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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: kyzevan23@mail.ru
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17561: Server crashes on executing row() with very long argument list
Date: Fri, 29 Jul 2022 10:40:55 -0400
Message-ID: <3768321.1659105655@sss.pgh.pa.us> (raw)
In-Reply-To: <3753050.1659102953@sss.pgh.pa.us>
References: <20220729101411.7b45rvhlrsgcajjo@alvherre.pgsql>
	<3753050.1659102953@sss.pgh.pa.us>

I wrote:
> I think the parser should've prevented this.  It's in charge of
> rejecting overlength SELECT lists, for example.  Also, the limit
> probably needs to be just MaxTupleAttributeNumber.

Concretely, about as attached.

In the existing code, if you just supply 10000 or so columns you
reach this error in heaptuple.c:

    if (numberOfAttributes > MaxTupleAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                 errmsg("number of columns (%d) exceeds limit (%d)",
                        numberOfAttributes, MaxTupleAttributeNumber)));

I borrowed the errcode from that, but the wording from parse_node.c:

    if (pstate->p_next_resno - 1 > MaxTupleAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("target lists can have at most %d entries",
                        MaxTupleAttributeNumber)));

I'm a bit inclined to adjust parse_node.c to also use TOO_MANY_COLUMNS
(54011) instead of the generic PROGRAM_LIMIT_EXCEEDED (54000).

			regards, tom lane

Attachments:

prevent-too-many-cols-in-ROW-expr.patch (text/x-diff, 836B) download
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 9f567f4bf4..059cb7097c 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -2140,6 +2140,14 @@ transformRowExpr(ParseState *pstate, RowExpr *r, bool allowDefault)
 	newr->args = transformExpressionList(pstate, r->args,
 										 pstate->p_expr_kind, allowDefault);
 
+	/* Disallow more columns than will fit in a tuple */
+	if (list_length(newr->args) > MaxTupleAttributeNumber)
+		ereport(ERROR,
+				(errcode(ERRCODE_TOO_MANY_COLUMNS),
+				 errmsg("ROW expressions can have at most %d entries",
+						MaxTupleAttributeNumber),
+				 parser_errposition(pstate, r->location)));
+
 	/* Barring later casting, we consider the type RECORD */
 	newr->row_typeid = RECORDOID;
 	newr->row_format = COERCE_IMPLICIT_CAST;

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  Cc: tgl@sss.pgh.pa.us, alvherre@alvh.no-ip.org, kyzevan23@mail.ru, pgsql-bugs@lists.postgresql.org
  Subject: Re: BUG #17561: Server crashes on executing row() with very long argument list
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