diff options
| -rw-r--r-- | pkg/merkletree/merkletree.go | 10 | ||||
| -rw-r--r-- | pkg/sentry/fsimpl/verity/verity_test.go | 42 |
2 files changed, 49 insertions, 3 deletions
diff --git a/pkg/merkletree/merkletree.go b/pkg/merkletree/merkletree.go index 6acee90ef..aea7dde38 100644 --- a/pkg/merkletree/merkletree.go +++ b/pkg/merkletree/merkletree.go @@ -350,9 +350,13 @@ type VerifyParams struct { // For verifyMetadata, params.data is not needed. It only accesses params.tree // for the raw root hash. func verifyMetadata(params *VerifyParams, layout *Layout) error { - root := make([]byte, layout.digestSize) - if _, err := params.Tree.ReadAt(root, layout.blockOffset(layout.rootLevel(), 0 /* index */)); err != nil { - return fmt.Errorf("failed to read root hash: %w", err) + var root []byte + // Only read the root hash if we expect that the Merkle tree file is non-empty. + if params.Size != 0 { + root = make([]byte, layout.digestSize) + if _, err := params.Tree.ReadAt(root, layout.blockOffset(layout.rootLevel(), 0 /* index */)); err != nil { + return fmt.Errorf("failed to read root hash: %w", err) + } } descriptor := VerityDescriptor{ Name: params.Name, diff --git a/pkg/sentry/fsimpl/verity/verity_test.go b/pkg/sentry/fsimpl/verity/verity_test.go index 6ced0afc9..bd948715f 100644 --- a/pkg/sentry/fsimpl/verity/verity_test.go +++ b/pkg/sentry/fsimpl/verity/verity_test.go @@ -239,6 +239,18 @@ func newFileFD(ctx context.Context, t *testing.T, vfsObj *vfs.VirtualFilesystem, return fd, dataSize, err } +// newEmptyFileFD creates a new empty file in the verity mount, and returns the FD. +func newEmptyFileFD(ctx context.Context, t *testing.T, vfsObj *vfs.VirtualFilesystem, root vfs.VirtualDentry, filePath string, mode linux.FileMode) (*vfs.FileDescription, error) { + // Create the file in the underlying file system. + _, err := dentryFromVD(t, root).openLowerAt(ctx, vfsObj, filePath, linux.O_RDWR|linux.O_CREAT|linux.O_EXCL, linux.ModeRegular|mode) + if err != nil { + return nil, err + } + // Now open the verity file descriptor. + fd, err := openVerityAt(ctx, vfsObj, root, filePath, linux.O_RDONLY, mode) + return fd, err +} + // flipRandomBit randomly flips a bit in the file represented by fd. func flipRandomBit(ctx context.Context, fd *vfs.FileDescription, size int) error { randomPos := int64(rand.Intn(size)) @@ -349,6 +361,36 @@ func TestReadUnmodifiedFileSucceeds(t *testing.T) { } } +// TestReadUnmodifiedEmptyFileSucceeds ensures that read from an untouched empty verity +// file succeeds after enabling verity for it. +func TestReadUnmodifiedEmptyFileSucceeds(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-empty-file" + fd, err := newEmptyFileFD(ctx, t, vfsObj, root, filename, 0644) + if err != nil { + t.Fatalf("newEmptyFileFD: %v", err) + } + + // Enable verity on the file and confirm a normal read succeeds. + enableVerity(ctx, t, fd) + + var buf []byte + n, err := fd.Read(ctx, usermem.BytesIOSequence(buf), vfs.ReadOptions{}) + if err != nil && err != io.EOF { + t.Fatalf("fd.Read: %v", err) + } + + if n != 0 { + t.Errorf("fd.Read got read length %d, expected 0", n) + } + } +} + // TestReopenUnmodifiedFileSucceeds ensures that reopen an untouched verity file // succeeds after enabling verity for it. func TestReopenUnmodifiedFileSucceeds(t *testing.T) { |