Re: Bypassing Directory Ownership Check in PostgreSQL 16.6 with Secure z/OS NFS (AT-TLS) - Mailing list pgsql-general

From Amol Inamdar
Subject Re: Bypassing Directory Ownership Check in PostgreSQL 16.6 with Secure z/OS NFS (AT-TLS)
Date
Msg-id CAGOe9Ri8aNao0SB8kkm0F6xp=TPe5XWHpcA9MEBkY4kp-6Bjig@mail.gmail.com
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In response to Re: Bypassing Directory Ownership Check in PostgreSQL 16.6 with Secure z/OS NFS (AT-TLS)  (Laurenz Albe <laurenz.albe@cybertec.at>)
Responses Re: Bypassing Directory Ownership Check in PostgreSQL 16.6 with Secure z/OS NFS (AT-TLS)
List pgsql-general
Thanks Laurenz, 

The data directory can either be created by "initdb", in which case
the mount point must allow the PostgreSQL user to create a directory.
You could set the group of the mount point to the group of the
PostgreSQL user and use permissions 1770, which should be perfectly safe.

This exactly is the problem we are facing, to give you a summary, 
our NFS server is enabled with AT-TLS authentication
and we are accessing the server via a proxy server (Haproxy). 
This acts as our NFS client and it is configured with the 
required client certificates.

The outcome of above configuration is that any directory created 
in the NFS mount is always owned by the user in the certificates 
and if that user isn't present in the proxy container it is marked 
as nobody:nogroup, we tried various things like
created the user similar to postgres user so that the users ids match but 
always ended up giving error  “data directory “/var/lib” has wrong ownership 

Hence, we thought of skipping this check (Directory owner and postgres user validation) and 
wanted to understand the implication of the same. 

Thanks,
Amol,



On Mon, Jul 14, 2025 at 6:14 PM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
On Mon, 2025-07-14 at 17:59 +0530, Amol Inamdar wrote:
> If I am not mistaken, below is my understanding of your suggestion. 
>
> Suppose that My mount point on the NFS server is say /nfs-mount/postgres/ 
> and you are suggesting to have a data directory as say /nfs-mount/postgres/db or something like that ? 
> and assign this value to the PGDATA ? 
>
> If that is the case, then when and who should be creating the directory DB ? 
>
> Please correct me if I am wrong about the understanding.

You understood me perfectly well.

The data directory can either be created by "initdb", in which case
the mount point must allow the PostgreSQL user to create a directory.
You could set the group of the mount point to the group of the
PostgreSQL user and use permissions 1770, which should be perfectly safe.

Alternatively, the root user could create the data directory with the
correct ownership and permissions prior to running "initdb".

Yours,
Laurenz Albe


--
-regards
Amol

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