samba - Nov 2025 - Change in mount behavior of the CIFS module from Debian kernel 6.12 to 6.16

Hi folks,

I got a seriously unpleasant problem, when LXDE stopped working in a 
bunch of terminals after kernel upgrade from 6.12.48 to 6.16.3. There 
were no indications about errors in the log files, so tracking down the 
bug was very hard. The only find was a couple of errors in the 
~/.xsession-errors file. The error was basically that ssh-agent could 
not bind to sockets in the ~/.ssh/agent directory, as they were missing.

I'm mounting the user's folder under /home from a CIFS server with 
pam-mount after successful authentication. The mount parameters were:

dir_mode=0700,nosuid,nodev,sec=krb5i,cruid=<userid>,mfsymlinks,nobrl,vers=3.0

Using kernel 6.16.3, the sshd-agent could not create sockets in the 
~/.ssh/agent directory. That worked with kernel 6.12.48, and LXDE was 
happy. I read through the CIFS documentation and found that the 
parameter sfu had any relevance. I replaced mfsymlinks with sfu so the 
parameters sent to cifs mount were:

dir_mode=0700,nosuid,nodev,sec=krb5i,cruid=<userid>,sfu,nobrl,vers=3.0

After this change, sockets were created, and LXDE started on the terminal.

Please, could somebody who knows explain to me, if the change in 
mfsymlinks behavior was intentional, or if it is a bug? Is the sfu 
parameter expected to stay for the foreseeable future, or will that also 
be changed or removed? Are there any alternatives to mfsymlinks and sfu?

Best regards,

Peter

On Wed, 19 Nov 2025 14:42:27 +0100
Peter Milesson via samba <samba at lists.samba.org> wrote:
> Hi folks,
> 
> I got a seriously unpleasant problem, when LXDE stopped working in a 
> bunch of terminals after kernel upgrade from 6.12.48 to 6.16.3. There 
> were no indications about errors in the log files, so tracking down
> the bug was very hard. The only find was a couple of errors in the 
> ~/.xsession-errors file. The error was basically that ssh-agent could 
> not bind to sockets in the ~/.ssh/agent directory, as they were
> missing.
> 
> I'm mounting the user's folder under /home from a CIFS server with 
> pam-mount after successful authentication. The mount parameters were:
> 
>
dir_mode=0700,nosuid,nodev,sec=krb5i,cruid=<userid>,mfsymlinks,nobrl,vers=3.0
> 
> Using kernel 6.16.3, the sshd-agent could not create sockets in the 
> ~/.ssh/agent directory. That worked with kernel 6.12.48, and LXDE was 
> happy. I read through the CIFS documentation and found that the 
> parameter sfu had any relevance. I replaced mfsymlinks with sfu so
> the parameters sent to cifs mount were:
> 
>
dir_mode=0700,nosuid,nodev,sec=krb5i,cruid=<userid>,sfu,nobrl,vers=3.0
> 
> After this change, sockets were created, and LXDE started on the
> terminal.
> 
> Please, could somebody who knows explain to me, if the change in 
> mfsymlinks behavior was intentional, or if it is a bug? Is the sfu 
> parameter expected to stay for the foreseeable future, or will that
> also be changed or removed? Are there any alternatives to mfsymlinks
> and sfu?
> 
> Best regards,
> 
> Peter
I have no idea about this, but feel you stand more chance of getting a
response on this if you post to the samba-technical list, that may
attract the attention of Steve French (the 'f' in mfsymlinks).

Rowland