Handle PCX images with an odd stride

Tests/test_file_pcx.py

@@ -44,6 +44,14 @@ def test_odd(tmp_path):
         _roundtrip(tmp_path, hopper(mode).resize((511, 511)))
 
 
+def test_odd_read():
+    # Reading an image with an odd stride, making it malformed
+    with Image.open("Tests/images/odd_stride.pcx") as im:
+        im.load()
+
+        assert im.size == (371, 150)
+
+
 def test_pil184():
     # Check reading of files where xmin/xmax is not zero.
 

src/PIL/PcxImagePlugin.py

@@ -66,13 +66,13 @@ class PcxImageFile(ImageFile.ImageFile):
         version = s[1]
         bits = s[3]
         planes = s[65]
-        ignored_stride = i16(s, 66)
+        provided_stride = i16(s, 66)
         logger.debug(
             "PCX version %s, bits %s, planes %s, stride %s",
             version,
             bits,
             planes,
-            ignored_stride,
+            provided_stride,
         )
 
         self.info["dpi"] = i16(s, 12), i16(s, 14)
@@ -110,10 +110,15 @@ class PcxImageFile(ImageFile.ImageFile):
         self.mode = mode
         self._size = bbox[2] - bbox[0], bbox[3] - bbox[1]
 
-        # don't trust the passed in stride. Calculate for ourselves.
+        # Don't trust the passed in stride.
+        # Calculate the approximate position for ourselves.
         # CVE-2020-35653
         stride = (self._size[0] * bits + 7) // 8
-        stride += stride % 2
+
+        # While the specification states that this must be even,
+        # not all images follow this
+        if provided_stride != stride:
+            stride += stride % 2
 
         bbox = (0, 0) + self.size
         logger.debug("size: %sx%s", *self.size)