Breaking changes in CIFS kernel module from 6.12 to 6.16

[Peter Milesson]

Hi folks,

OS: Debian 13
Kernel: current 6.16.3 from Trixie backports, previous kernel 6.12.48 
from Trixie security updates

I got the advice to post my problem here by Rowland Penny from 
samba-users list.

I'm using CIFS to mount user home directories on terminals through 
pam-mount. After successful authentication with display manager LightDM, 
the user's home directory is mounted to /home/<user>. The window manager 
is LXDE, and it's creating sockets under ~/.ssh/agent.

This was working with the previous kernel 6.12.48.

After installation of kernel 6.16.3, the window manager terminated 
unexpectedly, just before displaying the desktop environment. I tracked 
down the problem, and it seems creating sockets on the mounted share is 
no longer permitted.

The CIFS mount parameters are:

    dir_mode=0700,nosuid,nodev,sec=krb5i,cruid=%(USERUID),mfsymlinks,nobrl,vers=3.1.1

When I changed the mount parameters to:

    dir_mode=0700,nosuid,nodev,sec=krb5i,cruid=%(USERUID),sfu,nobrl,vers=3.1.1

everything seemed to work as before.

Is the change in behavior of mfsymlinks intentional or is it a bug? If 
it is intentional, is using the sfu parameter as a replacement a valid 
alternative?

Best regards,

Peter Milesson