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Re: Security leak with trigger functions?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Albe Laurenz" <all(at)adv(dot)magwien(dot)gv(dot)at>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Security leak with trigger functions?
Date: 2006-12-14 17:06:18
Message-ID: 21827.1166115978@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Albe Laurenz" <all(at)adv(dot)magwien(dot)gv(dot)at> writes:
> Permissions on a trigger function seem not to be checked,
> and I can execute a function for which I have no privileges.

Only if it's a trigger function, but I agree this is not very good.
The question in my mind is what privilege to check and when.

I believe the check probably ought to be whether the table owner can
call the function (certainly not the person doing the command that
invokes the trigger).  However, that raises the question of whether
having a separate TRIGGER privilege to attach triggers to tables isn't
itself a security hole: it means someone who might not himself have call
privileges could cause other people to call a function.  We just removed
the separate RULE privilege, and said you must be table owner to put a
rule on a table, for exactly analogous reasons.

The other question is when to check it.  If we check only at CREATE
TRIGGER time then there's the problem that revoking execute privilege
on a trigger function would not do what you'd expect.  OTOH checking
at every trigger call seems quite unpleasant.  Would it be all right
to check all the triggers once at statement start (eg, in
ExecBSInsertTriggers) whether or not they actually get called?

BTW, I just noticed another bug in the trigger stuff: in a statement
with multiple target relations, such as UPDATE across an inheritance
tree, ExecBSUpdateTriggers and friends get called only on the first
(parent) target relation.  Hence any statement-level triggers on child
tables aren't invoked.  This probably isn't very critical today, but
it would be if we use those functions to enforce permissions checks.

			regards, tom lane

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