Simplify ACL handling for large objects and removal of superuser() checks

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Simplify ACL handling for large objects and removal of superuser() checks
Date: 2017-08-14 03:20:41
Message-ID: CAB7nPqRHmNOYbETnc_2EjsuzSM00Z+BWKv9sy6tnvSd5gWT_JA@mail.gmail.com
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Hi all,

Recent commit 8d98819 has added a missing permissoin check to lo_put()
to make sure that the write permissions of the object are properly set
before writing to a large object. When studying the problem, we bumped
into the fact that it is possible to actually simplify those ACL
checks and replace them by checks when opening the large object. This
makes all the checks now in be-fsstubs.c happen in inv_api.c, which is
where all the large object handling happens at a lower level. This
way, it is also possible to remove the extra logic in place to have
the permission checks happen only once.

At the same time, we have bumped into two things:
- ALLOW_DANGEROUS_LO_FUNCTIONS has been introduced in 1999, so it
could be time to let it go. I have known of no place where this is
actively used.
- lo_import and lo_export on the backend have superuser checks. We
could remove them and replace them with proper REVOKE permissions to
allow administrators to give access to those functions.

Attached is a set of 3 patches:
- 0001 removes ALLOW_DANGEROUS_LO_FUNCTIONS
- 0002 replaces the superuser checks with GRANT permissions
- 0003 refactors the LO code to improve the ACL handling. Note that
this patch introduces a more debatable change: now there is no
distinction between INV_WRITE and INV_WRITE|INV_READ, as when
INV_WRITE is used INV_READ is implied. The patch as proposed does a
complete split of both permissions to give a system more natural and
more flexible. The current behavior is documented. Please note as well
that it is possible to implement a patch that keeps compatibility as
well, but I would welcome a debate on the matter. This patch owns also
a good deal to Tom.

I am parking them to the next commit fest for PG11.

Thanks,
--
Michael

Attachment Content-Type Size
0003-Move-ACL-checks-for-large-objects-when-opening-them.patch text/x-patch 18.3 KB
0002-Replace-superuser-checks-of-large-object-import-expo.patch text/x-patch 4.5 KB
0001-Remove-ALLOW_DANGEROUS_LO_FUNCTIONS-for-LO-related-s.patch text/x-patch 1.4 KB

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