fix: prevent directory type object uploads containing data

Since objects with trailing "/" are mapped to directories in the
posix filesystem, they must not contain data since there is no
place to store that data.

This checks both PutObject and CreateMultipartUpload for invalid
directory object types containing data.

backend/posix/posix.go

@@ -223,6 +223,12 @@ func (p *Posix) CreateMultipartUpload(_ context.Context, mpu *s3.CreateMultipart
 		return nil, fmt.Errorf("stat bucket: %w", err)
 	}
 
+	if strings.HasSuffix(*mpu.Key, "/") {
+		// directory objects can't be uploaded with mutlipart uploads
+		// because posix directories can't contain data
+		return nil, s3err.GetAPIError(s3err.ErrDirectoryObjectContainsData)
+	}
+
 	// generate random uuid for upload id
 	uploadID := uuid.New().String()
 	// hash object name for multipart container
@@ -960,6 +966,13 @@ func (p *Posix) PutObject(ctx context.Context, po *s3.PutObjectInput) (string, e
 
 	if strings.HasSuffix(*po.Key, "/") {
 		// object is directory
+		if po.ContentLength != 0 {
+			// posix directories can't contain data, send error
+			// if reuests has a data payload associated with a
+			// directory object
+			return "", s3err.GetAPIError(s3err.ErrDirectoryObjectContainsData)
+		}
+
 		err = mkdirAll(name, os.FileMode(0755), *po.Bucket, *po.Key)
 		if err != nil {
 			return "", err

s3err/s3err.go

@@ -115,6 +115,7 @@ const (
 	// Non-AWS errors
 	ErrExistingObjectIsDirectory
 	ErrObjectParentIsFile
+	ErrDirectoryObjectContainsData
 )
 
 var errorCodeResponse = map[ErrorCode]APIError{
@@ -408,6 +409,11 @@ var errorCodeResponse = map[ErrorCode]APIError{
 		Description:    "Object parent already exists as a file.",
 		HTTPStatusCode: http.StatusConflict,
 	},
+	ErrDirectoryObjectContainsData: {
+		Code:           "DirectoryObjectContainsData",
+		Description:    "Directory object contains data payload.",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
 }
 
 // GetAPIError provides API Error for input API error code.