Add image verifier transfer service plugin system based on a binary directory

Signed-off-by: Ethan Lowman <ethan.lowman@datadoghq.com>

cmd/containerd/builtins/builtins.go

@@ -24,6 +24,7 @@ import (
 	_ "github.com/containerd/containerd/leases/plugin"
 	_ "github.com/containerd/containerd/metadata/plugin"
 	_ "github.com/containerd/containerd/pkg/nri/plugin"
+	_ "github.com/containerd/containerd/plugins/imageverifier"
 	_ "github.com/containerd/containerd/plugins/sandbox"
 	_ "github.com/containerd/containerd/plugins/streaming"
 	_ "github.com/containerd/containerd/plugins/transfer"

docs/image-verification.md

@@ -0,0 +1,51 @@
+# Image Verification
+
+The following covers the default "bindir" `ImageVerifier` plugin implementation.
+
+To enable image verification, add a stanza like the following to the containerd config:
+
+```yaml
+[plugins]
+  [plugins."io.containerd.image-verifier.v1.bindir"]
+    bin_dir = "/opt/containerd/image-verifier/bin"
+    max_verifiers = 10
+    per_verifier_timeout = "10s"
+```
+
+All files in `bin_dir`, if it exists, must be verifier executables which conform to the following API.
+
+## Image Verifier Binary API
+
+### CLI Arguments
+
+- `-name`: The given reference to the image that may be pulled.
+- `-digest`: The resolved digest of the image that may be pulled.
+- `-stdin-media-type`: The media type of the JSON data passed to stdin.
+
+### Standard Input
+
+A JSON encoded payload is passed to the verifier binary's standard input. The
+media type of this payload is specified by the `-stdin-media-type` CLI
+argument, and may change in future versions of containerd. Currently, the
+payload has a media type of `application/vnd.oci.descriptor.v1+json` and
+represents the OCI Content Descriptor of the image that may be pulled. See
+[the OCI specification](https://github.com/opencontainers/image-spec/blob/main/descriptor.md)
+for more details.
+
+### Image Pull Judgement
+
+Print to standard output a reason for the image pull judgement.
+
+Return an exit code of 0 to allow the image to be pulled and any other exit code to block the image from being pulled.
+
+## Image Verifier Caller Contract
+
+- If `bin_dir` does not exist or contains no files, the image verifier does not block image pulls.
+- An image is pulled only if all verifiers that are called return an "ok" judgement (exit with status code 0). In other words, image pull judgements are combined with an `AND` operator.
+- If any verifiers exceeds the `per_verifier_timeout` or fails to exec, the verification fails with an error and a `nil` judgement is returned.
+- If `max_verifiers < 0`, there is no imposed limit on the number of image verifiers called.
+- If `max_verifiers >= 0`, there is a limit imposed on the number of image verifiers called. The entries in `bin_dir` are lexicographically sorted by name, and the first `n = max_verifiers` of the verifiers will be called, and the rest will be skipped.
+- There is no guarantee for the order of execution of verifier binaries.
+- Standard error output of verifier binaries is logged at debug level by containerd, subject to truncation.
+- Standard output of verifier binaries (the "reason" for the judgement) is subject to truncation.
+- System resources used by verifier binaries are currently accounted for in and constrained by containerd's own cgroup, but this is subject to change.

pkg/imageverifier/bindir/bindir.go

@@ -0,0 +1,259 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package bindir
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/containerd/containerd/log"
+	"github.com/containerd/containerd/pkg/imageverifier"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/sirupsen/logrus"
+)
+
+const outputLimitBytes = 1 << 15 // 32 KiB
+
+type Config struct {
+	BinDir             string        `toml:"bin_dir"`
+	MaxVerifiers       int           `toml:"max_verifiers"`
+	PerVerifierTimeout time.Duration `toml:"per_verifier_timeout"`
+}
+
+type ImageVerifier struct {
+	config *Config
+}
+
+var _ imageverifier.ImageVerifier = (*ImageVerifier)(nil)
+
+func NewImageVerifier(c *Config) *ImageVerifier {
+	return &ImageVerifier{
+		config: c,
+	}
+}
+
+func (v *ImageVerifier) VerifyImage(ctx context.Context, name string, desc ocispec.Descriptor) (*imageverifier.Judgement, error) {
+	// os.ReadDir sorts entries by name.
+	entries, err := os.ReadDir(v.config.BinDir)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return &imageverifier.Judgement{
+				OK:     true,
+				Reason: fmt.Sprintf("image verifier directory %v does not exist", v.config.BinDir),
+			}, nil
+		}
+
+		return nil, fmt.Errorf("failed to list directory contents: %w", err)
+	}
+
+	if len(entries) == 0 {
+		return &imageverifier.Judgement{
+			OK:     true,
+			Reason: fmt.Sprintf("no image verifier binaries found in %v", v.config.BinDir),
+		}, nil
+	}
+
+	reason := &strings.Builder{}
+	for i, entry := range entries {
+		if (i+1) > v.config.MaxVerifiers && v.config.MaxVerifiers >= 0 {
+			log.G(ctx).Warnf("image verifiers are being skipped since directory %v has %v entries, more than configured max of %v verifiers", v.config.BinDir, len(entries), v.config.MaxVerifiers)
+			break
+		}
+
+		bin := entry.Name()
+		start := time.Now()
+		exitCode, vr, err := v.runVerifier(ctx, bin, name, desc)
+		runtime := time.Since(start)
+		if err != nil {
+			return nil, fmt.Errorf("failed to call verifier %v (runtime %v): %w", bin, runtime, err)
+		}
+
+		if exitCode != 0 {
+			return &imageverifier.Judgement{
+				OK:     false,
+				Reason: fmt.Sprintf("verifier %v rejected image (exit code %v): %v", bin, exitCode, vr),
+			}, nil
+		}
+
+		if i > 0 {
+			reason.WriteString(", ")
+		}
+		reason.WriteString(fmt.Sprintf("%v => %v", bin, vr))
+	}
+
+	return &imageverifier.Judgement{
+		OK:     true,
+		Reason: reason.String(),
+	}, nil
+}
+
+func (v *ImageVerifier) runVerifier(ctx context.Context, bin string, imageName string, desc ocispec.Descriptor) (exitCode int, reason string, err error) {
+	ctx, cancel := context.WithTimeout(ctx, v.config.PerVerifierTimeout)
+	defer cancel()
+
+	binPath := filepath.Join(v.config.BinDir, bin)
+	args := []string{
+		"-name", imageName,
+		"-digest", desc.Digest.String(),
+		"-stdin-media-type", ocispec.MediaTypeDescriptor,
+	}
+
+	cmd := exec.CommandContext(ctx, binPath, args...)
+
+	// We construct our own pipes instead of using the default StdinPipe,
+	// StoutPipe, and StderrPipe in order to set timeouts on reads and writes.
+	stdinRead, stdinWrite, err := os.Pipe()
+	if err != nil {
+		return -1, "", err
+	}
+	cmd.Stdin = stdinRead
+	defer stdinRead.Close()
+	defer stdinWrite.Close()
+
+	stdoutRead, stdoutWrite, err := os.Pipe()
+	if err != nil {
+		return -1, "", err
+	}
+	cmd.Stdout = stdoutWrite
+	defer stdoutRead.Close()
+	defer stdoutWrite.Close()
+
+	stderrRead, stderrWrite, err := os.Pipe()
+	if err != nil {
+		return -1, "", err
+	}
+	cmd.Stderr = stderrWrite
+	defer stderrRead.Close()
+	defer stderrWrite.Close()
+
+	// Close parent ends of pipes on timeout. Without this, I/O may hang in the
+	// parent process.
+	if d, ok := ctx.Deadline(); ok {
+		stdinWrite.SetDeadline(d)
+		stdoutRead.SetDeadline(d)
+		stderrRead.SetDeadline(d)
+	}
+
+	// Finish configuring, and then fork & exec the child process.
+	p, err := startProcess(ctx, cmd)
+	if err != nil {
+		return -1, "", err
+	}
+	defer p.cleanup(ctx)
+
+	// Close the child ends of the pipes in the parent process.
+	stdinRead.Close()
+	stdoutWrite.Close()
+	stderrWrite.Close()
+
+	// Write the descriptor to stdin.
+	go func() {
+		// Descriptors are usually small enough to fit in a pipe buffer (which is
+		// often 64 KiB on Linux) so this write usually won't block on the child
+		// process reading stdin. However, synchronously writing to stdin may cause
+		// the parent to block if the descriptor is larger than the pipe buffer and
+		// the child process doesn't read stdin. Therefore, we write to stdin
+		// asynchronously, limited by the stdinWrite deadline set above.
+		err := json.NewEncoder(stdinWrite).Encode(desc)
+		if err != nil {
+			// This may error out with a "broken pipe" error if the descriptor is
+			// larger than the pipe buffer and the child process does not read all
+			// of stdin.
+			log.G(ctx).WithError(err).Warn("failed to completely write descriptor to stdin")
+		}
+		stdinWrite.Close()
+	}()
+
+	// Pipe verifier stderr lines to debug logs.
+	stderrLog := log.G(ctx).Logger.WithFields(logrus.Fields{
+		"image_verifier": bin,
+		"stream":         "stderr",
+	})
+	stderrLogDone := make(chan struct{})
+	go func() {
+		defer close(stderrLogDone)
+		defer stderrRead.Close()
+		lr := &io.LimitedReader{
+			R: stderrRead,
+			N: outputLimitBytes,
+		}
+
+		s := bufio.NewScanner(lr)
+		for s.Scan() {
+			stderrLog.Debug(s.Text())
+		}
+		if err := s.Err(); err != nil {
+			stderrLog.WithError(err).Debug("error logging image verifier stderr")
+		}
+
+		if lr.N == 0 {
+			// Peek ahead to see if stderr reader was truncated.
+			b := make([]byte, 1)
+			if n, _ := stderrRead.Read(b); n > 0 {
+				stderrLog.Debug("(previous logs may be truncated)")
+			}
+		}
+
+		// Discard the truncated part of stderr. Doing this rather than closing the
+		// reader avoids broken pipe errors. This is bounded by the stderrRead
+		// deadline.
+		if _, err := io.Copy(io.Discard, stderrRead); err != nil {
+			log.G(ctx).WithError(err).Error("error flushing stderr")
+		}
+	}()
+
+	stdout, err := io.ReadAll(io.LimitReader(stdoutRead, outputLimitBytes))
+	if err != nil {
+		log.G(ctx).WithError(err).Error("error reading stdout")
+	} else {
+		m := strings.Builder{}
+		m.WriteString(strings.TrimSpace(string(stdout)))
+		// Peek ahead to see if stdout is truncated.
+		b := make([]byte, 1)
+		if n, _ := stdoutRead.Read(b); n > 0 {
+			m.WriteString("(stdout truncated)")
+		}
+		reason = m.String()
+	}
+
+	// Discard the truncated part of stdout. Doing this rather than closing the
+	// reader avoids broken pipe errors. This is bounded by the stdoutRead
+	// deadline.
+	if _, err := io.Copy(io.Discard, stdoutRead); err != nil {
+		log.G(ctx).WithError(err).Error("error flushing stdout")
+	}
+	stdoutRead.Close()
+
+	<-stderrLogDone
+	if err := cmd.Wait(); err != nil {
+		if ee := (&exec.ExitError{}); errors.As(err, &ee) && ee.ProcessState.Exited() {
+			return ee.ProcessState.ExitCode(), reason, nil
+		}
+		return -1, "", fmt.Errorf("waiting on command to exit: %v", err)
+	}
+
+	return cmd.ProcessState.ExitCode(), reason, nil
+}

pkg/imageverifier/bindir/bindir_test.go

@@ -0,0 +1,419 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package bindir
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"text/template"
+	"time"
+
+	"github.com/containerd/containerd/log"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// buildGoVerifiers uses the local Go toolchain to build each of the standalone
+// main package source files in srcDir into binaries placed in binDir.
+func buildGoVerifiers(t *testing.T, srcsDir string, binDir string) {
+	srcs, err := os.ReadDir(srcsDir)
+	require.NoError(t, err)
+
+	for _, srcFile := range srcs {
+		// Build the source into a Go binary.
+		src := filepath.Join(srcsDir, srcFile.Name())
+		bin := filepath.Join(binDir, strings.Split(srcFile.Name(), ".")[0]+exeIfWindows())
+		cmd := exec.Command("go", "build", "-o", bin, src)
+
+		code, err := os.ReadFile(src)
+		require.NoError(t, err)
+
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			t.Fatalf("failed to build test verifier %s: %v\n%s\nGo code:\n%s", src, err, out, code)
+		}
+	}
+}
+
+func exeIfWindows() string {
+	// The command `go build -o abc abc.go` creates abc.exe on Windows.
+	if runtime.GOOS == "windows" {
+		return ".exe"
+	}
+	return ""
+}
+
+// newBinDir creates a temporary directory and copies each of the selected bins
+// fromSrcDir into that directory. The copied verifier binaries are given names
+// such that they sort (and therefore execute) in the order that bins is given.
+func newBinDir(t *testing.T, srcDir string, bins ...string) string {
+	binDir := t.TempDir()
+
+	for i, bin := range bins {
+		src, err := os.Open(filepath.Join(srcDir, bin+exeIfWindows()))
+		require.NoError(t, err)
+		defer src.Close()
+
+		dst, err := os.OpenFile(filepath.Join(binDir, fmt.Sprintf("verifier-%v%v", i, exeIfWindows())), os.O_WRONLY|os.O_CREATE, 0755)
+		require.NoError(t, err)
+		defer dst.Close()
+
+		_, err = io.Copy(dst, src)
+		require.NoError(t, err)
+	}
+
+	return binDir
+}
+
+func TestBinDirVerifyImage(t *testing.T) {
+	// Enable debug logs to easily see stderr for verifiers upon test failure.
+	logger := log.L.Dup()
+	logger.Logger.SetLevel(logrus.DebugLevel)
+	ctx := log.WithLogger(context.Background(), logger)
+
+	// Build verifiers from plain Go file.
+	allBinsDir := t.TempDir()
+	buildGoVerifiers(t, "testdata/verifiers", allBinsDir)
+
+	// Build verifiers from templates.
+	data := struct {
+		ArgsFile  string
+		StdinFile string
+	}{
+		ArgsFile:  filepath.Join(t.TempDir(), "args.txt"),
+		StdinFile: filepath.Join(t.TempDir(), "stdin.txt"),
+	}
+
+	tmplDir := "testdata/verifier_templates"
+	templates, err := os.ReadDir(tmplDir)
+	require.NoError(t, err)
+
+	renderedVerifierTmplDir := t.TempDir()
+	for _, tmplFile := range templates {
+		tmplPath := filepath.Join(tmplDir, tmplFile.Name())
+
+		tmpl, err := template.New(tmplFile.Name()).ParseFiles(tmplPath)
+		require.NoError(t, err)
+
+		goFileName := strings.ReplaceAll(tmplFile.Name(), ".go.tmpl", ".go")
+		f, err := os.Create(filepath.Join(renderedVerifierTmplDir, goFileName))
+		require.NoError(t, err)
+		defer f.Close()
+
+		require.NoError(t, tmpl.Execute(f, data))
+		f.Close()
+	}
+	buildGoVerifiers(t, renderedVerifierTmplDir, allBinsDir)
+
+	// Actual tests begin here.
+	t.Run("proper input/output management", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"verifier_test_input_output_management",
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       -1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{
+			Digest:      "sha256:98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4",
+			MediaType:   "application/vnd.docker.distribution.manifest.list.v2+json",
+			Size:        2048,
+			Annotations: map[string]string{"a": "b"},
+		})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.Equal(t, fmt.Sprintf("verifier-0%[1]v => Reason A line 1\nReason A line 2", exeIfWindows()), j.Reason)
+
+		b, err := os.ReadFile(data.ArgsFile)
+		require.NoError(t, err)
+		assert.Equal(t, "-name registry.example.com/image:abc -digest sha256:98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4 -stdin-media-type application/vnd.oci.descriptor.v1+json", string(b))
+
+		b, err = os.ReadFile(data.StdinFile)
+		require.NoError(t, err)
+		assert.Equal(t, `{"mediaType":"application/vnd.docker.distribution.manifest.list.v2+json","digest":"sha256:98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4","size":2048,"annotations":{"a":"b"}}`, strings.TrimSpace(string(b)))
+	})
+
+	t.Run("large output is truncated", func(t *testing.T) {
+		bins := []string{
+			"large_stdout",
+			"large_stdout_chunked",
+			"large_stderr",
+			"large_stderr_chunked",
+		}
+		binDir := newBinDir(t, allBinsDir, bins...)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       -1,
+			PerVerifierTimeout: 30 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK, "expected OK, got not OK with reason: %v", j.Reason)
+		assert.Less(t, len(j.Reason), len(bins)*(outputLimitBytes+1024), "reason is: %v", j.Reason) // 1024 leaves margin for the formatting around the reason.
+	})
+
+	t.Run("missing directory", func(t *testing.T) {
+		v := NewImageVerifier(&Config{
+			BinDir:             filepath.Join(t.TempDir(), "missing_directory"),
+			MaxVerifiers:       10,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.NotEmpty(t, j.Reason)
+	})
+
+	t.Run("empty directory", func(t *testing.T) {
+		v := NewImageVerifier(&Config{
+			BinDir:             t.TempDir(),
+			MaxVerifiers:       10,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.NotEmpty(t, j.Reason)
+	})
+
+	t.Run("max verifiers = 0", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"reject_reason_d", // This never runs.
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       0,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.Empty(t, j.Reason)
+	})
+
+	t.Run("max verifiers = 1", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"reject_reason_d", // This never runs.
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.NotEmpty(t, j.Reason)
+	})
+
+	t.Run("max verifiers = 2", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"accept_reason_a",
+			"reject_reason_d", // This never runs.
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       2,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.NotEmpty(t, j.Reason)
+	})
+
+	t.Run("max verifiers = 3, all accept", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"accept_reason_b",
+			"accept_reason_c",
+		)
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       3,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.Equal(t, fmt.Sprintf("verifier-0%[1]v => Reason A, verifier-1%[1]v => Reason B, verifier-2%[1]v => Reason C", exeIfWindows()), j.Reason)
+	})
+
+	t.Run("max verifiers = 3, with reject", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"accept_reason_b",
+			"reject_reason_d",
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       3,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.False(t, j.OK)
+		assert.Equal(t, fmt.Sprintf("verifier verifier-2%[1]v rejected image (exit code 1): Reason D", exeIfWindows()), j.Reason)
+	})
+
+	t.Run("max verifiers = -1, all accept", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"accept_reason_b",
+			"accept_reason_c",
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       -1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.Equal(t, fmt.Sprintf("verifier-0%[1]v => Reason A, verifier-1%[1]v => Reason B, verifier-2%[1]v => Reason C", exeIfWindows()), j.Reason)
+	})
+
+	t.Run("max verifiers = -1, with reject", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"accept_reason_b",
+			"reject_reason_d",
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       -1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.NoError(t, err)
+		assert.False(t, j.OK)
+		assert.Equal(t, fmt.Sprintf("verifier verifier-2%[1]v rejected image (exit code 1): Reason D", exeIfWindows()), j.Reason)
+	})
+
+	t.Run("max verifiers = -1, with timeout", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+			"accept_reason_b",
+			"slow_child_process",
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       -1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		if runtime.GOOS == "windows" {
+			assert.NoError(t, err)
+			assert.False(t, j.OK)
+			assert.Equal(t, "verifier verifier-2.exe rejected image (exit code 1): ", j.Reason)
+		} else {
+			assert.ErrorContains(t, err, "signal: killed")
+			assert.Nil(t, j)
+		}
+
+		command := []string{"ps", "ax"}
+		if runtime.GOOS == "windows" {
+			command = []string{"tasklist"}
+		}
+		b, err := exec.Command(command[0], command[1:]...).CombinedOutput()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if strings.Contains(string(b), "verifier-") {
+			t.Fatalf("killing the verifier binary didn't kill all its children:\n%v", string(b))
+		}
+	})
+
+	t.Run("max verifiers = -1, with exec failure", func(t *testing.T) {
+		binDir := t.TempDir()
+		err := os.WriteFile(filepath.Join(binDir, "bad.sh"), []byte("BAD"), 0744)
+		require.NoError(t, err)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       -1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{})
+		assert.Error(t, err)
+		assert.Nil(t, j)
+	})
+
+	t.Run("descriptor larger than linux pipe buffer, verifier doesn't read stdin", func(t *testing.T) {
+		binDir := newBinDir(t, allBinsDir,
+			"accept_reason_a",
+		)
+
+		v := NewImageVerifier(&Config{
+			BinDir:             binDir,
+			MaxVerifiers:       1,
+			PerVerifierTimeout: 5 * time.Second,
+		})
+
+		j, err := v.VerifyImage(ctx, "registry.example.com/image:abc", ocispec.Descriptor{
+			Digest:    "sha256:98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4",
+			MediaType: "application/vnd.docker.distribution.manifest.list.v2+json",
+			Size:      2048,
+			Annotations: map[string]string{
+				// Pipe buffer is usually 64KiB.
+				"large_payload": strings.Repeat("0", 2*64*(1<<10)),
+			},
+		})
+
+		// Should see a log like the following, but verification still succeeds:
+		// time="2023-09-05T11:15:50-04:00" level=warning msg="failed to completely write descriptor to stdin" error="write |1: broken pipe"
+
+		assert.NoError(t, err)
+		assert.True(t, j.OK)
+		assert.NotEmpty(t, j.Reason)
+	})
+}

pkg/imageverifier/bindir/processes_unix.go

@@ -0,0 +1,55 @@
+//go:build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package bindir
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+
+	"golang.org/x/sys/unix"
+)
+
+type process struct {
+	cmd *exec.Cmd
+}
+
+// Configure the verifier command so that killing it kills all child
+// processes of the verifier process.
+func startProcess(ctx context.Context, cmd *exec.Cmd) (*process, error) {
+	// Assign the verifier a new process group so that killing its process group
+	// in Cancel() doesn't kill the parent process (containerd).
+	cmd.SysProcAttr = &unix.SysProcAttr{Setpgid: true}
+
+	cmd.Cancel = func() error {
+		// Passing a negative PID causes kill(2) to kill all processes in the
+		// process group whose ID is cmd.Process.Pid.
+		return unix.Kill(-cmd.Process.Pid, unix.SIGKILL)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return nil, fmt.Errorf("starting process: %w", err)
+	}
+
+	return &process{
+		cmd: cmd,
+	}, nil
+}
+
+func (p *process) cleanup(ctx context.Context) {}

pkg/imageverifier/bindir/processes_windows.go

@@ -0,0 +1,105 @@
+//go:build windows
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package bindir
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"unsafe"
+
+	"github.com/containerd/containerd/log"
+	"golang.org/x/sys/windows"
+)
+
+type process struct {
+	cmd *exec.Cmd
+
+	jobHandle     *windows.Handle
+	processHandle *windows.Handle
+}
+
+// Configure the verifier command so that killing it kills all child
+// processes of the verifier process.
+//
+// Job/process management based on:
+// https://devblogs.microsoft.com/oldnewthing/20131209-00/?p=2433
+func startProcess(ctx context.Context, cmd *exec.Cmd) (*process, error) {
+	p := &process{
+		cmd: cmd,
+	}
+
+	jobHandle, err := windows.CreateJobObject(nil, nil)
+	if err != nil {
+		return nil, fmt.Errorf("creating job object: %w", err)
+	}
+	p.jobHandle = &jobHandle
+
+	info := windows.JOBOBJECT_EXTENDED_LIMIT_INFORMATION{
+		BasicLimitInformation: windows.JOBOBJECT_BASIC_LIMIT_INFORMATION{
+			LimitFlags: windows.JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE,
+		},
+	}
+	_, err = windows.SetInformationJobObject(
+		jobHandle,
+		windows.JobObjectExtendedLimitInformation,
+		uintptr(unsafe.Pointer(&info)),
+		uint32(unsafe.Sizeof(info)),
+	)
+	if err != nil {
+		p.cleanup(ctx)
+		return nil, fmt.Errorf("setting limits for job object: %w", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		p.cleanup(ctx)
+		return nil, fmt.Errorf("starting process: %w", err)
+	}
+
+	processHandle, err := windows.OpenProcess(
+		windows.PROCESS_QUERY_INFORMATION|windows.PROCESS_SET_QUOTA|windows.PROCESS_TERMINATE,
+		false,
+		uint32(cmd.Process.Pid),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("getting handle for verifier process: %w", err)
+	}
+	p.processHandle = &processHandle
+
+	err = windows.AssignProcessToJobObject(jobHandle, processHandle)
+	if err != nil {
+		p.cleanup(ctx)
+		return nil, fmt.Errorf("associating new process to job object: %w", err)
+	}
+
+	return p, nil
+}
+
+func (p *process) cleanup(ctx context.Context) {
+	if p.jobHandle != nil {
+		if err := windows.CloseHandle(*p.jobHandle); err != nil {
+			log.G(ctx).WithError(err).Error("failed to close job handle")
+		}
+	}
+	if p.processHandle != nil {
+		if err := windows.CloseHandle(*p.processHandle); err != nil {
+			log.G(ctx).WithError(err).Error("failed to close process handle")
+		}
+	}
+}

pkg/imageverifier/bindir/testdata/verifier_templates/verifier_test_input_output_management.go.tmpl

@@ -0,0 +1,45 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+func main() {
+	err := os.WriteFile(`{{.ArgsFile}}`, []byte(strings.Join(os.Args[1:], " ")), 0644)
+	if err != nil {
+		panic(err)
+	}
+
+	stdin, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		panic(err)
+	}
+	err = os.WriteFile(`{{.StdinFile}}`, stdin, 0644)
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println("Reason A line 1")
+	fmt.Fprintln(os.Stderr, "Debug A line 1")
+	fmt.Println("Reason A line 2")
+	fmt.Fprintln(os.Stderr, "Debug A line 2")
+}

pkg/imageverifier/bindir/testdata/verifiers/accept_reason_a.go

@@ -0,0 +1,23 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Reason A")
+}

pkg/imageverifier/bindir/testdata/verifiers/accept_reason_b.go

@@ -0,0 +1,23 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Reason B")
+}

pkg/imageverifier/bindir/testdata/verifiers/accept_reason_c.go

@@ -0,0 +1,23 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Reason C")
+}

pkg/imageverifier/bindir/testdata/verifiers/large_stderr.go

@@ -0,0 +1,35 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func main() {
+	n := 50000
+	fmt.Fprintf(os.Stderr, "attempting to write %v bytes to stderr\n", n)
+
+	wrote, err := fmt.Fprintf(os.Stderr, strings.Repeat("A", n))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "got error writing to stderr: %v\n", err)
+	}
+
+	fmt.Fprintf(os.Stderr, "wrote %v bytes to stderr\n", wrote)
+}

pkg/imageverifier/bindir/testdata/verifiers/large_stderr_chunked.go

@@ -0,0 +1,45 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	n := 500000
+	fmt.Fprintf(os.Stderr, "attempting to write %v bytes to stderr\n", n)
+
+	// Writing this all in one fmt.Fprintf has a different interaction with
+	// stderr pipe buffering than writing one byte at a time.
+	wrote := 0
+	for i := 0; i < n; i++ {
+		w, err := fmt.Fprintf(os.Stderr, "A")
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "got error writing to stderr: %v\n", err)
+		}
+
+		wrote += w
+
+		if i%10000 == 0 {
+			fmt.Fprintf(os.Stderr, "progress: wrote %v bytes to stderr\n", wrote)
+		}
+	}
+
+	fmt.Fprintf(os.Stderr, "wrote %v bytes to stderr\n", wrote)
+}

pkg/imageverifier/bindir/testdata/verifiers/large_stdout.go

@@ -0,0 +1,35 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func main() {
+	n := 50000
+	fmt.Fprintf(os.Stderr, "attempting to write %v bytes to stdout\n", n)
+
+	wrote, err := fmt.Print(strings.Repeat("A", n))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "got error writing to stdout: %v\n", err)
+	}
+
+	fmt.Fprintf(os.Stderr, "wrote %v bytes to stdout\n", wrote)
+}

pkg/imageverifier/bindir/testdata/verifiers/large_stdout_chunked.go

@@ -0,0 +1,45 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	n := 500000
+	fmt.Fprintf(os.Stderr, "attempting to write %v bytes to stdout\n", n)
+
+	// Writing this all in one fmt.Print has a different interaction with stdout
+	// pipe buffering than writing one byte at a time.
+	wrote := 0
+	for i := 0; i < n; i++ {
+		w, err := fmt.Print("A")
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "got error writing to stdout: %v\n", err)
+		}
+
+		wrote += w
+
+		if i%10000 == 0 {
+			fmt.Fprintf(os.Stderr, "progress: wrote %v bytes to stdout\n", wrote)
+		}
+	}
+
+	fmt.Fprintf(os.Stderr, "wrote %v bytes to stdout\n", wrote)
+}

pkg/imageverifier/bindir/testdata/verifiers/reject_reason_d.go

@@ -0,0 +1,27 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	fmt.Println("Reason D")
+	os.Exit(1)
+}

pkg/imageverifier/bindir/testdata/verifiers/slow_child_process.go

@@ -0,0 +1,40 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+func main() {
+	// Launch a slow child process by re-executing this binary with the -sleep-forever flag.
+	if len(os.Args) == 2 && os.Args[1] == "-sleep-forever" {
+		fmt.Println("sleeping forever...")
+		for {
+		}
+	}
+
+	thisBin := os.Args[0]
+	cmd := exec.Command(thisBin, "-sleep-forever")
+	b, err := cmd.CombinedOutput()
+	fmt.Println(string(b))
+	if err != nil {
+		panic(err)
+	}
+}

pkg/imageverifier/image_verifier.go

@@ -0,0 +1,32 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package imageverifier
+
+import (
+	"context"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+type ImageVerifier interface {
+	VerifyImage(ctx context.Context, name string, desc ocispec.Descriptor) (*Judgement, error)
+}
+
+type Judgement struct {
+	OK     bool
+	Reason string
+}

pkg/transfer/local/pull.go

@@ -30,6 +30,7 @@ import (
 	"github.com/containerd/containerd/remotes"
 	"github.com/containerd/containerd/remotes/docker"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/sirupsen/logrus"
 )
 
 func (ts *localTransferService) pull(ctx context.Context, ir transfer.ImageFetcher, is transfer.ImageStorer, tops *transfer.Config) error {
@@ -54,6 +55,32 @@ func (ts *localTransferService) pull(ctx context.Context, ir transfer.ImageFetch
 		return fmt.Errorf("schema 1 image manifests are no longer supported: %w", errdefs.ErrInvalidArgument)
 	}
 
+	// Verify image before pulling.
+	for vfName, vf := range ts.verifiers {
+		log := log.G(ctx).WithFields(logrus.Fields{
+			"name":     name,
+			"digest":   desc.Digest.String(),
+			"verifier": vfName,
+		})
+		log.Debug("Verifying image pull")
+
+		jdg, err := vf.VerifyImage(ctx, name, desc)
+		if err != nil {
+			log.WithError(err).Error("No judgement received from verifier")
+			return fmt.Errorf("blocking pull of %v with digest %v: image verifier %v returned error: %w", name, desc.Digest.String(), vfName, err)
+		}
+		log = log.WithFields(logrus.Fields{
+			"ok":     jdg.OK,
+			"reason": jdg.Reason,
+		})
+
+		if !jdg.OK {
+			log.Warn("Image verifier blocked pull")
+			return fmt.Errorf("image verifier %s blocked pull of %v with digest %v for reason: %v", vfName, name, desc.Digest.String(), jdg.Reason)
+		}
+		log.Debug("Image verifier allowed pull")
+	}
+
 	// TODO: Handle already exists
 	if tops.Progress != nil {
 		tops.Progress(transfer.Progress{

pkg/transfer/local/transfer.go

@@ -29,15 +29,17 @@ import (
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/images"
 	"github.com/containerd/containerd/leases"
+	"github.com/containerd/containerd/pkg/imageverifier"
 	"github.com/containerd/containerd/pkg/kmutex"
 	"github.com/containerd/containerd/pkg/transfer"
 	"github.com/containerd/containerd/pkg/unpack"
 )
 
 type localTransferService struct {
-	leases  leases.Manager
-	content content.Store
-	images  images.Store
+	leases    leases.Manager
+	content   content.Store
+	images    images.Store
+	verifiers map[string]imageverifier.ImageVerifier
 	// limiter for upload
 	limiterU *semaphore.Weighted
 	// limiter for download operation
@@ -45,12 +47,13 @@ type localTransferService struct {
 	config   TransferConfig
 }
 
-func NewTransferService(lm leases.Manager, cs content.Store, is images.Store, tc *TransferConfig) transfer.Transferrer {
+func NewTransferService(lm leases.Manager, cs content.Store, is images.Store, vfs map[string]imageverifier.ImageVerifier, tc *TransferConfig) transfer.Transferrer {
 	ts := &localTransferService{
-		leases:  lm,
-		content: cs,
-		images:  is,
-		config:  *tc,
+		leases:    lm,
+		content:   cs,
+		images:    is,
+		verifiers: vfs,
+		config:    *tc,
 	}
 	if tc.MaxConcurrentUploadedLayers > 0 {
 		ts.limiterU = semaphore.NewWeighted(int64(tc.MaxConcurrentUploadedLayers))
@@ -88,6 +91,7 @@ func (ts *localTransferService) Transfer(ctx context.Context, src interface{}, d
 		case transfer.ImageExportStreamer:
 			return ts.echo(ctx, s, d, topts)
 		case transfer.ImageStorer:
+			// TODO: verify imports with ImageVerifiers?
 			return ts.importStream(ctx, s, d, topts)
 		}
 	}

plugin/plugin.go

@@ -90,6 +90,8 @@ const (
 	SandboxStorePlugin Type = "io.containerd.sandbox.store.v1"
 	// SandboxControllerPlugin implements a sandbox controller
 	SandboxControllerPlugin Type = "io.containerd.sandbox.controller.v1"
+	// ImageVerifierPlugin implements an image verifier service
+	ImageVerifierPlugin Type = "io.containerd.image-verifier.v1"
 )
 
 const (

plugins/imageverifier/path_unix.go

@@ -0,0 +1,21 @@
+//go:build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package imageverifier
+
+var defaultPath = "/opt/containerd/image-verifier/bin"

plugins/imageverifier/path_windows.go

@@ -0,0 +1,25 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package imageverifier
+
+import (
+	"path/filepath"
+
+	"github.com/containerd/containerd/defaults"
+)
+
+var defaultPath = filepath.Join(defaults.DefaultRootDir, "opt", "image-verifier", "bin")

plugins/imageverifier/plugin.go

@@ -0,0 +1,45 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package imageverifier
+
+import (
+	"time"
+
+	"github.com/containerd/containerd/pkg/imageverifier/bindir"
+	"github.com/containerd/containerd/plugin"
+)
+
+// Register default image verifier service plugin
+func init() {
+	plugin.Register(&plugin.Registration{
+		Type:   plugin.ImageVerifierPlugin,
+		ID:     "bindir",
+		Config: defaultConfig(),
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			cfg := ic.Config.(*bindir.Config)
+			return bindir.NewImageVerifier(cfg), nil
+		},
+	})
+}
+
+func defaultConfig() *bindir.Config {
+	return &bindir.Config{
+		BinDir:             defaultPath,
+		MaxVerifiers:       10,
+		PerVerifierTimeout: 10 * time.Second,
+	}
+}

plugins/transfer/plugin.go

@@ -25,6 +25,7 @@ import (
 	"github.com/containerd/containerd/leases"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/metadata"
+	"github.com/containerd/containerd/pkg/imageverifier"
 	"github.com/containerd/containerd/pkg/transfer/local"
 	"github.com/containerd/containerd/pkg/unpack"
 	"github.com/containerd/containerd/platforms"
@@ -45,6 +46,7 @@ func init() {
 			plugin.LeasePlugin,
 			plugin.MetadataPlugin,
 			plugin.DiffPlugin,
+			plugin.ImageVerifierPlugin,
 		},
 		Config: defaultConfig(),
 		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
@@ -59,6 +61,20 @@ func init() {
 				return nil, err
 			}
 
+			vfs := make(map[string]imageverifier.ImageVerifier)
+			vps, err := ic.GetByType(plugin.ImageVerifierPlugin)
+			if err != nil {
+				return nil, err
+			}
+
+			for name, vp := range vps {
+				inst, err := vp.Instance()
+				if err != nil {
+					return nil, err
+				}
+				vfs[name] = inst.(imageverifier.ImageVerifier)
+			}
+
 			// Set configuration based on default or user input
 			var lc local.TransferConfig
 			lc.MaxConcurrentDownloads = config.MaxConcurrentDownloads
@@ -126,7 +142,7 @@ func init() {
 			}
 			lc.RegistryConfigPath = config.RegistryConfigPath
 
-			return local.NewTransferService(l.(leases.Manager), ms.ContentStore(), metadata.NewImageStore(ms), &lc), nil
+			return local.NewTransferService(l.(leases.Manager), ms.ContentStore(), metadata.NewImageStore(ms), vfs, &lc), nil
 		},
 	})
 }