The issue is still present with python 3.9 and macOS 10.15 as well as current macOS 11 betas.

The following python scriptlet reproduces the issue:

# ---
import socket
  
sd1, sd2 = socket.socketpair()

sd1.sendmsg([b"hello"], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, b"")])
sd2.recvmsg(1)
# ---

I think the attached file "repro.c" does the same in C, it also fails with "recvmsg: Cannot allocate memory".


I've filed an issue for this with Apple: FB8813140.  I filed it from an Arm Mac system, with some luck this will help to get attention :-)