Re: Interest in a SECURITY DEFINER function current_user stack access mechanism?

On Wed, Oct 18, 2017 at 01:43:30PM -0700, David G. Johnston wrote:
> Regardless of the merits of the proposed feature, the function
> "session_user" is SQL-defined and should not be modified or enhanced.
>
> I could see "calling_role()" being useful - it returns the same value
> as "current_role" normally and in security invoker functions while in
> a security definer function it would return whatever current_role
> would have returned if the function was a security invoker (i.e., the
> role that the system will put back into effect once the security
> definer function returns).

That... could be awkward where lots of SECURITY DEFINER functions may be
user-callable, but also called from each other. But it would be
minimally useful.

More useful than this, for me, would be a way to get the top-most user.

> Introducing the concept of a stack at the SQL level here seems, at
> first glance, to be over-complicating things.

Because of the current implementation of invocation of SECURITY DEFINER
functions, a stack is trivial to build, since it's a list of nodes
allocated on the C stack in fmgr_security_definer().

Nico
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