XL/fs: GetObject should validate all its inputs. (#2142)

Fixes #2141
Fixes #2139

xl-v1-object.go

@@ -52,6 +52,10 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 	if startOffset < 0 || length < 0 {
 		return toObjectErr(errUnexpected, bucket, object)
 	}
+	// Writer cannot be nil.
+	if writer == nil {
+		return toObjectErr(errUnexpected, bucket, object)
+	}
 	// Lock the object before reading.
 	nsMutex.RLock(bucket, object)
 	defer nsMutex.RUnlock(bucket, object)
@@ -78,6 +82,16 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 		}
 	}
 
+	// Reply back invalid range if the input offset and length fall out of range.
+	if startOffset > xlMeta.Stat.Size || length > xlMeta.Stat.Size {
+		return InvalidRange{startOffset, length, xlMeta.Stat.Size}
+	}
+
+	// Reply if we have inputs with offset and length.
+	if startOffset+length > xlMeta.Stat.Size {
+		return InvalidRange{startOffset, length, xlMeta.Stat.Size}
+	}
+
 	// Get start part index and offset.
 	partIndex, partOffset, err := xlMeta.ObjectToPartOffset(startOffset)
 	if err != nil {