp string) string {
 	}
 }
 
-// Sort mounts by number of path components so /dev/pts is listed after /dev
-type mlist []specs.Mount
-
-func (m mlist) Len() int {
-	return len(m)
-}
-func (m mlist) Less(i, j int) bool {
-	return m.parts(i) < m.parts(j)
-}
-func (m mlist) Swap(i, j int) {
-	m[i], m[j] = m[j], m[i]
-}
-func (m mlist) parts(i int) int {
-	return strings.Count(filepath.Clean(m[i].Destination), string(os.PathSeparator))
-}
-
 // assignBool does ordered overrides from JSON bool pointers
 func assignBool(v1, v2 *bool) bool {
 	if v2 != nil {
@@ -821,11 +803,15 @@ func ConfigInspectToOCI(yaml *Image, inspect types.ImageInspect, idMap map[strin
 		}
 		mounts[dest] = specs.Mount{Destination: dest, Type: tp, Source: src, Options: opts}
 	}
-	mountList := mlist{}
+	// Create a list of mounts and sort them by destination. This makes the order deterministic and
+	// ensures that, e.g., the mount for /dev comes before the mount for /dev/pts
+	var mountList []specs.Mount
 	for _, m := range mounts {
 		mountList = append(mountList, m)
 	}
-	sort.Sort(mountList)
+	sort.Slice(mountList, func(i, j int) bool {
+		return mountList[i].Destination < mountList[j].Destination
+	})
 
 	namespaces := []specs.LinuxNamespace{}
 
@@ -915,6 +901,8 @@ func ConfigInspectToOCI(yaml *Image, inspect types.ImageInspect, idMap map[strin
 	for capability := range boundingSet {
 		bounding = append(bounding, capability)
 	}
+	// Sort capabilities to make it deterministic
+	sort.Strings(bounding)
 
 	rlimitsString := assignStrings(label.Rlimits, yaml.Rlimits)
 	rlimits := []specs.POSIXRlimit{}

src/cmd/linuxkit/moby/image.go

@@ -53,6 +53,18 @@ ff02::2 ip6-allrouters
 `,
 }
 
+// Files which may be created as part of 'docker export'. These need their timestamp fixed.
+var touch = map[string]bool{
+	"dev/":            true,
+	"dev/pts/":        true,
+	"dev/shm/":        true,
+	"etc/":            true,
+	"etc/mtab":        true,
+	"etc/resolv.conf": true,
+	"proc/":           true,
+	"sys/":            true,
+}
+
 // tarPrefix creates the leading directories for a path
 func tarPrefix(path string, tw tarWriter) error {
 	if path == "" {
@@ -71,6 +83,7 @@ func tarPrefix(path string, tw tarWriter) error {
 		hdr := &tar.Header{
 			Name:     mkdir,
 			Mode:     0755,
+			ModTime:  defaultModTime,
 			Typeflag: tar.TypeDir,
 			Format:   tar.FormatPAX,
 		}
@@ -154,7 +167,8 @@ func ImageTar(ref *reference.Spec, prefix string, tw tarWriter, trust bool, pull
 				contents := replace[hdr.Name]
 				hdr.Size = int64(len(contents))
 				hdr.Name = prefix + hdr.Name
-				log.Debugf("image tar: %s %s add %s", ref, prefix, hdr.Name)
+				hdr.ModTime = defaultModTime
+				log.Debugf("image tar: %s %s add %s (replaced)", ref, prefix, hdr.Name)
 				if err := tw.WriteHeader(hdr); err != nil {
 					return err
 				}
@@ -169,6 +183,7 @@ func ImageTar(ref *reference.Spec, prefix string, tw tarWriter, trust bool, pull
 				hdr.Size = 0
 				hdr.Typeflag = tar.TypeSymlink
 				hdr.Linkname = resolv
+				hdr.ModTime = defaultModTime
 				log.Debugf("image tar: %s %s add resolv symlink /etc/resolv.conf -> %s", ref, prefix, resolv)
 				if err := tw.WriteHeader(hdr); err != nil {
 					return err
@@ -179,7 +194,12 @@ func ImageTar(ref *reference.Spec, prefix string, tw tarWriter, trust bool, pull
 				return err
 			}
 		} else {
-			log.Debugf("image tar: %s %s add %s", ref, prefix, hdr.Name)
+			if touch[hdr.Name] {
+				log.Debugf("image tar: %s %s add %s (touch)", ref, prefix, hdr.Name)
+				hdr.ModTime = defaultModTime
+			} else {
+				log.Debugf("image tar: %s %s add %s (original)", ref, prefix, hdr.Name)
+			}
 			hdr.Name = prefix + hdr.Name
 			if hdr.Typeflag == tar.TypeLink {
 				// hard links are referenced by full path so need to be adjusted
@@ -221,10 +241,11 @@ func ImageBundle(prefix string, ref *reference.Spec, config []byte, runtime Runt
 	}
 
 	hdr := &tar.Header{
-		Name:   path.Join(prefix, "config.json"),
-		Mode:   0644,
-		Size:   int64(len(config)),
-		Format: tar.FormatPAX,
+		Name:    path.Join(prefix, "config.json"),
+		Mode:    0644,
+		Size:    int64(len(config)),
+		ModTime: defaultModTime,
+		Format:  tar.FormatPAX,
 	}
 	if err := tw.WriteHeader(hdr); err != nil {
 		return err
@@ -242,6 +263,7 @@ func ImageBundle(prefix string, ref *reference.Spec, config []byte, runtime Runt
 			Name:     tmp,
 			Mode:     0755,
 			Typeflag: tar.TypeDir,
+			ModTime:  defaultModTime,
 			Format:   tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
@@ -252,6 +274,7 @@ func ImageBundle(prefix string, ref *reference.Spec, config []byte, runtime Runt
 			Name:     path.Join(prefix, "rootfs"),
 			Mode:     0755,
 			Typeflag: tar.TypeDir,
+			ModTime:  defaultModTime,
 			Format:   tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
@@ -271,6 +294,7 @@ func ImageBundle(prefix string, ref *reference.Spec, config []byte, runtime Runt
 				Name:     path.Join(prefix, "rootfs"),
 				Mode:     0755,
 				Typeflag: tar.TypeDir,
+				ModTime:  defaultModTime,
 				Format:   tar.FormatPAX,
 			}
 			if err := tw.WriteHeader(hdr); err != nil {
@@ -294,10 +318,11 @@ func ImageBundle(prefix string, ref *reference.Spec, config []byte, runtime Runt
 	}
 
 	hdr = &tar.Header{
-		Name:   path.Join(prefix, "runtime.json"),
-		Mode:   0644,
-		Size:   int64(len(runtimeConfig)),
-		Format: tar.FormatPAX,
+		Name:    path.Join(prefix, "runtime.json"),
+		Mode:    0644,
+		Size:    int64(len(runtimeConfig)),
+		ModTime: defaultModTime,
+		Format:  tar.FormatPAX,
 	}
 	if err := tw.WriteHeader(hdr); err != nil {
 		return err

src/cmd/linuxkit/moby/output.go

@@ -281,10 +281,11 @@ func tarInitrdKernel(kernel, initrd []byte, cmdline string) (*bytes.Buffer, erro
 	buf := new(bytes.Buffer)
 	tw := tar.NewWriter(buf)
 	hdr := &tar.Header{
-		Name:   "kernel",
-		Mode:   0600,
-		Size:   int64(len(kernel)),
-		Format: tar.FormatPAX,
+		Name:    "kernel",
+		Mode:    0600,
+		Size:    int64(len(kernel)),
+		ModTime: defaultModTime,
+		Format:  tar.FormatPAX,
 	}
 	err := tw.WriteHeader(hdr)
 	if err != nil {
@@ -295,10 +296,11 @@ func tarInitrdKernel(kernel, initrd []byte, cmdline string) (*bytes.Buffer, erro
 		return buf, err
 	}
 	hdr = &tar.Header{
-		Name:   "initrd.img",
-		Mode:   0600,
-		Size:   int64(len(initrd)),
-		Format: tar.FormatPAX,
+		Name:    "initrd.img",
+		Mode:    0600,
+		Size:    int64(len(initrd)),
+		ModTime: defaultModTime,
+		Format:  tar.FormatPAX,
 	}
 	err = tw.WriteHeader(hdr)
 	if err != nil {
@@ -309,10 +311,11 @@ func tarInitrdKernel(kernel, initrd []byte, cmdline string) (*bytes.Buffer, erro
 		return buf, err
 	}
 	hdr = &tar.Header{
-		Name:   "cmdline",
-		Mode:   0600,
-		Size:   int64(len(cmdline)),
-		Format: tar.FormatPAX,
+		Name:    "cmdline",
+		Mode:    0600,
+		Size:    int64(len(cmdline)),
+		ModTime: defaultModTime,
+		Format:  tar.FormatPAX,
 	}
 	err = tw.WriteHeader(hdr)
 	if err != nil {
@@ -410,10 +413,11 @@ func outputKernelInitrdTarball(base string, kernel []byte, initrd []byte, cmdlin
 	tw := tar.NewWriter(f)
 	if len(kernel) != 0 {
 		hdr := &tar.Header{
-			Name:   "kernel",
-			Mode:   0644,
-			Size:   int64(len(kernel)),
-			Format: tar.FormatPAX,
+			Name:    "kernel",
+			Mode:    0644,
+			Size:    int64(len(kernel)),
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
 			return err
@@ -424,10 +428,11 @@ func outputKernelInitrdTarball(base string, kernel []byte, initrd []byte, cmdlin
 	}
 	if len(initrd) != 0 {
 		hdr := &tar.Header{
-			Name:   "initrd.img",
-			Mode:   0644,
-			Size:   int64(len(initrd)),
-			Format: tar.FormatPAX,
+			Name:    "initrd.img",
+			Mode:    0644,
+			Size:    int64(len(initrd)),
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
 			return err
@@ -438,10 +443,11 @@ func outputKernelInitrdTarball(base string, kernel []byte, initrd []byte, cmdlin
 	}
 	if len(cmdline) != 0 {
 		hdr := &tar.Header{
-			Name:   "cmdline",
-			Mode:   0644,
-			Size:   int64(len(cmdline)),
-			Format: tar.FormatPAX,
+			Name:    "cmdline",
+			Mode:    0644,
+			Size:    int64(len(cmdline)),
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
 			return err
@@ -452,10 +458,11 @@ func outputKernelInitrdTarball(base string, kernel []byte, initrd []byte, cmdlin
 	}
 	if len(ucode) != 0 {
 		hdr := &tar.Header{
-			Name:   "ucode.cpio",
-			Mode:   0644,
-			Size:   int64(len(ucode)),
-			Format: tar.FormatPAX,
+			Name:    "ucode.cpio",
+			Mode:    0644,
+			Size:    int64(len(ucode)),
+			ModTime: defaultModTime,
+			Format:  tar.FormatPAX,
 		}
 		if err := tw.WriteHeader(hdr); err != nil {
 			return err

src/cmd/linuxkit/moby/util.go

@@ -2,11 +2,14 @@ package moby
 
 import (
 	"path/filepath"
+	"time"
 )
 
 var (
 	// MobyDir is the location of the cache directory, defaults to ~/.moby
 	MobyDir string
+	// Default ModTime for files created during build. Roughly the time LinuxKit got open sourced.
+	defaultModTime = time.Date(2017, time.April, 18, 16, 30, 0, 0, time.UTC)
 )
 
 func defaultMobyConfigDir() string {

test/cases/000_build/010_reproducible/000_tar/test.sh

@@ -0,0 +1,25 @@
+#!/bin/sh
+# SUMMARY: Check that tar output format build is reproducible
+# LABELS:
+
+set -e
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+NAME=check
+
+clean_up() {
+	rm -f ${NAME}*
+}
+
+trap clean_up EXIT
+
+# -disable-content-trust to speed up the test
+linuxkit build -disable-content-trust -format tar -name "${NAME}-1" ../test.yml
+linuxkit build -disable-content-trust -format tar -name "${NAME}-2" ../test.yml
+
+diff -q "${NAME}-1.tar" "${NAME}-2.tar" || exit 1
+
+exit 0

test/cases/000_build/010_reproducible/002_kernel+initrd/test.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+# SUMMARY: Check that kernel+initrd output format build is reproducible
+# LABELS:
+
+set -e
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+NAME=check
+
+clean_up() {
+	rm -f ${NAME}*
+}
+
+trap clean_up EXIT
+
+# -disable-content-trust to speed up the test
+linuxkit build -disable-content-trust -format kernel+initrd -name "${NAME}-1" ../test.yml
+linuxkit build -disable-content-trust -format kernel+initrd -name "${NAME}-2" ../test.yml
+
+diff -q "${NAME}-1-cmdline"    "${NAME}-2-cmdline"    || exit 1
+diff -q "${NAME}-1-kernel"     "${NAME}-2-kernel"     || exit 1
+diff -q "${NAME}-1-initrd.img" "${NAME}-2-initrd.img" || exit 1
+
+exit 0

test/cases/000_build/010_reproducible/test.yml

@@ -0,0 +1,52 @@
+# NOTE: Images build from this file likely do not run
+kernel:
+  image: linuxkit/kernel:4.14.90
+  cmdline: "console=ttyS0"
+init:
+  - linuxkit/init:c563953a2277eb73a89d89f70e4b6dcdcfebc2d1
+  - linuxkit/runc:83d0edb4552b1a5df1f0976f05f442829eac38fe
+  - linuxkit/containerd:326b096cd5fbab0f864e52721d036cade67599d6
+
+onboot:
+  - name: dhcpcd
+    image: linuxkit/dhcpcd:v0.6
+    command: ["/sbin/dhcpcd", "--nobackground", "-f", "/dhcpcd.conf", "-1"]
+    # Add some random unsorted caps
+    capabilities:
+      - CAP_SETGID
+      - CAP_DAC_OVERRIDE
+
+services:
+  - name: testservice
+    image: linuxkit/ip:v0.6
+    # Some environments
+    env:
+      - BENV=true
+      - ARANDOMENV=foobar
+    # Some mounts
+    mounts:
+      - type: cgroup
+        options: ["rw","nosuid","noexec","nodev","relatime"]
+      - type: overlay
+        source: overlay
+        destination: writeable-host-etc
+        options: ["rw", "lowerdir=/etc", "upperdir=/run/hostetc/upper", "workdir=/run/hostetc/work"]
+    # Some binds
+    binds:
+      - /var/run:/var/run
+      - /foobar:/foobar
+      - /etc/foobar:/etc/foobar
+      - /etc/aaa:/etc/aaa
+    # And some runtime settings
+    runtime:
+      mkdir: ["/var/lib/docker"]
+      mkdir: ["/var/lib/aaa"]
+
+files:
+  - path: etc/linuxkit-config
+    metadata: yaml
+
+trust:
+  org:
+    - linuxkit
+    - library