cifs mount error when specifying prefixpath and having as part of the path

[Jochen Schroeder]

Recently some of my cifs mounts have stopped working. This could have happened due to an upgrade on the server (over which I do not have any control) or if there was a package update to cifs-utils.

The issue I am seeing is if I try to mount a subdirectory of the network share, by appending the path to the unc when mounting, the mount fails with mount error(22): invalid argument

$mount.cifs -vvv //sol.ita.chalmers.se/groups/mc2-common-photonics -o credentials=/etc/smbcredentials /mnt/PhotonicsGroup/

domain=NET
mount.cifs kernel mount options: ip=129.16.226.60,unc=\\sol.ita.chalmers.se\groups,user=jochens,,domain=NET,prefixpath=mc2-common-photonics,pass=********
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

If I specify the prefixpath via an option the mount succeeds.

$mount.cifs -vvv //sol.ita.chalmers.se/groups/ -o credentials=/etc/smbcredentials,prefixpath=mc2-common-photonics /mnt/PhotonicsGroup/

domain=NET
mount.cifs kernel mount options: ip=129.16.226.60,unc=\\sol.ita.chalmers.se\groups,prefixpath=mc2-common-photonics,user=jochens,,domain=NET,pass=********

I don't really see any difference between the mount options, so I don't understand what's going on. Also smbclient and gvfs can mount the path without issues.

$ mount.cifs -V

mount.cifs version: 6.6

$ lsb_release -rd

Description: Ubuntu 17.04
Release: 17.04

$ uname -a

Linux MC2-F093 4.10.0-33-generic #37-Ubuntu SMP Fri Aug 11 10:55:28 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux