Feedback-ID: ia2694551:Fastmail
Date: Wed, 8 Nov 2023 18:53:27 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>,
	Peter Eisentraut <peter@eisentraut.org>, Robert Haas <robertmhaas@gmail.com>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: cataloguing NOT NULL constraints
Message-ID: <202311081753.paidc6czdtmr@alvherre.pgsql>
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On 2023-Oct-12, Alexander Lakhin wrote:

Hello,

> I've discovered that that commit added several recursive functions, and
> some of them are not protected from stack overflow.

True.  I reproduced the first two, but didn't attempt to reproduce the
third one -- patching all these to check for stack depth is cheap
protection.  I also patched ATAddCheckNNConstraint:

> (ATAddCheckNNConstraint() is protected because it calls
> AddRelationNewConstraints(), which in turn calls StoreRelCheck() ->
> CreateConstraintEntry() ->  recordDependencyOnSingleRelExpr() ->
> find_expr_references_walker() ->  expression_tree_walker() ->
> expression_tree_walker() -> check_stack_depth().)

because it seems uselessly risky to rely on depth checks that exist on
completely unrelated pieces of code, when the function visibly recurses
on itself.  Especially so since the test cases that demonstrate crashes
are so expensive to run, which means we're not going to detect it if at
some point that other stack depth check stops being called for whatever
reason.

BTW probably the tests could be made much cheaper by running the server
with a lower "ulimit -s" setting.  I didn't try.

I noticed one more crash while trying to "drop table" one of the
hierarchies your scripts create.  But it's a preexisting issue which
needs a backpatched fix, and I think Egor already reported it in the
other thread.

Thank you

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"Industry suffers from the managerial dogma that for the sake of stability
and continuity, the company should be independent of the competence of
individual employees."                                      (E. Dijkstra)