Fix length check between kzg commitments and exist (#14581)

CHANGELOG.md

@@ -46,6 +46,7 @@ The format is based on Keep a Changelog, and this project adheres to Semantic Ve
 - wait for the async StreamEvent writer to exit before leaving the http handler, avoiding race condition panics [pr](https://github.com/prysmaticlabs/prysm/pull/14557)
 - Certain deb files were returning a 404 which made building new docker images without an existing
   cache impossible. This has been fixed with updates to rules_oci and bazel-lib.
+- Fixed an issue where the length check between block body KZG commitments and the existing cache from the database was incompatible.
 
 ### Security
 

beacon-chain/execution/engine_client.go

@@ -560,8 +560,8 @@ func (s *Service) ReconstructBlobSidecars(ctx context.Context, block interfaces.
 	if err != nil {
 		return nil, errors.Wrap(err, "could not get blob KZG commitments")
 	}
-	if len(kzgCommitments) != len(exists) {
-		return nil, fmt.Errorf("mismatched lengths: KZG commitments %d, exists %d", len(kzgCommitments), len(exists))
+	if len(kzgCommitments) > len(exists) {
+		return nil, fmt.Errorf("length of KZG commitments (%d) is greater than length of exists (%d)", len(kzgCommitments), len(exists))
 	}
 
 	// Collect KZG hashes for non-existing blobs

beacon-chain/execution/engine_client_test.go

@@ -2446,6 +2446,18 @@ func TestReconstructBlobSidecars(t *testing.T) {
 		require.NoError(t, err)
 		require.Equal(t, 3, len(verifiedBlobs))
 	})
+
+	t.Run("kzg is longer than exist", func(t *testing.T) {
+		srv := createBlobServer(t, 3)
+		defer srv.Close()
+
+		rpcClient, client := setupRpcClient(t, srv.URL, client)
+		defer rpcClient.Close()
+
+		exists := []bool{true, false, true, false, true}
+		_, err := client.ReconstructBlobSidecars(ctx, sb, r, exists)
+		require.ErrorContains(t, "length of KZG commitments (6) is greater than length of exists (5)", err)
+	})
 }
 
 func createRandomKzgCommitments(t *testing.T, num int) [][]byte {