avoid part path collisions with mem addr entropy (#13648)

* avoid part path collisions with mem addr entropy

* Regression test

---------

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>
Co-authored-by: Preston Van Loon <pvanloon@offchainlabs.com>
(cherry picked from commit 4c66e4d060)

beacon-chain/db/filesystem/blob.go

@@ -21,7 +21,9 @@ import (
 )
 
 var (
-	errIndexOutOfBounds = errors.New("blob index in file name >= MaxBlobsPerBlock")
+	errIndexOutOfBounds    = errors.New("blob index in file name >= MaxBlobsPerBlock")
+	errEmptyBlobWritten    = errors.New("zero bytes written to disk when saving blob sidecar")
+	errSidecarEmptySSZData = errors.New("sidecar marshalled to an empty ssz byte slice")
 )
 
 const (
@@ -111,11 +113,14 @@ func (bs *BlobStorage) Save(sidecar blocks.VerifiedROBlob) error {
 	sidecarData, err := sidecar.MarshalSSZ()
 	if err != nil {
 		return errors.Wrap(err, "failed to serialize sidecar data")
+	} else if len(sidecarData) == 0 {
+		return errSidecarEmptySSZData
 	}
+
 	if err := bs.fs.MkdirAll(fname.dir(), directoryPermissions); err != nil {
 		return err
 	}
-	partPath := fname.partPath()
+	partPath := fname.partPath(fmt.Sprintf("%p", sidecarData))
 
 	partialMoved := false
 	// Ensure the partial file is deleted.
@@ -138,7 +143,7 @@ func (bs *BlobStorage) Save(sidecar blocks.VerifiedROBlob) error {
 		return errors.Wrap(err, "failed to create partial file")
 	}
 
-	_, err = partialFile.Write(sidecarData)
+	n, err := partialFile.Write(sidecarData)
 	if err != nil {
 		closeErr := partialFile.Close()
 		if closeErr != nil {
@@ -151,6 +156,14 @@ func (bs *BlobStorage) Save(sidecar blocks.VerifiedROBlob) error {
 		return err
 	}
 
+	if n != len(sidecarData) {
+		return fmt.Errorf("failed to write the full bytes of sidecarData, wrote only %d of %d bytes", n, len(sidecarData))
+	}
+
+	if n == 0 {
+		return errEmptyBlobWritten
+	}
+
 	// Atomically rename the partial file to its final name.
 	err = bs.fs.Rename(partPath, sszPath)
 	if err != nil {
@@ -257,16 +270,12 @@ func (p blobNamer) dir() string {
 	return rootString(p.root)
 }
 
-func (p blobNamer) fname(ext string) string {
-	return path.Join(p.dir(), fmt.Sprintf("%d.%s", p.index, ext))
-}
-
-func (p blobNamer) partPath() string {
-	return p.fname(partExt)
+func (p blobNamer) partPath(entropy string) string {
+	return path.Join(p.dir(), fmt.Sprintf("%s-%d.%s", entropy, p.index, partExt))
 }
 
 func (p blobNamer) path() string {
-	return p.fname(sszExt)
+	return path.Join(p.dir(), fmt.Sprintf("%d.%s", p.index, sszExt))
 }
 
 func rootString(root [32]byte) string {

beacon-chain/db/filesystem/blob_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"os"
 	"path"
+	"sync"
 	"testing"
 	"time"
 
@@ -101,6 +102,30 @@ func TestBlobStorage_SaveBlobData(t *testing.T) {
 		_, err = b.Get(blob.BlockRoot(), blob.Index)
 		require.ErrorIs(t, err, os.ErrNotExist)
 	})
+
+	t.Run("race conditions", func(t *testing.T) {
+		// There was a bug where saving the same blob in multiple go routines would cause a partial blob
+		// to be empty. This test ensures that several routines can safely save the same blob at the
+		// same time. This isn't ideal behavior from the caller, but should be handled safely anyway.
+		// See https://github.com/prysmaticlabs/prysm/pull/13648
+		b, err := NewBlobStorage(t.TempDir())
+		require.NoError(t, err)
+		blob := testSidecars[0]
+
+		var wg sync.WaitGroup
+		for i := 0; i < 100; i++ {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				require.NoError(t, b.Save(blob))
+			}()
+		}
+
+		wg.Wait()
+		res, err := b.Get(blob.BlockRoot(), blob.Index)
+		require.NoError(t, err)
+		require.DeepSSZEqual(t, blob, res)
+	})
 }
 
 // pollUntil polls a condition function until it returns true or a timeout is reached.