openssl 1.1.1d-0+deb10u1 breaks sshd publickey authentication

[Juan Agüí <turing@teslacoollab.com>]

Hi there,

after upgrading to openssl 1.1.1d-0+deb10u1, openssh-server 1:7.9p1-10 
prevents login via publickey.

On the server side:

* systemctl status sshd reports: fatal: privsep_preauth: preauth child 
terminated by signal 31

* journalctl -u sshd.service reports: audit: type=1326 audit 
(1570005452.956:21): auid=4294967295 ui=104 gid=65534 ses=4294967295 
pid=5025 comm="sshd" exe="/usr/bin/sshd" sig=31 syscall=67 compat=0 
ip=0x7f0867c1f377 code=0x0

On the client side

*  ssh reports packet_write_wait: Connection to x.y.z.w port 22: Broken pipe

Might be already reported on the openssl repo: 
https://github.com/openssl/openssl/issues/9984

I'll gladly provide more info.

Thanks,

Juan