samba - May 2020 - Server RAM filling up when writing to share from macOS

Hi,

I noticed an absolutely work-breaking behavior in Samba 4.12 (not present in
4.11 or lower): when writing to a share (Arch Linux server) from macOS, smbd?s
RAM usage is going up pretty much exactly the size of the transferred files -
and is released *only* when the connection is completely closed. So obviously,
when keeping the share mounted, copying files finally leads to Samba eating up
all of my server?s memory, finally crashing.

After some fiddling, I discovered this happens whenever either ?smb encrypt?,
?server signing? or SMB2 are forced/required by the server. Again: this only
happens with Samba 4.12.

Of course, this renders my Samba shares completely unusable - any idea what to
do?

Here?s my testparm output:

Load smb config files from /etc/samba/smb.conf
Loaded services file OK.
Server role: ROLE_STANDALONE

Press enter to see a dump of your service definitions

# Global parameters
[global]
	log file = /var/log/samba/%m.log
	map to guest = Bad User
	security = USER
	server string = marius-arch Samba Server
	idmap config * : backend = tdb
	smb encrypt = required


[marius]
	path = /home/marius
	read only = No
	valid users = marius

Best regards,
Marius Steffen
privat at mariussteffen.de