Comment 3 for bug 1863086

I cannot reproduce this. I compiled the reproducer program and tested on a Eoan VM running in KVM, with the same 5.3.0-29-generic kernel:

ubuntu@ubuntu:~$ ./socktest
Segmentation fault (core dumped)
ubuntu@ubuntu:~$ tail /var/log/kern.log
Feb 14 04:00:41 ubuntu kernel: [ 134.951620] socktest[1598]: segfault at 21 ip 000055892e4cb2a3 sp 00007ffed8905de0 error 6 in socktest[55892e4cb000+1000]
Feb 14 04:00:41 ubuntu kernel: [ 134.951634] Code: 48 8d 4d e0 8b 45 dc ba 10 00 00 00 48 89 ce 89 c7 e8 71 fe ff ff 8b 45 dc be 0a 00 00 00 89 c7 e8 52 fe ff ff b8 21 00 00 00 <c7> 00 21 00 00 00 b8 00 00 00 00 48 8b 4d f8 64 48 33 0c 25 28 00
ubuntu@ubuntu:~$ ps ax | grep socktest
 1602 pts/0 S+ 0:00 grep --color=auto socktest
ubuntu@ubuntu:~$ uname -rv
5.3.0-29-generic #31-Ubuntu SMP Fri Jan 17 17:27:26 UTC 2020

The segfault happens as expected, but there is no null pointer dereference and no stack trace in dmesg. The process is terminated and I can still bind to port 6000 with netcat.

I see that you have Virtual Box kernel modules loaded. Can you try reproduce this on a fresh Eoan VM with no Virtual Box drivers installed?