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Catch struct.errors when verifying png files #1805

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Apr 4, 2016
Merged

Catch struct.errors when verifying png files #1805

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77da73c
Catch struct.errors when verifying png files, convert to SyntaxErrors…
wiredfool Apr 4, 2016
90378c8
Fixing compatibility with the truncated images tests
wiredfool Apr 4, 2016
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24 changes: 17 additions & 7 deletions PIL/PngImagePlugin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@
import logging
import re
import zlib
import struct

from PIL import Image, ImageFile, ImagePalette, _binary

Expand Down Expand Up @@ -106,6 +107,7 @@ def __init__(self, fp):

def read(self):
"Fetch a new chunk. Returns header information."
cid = None

if self.queue:
cid, pos, length = self.queue[-1]
Expand All @@ -116,7 +118,7 @@ def read(self):
cid = s[4:]
pos = self.fp.tell()
length = i32(s)

if not is_cid(cid):
raise SyntaxError("broken PNG file (chunk %s)" % repr(cid))

Expand All @@ -138,11 +140,15 @@ def call(self, cid, pos, length):
def crc(self, cid, data):
"Read and verify checksum"

crc1 = Image.core.crc32(data, Image.core.crc32(cid))
crc2 = i16(self.fp.read(2)), i16(self.fp.read(2))
if crc1 != crc2:
raise SyntaxError("broken PNG file"
"(bad header checksum in %s)" % cid)
try:
crc1 = Image.core.crc32(data, Image.core.crc32(cid))
crc2 = i16(self.fp.read(2)), i16(self.fp.read(2))
if crc1 != crc2:
raise SyntaxError("broken PNG file (bad header checksum in %s)"
% cid)
except struct.error:
raise SyntaxError("broken PNG file (incomplete checksum in %s)"
% cid)

def crc_skip(self, cid, data):
"Read checksum. Used if the C module is not present"
Expand All @@ -157,7 +163,11 @@ def verify(self, endchunk=b"IEND"):
cids = []

while True:
cid, pos, length = self.read()
try:
cid, pos, length = self.read()
except struct.error:
raise IOError("truncated PNG file")

if cid == endchunk:
break
self.crc(cid, ImageFile._safe_read(self.fp, length))
Expand Down
16 changes: 16 additions & 0 deletions Tests/test_file_png.py
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Original file line number Diff line number Diff line change
Expand Up @@ -253,6 +253,22 @@ def test_load_verify(self):
im.load()
self.assertRaises(RuntimeError, im.verify)

def test_verify_struct_error(self):
# Check open/load/verify exception (#1755)

# offsets to test, -10: breaks in i32() in read. (IOError)
# -13: breaks in crc, txt chunk.
# -14: malformed chunk

for offset in (-10, -13, -14):
with open(TEST_PNG_FILE,'rb') as f:
test_file = f.read()[:offset]

im = Image.open(BytesIO(test_file))
self.assertTrue(im.fp is not None)
self.assertRaises((IOError, SyntaxError), im.verify)


def test_roundtrip_dpi(self):
# Check dpi roundtripping

Expand Down