Include stat in Verity hash

PiperOrigin-RevId: 336395445

3 files changed, 280 insertions, 42 deletions

diff --git a/pkg/sentry/fsimpl/verity/filesystem.go b/pkg/sentry/fsimpl/verity/filesystem.go
index a560b0797..7779271a9 100644
--- a/pkg/sentry/fsimpl/verity/filesystem.go
+++ b/pkg/sentry/fsimpl/verity/filesystem.go
@@ -20,6 +20,7 @@ import (
 	"io"
 	"strconv"
 	"strings"
+	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
@@ -251,11 +252,35 @@ func (fs *filesystem) verifyChild(ctx context.Context, parent *dentry, child *de
 		Ctx: ctx,
 	}
 
+	parentStat, err := vfsObj.StatAt(ctx, fs.creds, &vfs.PathOperation{
+		Root:  parent.lowerVD,
+		Start: parent.lowerVD,
+	}, &vfs.StatOptions{})
+	if err == syserror.ENOENT {
+		return nil, alertIntegrityViolation(err, fmt.Sprintf("Failed to get parent stat for %s: %v", childPath, err))
+	}
+	if err != nil {
+		return nil, err
+	}
+
 	// Since we are verifying against a directory Merkle tree, buf should
 	// contain the root hash of the children in the parent Merkle tree when
 	// Verify returns with success.
 	var buf bytes.Buffer
-	if _, err := merkletree.Verify(&buf, &fdReader, &fdReader, int64(parentSize), int64(offset), int64(merkletree.DigestSize()), parent.rootHash, true /* dataAndTreeInSameFile */); err != nil && err != io.EOF {
+	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,
+		ReadOffset:            int64(offset),
+		ReadSize:              int64(merkletree.DigestSize()),
+		ExpectedRoot:          parent.rootHash,
+		DataAndTreeInSameFile: true,
+	}); err != nil && err != io.EOF {
 		return nil, alertIntegrityViolation(syserror.EIO, fmt.Sprintf("Verification for %s failed: %v", childPath, err))
 	}
 
@@ -266,6 +291,84 @@ func (fs *filesystem) verifyChild(ctx context.Context, parent *dentry, child *de
 	return child, nil
 }
 
+// verifyStat verifies the stat against the verified root 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 {
+	vfsObj := fs.vfsfs.VirtualFilesystem()
+
+	// Get the path to the child dentry. This is only used to provide path
+	// information in failure case.
+	childPath, err := vfsObj.PathnameWithDeleted(ctx, d.fs.rootDentry.lowerVD, d.lowerVD)
+	if err != nil {
+		return err
+	}
+
+	verityMu.RLock()
+	defer verityMu.RUnlock()
+
+	fd, err := vfsObj.OpenAt(ctx, fs.creds, &vfs.PathOperation{
+		Root:  d.lowerMerkleVD,
+		Start: d.lowerMerkleVD,
+	}, &vfs.OpenOptions{
+		Flags: linux.O_RDONLY,
+	})
+	if err == syserror.ENOENT {
+		return alertIntegrityViolation(err, fmt.Sprintf("Failed to open merkle file for %s: %v", childPath, err))
+	}
+	if err != nil {
+		return err
+	}
+
+	merkleSize, err := fd.GetXattr(ctx, &vfs.GetXattrOptions{
+		Name: merkleSizeXattr,
+		Size: sizeOfStringInt32,
+	})
+
+	if err == syserror.ENODATA {
+		return alertIntegrityViolation(err, fmt.Sprintf("Failed to get xattr %s for merkle file of %s: %v", merkleSizeXattr, childPath, err))
+	}
+	if err != nil {
+		return err
+	}
+
+	size, err := strconv.Atoi(merkleSize)
+	if err != nil {
+		return alertIntegrityViolation(syserror.EINVAL, fmt.Sprintf("Failed to convert xattr %s for %s to int: %v", merkleSizeXattr, childPath, err))
+	}
+
+	fdReader := vfs.FileReadWriteSeeker{
+		FD:  fd,
+		Ctx: ctx,
+	}
+
+	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,
+		ReadOffset: 0,
+		// Set read size to 0 so only the metadata is verified.
+		ReadSize:              0,
+		ExpectedRoot:          d.rootHash,
+		DataAndTreeInSameFile: false,
+	}
+	if atomic.LoadUint32(&d.mode)&linux.S_IFMT == linux.S_IFDIR {
+		params.DataAndTreeInSameFile = true
+	}
+
+	if _, err := merkletree.Verify(params); err != nil && err != io.EOF {
+		return alertIntegrityViolation(err, fmt.Sprintf("Verification stat for %s failed: %v", childPath, err))
+	}
+	d.mode = uint32(stat.Mode)
+	d.uid = stat.UID
+	d.gid = stat.GID
+	return nil
+}
+
 // Preconditions: fs.renameMu must be locked. d.dirMu must be locked.
 func (fs *filesystem) getChildLocked(ctx context.Context, parent *dentry, name string, ds **[]*dentry) (*dentry, error) {
 	if child, ok := parent.children[name]; ok {
@@ -274,9 +377,27 @@ func (fs *filesystem) getChildLocked(ctx context.Context, parent *dentry, name s
 		// runtime enable is allowed and the parent directory is
 		// enabled, we should verify the child root hash here because
 		// it may be cached before enabled.
-		if fs.allowRuntimeEnable && len(parent.rootHash) != 0 {
-			if _, err := fs.verifyChild(ctx, parent, child); err != nil {
-				return nil, err
+		if fs.allowRuntimeEnable {
+			if isEnabled(parent) {
+				if _, err := fs.verifyChild(ctx, parent, child); err != nil {
+					return nil, err
+				}
+			}
+			if isEnabled(child) {
+				vfsObj := fs.vfsfs.VirtualFilesystem()
+				mask := uint32(linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID)
+				stat, err := vfsObj.StatAt(ctx, fs.creds, &vfs.PathOperation{
+					Root:  child.lowerVD,
+					Start: child.lowerVD,
+				}, &vfs.StatOptions{
+					Mask: mask,
+				})
+				if err != nil {
+					return nil, err
+				}
+				if err := fs.verifyStat(ctx, child, stat); err != nil {
+					return nil, err
+				}
 			}
 		}
 		return child, nil
@@ -426,7 +547,6 @@ func (fs *filesystem) lookupAndVerifyLocked(ctx context.Context, parent *dentry,
 	child.parent = parent
 	child.name = name
 
-	// TODO(b/162788573): Verify child metadata.
 	child.mode = uint32(stat.Mode)
 	child.uid = stat.UID
 	child.gid = stat.GID
@@ -434,12 +554,18 @@ func (fs *filesystem) lookupAndVerifyLocked(ctx context.Context, parent *dentry,
 	// Verify child root hash. This should always be performed unless in
 	// allowRuntimeEnable mode and the parent directory hasn't been enabled
 	// yet.
-	if !(fs.allowRuntimeEnable && len(parent.rootHash) == 0) {
+	if isEnabled(parent) {
 		if _, err := fs.verifyChild(ctx, parent, child); err != nil {
 			child.destroyLocked(ctx)
 			return nil, err
 		}
 	}
+	if isEnabled(child) {
+		if err := fs.verifyStat(ctx, child, stat); err != nil {
+			child.destroyLocked(ctx)
+			return nil, err
+		}
+	}
 
 	return child, nil
 }
@@ -771,6 +897,8 @@ func (fs *filesystem) SetStatAt(ctx context.Context, rp *vfs.ResolvingPath, opts
 }
 
 // StatAt implements vfs.FilesystemImpl.StatAt.
+// TODO(b/170157489): Investigate whether stats other than Mode/UID/GID should
+// be verified.
 func (fs *filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.StatOptions) (linux.Statx, error) {
 	var ds *[]*dentry
 	fs.renameMu.RLock()
@@ -788,6 +916,11 @@ func (fs *filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 	if err != nil {
 		return linux.Statx{}, err
 	}
+	if isEnabled(d) {
+		if err := fs.verifyStat(ctx, d, stat); err != nil {
+			return linux.Statx{}, err
+		}
+	}
 	return stat, nil
 }
 
diff --git a/pkg/sentry/fsimpl/verity/verity.go b/pkg/sentry/fsimpl/verity/verity.go
index fc5eabbca..3eb972237 100644
--- a/pkg/sentry/fsimpl/verity/verity.go
+++ b/pkg/sentry/fsimpl/verity/verity.go
@@ -142,6 +142,14 @@ func (FilesystemType) Name() string {
 	return Name
 }
 
+// isEnabled checks whether the target is enabled with verity features. It
+// should always be true if runtime enable is not allowed. In runtime enable
+// mode, it returns true if the target has been enabled with
+// ioctl(FS_IOC_ENABLE_VERITY).
+func isEnabled(d *dentry) bool {
+	return !d.fs.allowRuntimeEnable || len(d.rootHash) != 0
+}
+
 // alertIntegrityViolation alerts a violation of integrity, which usually means
 // unexpected modification to the file system is detected. In
 // noCrashOnVerificationFailure mode, it returns an error, otherwise it panic.
@@ -245,12 +253,17 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		return nil, nil, err
 	}
 
-	// TODO(b/162788573): Verify Metadata.
 	d.mode = uint32(stat.Mode)
 	d.uid = stat.UID
 	d.gid = stat.GID
-
 	d.rootHash = make([]byte, len(iopts.RootHash))
+
+	if !fs.allowRuntimeEnable {
+		if err := fs.verifyStat(ctx, d, stat); err != nil {
+			return nil, nil, err
+		}
+	}
+
 	copy(d.rootHash, iopts.RootHash)
 	d.vfsd.Init(d)
 
@@ -488,6 +501,11 @@ func (fd *fileDescription) Stat(ctx context.Context, opts vfs.StatOptions) (linu
 	if err != nil {
 		return linux.Statx{}, err
 	}
+	if isEnabled(fd.d) {
+		if err := fd.d.fs.verifyStat(ctx, fd.d, stat); err != nil {
+			return linux.Statx{}, err
+		}
+	}
 	return stat, nil
 }
 
@@ -516,8 +534,10 @@ func (fd *fileDescription) generateMerkle(ctx context.Context) ([]byte, uint64,
 		FD:  fd.merkleWriter,
 		Ctx: ctx,
 	}
-	var rootHash []byte
-	var dataSize uint64
+	params := &merkletree.GenerateParams{
+		TreeReader: &merkleReader,
+		TreeWriter: &merkleWriter,
+	}
 
 	switch atomic.LoadUint32(&fd.d.mode) & linux.S_IFMT {
 	case linux.S_IFREG:
@@ -528,12 +548,14 @@ func (fd *fileDescription) generateMerkle(ctx context.Context) ([]byte, uint64,
 		if err != nil {
 			return nil, 0, err
 		}
-		dataSize = stat.Size
 
-		rootHash, err = merkletree.Generate(&fdReader, int64(dataSize), &merkleReader, &merkleWriter, false /* dataAndTreeInSameFile */)
-		if err != nil {
-			return nil, 0, err
-		}
+		params.File = &fdReader
+		params.Size = int64(stat.Size)
+		params.Name = fd.d.name
+		params.Mode = uint32(stat.Mode)
+		params.UID = stat.UID
+		params.GID = stat.GID
+		params.DataAndTreeInSameFile = false
 	case linux.S_IFDIR:
 		// For a directory, generate a Merkle tree based on the root
 		// hashes of its children that has already been written to the
@@ -542,18 +564,27 @@ func (fd *fileDescription) generateMerkle(ctx context.Context) ([]byte, uint64,
 		if err != nil {
 			return nil, 0, err
 		}
-		dataSize = merkleStat.Size
 
-		rootHash, err = merkletree.Generate(&merkleReader, int64(dataSize), &merkleReader, &merkleWriter, true /* dataAndTreeInSameFile */)
+		params.Size = int64(merkleStat.Size)
+
+		stat, err := fd.lowerFD.Stat(ctx, vfs.StatOptions{})
 		if err != nil {
 			return nil, 0, err
 		}
+
+		params.File = &merkleReader
+		params.Name = fd.d.name
+		params.Mode = uint32(stat.Mode)
+		params.UID = stat.UID
+		params.GID = stat.GID
+		params.DataAndTreeInSameFile = true
 	default:
 		// TODO(b/167728857): Investigate whether and how we should
 		// enable other types of file.
 		return nil, 0, syserror.EINVAL
 	}
-	return rootHash, dataSize, nil
+	rootHash, err := merkletree.Generate(params)
+	return rootHash, uint64(params.Size), err
 }
 
 // enableVerity enables verity features on fd by generating a Merkle tree file
@@ -688,7 +719,7 @@ func (fd *fileDescription) Ioctl(ctx context.Context, uio usermem.IO, args arch.
 func (fd *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
 	// No need to verify if the file is not enabled yet in
 	// allowRuntimeEnable mode.
-	if fd.d.fs.allowRuntimeEnable && len(fd.d.rootHash) == 0 {
+	if !isEnabled(fd.d) {
 		return fd.lowerFD.PRead(ctx, dst, offset, opts)
 	}
 
@@ -725,9 +756,22 @@ func (fd *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, of
 		Ctx: ctx,
 	}
 
-	n, err := merkletree.Verify(dst.Writer(ctx), &dataReader, &merkleReader, int64(size), offset, dst.NumBytes(), fd.d.rootHash, false /* dataAndTreeInSameFile */)
+	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,
+		ReadOffset:            offset,
+		ReadSize:              dst.NumBytes(),
+		ExpectedRoot:          fd.d.rootHash,
+		DataAndTreeInSameFile: false,
+	})
 	if err != nil {
-		return 0, alertIntegrityViolation(syserror.EINVAL, fmt.Sprintf("Verification failed: %v", err))
+		return 0, alertIntegrityViolation(syserror.EIO, fmt.Sprintf("Verification failed: %v", err))
 	}
 	return n, err
 }
diff --git a/pkg/sentry/fsimpl/verity/verity_test.go b/pkg/sentry/fsimpl/verity/verity_test.go
index 8bcc14131..8d0926bc4 100644
--- a/pkg/sentry/fsimpl/verity/verity_test.go
+++ b/pkg/sentry/fsimpl/verity/verity_test.go
@@ -41,11 +41,11 @@ const maxDataSize = 100000
 // newVerityRoot creates a new verity mount, and returns the root. The
 // underlying file system is tmpfs. If the error is not nil, then cleanup
 // should be called when the root is no longer needed.
-func newVerityRoot(ctx context.Context) (*vfs.VirtualFilesystem, vfs.VirtualDentry, func(), error) {
+func newVerityRoot(ctx context.Context, t *testing.T) (*vfs.VirtualFilesystem, vfs.VirtualDentry, error) {
 	rand.Seed(time.Now().UnixNano())
 	vfsObj := &vfs.VirtualFilesystem{}
 	if err := vfsObj.Init(ctx); err != nil {
-		return nil, vfs.VirtualDentry{}, nil, fmt.Errorf("VFS init: %v", err)
+		return nil, vfs.VirtualDentry{}, fmt.Errorf("VFS init: %v", err)
 	}
 
 	vfsObj.MustRegisterFilesystemType("verity", FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
@@ -67,13 +67,15 @@ func newVerityRoot(ctx context.Context) (*vfs.VirtualFilesystem, vfs.VirtualDent
 		},
 	})
 	if err != nil {
-		return nil, vfs.VirtualDentry{}, nil, fmt.Errorf("NewMountNamespace: %v", err)
+		return nil, vfs.VirtualDentry{}, fmt.Errorf("NewMountNamespace: %v", err)
 	}
 	root := mntns.Root()
-	return vfsObj, root, func() {
+	t.Helper()
+	t.Cleanup(func() {
 		root.DecRef(ctx)
 		mntns.DecRef(ctx)
-	}, nil
+	})
+	return vfsObj, root, nil
 }
 
 // newFileFD creates a new file in the verity mount, and returns the FD. The FD
@@ -143,11 +145,10 @@ func corruptRandomBit(ctx context.Context, fd *vfs.FileDescription, size int) er
 // file and the root Merkle tree file exist.
 func TestOpen(t *testing.T) {
 	ctx := contexttest.Context(t)
-	vfsObj, root, cleanup, err := newVerityRoot(ctx)
+	vfsObj, root, err := newVerityRoot(ctx, t)
 	if err != nil {
 		t.Fatalf("newVerityRoot: %v", err)
 	}
-	defer cleanup()
 
 	filename := "verity-test-file"
 	if _, _, err := newFileFD(ctx, vfsObj, root, filename, 0644); err != nil {
@@ -178,15 +179,14 @@ func TestOpen(t *testing.T) {
 	}
 }
 
-// TestUntouchedFileSucceeds ensures that read from an untouched verity file
+// TestUnmodifiedFileSucceeds ensures that read from an untouched verity file
 // succeeds after enabling verity for it.
-func TestReadUntouchedFileSucceeds(t *testing.T) {
+func TestReadUnmodifiedFileSucceeds(t *testing.T) {
 	ctx := contexttest.Context(t)
-	vfsObj, root, cleanup, err := newVerityRoot(ctx)
+	vfsObj, root, err := newVerityRoot(ctx, t)
 	if err != nil {
 		t.Fatalf("newVerityRoot: %v", err)
 	}
-	defer cleanup()
 
 	filename := "verity-test-file"
 	fd, size, err := newFileFD(ctx, vfsObj, root, filename, 0644)
@@ -212,15 +212,14 @@ func TestReadUntouchedFileSucceeds(t *testing.T) {
 	}
 }
 
-// TestReopenUntouchedFileSucceeds ensures that reopen an untouched verity file
+// TestReopenUnmodifiedFileSucceeds ensures that reopen an untouched verity file
 // succeeds after enabling verity for it.
-func TestReopenUntouchedFileSucceeds(t *testing.T) {
+func TestReopenUnmodifiedFileSucceeds(t *testing.T) {
 	ctx := contexttest.Context(t)
-	vfsObj, root, cleanup, err := newVerityRoot(ctx)
+	vfsObj, root, err := newVerityRoot(ctx, t)
 	if err != nil {
 		t.Fatalf("newVerityRoot: %v", err)
 	}
-	defer cleanup()
 
 	filename := "verity-test-file"
 	fd, _, err := newFileFD(ctx, vfsObj, root, filename, 0644)
@@ -251,11 +250,10 @@ func TestReopenUntouchedFileSucceeds(t *testing.T) {
 // TestModifiedFileFails ensures that read from a modified verity file fails.
 func TestModifiedFileFails(t *testing.T) {
 	ctx := contexttest.Context(t)
-	vfsObj, root, cleanup, err := newVerityRoot(ctx)
+	vfsObj, root, err := newVerityRoot(ctx, t)
 	if err != nil {
 		t.Fatalf("newVerityRoot: %v", err)
 	}
-	defer cleanup()
 
 	filename := "verity-test-file"
 	fd, size, err := newFileFD(ctx, vfsObj, root, filename, 0644)
@@ -298,11 +296,10 @@ func TestModifiedFileFails(t *testing.T) {
 // corresponding Merkle tree file is modified.
 func TestModifiedMerkleFails(t *testing.T) {
 	ctx := contexttest.Context(t)
-	vfsObj, root, cleanup, err := newVerityRoot(ctx)
+	vfsObj, root, err := newVerityRoot(ctx, t)
 	if err != nil {
 		t.Fatalf("newVerityRoot: %v", err)
 	}
-	defer cleanup()
 
 	filename := "verity-test-file"
 	fd, size, err := newFileFD(ctx, vfsObj, root, filename, 0644)
@@ -353,11 +350,10 @@ func TestModifiedMerkleFails(t *testing.T) {
 // the parent Merkle tree file is modified.
 func TestModifiedParentMerkleFails(t *testing.T) {
 	ctx := contexttest.Context(t)
-	vfsObj, root, cleanup, err := newVerityRoot(ctx)
+	vfsObj, root, err := newVerityRoot(ctx, t)
 	if err != nil {
 		t.Fatalf("newVerityRoot: %v", err)
 	}
-	defer cleanup()
 
 	filename := "verity-test-file"
 	fd, _, err := newFileFD(ctx, vfsObj, root, filename, 0644)
@@ -427,3 +423,68 @@ func TestModifiedParentMerkleFails(t *testing.T) {
 		t.Errorf("OpenAt file with modified parent Merkle succeeded")
 	}
 }
+
+// TestUnmodifiedStatSucceeds ensures that stat of an untouched verity file
+// succeeds after enabling verity for it.
+func TestUnmodifiedStatSucceeds(t *testing.T) {
+	ctx := contexttest.Context(t)
+	vfsObj, root, err := newVerityRoot(ctx, t)
+	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 stat 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("fd.Ioctl: %v", err)
+	}
+
+	if _, err := fd.Stat(ctx, vfs.StatOptions{}); err != nil {
+		t.Errorf("fd.Stat: %v", err)
+	}
+}
+
+// TestModifiedStatFails checks that getting stat for a file with modified stat
+// should fail.
+func TestModifiedStatFails(t *testing.T) {
+	ctx := contexttest.Context(t)
+	vfsObj, root, err := newVerityRoot(ctx, t)
+	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("fd.Ioctl: %v", err)
+	}
+
+	lowerFD := fd.Impl().(*fileDescription).lowerFD
+	// Change the stat of the underlying file, and check that stat fails.
+	if err := lowerFD.SetStat(ctx, vfs.SetStatOptions{
+		Stat: linux.Statx{
+			Mask: uint32(linux.STATX_MODE),
+			Mode: 0777,
+		},
+	}); err != nil {
+		t.Fatalf("lowerFD.SetStat: %v", err)
+	}
+
+	if _, err := fd.Stat(ctx, vfs.StatOptions{}); err == nil {
+		t.Errorf("fd.Stat succeeded when it should fail")
+	}
+}