Add children names into verity hash

children names map can be used to verify whether a child is expected
during walking, so that we can detect unexpected modifications that
deleted/renamed both the target file and the corresponding merkle tree
file.

PiperOrigin-RevId: 342170715

3 files changed, 443 insertions, 207 deletions

diff --git a/pkg/sentry/fsimpl/verity/filesystem.go b/pkg/sentry/fsimpl/verity/filesystem.go
index 4e8d63d51..add5dd48e 100644
--- a/pkg/sentry/fsimpl/verity/filesystem.go
+++ b/pkg/sentry/fsimpl/verity/filesystem.go
@@ -16,6 +16,7 @@ package verity
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
 	"strconv"
@@ -31,6 +32,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
 )
 
 // Sync implements vfs.FilesystemImpl.Sync.
@@ -267,14 +269,15 @@ func (fs *filesystem) verifyChild(ctx context.Context, parent *dentry, child *de
 	// Verify returns with success.
 	var buf bytes.Buffer
 	if _, err := merkletree.Verify(&merkletree.VerifyParams{
-		Out:  &buf,
-		File: &fdReader,
-		Tree: &fdReader,
-		Size: int64(parentSize),
-		Name: parent.name,
-		Mode: uint32(parentStat.Mode),
-		UID:  parentStat.UID,
-		GID:  parentStat.GID,
+		Out:      &buf,
+		File:     &fdReader,
+		Tree:     &fdReader,
+		Size:     int64(parentSize),
+		Name:     parent.name,
+		Mode:     uint32(parentStat.Mode),
+		UID:      parentStat.UID,
+		GID:      parentStat.GID,
+		Children: parent.childrenNames,
 		//TODO(b/156980949): Support passing other hash algorithms.
 		HashAlgorithms:        fs.alg.toLinuxHashAlg(),
 		ReadOffset:            int64(offset),
@@ -292,9 +295,10 @@ func (fs *filesystem) verifyChild(ctx context.Context, parent *dentry, child *de
 	return child, nil
 }
 
-// verifyStat verifies the stat against the verified hash. The mode/uid/gid of
-// the file is cached after verified.
-func (fs *filesystem) verifyStat(ctx context.Context, d *dentry, stat linux.Statx) error {
+// verifyStatAndChildren verifies the stat and children names against the
+// verified hash. The mode/uid/gid and childrenNames of the file is cached
+// after verified.
+func (fs *filesystem) verifyStatAndChildren(ctx context.Context, d *dentry, stat linux.Statx) error {
 	vfsObj := fs.vfsfs.VirtualFilesystem()
 
 	// Get the path to the child dentry. This is only used to provide path
@@ -337,6 +341,49 @@ func (fs *filesystem) verifyStat(ctx context.Context, d *dentry, stat linux.Stat
 		return alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s for %s to int: %v", merkleSizeXattr, childPath, err))
 	}
 
+	if d.isDir() && len(d.childrenNames) == 0 {
+		childrenOffString, err := fd.GetXattr(ctx, &vfs.GetXattrOptions{
+			Name: childrenOffsetXattr,
+			Size: sizeOfStringInt32,
+		})
+
+		if err == syserror.ENODATA {
+			return alertIntegrityViolation(fmt.Sprintf("Failed to get xattr %s for merkle file of %s: %v", childrenOffsetXattr, childPath, err))
+		}
+		if err != nil {
+			return err
+		}
+		childrenOffset, err := strconv.Atoi(childrenOffString)
+		if err != nil {
+			return alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s to int: %v", childrenOffsetXattr, err))
+		}
+
+		childrenSizeString, err := fd.GetXattr(ctx, &vfs.GetXattrOptions{
+			Name: childrenSizeXattr,
+			Size: sizeOfStringInt32,
+		})
+
+		if err == syserror.ENODATA {
+			return alertIntegrityViolation(fmt.Sprintf("Failed to get xattr %s for merkle file of %s: %v", childrenSizeXattr, childPath, err))
+		}
+		if err != nil {
+			return err
+		}
+		childrenSize, err := strconv.Atoi(childrenSizeString)
+		if err != nil {
+			return alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s to int: %v", childrenSizeXattr, err))
+		}
+
+		childrenNames := make([]byte, childrenSize)
+		if _, err := fd.PRead(ctx, usermem.BytesIOSequence(childrenNames), int64(childrenOffset), vfs.ReadOptions{}); err != nil {
+			return alertIntegrityViolation(fmt.Sprintf("Failed to read children map for %s: %v", childPath, err))
+		}
+
+		if err := json.Unmarshal(childrenNames, &d.childrenNames); err != nil {
+			return alertIntegrityViolation(fmt.Sprintf("Failed to deserialize childrenNames of %s: %v", childPath, err))
+		}
+	}
+
 	fdReader := vfs.FileReadWriteSeeker{
 		FD:  fd,
 		Ctx: ctx,
@@ -344,13 +391,14 @@ func (fs *filesystem) verifyStat(ctx context.Context, d *dentry, stat linux.Stat
 
 	var buf bytes.Buffer
 	params := &merkletree.VerifyParams{
-		Out:  &buf,
-		Tree: &fdReader,
-		Size: int64(size),
-		Name: d.name,
-		Mode: uint32(stat.Mode),
-		UID:  stat.UID,
-		GID:  stat.GID,
+		Out:      &buf,
+		Tree:     &fdReader,
+		Size:     int64(size),
+		Name:     d.name,
+		Mode:     uint32(stat.Mode),
+		UID:      stat.UID,
+		GID:      stat.GID,
+		Children: d.childrenNames,
 		//TODO(b/156980949): Support passing other hash algorithms.
 		HashAlgorithms: fs.alg.toLinuxHashAlg(),
 		ReadOffset:     0,
@@ -438,7 +486,7 @@ func (fs *filesystem) getChildLocked(ctx context.Context, parent *dentry, name s
 				if err != nil {
 					return nil, err
 				}
-				if err := fs.verifyStat(ctx, child, stat); err != nil {
+				if err := fs.verifyStatAndChildren(ctx, child, stat); err != nil {
 					return nil, err
 				}
 			}
@@ -462,92 +510,58 @@ func (fs *filesystem) getChildLocked(ctx context.Context, parent *dentry, name s
 func (fs *filesystem) lookupAndVerifyLocked(ctx context.Context, parent *dentry, name string) (*dentry, error) {
 	vfsObj := fs.vfsfs.VirtualFilesystem()
 
-	childVD, childErr := parent.getLowerAt(ctx, vfsObj, name)
-	// We will handle ENOENT separately, as it may indicate unexpected
-	// modifications to the file system, and may cause a sentry panic.
-	if childErr != nil && childErr != syserror.ENOENT {
-		return nil, childErr
+	if parent.verityEnabled() {
+		if _, ok := parent.childrenNames[name]; !ok {
+			return nil, syserror.ENOENT
+		}
 	}
 
-	// The dentry needs to be cleaned up if any error occurs. IncRef will be
-	// called if a verity child dentry is successfully created.
-	if childErr == nil {
-		defer childVD.DecRef(ctx)
+	parentPath, err := vfsObj.PathnameWithDeleted(ctx, parent.fs.rootDentry.lowerVD, parent.lowerVD)
+	if err != nil {
+		return nil, err
 	}
 
-	childMerkleVD, childMerkleErr := parent.getLowerAt(ctx, vfsObj, merklePrefix+name)
-	// We will handle ENOENT separately, as it may indicate unexpected
-	// modifications to the file system, and may cause a sentry panic.
-	if childMerkleErr != nil && childMerkleErr != syserror.ENOENT {
-		return nil, childMerkleErr
+	childVD, err := parent.getLowerAt(ctx, vfsObj, name)
+	if err == syserror.ENOENT {
+		return nil, alertIntegrityViolation(fmt.Sprintf("file %s expected but not found", parentPath+"/"+name))
+	}
+	if err != nil {
+		return nil, err
 	}
 
 	// The dentry needs to be cleaned up if any error occurs. IncRef will be
 	// called if a verity child dentry is successfully created.
-	if childMerkleErr == nil {
-		defer childMerkleVD.DecRef(ctx)
-	}
+	defer childVD.DecRef(ctx)
 
-	// Get the path to the parent dentry. This is only used to provide path
-	// information in failure case.
-	parentPath, err := vfsObj.PathnameWithDeleted(ctx, parent.fs.rootDentry.lowerVD, parent.lowerVD)
-	if err != nil {
+	childMerkleVD, err := parent.getLowerAt(ctx, vfsObj, merklePrefix+name)
+	if err == syserror.ENOENT {
+		if !fs.allowRuntimeEnable {
+			return nil, alertIntegrityViolation(fmt.Sprintf("Merkle file for %s expected but not found", parentPath+"/"+name))
+		}
+		childMerkleFD, err := vfsObj.OpenAt(ctx, fs.creds, &vfs.PathOperation{
+			Root:  parent.lowerVD,
+			Start: parent.lowerVD,
+			Path:  fspath.Parse(merklePrefix + name),
+		}, &vfs.OpenOptions{
+			Flags: linux.O_RDWR | linux.O_CREAT,
+			Mode:  0644,
+		})
+		if err != nil {
+			return nil, err
+		}
+		childMerkleFD.DecRef(ctx)
+		childMerkleVD, err = parent.getLowerAt(ctx, vfsObj, merklePrefix+name)
+		if err != nil {
+			return nil, err
+		}
+	}
+	if err != nil && err != syserror.ENOENT {
 		return nil, err
 	}
 
-	// TODO(b/166474175): Investigate all possible errors of childErr and
-	// childMerkleErr, and make sure we differentiate all errors that
-	// indicate unexpected modifications to the file system from the ones
-	// that are not harmful.
-	if childErr == syserror.ENOENT && childMerkleErr == nil {
-		// Failed to get child file/directory dentry. However the
-		// corresponding Merkle tree is found. This indicates an
-		// unexpected modification to the file system that
-		// removed/renamed the child.
-		return nil, alertIntegrityViolation(fmt.Sprintf("Target file %s is expected but missing", parentPath+"/"+name))
-	} else if childErr == nil && childMerkleErr == syserror.ENOENT {
-		// If in allowRuntimeEnable mode, and the Merkle tree file is
-		// not created yet, we create an empty Merkle tree file, so that
-		// if the file is enabled through ioctl, we have the Merkle tree
-		// file open and ready to use.
-		// This may cause empty and unused Merkle tree files in
-		// allowRuntimeEnable mode, if they are never enabled. This
-		// does not affect verification, as we rely on cached hash to
-		// decide whether to perform verification, not the existence of
-		// the Merkle tree file. Also, those Merkle tree files are
-		// always hidden and cannot be accessed by verity fs users.
-		if fs.allowRuntimeEnable {
-			childMerkleFD, err := vfsObj.OpenAt(ctx, fs.creds, &vfs.PathOperation{
-				Root:  parent.lowerVD,
-				Start: parent.lowerVD,
-				Path:  fspath.Parse(merklePrefix + name),
-			}, &vfs.OpenOptions{
-				Flags: linux.O_RDWR | linux.O_CREAT,
-				Mode:  0644,
-			})
-			if err != nil {
-				return nil, err
-			}
-			childMerkleFD.DecRef(ctx)
-			childMerkleVD, err = parent.getLowerAt(ctx, vfsObj, merklePrefix+name)
-			if err != nil {
-				return nil, err
-			}
-		} else {
-			// If runtime enable is not allowed. This indicates an
-			// unexpected modification to the file system that
-			// removed/renamed the Merkle tree file.
-			return nil, alertIntegrityViolation(fmt.Sprintf("Expected Merkle file for target %s but none found", parentPath+"/"+name))
-		}
-	} else if childErr == syserror.ENOENT && childMerkleErr == syserror.ENOENT {
-		// Both the child and the corresponding Merkle tree are missing.
-		// This could be an unexpected modification or due to incorrect
-		// parameter.
-		// TODO(b/167752508): Investigate possible ways to differentiate
-		// cases that both files are deleted from cases that they never
-		// exist in the file system.
-		return nil, alertIntegrityViolation(fmt.Sprintf("Failed to find file %s", parentPath+"/"+name))
-	}
+	// The dentry needs to be cleaned up if any error occurs. IncRef will be
+	// called if a verity child dentry is successfully created.
+	defer childMerkleVD.DecRef(ctx)
 
 	mask := uint32(linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID)
 	stat, err := vfsObj.StatAt(ctx, fs.creds, &vfs.PathOperation{
@@ -577,6 +591,7 @@ func (fs *filesystem) lookupAndVerifyLocked(ctx context.Context, parent *dentry,
 	child.mode = uint32(stat.Mode)
 	child.uid = stat.UID
 	child.gid = stat.GID
+	child.childrenNames = make(map[string]struct{})
 
 	// Verify child hash. This should always be performed unless in
 	// allowRuntimeEnable mode and the parent directory hasn't been enabled
@@ -588,7 +603,7 @@ func (fs *filesystem) lookupAndVerifyLocked(ctx context.Context, parent *dentry,
 		}
 	}
 	if child.verityEnabled() {
-		if err := fs.verifyStat(ctx, child, stat); err != nil {
+		if err := fs.verifyStatAndChildren(ctx, child, stat); err != nil {
 			child.destroyLocked(ctx)
 			return nil, err
 		}
@@ -944,7 +959,7 @@ func (fs *filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 		return linux.Statx{}, err
 	}
 	if d.verityEnabled() {
-		if err := fs.verifyStat(ctx, d, stat); err != nil {
+		if err := fs.verifyStatAndChildren(ctx, d, stat); err != nil {
 			return linux.Statx{}, err
 		}
 	}
diff --git a/pkg/sentry/fsimpl/verity/verity.go b/pkg/sentry/fsimpl/verity/verity.go
index faa862c55..87dabe038 100644
--- a/pkg/sentry/fsimpl/verity/verity.go
+++ b/pkg/sentry/fsimpl/verity/verity.go
@@ -22,6 +22,7 @@
 package verity
 
 import (
+	"encoding/json"
 	"fmt"
 	"math"
 	"strconv"
@@ -60,6 +61,15 @@ const (
 	// file size. For a directory, this is the size of all its children's hashes.
 	merkleSizeXattr = "user.merkle.size"
 
+	// childrenOffsetXattr is the extended attribute name specifying the
+	// names of the offset of the serialized children names in the Merkle
+	// tree file.
+	childrenOffsetXattr = "user.merkle.childrenOffset"
+
+	// childrenSizeXattr is the extended attribute name specifying the size
+	// of the serialized children names.
+	childrenSizeXattr = "user.merkle.childrenSize"
+
 	// sizeOfStringInt32 is the size for a 32 bit integer stored as string in
 	// extended attributes. The maximum value of a 32 bit integer has 10 digits.
 	sizeOfStringInt32 = 10
@@ -299,9 +309,70 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 	d.uid = stat.UID
 	d.gid = stat.GID
 	d.hash = make([]byte, len(iopts.RootHash))
+	d.childrenNames = make(map[string]struct{})
 
 	if !fs.allowRuntimeEnable {
-		if err := fs.verifyStat(ctx, d, stat); err != nil {
+		// Get children names from the underlying file system.
+		offString, err := vfsObj.GetXattrAt(ctx, creds, &vfs.PathOperation{
+			Root:  lowerMerkleVD,
+			Start: lowerMerkleVD,
+		}, &vfs.GetXattrOptions{
+			Name: childrenOffsetXattr,
+			Size: sizeOfStringInt32,
+		})
+		if err == syserror.ENOENT || err == syserror.ENODATA {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to get xattr %s: %v", childrenOffsetXattr, err))
+		}
+		if err != nil {
+			return nil, nil, err
+		}
+
+		off, err := strconv.Atoi(offString)
+		if err != nil {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s to int: %v", childrenOffsetXattr, err))
+		}
+
+		sizeString, err := vfsObj.GetXattrAt(ctx, creds, &vfs.PathOperation{
+			Root:  lowerMerkleVD,
+			Start: lowerMerkleVD,
+		}, &vfs.GetXattrOptions{
+			Name: childrenSizeXattr,
+			Size: sizeOfStringInt32,
+		})
+		if err == syserror.ENOENT || err == syserror.ENODATA {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to get xattr %s: %v", childrenSizeXattr, err))
+		}
+		if err != nil {
+			return nil, nil, err
+		}
+		size, err := strconv.Atoi(sizeString)
+		if err != nil {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to convert xattr %s to int: %v", childrenSizeXattr, err))
+		}
+
+		lowerMerkleFD, err := vfsObj.OpenAt(ctx, fs.creds, &vfs.PathOperation{
+			Root:  lowerMerkleVD,
+			Start: lowerMerkleVD,
+		}, &vfs.OpenOptions{
+			Flags: linux.O_RDONLY,
+		})
+		if err == syserror.ENOENT {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to open root Merkle file: %v", err))
+		}
+		if err != nil {
+			return nil, nil, err
+		}
+
+		childrenNames := make([]byte, size)
+		if _, err := lowerMerkleFD.PRead(ctx, usermem.BytesIOSequence(childrenNames), int64(off), vfs.ReadOptions{}); err != nil {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to read root children map: %v", err))
+		}
+
+		if err := json.Unmarshal(childrenNames, &d.childrenNames); err != nil {
+			return nil, nil, alertIntegrityViolation(fmt.Sprintf("Failed to deserialize childrenNames: %v", err))
+		}
+
+		if err := fs.verifyStatAndChildren(ctx, d, stat); err != nil {
 			return nil, nil, err
 		}
 	}
@@ -352,6 +423,11 @@ type dentry struct {
 	dirMu    sync.Mutex `state:"nosave"`
 	children map[string]*dentry
 
+	// childrenNames stores the name of all children of the dentry. This is
+	// used by verity to check whether a child is expected. This is only
+	// populated by enableVerity.
+	childrenNames map[string]struct{}
+
 	// lowerVD is the VirtualDentry in the underlying file system.
 	lowerVD vfs.VirtualDentry
 
@@ -603,7 +679,7 @@ func (fd *fileDescription) Stat(ctx context.Context, opts vfs.StatOptions) (linu
 		return linux.Statx{}, err
 	}
 	if fd.d.verityEnabled() {
-		if err := fd.d.fs.verifyStat(ctx, fd.d, stat); err != nil {
+		if err := fd.d.fs.verifyStatAndChildren(ctx, fd.d, stat); err != nil {
 			return linux.Statx{}, err
 		}
 	}
@@ -664,6 +740,7 @@ func (fd *fileDescription) generateMerkle(ctx context.Context) ([]byte, uint64,
 	params := &merkletree.GenerateParams{
 		TreeReader: &merkleReader,
 		TreeWriter: &merkleWriter,
+		Children:   fd.d.childrenNames,
 		//TODO(b/156980949): Support passing other hash algorithms.
 		HashAlgorithms: fd.d.fs.alg.toLinuxHashAlg(),
 	}
@@ -716,9 +793,45 @@ func (fd *fileDescription) generateMerkle(ctx context.Context) ([]byte, uint64,
 	return hash, uint64(params.Size), err
 }
 
+// recordChildren writes the names of fd's children into the corresponding
+// Merkle tree file, and saves the offset/size of the map into xattrs.
+//
+// Preconditions: fd.d.isDir() == true
+func (fd *fileDescription) recordChildren(ctx context.Context) error {
+	// Record the children names in the Merkle tree file.
+	childrenNames, err := json.Marshal(fd.d.childrenNames)
+	if err != nil {
+		return err
+	}
+
+	stat, err := fd.merkleWriter.Stat(ctx, vfs.StatOptions{})
+	if err != nil {
+		return err
+	}
+
+	if err := fd.merkleWriter.SetXattr(ctx, &vfs.SetXattrOptions{
+		Name:  childrenOffsetXattr,
+		Value: strconv.Itoa(int(stat.Size)),
+	}); err != nil {
+		return err
+	}
+	if err := fd.merkleWriter.SetXattr(ctx, &vfs.SetXattrOptions{
+		Name:  childrenSizeXattr,
+		Value: strconv.Itoa(len(childrenNames)),
+	}); err != nil {
+		return err
+	}
+
+	if _, err = fd.merkleWriter.Write(ctx, usermem.BytesIOSequence(childrenNames), vfs.WriteOptions{}); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // enableVerity enables verity features on fd by generating a Merkle tree file
 // and stores its hash in its parent directory's Merkle tree.
-func (fd *fileDescription) enableVerity(ctx context.Context, uio usermem.IO) (uintptr, error) {
+func (fd *fileDescription) enableVerity(ctx context.Context) (uintptr, error) {
 	if !fd.d.fs.allowRuntimeEnable {
 		return 0, syserror.EPERM
 	}
@@ -761,6 +874,9 @@ func (fd *fileDescription) enableVerity(ctx context.Context, uio usermem.IO) (ui
 		}); err != nil {
 			return 0, err
 		}
+
+		// Add the current child's name to parent's childrenNames.
+		fd.d.parent.childrenNames[fd.d.name] = struct{}{}
 	}
 
 	// Record the size of the data being hashed for fd.
@@ -770,12 +886,18 @@ func (fd *fileDescription) enableVerity(ctx context.Context, uio usermem.IO) (ui
 	}); err != nil {
 		return 0, err
 	}
+
+	if fd.d.isDir() {
+		if err := fd.recordChildren(ctx); err != nil {
+			return 0, err
+		}
+	}
 	fd.d.hash = append(fd.d.hash, hash...)
 	return 0, nil
 }
 
 // measureVerity returns the hash of fd, saved in verityDigest.
-func (fd *fileDescription) measureVerity(ctx context.Context, uio usermem.IO, verityDigest usermem.Addr) (uintptr, error) {
+func (fd *fileDescription) measureVerity(ctx context.Context, verityDigest usermem.Addr) (uintptr, error) {
 	t := kernel.TaskFromContext(ctx)
 	if t == nil {
 		return 0, syserror.EINVAL
@@ -815,7 +937,7 @@ func (fd *fileDescription) measureVerity(ctx context.Context, uio usermem.IO, ve
 	return 0, err
 }
 
-func (fd *fileDescription) verityFlags(ctx context.Context, uio usermem.IO, flags usermem.Addr) (uintptr, error) {
+func (fd *fileDescription) verityFlags(ctx context.Context, flags usermem.Addr) (uintptr, error) {
 	f := int32(0)
 
 	// All enabled files should store a hash. This flag is not settable via
@@ -836,11 +958,11 @@ func (fd *fileDescription) verityFlags(ctx context.Context, uio usermem.IO, flag
 func (fd *fileDescription) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
 	switch cmd := args[1].Uint(); cmd {
 	case linux.FS_IOC_ENABLE_VERITY:
-		return fd.enableVerity(ctx, uio)
+		return fd.enableVerity(ctx)
 	case linux.FS_IOC_MEASURE_VERITY:
-		return fd.measureVerity(ctx, uio, args[2].Pointer())
+		return fd.measureVerity(ctx, args[2].Pointer())
 	case linux.FS_IOC_GETFLAGS:
-		return fd.verityFlags(ctx, uio, args[2].Pointer())
+		return fd.verityFlags(ctx, args[2].Pointer())
 	default:
 		// TODO(b/169682228): Investigate which ioctl commands should
 		// be allowed.
@@ -902,14 +1024,15 @@ func (fd *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, of
 	}
 
 	n, err := merkletree.Verify(&merkletree.VerifyParams{
-		Out:  dst.Writer(ctx),
-		File: &dataReader,
-		Tree: &merkleReader,
-		Size: int64(size),
-		Name: fd.d.name,
-		Mode: fd.d.mode,
-		UID:  fd.d.uid,
-		GID:  fd.d.gid,
+		Out:      dst.Writer(ctx),
+		File:     &dataReader,
+		Tree:     &merkleReader,
+		Size:     int64(size),
+		Name:     fd.d.name,
+		Mode:     fd.d.mode,
+		UID:      fd.d.uid,
+		GID:      fd.d.gid,
+		Children: fd.d.childrenNames,
 		//TODO(b/156980949): Support passing other hash algorithms.
 		HashAlgorithms:        fd.d.fs.alg.toLinuxHashAlg(),
 		ReadOffset:            offset,
diff --git a/pkg/sentry/fsimpl/verity/verity_test.go b/pkg/sentry/fsimpl/verity/verity_test.go
index b2da9dd96..7196e74eb 100644
--- a/pkg/sentry/fsimpl/verity/verity_test.go
+++ b/pkg/sentry/fsimpl/verity/verity_test.go
@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"io"
 	"math/rand"
+	"strconv"
 	"testing"
 	"time"
 
@@ -307,6 +308,56 @@ func TestReopenUnmodifiedFileSucceeds(t *testing.T) {
 	}
 }
 
+// TestOpenNonexistentFile ensures that opening a nonexistent file does not
+// trigger verification failure, even if the parent directory is verified.
+func TestOpenNonexistentFile(t *testing.T) {
+	vfsObj, root, ctx, err := newVerityRoot(t, SHA256)
+	if err != nil {
+		t.Fatalf("newVerityRoot: %v", err)
+	}
+
+	filename := "verity-test-file"
+	fd, _, err := newFileFD(ctx, vfsObj, root, filename, 0644)
+	if err != nil {
+		t.Fatalf("newFileFD: %v", err)
+	}
+
+	// Enable verity on the file and confirms a normal read succeeds.
+	var args arch.SyscallArguments
+	args[1] = arch.SyscallArgument{Value: linux.FS_IOC_ENABLE_VERITY}
+	if _, err := fd.Ioctl(ctx, nil /* uio */, args); err != nil {
+		t.Fatalf("Ioctl: %v", err)
+	}
+
+	// Enable verity on the parent directory.
+	parentFD, err := vfsObj.OpenAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+		Root:  root,
+		Start: root,
+	}, &vfs.OpenOptions{
+		Flags: linux.O_RDONLY,
+	})
+	if err != nil {
+		t.Fatalf("OpenAt: %v", err)
+	}
+
+	if _, err := parentFD.Ioctl(ctx, nil /* uio */, args); err != nil {
+		t.Fatalf("Ioctl: %v", err)
+	}
+
+	// Ensure open an unexpected file in the parent directory fails with
+	// ENOENT rather than verification failure.
+	if _, err = vfsObj.OpenAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+		Root:  root,
+		Start: root,
+		Path:  fspath.Parse(filename + "abc"),
+	}, &vfs.OpenOptions{
+		Flags: linux.O_RDONLY,
+		Mode:  linux.ModeRegular,
+	}); err != syserror.ENOENT {
+		t.Errorf("OpenAt unexpected error: %v", err)
+	}
+}
+
 // TestPReadModifiedFileFails ensures that read from a modified verity file
 // fails.
 func TestPReadModifiedFileFails(t *testing.T) {
@@ -439,10 +490,10 @@ func TestModifiedMerkleFails(t *testing.T) {
 		// Flip a random bit in the Merkle tree file.
 		stat, err := lowerMerkleFD.Stat(ctx, vfs.StatOptions{})
 		if err != nil {
-			t.Fatalf("stat: %v", err)
+			t.Errorf("lowerMerkleFD.Stat: %v", err)
 		}
-		merkleSize := int(stat.Size)
-		if err := corruptRandomBit(ctx, lowerMerkleFD, merkleSize); err != nil {
+
+		if err := corruptRandomBit(ctx, lowerMerkleFD, int(stat.Size)); err != nil {
 			t.Fatalf("corruptRandomBit: %v", err)
 		}
 
@@ -510,11 +561,17 @@ func TestModifiedParentMerkleFails(t *testing.T) {
 		// This parent directory contains only one child, so any random
 		// modification in the parent Merkle tree should cause verification
 		// failure when opening the child file.
-		stat, err := parentLowerMerkleFD.Stat(ctx, vfs.StatOptions{})
+		sizeString, err := parentLowerMerkleFD.GetXattr(ctx, &vfs.GetXattrOptions{
+			Name: childrenOffsetXattr,
+			Size: sizeOfStringInt32,
+		})
+		if err != nil {
+			t.Fatalf("parentLowerMerkleFD.GetXattr: %v", err)
+		}
+		parentMerkleSize, err := strconv.Atoi(sizeString)
 		if err != nil {
-			t.Fatalf("stat: %v", err)
+			t.Fatalf("Failed convert size to int: %v", err)
 		}
-		parentMerkleSize := int(stat.Size)
 		if err := corruptRandomBit(ctx, parentLowerMerkleFD, parentMerkleSize); err != nil {
 			t.Fatalf("corruptRandomBit: %v", err)
 		}
@@ -602,124 +659,165 @@ func TestModifiedStatFails(t *testing.T) {
 	}
 }
 
-// TestOpenDeletedOrRenamedFileFails ensures that opening a deleted/renamed
-// verity enabled file or the corresponding Merkle tree file fails with the
-// verify error.
+// TestOpenDeletedFileFails ensures that opening a deleted verity enabled file
+// and/or the corresponding Merkle tree file fails with the verity error.
 func TestOpenDeletedFileFails(t *testing.T) {
 	testCases := []struct {
-		// Tests removing files is remove is true. Otherwise tests
-		// renaming files.
-		remove bool
-		// The original file is removed/renamed if changeFile is true.
+		// The original file is removed if changeFile is true.
 		changeFile bool
-		// The Merkle tree file is removed/renamed if changeMerkleFile
-		// is true.
+		// The Merkle tree file is removed if changeMerkleFile is true.
 		changeMerkleFile bool
 	}{
 		{
-			remove:           true,
 			changeFile:       true,
 			changeMerkleFile: false,
 		},
 		{
-			remove:           true,
 			changeFile:       false,
 			changeMerkleFile: true,
 		},
 		{
-			remove:           false,
 			changeFile:       true,
-			changeMerkleFile: false,
+			changeMerkleFile: true,
 		},
+	}
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("changeFile:%t, changeMerkleFile:%t", tc.changeFile, tc.changeMerkleFile), func(t *testing.T) {
+			vfsObj, root, ctx, err := newVerityRoot(t, SHA256)
+			if err != nil {
+				t.Fatalf("newVerityRoot: %v", err)
+			}
+
+			filename := "verity-test-file"
+			fd, _, err := newFileFD(ctx, vfsObj, root, filename, 0644)
+			if err != nil {
+				t.Fatalf("newFileFD: %v", err)
+			}
+
+			// Enable verity on the file.
+			var args arch.SyscallArguments
+			args[1] = arch.SyscallArgument{Value: linux.FS_IOC_ENABLE_VERITY}
+			if _, err := fd.Ioctl(ctx, nil /* uio */, args); err != nil {
+				t.Fatalf("Ioctl: %v", err)
+			}
+
+			rootLowerVD := root.Dentry().Impl().(*dentry).lowerVD
+			if tc.changeFile {
+				if err := vfsObj.UnlinkAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+					Root:  rootLowerVD,
+					Start: rootLowerVD,
+					Path:  fspath.Parse(filename),
+				}); err != nil {
+					t.Fatalf("UnlinkAt: %v", err)
+				}
+			}
+			if tc.changeMerkleFile {
+				if err := vfsObj.UnlinkAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+					Root:  rootLowerVD,
+					Start: rootLowerVD,
+					Path:  fspath.Parse(merklePrefix + filename),
+				}); err != nil {
+					t.Fatalf("UnlinkAt: %v", err)
+				}
+			}
+
+			// Ensure reopening the verity enabled file fails.
+			if _, err = vfsObj.OpenAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+				Root:  root,
+				Start: root,
+				Path:  fspath.Parse(filename),
+			}, &vfs.OpenOptions{
+				Flags: linux.O_RDONLY,
+				Mode:  linux.ModeRegular,
+			}); err != syserror.EIO {
+				t.Errorf("got OpenAt error: %v, expected EIO", err)
+			}
+		})
+	}
+}
+
+// TestOpenRenamedFileFails ensures that opening a renamed verity enabled file
+// and/or the corresponding Merkle tree file fails with the verity error.
+func TestOpenRenamedFileFails(t *testing.T) {
+	testCases := []struct {
+		// The original file is renamed if changeFile is true.
+		changeFile bool
+		// The Merkle tree file is renamed if changeMerkleFile is true.
+		changeMerkleFile bool
+	}{
 		{
-			remove:           false,
 			changeFile:       true,
 			changeMerkleFile: false,
 		},
+		{
+			changeFile:       false,
+			changeMerkleFile: true,
+		},
+		{
+			changeFile:       true,
+			changeMerkleFile: true,
+		},
 	}
 	for _, tc := range testCases {
-		t.Run(fmt.Sprintf("remove:%t", tc.remove), func(t *testing.T) {
-			for _, alg := range hashAlgs {
-				vfsObj, root, ctx, err := newVerityRoot(t, alg)
-				if err != nil {
-					t.Fatalf("newVerityRoot: %v", err)
-				}
-
-				filename := "verity-test-file"
-				fd, _, err := newFileFD(ctx, vfsObj, root, filename, 0644)
-				if err != nil {
-					t.Fatalf("newFileFD: %v", err)
-				}
+		t.Run(fmt.Sprintf("changeFile:%t, changeMerkleFile:%t", tc.changeFile, tc.changeMerkleFile), func(t *testing.T) {
+			vfsObj, root, ctx, err := newVerityRoot(t, SHA256)
+			if err != nil {
+				t.Fatalf("newVerityRoot: %v", err)
+			}
 
-				// Enable verity on the file.
-				var args arch.SyscallArguments
-				args[1] = arch.SyscallArgument{Value: linux.FS_IOC_ENABLE_VERITY}
-				if _, err := fd.Ioctl(ctx, nil /* uio */, args); err != nil {
-					t.Fatalf("Ioctl: %v", err)
-				}
+			filename := "verity-test-file"
+			fd, _, err := newFileFD(ctx, vfsObj, root, filename, 0644)
+			if err != nil {
+				t.Fatalf("newFileFD: %v", err)
+			}
 
-				rootLowerVD := root.Dentry().Impl().(*dentry).lowerVD
-				if tc.remove {
-					if tc.changeFile {
-						if err := vfsObj.UnlinkAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
-							Root:  rootLowerVD,
-							Start: rootLowerVD,
-							Path:  fspath.Parse(filename),
-						}); err != nil {
-							t.Fatalf("UnlinkAt: %v", err)
-						}
-					}
-					if tc.changeMerkleFile {
-						if err := vfsObj.UnlinkAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
-							Root:  rootLowerVD,
-							Start: rootLowerVD,
-							Path:  fspath.Parse(merklePrefix + filename),
-						}); err != nil {
-							t.Fatalf("UnlinkAt: %v", err)
-						}
-					}
-				} else {
-					newFilename := "renamed-test-file"
-					if tc.changeFile {
-						if err := vfsObj.RenameAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
-							Root:  rootLowerVD,
-							Start: rootLowerVD,
-							Path:  fspath.Parse(filename),
-						}, &vfs.PathOperation{
-							Root:  rootLowerVD,
-							Start: rootLowerVD,
-							Path:  fspath.Parse(newFilename),
-						}, &vfs.RenameOptions{}); err != nil {
-							t.Fatalf("RenameAt: %v", err)
-						}
-					}
-					if tc.changeMerkleFile {
-						if err := vfsObj.RenameAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
-							Root:  rootLowerVD,
-							Start: rootLowerVD,
-							Path:  fspath.Parse(merklePrefix + filename),
-						}, &vfs.PathOperation{
-							Root:  rootLowerVD,
-							Start: rootLowerVD,
-							Path:  fspath.Parse(merklePrefix + newFilename),
-						}, &vfs.RenameOptions{}); err != nil {
-							t.Fatalf("UnlinkAt: %v", err)
-						}
-					}
-				}
+			// Enable verity on the file.
+			var args arch.SyscallArguments
+			args[1] = arch.SyscallArgument{Value: linux.FS_IOC_ENABLE_VERITY}
+			if _, err := fd.Ioctl(ctx, nil /* uio */, args); err != nil {
+				t.Fatalf("Ioctl: %v", err)
+			}
 
-				// Ensure reopening the verity enabled file fails.
-				if _, err = vfsObj.OpenAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
-					Root:  root,
-					Start: root,
+			rootLowerVD := root.Dentry().Impl().(*dentry).lowerVD
+			newFilename := "renamed-test-file"
+			if tc.changeFile {
+				if err := vfsObj.RenameAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+					Root:  rootLowerVD,
+					Start: rootLowerVD,
 					Path:  fspath.Parse(filename),
-				}, &vfs.OpenOptions{
-					Flags: linux.O_RDONLY,
-					Mode:  linux.ModeRegular,
-				}); err != syserror.EIO {
-					t.Errorf("got OpenAt error: %v, expected EIO", err)
+				}, &vfs.PathOperation{
+					Root:  rootLowerVD,
+					Start: rootLowerVD,
+					Path:  fspath.Parse(newFilename),
+				}, &vfs.RenameOptions{}); err != nil {
+					t.Fatalf("RenameAt: %v", err)
 				}
 			}
+			if tc.changeMerkleFile {
+				if err := vfsObj.RenameAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+					Root:  rootLowerVD,
+					Start: rootLowerVD,
+					Path:  fspath.Parse(merklePrefix + filename),
+				}, &vfs.PathOperation{
+					Root:  rootLowerVD,
+					Start: rootLowerVD,
+					Path:  fspath.Parse(merklePrefix + newFilename),
+				}, &vfs.RenameOptions{}); err != nil {
+					t.Fatalf("UnlinkAt: %v", err)
+				}
+			}
+
+			// Ensure reopening the verity enabled file fails.
+			if _, err = vfsObj.OpenAt(ctx, auth.CredentialsFromContext(ctx), &vfs.PathOperation{
+				Root:  root,
+				Start: root,
+				Path:  fspath.Parse(filename),
+			}, &vfs.OpenOptions{
+				Flags: linux.O_RDONLY,
+				Mode:  linux.ModeRegular,
+			}); err != syserror.EIO {
+				t.Errorf("got OpenAt error: %v, expected EIO", err)
+			}
 		})
 	}
 }