Raise SyntaxError if data is not as expected

Author: radarhere

Tests/test_file_xbm.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from PIL import Image
+from PIL import Image, XbmImagePlugin
 
 from .helper import hopper
 
@@ -63,6 +63,13 @@ def test_open_filename_with_underscore():
         assert im.size == (128, 128)
 
 
+def test_invalid_file():
+    invalid_file = "Tests/images/flower.jpg"
+
+    with pytest.raises(SyntaxError):
+        XbmImagePlugin.XbmImageFile(invalid_file)
+
+
 def test_save_wrong_mode(tmp_path):
     im = hopper()
     out = str(tmp_path / "temp.xbm")

src/PIL/XbmImagePlugin.py

@@ -52,18 +52,19 @@ def _open(self):
 
         m = xbm_head.match(self.fp.read(512))
 
-        if m:
+        if not m:
+            raise SyntaxError("not a XBM file")
 
-            xsize = int(m.group("width"))
-            ysize = int(m.group("height"))
+        xsize = int(m.group("width"))
+        ysize = int(m.group("height"))
 
-            if m.group("hotspot"):
-                self.info["hotspot"] = (int(m.group("xhot")), int(m.group("yhot")))
+        if m.group("hotspot"):
+            self.info["hotspot"] = (int(m.group("xhot")), int(m.group("yhot")))
 
-            self.mode = "1"
-            self._size = xsize, ysize
+        self.mode = "1"
+        self._size = xsize, ysize
 
-            self.tile = [("xbm", (0, 0) + self.size, m.end(), None)]
+        self.tile = [("xbm", (0, 0) + self.size, m.end(), None)]
 
 
 def _save(im, fp, filename):