Added ImageFont.MAX_STRING_LENGTH

Tests/test_imagefont.py

@@ -1038,6 +1038,25 @@ def test_render_mono_size():
     assert_image_equal_tofile(im, "Tests/images/text_mono.gif")
 
 
+def test_too_many_characters(font):
+    with pytest.raises(ValueError):
+        font.getlength("A" * 1_000_001)
+    with pytest.raises(ValueError):
+        font.getbbox("A" * 1_000_001)
+    with pytest.raises(ValueError):
+        font.getmask2("A" * 1_000_001)
+
+    transposed_font = ImageFont.TransposedFont(font)
+    with pytest.raises(ValueError):
+        transposed_font.getlength("A" * 1_000_001)
+
+    default_font = ImageFont.load_default()
+    with pytest.raises(ValueError):
+        default_font.getlength("A" * 1_000_001)
+    with pytest.raises(ValueError):
+        default_font.getbbox("A" * 1_000_001)
+
+
 @pytest.mark.parametrize(
     "test_file",
     [

docs/reference/ImageFont.rst

@@ -18,6 +18,15 @@ OpenType fonts (as well as other font formats supported by the FreeType
 library). For earlier versions, TrueType support is only available as part of
 the imToolkit package.
 
+.. warning::
+    To protect against potential DOS attacks when using arbitrary strings as
+    text input, Pillow will raise a ``ValueError`` if the number of characters
+    is over a certain limit, :py:data:`MAX_STRING_LENGTH`.
+
+    This threshold can be changed by setting
+    :py:data:`MAX_STRING_LENGTH`. It can be disabled by setting
+    ``ImageFont.MAX_STRING_LENGTH = None``.
+
 Example
 -------
 
@@ -73,3 +82,12 @@ Constants
 
     Requires Raqm, you can check support using
     :py:func:`PIL.features.check_feature` with ``feature="raqm"``.
+
+Constants
+---------
+
+.. data:: MAX_STRING_LENGTH
+
+    Set to 1,000,000, to protect against potential DOS attacks. Pillow will
+    raise a ``ValueError`` if the number of characters is over this limit. The
+    check can be disabled by setting ``ImageFont.MAX_STRING_LENGTH = None``.

docs/releasenotes/10.0.0.rst

@@ -170,6 +170,18 @@ now been fixed.
 This effectively dates to the PIL fork, since problem images would still have
 been processed before Pillow started checking for decompression bombs.
 
+Added ImageFont.MAX_STRING_LENGTH
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To protect against potential DOS attacks when using arbitrary strings as text
+input, Pillow will now raise a ``ValueError`` if the number of characters
+passed into ImageFont methods is over a certain limit,
+:py:data:`PIL.ImageFont.MAX_STRING_LENGTH`.
+
+This threshold can be changed by setting
+:py:data:`PIL.ImageFont.MAX_STRING_LENGTH`. It can be disabled by setting
+``ImageFont.MAX_STRING_LENGTH = None``.
+
 Other Changes
 =============
 

src/PIL/ImageFont.py

@@ -41,6 +41,9 @@ class Layout(IntEnum):
     RAQM = 1
 
 
+MAX_STRING_LENGTH = 1_000_000
+
+
 try:
     from . import _imagingft as core
 except ImportError as ex:
@@ -49,6 +52,12 @@ class Layout(IntEnum):
     core = DeferredError(ex)
 
 
+def _string_length_check(text):
+    if MAX_STRING_LENGTH is not None and len(text) > MAX_STRING_LENGTH:
+        msg = "too many characters in string"
+        raise ValueError(msg)
+
+
 # FIXME: add support for pilfont2 format (see FontFile.py)
 
 # --------------------------------------------------------------------
@@ -152,6 +161,7 @@ def getbbox(self, text, *args, **kwargs):
 
         :return: ``(left, top, right, bottom)`` bounding box
         """
+        _string_length_check(text)
         width, height = self.font.getsize(text)
         return 0, 0, width, height
 
@@ -162,6 +172,7 @@ def getlength(self, text, *args, **kwargs):
 
         .. versionadded:: 9.2.0
         """
+        _string_length_check(text)
         width, height = self.font.getsize(text)
         return width
 
@@ -309,6 +320,7 @@ def getlength(self, text, mode="", direction=None, features=None, language=None)
 
         :return: Width for horizontal, height for vertical text.
         """
+        _string_length_check(text)
         return self.font.getlength(text, mode, direction, features, language) / 64
 
     def getbbox(
@@ -368,6 +380,7 @@ def getbbox(
 
         :return: ``(left, top, right, bottom)`` bounding box
         """
+        _string_length_check(text)
         size, offset = self.font.getsize(
             text, mode, direction, features, language, anchor
         )
@@ -546,6 +559,7 @@ def getmask2(
                  :py:mod:`PIL.Image.core` interface module, and the text offset, the
                  gap between the starting coordinate and the first marking
         """
+        _string_length_check(text)
         if start is None:
             start = (0, 0)
         im, size, offset = self.font.render(
@@ -684,6 +698,7 @@ def getlength(self, text, *args, **kwargs):
         if self.orientation in (Image.Transpose.ROTATE_90, Image.Transpose.ROTATE_270):
             msg = "text length is undefined for text rotated by 90 or 270 degrees"
             raise ValueError(msg)
+        _string_length_check(text)
         return self.font.getlength(text, *args, **kwargs)