Skip truncated ICO mask if LOAD_TRUNCATED_IMAGES is enabled

Tests/test_file_ico.py

@@ -6,7 +6,7 @@
 
 import pytest
 
-from PIL import IcoImagePlugin, Image, ImageDraw
+from PIL import IcoImagePlugin, Image, ImageDraw, ImageFile
 
 from .helper import assert_image_equal, assert_image_equal_tofile, hopper
 
@@ -241,3 +241,29 @@ def test_draw_reloaded(tmp_path: Path) -> None:
 
     with Image.open(outfile) as im:
         assert_image_equal_tofile(im, "Tests/images/hopper_draw.ico")
+
+
+def test_truncated_mask() -> None:
+    # 1 bpp
+    with open("Tests/images/hopper_mask.ico", "rb") as fp:
+        data = fp.read()
+
+    ImageFile.LOAD_TRUNCATED_IMAGES = True
+    data = data[:-3]
+
+    try:
+        with Image.open(io.BytesIO(data)) as im:
+            with Image.open("Tests/images/hopper_mask.png") as expected:
+                assert im.mode == "1"
+
+        # 32 bpp
+        output = io.BytesIO()
+        expected = hopper("RGBA")
+        expected.save(output, "ico", bitmap_format="bmp")
+
+        data = output.getvalue()[:-1]
+
+        with Image.open(io.BytesIO(data)) as im:
+            assert im.mode == "RGB"
+    finally:
+        ImageFile.LOAD_TRUNCATED_IMAGES = False

src/PIL/IcoImagePlugin.py

@@ -235,13 +235,19 @@ def frame(self, idx: int) -> Image.Image:
                 alpha_bytes = self.buf.read(im.size[0] * im.size[1] * 4)[3::4]
 
                 # convert to an 8bpp grayscale image
-                mask = Image.frombuffer(
-                    "L",  # 8bpp
-                    im.size,  # (w, h)
-                    alpha_bytes,  # source chars
-                    "raw",  # raw decoder
-                    ("L", 0, -1),  # 8bpp inverted, unpadded, reversed
-                )
+                try:
+                    mask = Image.frombuffer(
+                        "L",  # 8bpp
+                        im.size,  # (w, h)
+                        alpha_bytes,  # source chars
+                        "raw",  # raw decoder
+                        ("L", 0, -1),  # 8bpp inverted, unpadded, reversed
+                    )
+                except ValueError:
+                    if ImageFile.LOAD_TRUNCATED_IMAGES:
+                        mask = None
+                    else:
+                        raise
             else:
                 # get AND image from end of bitmap
                 w = im.size[0]
@@ -259,19 +265,26 @@ def frame(self, idx: int) -> Image.Image:
                 mask_data = self.buf.read(total_bytes)
 
                 # convert raw data to image
-                mask = Image.frombuffer(
-                    "1",  # 1 bpp
-                    im.size,  # (w, h)
-                    mask_data,  # source chars
-                    "raw",  # raw decoder
-                    ("1;I", int(w / 8), -1),  # 1bpp inverted, padded, reversed
-                )
+                try:
+                    mask = Image.frombuffer(
+                        "1",  # 1 bpp
+                        im.size,  # (w, h)
+                        mask_data,  # source chars
+                        "raw",  # raw decoder
+                        ("1;I", int(w / 8), -1),  # 1bpp inverted, padded, reversed
+                    )
+                except ValueError:
+                    if ImageFile.LOAD_TRUNCATED_IMAGES:
+                        mask = None
+                    else:
+                        raise
 
                 # now we have two images, im is XOR image and mask is AND image
 
             # apply mask image as alpha channel
-            im = im.convert("RGBA")
-            im.putalpha(mask)
+            if mask:
+                im = im.convert("RGBA")
+                im.putalpha(mask)
 
         return im