overlay, composefs: add fs-verity to files

at the moment it is a best-effort implementation to enable fs-verity
for the composefs blob as well as for the data files.

Signed-off-by: Giuseppe Scrivano <[email protected]>

drivers/driver.go

@@ -206,6 +206,7 @@ const (
 type DifferOptions struct {
 	// Format defines the destination directory layout format
 	Format DifferOutputFormat
+	FilePostProcess func(f* os.File) error
 }
 
 // Differ defines the interface for using a custom differ.

drivers/overlay/composefs_notsupported.go

@@ -21,3 +21,7 @@ func generateComposeFsBlob(toc []byte, destFile string) error {
 func mountErofsBlob(blobFile, mountPoint string) error {
 	return fmt.Errorf("composefs is not supported")
 }
+
+func enableVerityRecursive(path string) error {
+	return fmt.Errorf("composefs is not supported")
+}

drivers/overlay/composefs_supported.go

@@ -5,11 +5,16 @@ package overlay
 
 import (
 	"fmt"
+	"io/fs"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"sync"
+	"syscall"
+	"unsafe"
 
 	"github.com/containers/storage/pkg/loopback"
+	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
 
@@ -31,12 +36,54 @@ func composeFsSupported() bool {
 	return err == nil
 }
 
+func enableVerity(description string, fd int) error {
+	enableArg := unix.FsverityEnableArg{
+		Version:        1,
+		Hash_algorithm: unix.FS_VERITY_HASH_ALG_SHA256,
+		Block_size:     4096,
+	}
+
+	_, _, e1 := syscall.Syscall(unix.SYS_IOCTL, uintptr(fd), uintptr(unix.FS_IOC_ENABLE_VERITY), uintptr(unsafe.Pointer(&enableArg)))
+	if e1 != 0 {
+		return fmt.Errorf("failed to enable verity for %q", description)
+	}
+	return nil
+}
+
+func enableVerityRecursive(path string) error {
+	walkFn := func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if !d.Type().IsRegular() {
+			return nil
+		}
+
+		f, err := os.Open(path)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+
+		if err := enableVerity(path, int(f.Fd())); err != nil {
+			return fmt.Errorf("file %s: %w", path, err)
+		}
+		return nil
+	}
+	return filepath.WalkDir(path, walkFn)
+}
+
 func generateComposeFsBlob(toc []byte, destFile string) error {
 	outFd, err := unix.Openat(unix.AT_FDCWD, destFile, unix.O_WRONLY|unix.O_CREAT|unix.O_TRUNC|unix.O_EXCL, 0644)
 	if err != nil {
 		return fmt.Errorf("failed to open output file: %w", err)
 	}
 
+	newFd, err := unix.Open(fmt.Sprintf("/proc/self/fd/%d", outFd), unix.O_RDONLY, 0)
+	if err != nil {
+		return fmt.Errorf("failed to dup output file: %w", err)
+	}
+	defer unix.Close(newFd)
 
 	writerJson, err := getComposeFsHelper()
 	if err != nil {
@@ -77,6 +124,11 @@ func generateComposeFsBlob(toc []byte, destFile string) error {
 	if err != nil {
 		return err
 	}
+
+	if err := enableVerity("manifest file", newFd); err != nil {
+		logrus.Warningf("%s", err)
+	}
+
 	return nil
 }
 

drivers/overlay/overlay.go

@@ -2062,7 +2062,13 @@ func (d *Driver) ApplyDiffFromStagingDirectory(id, parent, stagingDirectory stri
 	}
 
 	dest := ""
+
 	if d.useComposeFs() {
+		// FIXME: move this logic into the differ so we don't have to open
+		// the file twice.
+		if err := enableVerityRecursive(stagingDirectory); err != nil {
+			logrus.Warningf("%s", err)
+		}
 		toc := diffOutput.BigData[zstdChunkedManifest]
 		if err := generateComposeFsBlob(toc, d.getErofsBlob(id)); err != nil {
 			return err