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Ability to skip crc checks for ancillary chunks

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This commit is contained in:
Konstantin Kopachev 2016-06-29 12:24:37 -07:00
parent 30eced6286
commit c3b970f046
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GPG Key ID: CECF757E656F4F62
2 changed files with 36 additions and 0 deletions
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6
PIL/PngImagePlugin.py
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@ -138,6 +138,12 @@ class ChunkStream(object):
def crc(self, cid, data):
"Read and verify checksum"
# Skip CRC checks for ancillary chunks if allowed to load truncated images
# 5th byte of first char is 1 [specs, section 5.4]
if ImageFile.LOAD_TRUNCATED_IMAGES and (ord(cid[0]) >> 5 & 1):
self.crc_skip(cid, data)
return
try:
crc1 = Image.core.crc32(data, Image.core.crc32(cid))
crc2 = i16(self.fp.read(2)), i16(self.fp.read(2))

30
Tests/test_file_png.py
View File

@ -3,6 +3,7 @@ from helper import unittest, PillowTestCase, hopper
from io import BytesIO
from PIL import Image
from PIL import ImageFile
from PIL import PngImagePlugin
import zlib
@ -319,6 +320,35 @@ class TestFilePng(PillowTestCase):
self.assertTrue(im.fp is not None)
self.assertRaises((IOError, SyntaxError), im.verify)
def test_verify_ignores_crc_error(self):
# check ignores crc errors in ancillary chunks
chunk_data = chunk(b'tEXt', b'spam')
broken_crc_chunk_data = chunk_data[:-1] + 'q' # break CRC
image_data = HEAD + broken_crc_chunk_data + TAIL
self.assertRaises(SyntaxError,
lambda: PngImagePlugin.PngImageFile(BytesIO(image_data)))
ImageFile.LOAD_TRUNCATED_IMAGES = True
try:
im = load(image_data)
self.assertTrue(im is not None)
finally:
ImageFile.LOAD_TRUNCATED_IMAGES = False
def test_verify_not_ignores_crc_error_in_required_chunk(self):
# check does not ignore crc errors in required chunks
image_data = MAGIC + IHDR[:-1] + 'q' + TAIL
ImageFile.LOAD_TRUNCATED_IMAGES = True
try:
self.assertRaises(SyntaxError,
lambda: PngImagePlugin.PngImageFile(BytesIO(image_data)))
finally:
ImageFile.LOAD_TRUNCATED_IMAGES = False
def test_roundtrip_dpi(self):
# Check dpi roundtripping