ReadyNAS102 - protection of truecrypt-file against delete

Question

All my data on RN102 are saved in one truecrypt-file -"truecrypt_dad"- created on a laptop (OS Debian 8). This means that the RN102 manages only one file -"truecrypt_dad"-.

With the below described permission structure both users "dad" and "mom" can read and write the file "truecrypt_dad" from the laptop (OS Debian 8).

I want to protect the file "truecrypt_dad" against delete from user "mom", but I cannot find a solution.

MY PROBLEM: The user "mom", by attempting to delete "truecrypt_dad" does receive an errore message - "permission denied - you have not sufficient permissions to move the file into the trash" (free translated from german) - which is OK for me. But on the same window the button "DELETE" is still active and the user "mom" can delete the file!. To complete the confusion the user "mom" cannot rename the file due to insufficient permissions, which is also OK for me.

On one side the user "mom" cannot rename (OK for me) and cannot move into trash (OK for me), but on the other side can delete (not OK for me) the file.

I want to protect the file "truecrypt_dad" against delete from user "mom". There is a solution and an explanation for the strange behaviour mentioned above?

Thank you.

Technical data

Laptop description: OS Debain 8

extract from /etc/fstab of user "dad"

#nas

//IP/dad/ /media/dad cifs users,noauto,username=dad,passwd=dad 0 0

extract from /etc/fstab of user "mom"

#nas

//IP/dad/ /media/dad cifs users,noauto,username=mom,passwd=mom 0 0

NAS description: ReadyNAS102, Firmware 6.6.0, 2x 2TB

Configuration after factory reset:

SSH: activated

USERS/GROUPS

User Group comment

admin admin default user

dad parents

mom parents

SHARES

file/directory owner group permissions comment

/data root root drwxr-xr-x default share; default permissions

/data/dad dad parents drwxrwx--T+ ACLs and Sticky-bit created by RN102; ALSs: rwx for admin

/data/dad/truecrypt_dad dad parents -rwxrwx---+ file created with tuecrypt on laptop

StephenB · Answer

Try changing the permissions on the dad directory so that the group doesn't have write permission.

merlinux16 · Answer

Thank you for your reply.&nbsp;Both users "dad" and "mom" shall&nbsp;access to the file "truecrypt_dad". Only the user "dad" shall have the permission to delete "truecrypt_dad".&nbsp;The question is: why is the user "mom" allowed to delete the "truecrypt_dad" if&nbsp;there are&nbsp;no permissions to rename it and move it into trash? Why is "DELETE" still active? I cannot understand this behavior.&nbsp;If "DELETE" would not be active than everything would be fine for me.&nbsp;&nbsp;

StephenB · Answer

merlinux16 wrote:
Why is "DELETE" still active? I cannot understand this behavior.
&nbsp;&nbsp;

Linux doesn't have a separate "delete" permission. Deleting a file is done by modifying the folder the file is in. &nbsp;If you give someone write permission to that folder, then you are giving them permission to delete the files in it.
&nbsp;
You are allowing mom the ability to write to /data/dad (since anyone in the parents group has that permission).

merlinux16 · Answer

Thank you for your reply. I modified the permission structure of folder "dad" as suggested by you and eliminated the write permission for group parents. Now /data/dad has "drwxr-x--T+" instead of "drwxrwx--T+". Owner and group are "dad" and "parents" as before. Unfortunately the user "mom" has still the possibility to delete all files! The only change is that (obviously) no new files can be created by "mom". The only possibility to avoid that the group "parents" delete something in /data/dad is to set "read only" in the window "network access" of share "dad" on the NAS-web-administration-surface. But in this way the user "mom" cannot work anymore with file "truecrypt_dad". I have the impression that the settings in "network access" of each NAS share have the right of way compared to the standard Linux permissions. According my understanding the NAS-system is given write permissions to the group parent in the folder "dad", even if the permissions structure is modified into "drwxr-x--T+". Do you see any possibility to solve my question? Thank you in advance for your support.

StephenB · Answer

You should be able to make the share read-only for mom (or perhaps "everyone") and read/write for dad via the network settings for the share. &nbsp;That should block mom's ability to delete the file. &nbsp;It should also prevent mom from writing to the file.

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ReadyNAS102 - protection of truecrypt-file against delete

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