Change Merkle tree library to use ReaderAt

Merkle tree library was originally using Read/Seek to access data and
tree, since the parameters are io.ReadSeeker. This could cause race
conditions if multiple threads accesses the same fd to read. Here we
change to use ReaderAt, and implement it with PRead to make it thread
safe.

PiperOrigin-RevId: 336779260

1 files changed, 19 insertions, 5 deletions

diff --git a/pkg/sentry/vfs/file_description.go b/pkg/sentry/vfs/file_description.go
index 1eba0270f..183957ad8 100644
--- a/pkg/sentry/vfs/file_description.go
+++ b/pkg/sentry/vfs/file_description.go
@@ -827,7 +827,7 @@ func (fd *FileDescription) SetAsyncHandler(newHandler func() FileAsync) FileAsyn
 }
 
 // FileReadWriteSeeker is a helper struct to pass a FileDescription as
-// io.Reader/io.Writer/io.ReadSeeker/etc.
+// io.Reader/io.Writer/io.ReadSeeker/io.ReaderAt/io.WriterAt/etc.
 type FileReadWriteSeeker struct {
 	FD    *FileDescription
 	Ctx   context.Context
@@ -835,11 +835,18 @@ type FileReadWriteSeeker struct {
 	WOpts WriteOptions
 }
 
+// ReadAt implements io.ReaderAt.ReadAt.
+func (f *FileReadWriteSeeker) ReadAt(p []byte, off int64) (int, error) {
+	dst := usermem.BytesIOSequence(p)
+	n, err := f.FD.PRead(f.Ctx, dst, off, f.ROpts)
+	return int(n), err
+}
+
 // Read implements io.ReadWriteSeeker.Read.
 func (f *FileReadWriteSeeker) Read(p []byte) (int, error) {
 	dst := usermem.BytesIOSequence(p)
-	ret, err := f.FD.Read(f.Ctx, dst, f.ROpts)
-	return int(ret), err
+	n, err := f.FD.Read(f.Ctx, dst, f.ROpts)
+	return int(n), err
 }
 
 // Seek implements io.ReadWriteSeeker.Seek.
@@ -847,9 +854,16 @@ func (f *FileReadWriteSeeker) Seek(offset int64, whence int) (int64, error) {
 	return f.FD.Seek(f.Ctx, offset, int32(whence))
 }
 
+// WriteAt implements io.WriterAt.WriteAt.
+func (f *FileReadWriteSeeker) WriteAt(p []byte, off int64) (int, error) {
+	dst := usermem.BytesIOSequence(p)
+	n, err := f.FD.PWrite(f.Ctx, dst, off, f.WOpts)
+	return int(n), err
+}
+
 // Write implements io.ReadWriteSeeker.Write.
 func (f *FileReadWriteSeeker) Write(p []byte) (int, error) {
 	buf := usermem.BytesIOSequence(p)
-	ret, err := f.FD.Write(f.Ctx, buf, f.WOpts)
-	return int(ret), err
+	n, err := f.FD.Write(f.Ctx, buf, f.WOpts)
+	return int(n), err
 }