Patched code sample

import PIL.Image

def _load_bitmaps_fixed(self, metrics, nbitmaps, bitmap_size):
    """
    A simplified representation of the fixed _load_bitmaps function
    from Pillow's PcfFontFile.py, demonstrating the security fix.

    In the original library:
    - 'self' is an instance of the PcfFontFile class.
    - 'metrics' is a list of glyph metric tuples read from the font file.
    - 'nbitmaps' is the total number of glyphs.
    - 'self.fp' is the file pointer to the font file.
    """
    # In a real scenario, self.glyph would be initialized as an empty list.
    self.glyph = []

    for i in range(nbitmaps):
        # The dimensions (width, height) of the glyph are read from the metrics.
        # A malicious font could specify extremely large dimensions here.
        glyph_size = (metrics[i][2], metrics[i][3])

        # --- THE FIX ---
        # This check was added to validate the glyph dimensions before memory is
        # allocated. It prevents a decompression bomb attack by raising an
        # exception if the required memory exceeds a safe limit.
        # This line was missing in the vulnerable version.
        PIL.Image._decompression_bomb_check(glyph_size)
        # --- END OF FIX ---

        # This call is now safe because glyph_size has been validated.
        # In the vulnerable code, this could lead to excessive memory allocation.
        # bitmap_data = self.fp.read(bitmap_size[i]) # Reading from the file
        # self.glyph.append(
        #     PIL.Image.frombytes("1", glyph_size, bitmap_data)
        # )