Hide/Don't list non-readable folders

Question

In a multi-user environment using Ubuntu server 14.04 as a shared drive

All users connect via SFTP using Filezilla/WinSCP and are chroot to /home/company-folder/

Each user has also its own personal folder under /home/company-folder/users/. Eg. /home/company-folder/users/username-1, /home/company-folder/users/username-2 and so on...

Now username-1 can see other users personal folders (/home/company-folder/users/username-2, /home/company-folder/users/username-3, etc), he cannot access other user folders but he can see them listed.

Question is: what can I do so users cannot see each others personal directory under /home/company-folder/users/? Is there anyway in Ubuntu-Linux to hide non-readable folders?

Since in a system with 100+ users is not convenient for users to browse through the whole list of user folders to find his personal folder.

Solution 1

In general, no. Only the permission of the (from your point of view) parent directories determine, whether its content can be listed by a particular user. This includes directory entries, that this user cannot open/read. The mechanism for SSH/SFTP access is the same as with local tools, since the SSH/SFTP server spawns a subprocess for each session and changes the ownership of the subprocess to the respective user, as soon as they're authenticated successfully.

Consider the following example:

david@localhost:~$ ls -la /home
dr-xr-xr-x  1  root   root    80 Nov 10 09:05 .
drwxr-xr-x 23  root   root  4,0K Dec 17 11:09 ..
drwxr-xr-x  1 guest  guest   836 Sep  4 20:58 guest
drwxr-x---  1 david  users  4,2K Dec 14 22:07 david
drwx------  1  root   root   614 Nov 10 12:42 root

As you can see, I, david, can list the content of /home even though I am not its owner, since everybody can read it (see the permission mask in front of the . entry). I can list the content of /home/guest for the same reason. I can also list the content of /home/david, since I'm its owner and the owner has read permission. However, I cannot list the content of /home/root, since I'm not the owner and nobody but the owner has read permissions on that directory:

david@localhost:~$ ls /home/root
ls: cannot open directory /home/root: Permission denied

If one changed the ownership of /home to remove read permission for non-owners, I could not list the content of /home any longer:

david@localhost:~$ sudo chmod o-r /home
david@localhost:~$ ls -ld /home
drwxr-x--x 2 root root 40 Dez 17 21:17 /home
david@localhost:~$ ls -l /home
ls: cannot open directory /home: Permission denied

Though, I can still traverse /home and read /home/david, because the traverse permission (that's the semantic of the “execute” bit on directories) is still set on /home (and /):

david@localhost:~$ ls -l /home/david
total 732K
drwx------  1 david users 4,2K Dec 14 22:07 .
dr-xr-x--x  1 root  root    80 Nov 10 09:05 ..
drwx------  1 david users   60 Aug 24  2014 .adobe
-rw-------  1 david users   83 Dec  6 19:49 .bash_aliases
-rw-------  1 david users   66 May 12  2011 .bash_completion
-rw-------  1 david users  703 Nov 23 05:41 .bash_exports
[etc...]

See Jakuje's answer for a possible alternative approach to your underlying aim.

Solution 2

I don't know about any way to do what you describe, but there is -d option for openssh sftp-server, which specifies users starting directory, which can solve your problem about

[...] to browse through the whole list of user folders to find his personal folder.

If you specify your sftp-server such as:

Subsystem sftp internal-sftp -d /users/%u

(you need to omit /home/company-folder/, since you are already chrooted there).

Comments

[David Foerster]

In general, no. Only the permission of the parent directories determine, whether its content can be listed by a particular user.

[David Foerster]

Samba may be another option, that can definitely do something to that effect, if CIFS is a viable file access protocol for you case. On the other hand, I don't see, what's so bad about listing all user homes to everyone. This has the advantage, that users may share a subset of their files with other users.

[David Foerster]

@Jakuje: Done. My mistake. J and K are so close on the keyboard.

[berriop]

but they still need to access /home/company-folder/ which also contains common folders (eg. /home/company-folder/projects), so specifying starting directory like that doesn't work. Anyway thanks for your reply.

[berriop]

thanks for your reply David, but that still not solving the issue as users cannot type commands to move between directories, neither guess the directory path, they are using Filezilla/WinSCP. I am a bit surprised that hiding folders from users without permission cannot be accomplish. I have also tried another way, mounting /home/company-folder into the user directory by: mount --bind /home/company-folder /home/company-folder/users/username-1 but this have to be done individually for every existing and new user, and I may need it to be done automatically when creating a new user.

[David Foerster]

My university (and many other places) mount required network drives upon login and unmount it on logout. Maybe you can use a similar approach.

[David Foerster]

@berriop: What about an additional user for the shared folder?

[Jakuje]

Or some default symlinks from users own directories? It is not elegant, but it should work.