PythonExtra/tests/basics/struct1.py
Damien George 2daacc5cee py/modstruct: Check and prevent buffer-write overflow in struct packing.
Prior to this patch, the size of the buffer given to pack_into() was checked
for being too small by using the count of the arguments, not their actual
size.  For example, a format spec of '4I' would only check that there was 4
bytes available, not 16; and 'I' would check for 1 byte, not 4.

The pack() function is ok because its buffer is created to be exactly the
correct size.

The fix in this patch calculates the total size of the format spec at the
start of pack_into() and verifies that the buffer is large enough.  This
adds some computational overhead, to iterate through the whole format spec.
The alternative is to check during the packing, but that requires extra
code to handle alignment, and the check is anyway not needed for pack().
So to maintain minimal code size the check is done using struct_calcsize.
2017-09-01 11:11:09 +10:00

99 lines
2.3 KiB
Python

try:
import ustruct as struct
except:
try:
import struct
except ImportError:
print("SKIP")
raise SystemExit
print(struct.calcsize("<bI"))
print(struct.unpack("<bI", b"\x80\0\0\x01\0"))
print(struct.calcsize(">bI"))
print(struct.unpack(">bI", b"\x80\0\0\x01\0"))
# 32-bit little-endian specific
#print(struct.unpack("bI", b"\x80\xaa\x55\xaa\0\0\x01\0"))
print(struct.pack("<l", 1))
print(struct.pack(">l", 1))
print(struct.pack("<i", 1))
print(struct.pack(">i", 1))
print(struct.pack("<h", 1))
print(struct.pack(">h", 1))
print(struct.pack("<b", 1))
print(struct.pack(">b", 1))
print(struct.pack("<bI", -128, 256))
print(struct.pack(">bI", -128, 256))
print(struct.calcsize("100sI"))
print(struct.calcsize("97sI"))
print(struct.unpack("<6sH", b"foo\0\0\0\x12\x34"))
print(struct.pack("<6sH", b"foo", 10000))
s = struct.pack("BHBI", 10, 100, 200, 300)
v = struct.unpack("BHBI", s)
print(v == (10, 100, 200, 300))
# network byte order
print(struct.pack('!i', 123))
# check that we get an error if the buffer is too small
try:
struct.unpack('I', b'\x00\x00\x00')
except:
print('struct.error')
# first arg must be a string
try:
struct.pack(1, 2)
except TypeError:
print('TypeError')
# make sure that unknown types are detected
try:
struct.pack("z", 1)
except:
print("Unknown type")
# Initially repitition counters were supported only for strings,
# but later were implemented for all.
print(struct.unpack("<3B2h", b"foo\x12\x34\xff\xff"))
print(struct.pack("<3B", 1, 2, 3))
# pack_into
buf = bytearray(b'>>>123<<<')
struct.pack_into('<bbb', buf, 3, 0x41, 0x42, 0x43)
print(buf)
struct.pack_into('<bbb', buf, -6, 0x44, 0x45, 0x46)
print(buf)
# check that we get an error if the buffer is too small
try:
struct.pack_into('I', bytearray(1), 0, 0)
except:
print('struct.error')
try:
struct.pack_into('<bbb', buf, 7, 0x41, 0x42, 0x43)
except:
print('struct.error')
try:
struct.pack_into('<bbb', buf, -10, 0x41, 0x42, 0x43)
except:
print('struct.error')
# unpack_from
buf = b'0123456789'
print(struct.unpack_from('<b', buf, 4))
print(struct.unpack_from('<b', buf, -4))
try:
print(struct.unpack_from('<b', buf, 10))
except:
print('struct.error')
try:
print(struct.unpack_from('<b', buf, -11))
except:
print('struct.error')