Created attachment 1937150 [details]
dmesg.txt from 6.0.16 on a libvirt VM showing this problem

1. Please describe the problem:
Starting in 6.0.16, calls to bind() on a duplicate port on at least localhost don't fail. I first noticed this issue when the Go test suite began failing on a TCP listen test, where it expects such a duplicate bind() to fail.

2. What is the Version-Release number of the kernel:
6.0.16-300.fc37.x86_64 and 6.0.18-300.fc37.x86_64

3. Did it work previously in Fedora? If so, what kernel version did the issue
   *first* appear?  Old kernels are available for download at
   https://koji.fedoraproject.org/koji/packageinfo?packageID=8 :
Yes, this worked in 6.0.15 and before.

4. Can you reproduce this issue? If so, please provide the steps to reproduce
   the issue below:

In Python:
>>> from socket import *
>>> s1 = socket(AF_INET, SOCK_STREAM)
>>> s2 = socket(AF_INET, SOCK_STREAM)
>>> s1.bind(('127.0.0.1', 0))
>>> # Reuse same assigned port
>>> s2.bind(('127.0.0.1', s1.getsockname()[1]))
>>> s1.getsockname()
('127.0.0.1', 36483)
>>> s2.getsockname()
('0.0.0.0', 0)

5. Does this problem occur with the latest Rawhide kernel? To install the
   Rawhide kernel, run ``sudo dnf install fedora-repos-rawhide`` followed by
   ``sudo dnf update --enablerepo=rawhide kernel``:
This doesn't occur in the latest Rawhide, which is 6.2.0-0.rc2.20230105git41c03ba9beea.20.fc38.x86_64 as I write this. Running with that kernel, the last step in the Python reproducer gets the expected error:

>>> s2.bind(('127.0.0.1', s1.getsockname()[1]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 98] Address already in use


6. Are you running any modules that not shipped with directly Fedora's kernel?:
This reproduces on a Fedora 37 virtual machine with only standard modules. My normal kernels use OpenZFS as well.

7. Please attach the kernel logs. You can get the complete kernel log
   for a boot with ``journalctl --no-hostname -k > dmesg.txt``. If the
   issue occurred on a previous boot, use the journalctl ``-b`` flag.