From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Peter J. Holzer" <hjp-pgsql@hjp.at>
cc: pgsql-general@lists.postgresql.org
Subject: Re: Bypassing Directory Ownership Check in PostgreSQL 16.6 with Secure z/OS NFS (AT-TLS)
In-reply-to: <20250714182016.23ypyxgtq6vbgl4c@hjp.at>
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Comments: In-reply-to "Peter J. Holzer" <hjp-pgsql@hjp.at>
	message dated "Mon, 14 Jul 2025 20:20:16 +0200"
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Date: Mon, 14 Jul 2025 14:30:45 -0400
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"Peter J. Holzer" <hjp-pgsql@hjp.at> writes:
> On 2025-07-14 10:07:20 -0400, Tom Lane wrote:
>> That is primarily for safety reasons: if for some reason the
>> filesystem gets dismounted, or hasn't come on-line yet during
>> a reboot, you do not want Postgres to be able to write on the
>> underlying mount-point directory.

> Be careful: There are two different directorys involved in a mount
> point. The one in the parent filesystem and the one in the mounted file
> system.

True, and the safety requirement really is only that the parent
filesystem's mount-point directory not be writable by us.
But normal practice is that both directories are root-owned,
or at least owned by highly privileged users.

(I have a vague idea that there are system-level security hazards,
not specific to Postgres, if mount-point directories are publicly
writable.  Don't feel like researching that though.)

			regards, tom lane