fix: Adds the minimum allowed size(5 Mib) check for mp parts sizes in CompleteMultipartUpload

backend/azure/azure.go

@@ -1201,6 +1201,7 @@ func (az *Azure) CompleteMultipartUpload(ctx context.Context, input *s3.Complete
 		return ptNumber - nextPtNumber
 	})
 
+	last := len(blockList.UncommittedBlocks) - 1
 	for i, block := range blockList.UncommittedBlocks {
 		ptNumber, err := decodeBlockId(*block.Name)
 		if err != nil {
@@ -1213,6 +1214,11 @@ func (az *Azure) CompleteMultipartUpload(ctx context.Context, input *s3.Complete
 		if *input.MultipartUpload.Parts[i].PartNumber != int32(ptNumber) {
 			return nil, s3err.GetAPIError(s3err.ErrInvalidPart)
 		}
+		// all parts except the last need to be greater, thena
+		// the minimum allowed size (5 Mib)
+		if i < last && *block.Size < backend.MinPartSize {
+			return nil, s3err.GetAPIError(s3err.ErrEntityTooSmall)
+		}
 		blockIds = append(blockIds, *block.Name)
 	}
 

backend/common.go

@@ -34,6 +34,9 @@ const (
 	// this is the media type for directories in AWS and Nextcloud
 	DirContentType     = "application/x-directory"
 	DefaultContentType = "binary/octet-stream"
+
+	// this is the minimum allowed size for mp parts
+	MinPartSize = 5 * 1024 * 1024
 )
 
 func IsValidBucketName(name string) bool { return true }

backend/posix/posix.go

@@ -1375,7 +1375,6 @@ func (p *Posix) CompleteMultipartUpload(ctx context.Context, input *s3.CompleteM
 
 	// check all parts ok
 	last := len(parts) - 1
-	partsize := int64(0)
 	var totalsize int64
 	for i, part := range parts {
 		if part.PartNumber == nil || *part.PartNumber < 1 {
@@ -1389,13 +1388,11 @@ func (p *Posix) CompleteMultipartUpload(ctx context.Context, input *s3.CompleteM
 			return nil, s3err.GetAPIError(s3err.ErrInvalidPart)
 		}
 
-		if i == 0 {
-			partsize = fi.Size()
-		}
 		totalsize += fi.Size()
-		// all parts except the last need to be the same size
-		if i < last && partsize != fi.Size() {
-			return nil, s3err.GetAPIError(s3err.ErrInvalidPart)
+		// all parts except the last need to be greater, thena
+		// the minimum allowed size (5 Mib)
+		if i < last && fi.Size() < backend.MinPartSize {
+			return nil, s3err.GetAPIError(s3err.ErrEntityTooSmall)
 		}
 
 		b, err := p.meta.RetrieveAttribute(nil, bucket, partObjPath, etagkey)