[Martin Kalcher <martin.kalcher@aboutsource.net>]

Hi,

while working on something else i encountered a bug in the trim_array() 
function. The bounds check fails for empty arrays without any 
dimensions. It reads the size of the non existing first dimension to 
determine the arrays length.

   select trim_array('{}'::int[], 10);
   ------------
    {}

   select trim_array('{}'::int[], 100);
   ERROR:  number of elements to trim must be between 0 and 64

The attached patch fixes that check.

Martin

Attachments:

  [text/x-patch] 0001-Fix-bounds-check-in-trim_array.patch (1.9K, ../baaeb413-b8a8-4656-5757-ef347e5ec11f@aboutsource.net/2-0001-Fix-bounds-check-in-trim_array.patch)
  download | inline diff:
From b6173a8f8f94cddd5347db482b8e4480c0e546e7 Mon Sep 17 00:00:00 2001
From: Martin Kalcher <martin.kalcher@aboutsource.net>
Date: Mon, 25 Jul 2022 16:26:14 +0200
Subject: [PATCH] Fix bounds check in trim_array()

The bounds check in trim_array() failed for empty arrays without any
dimension. It read the size of the first dimension without checking its
existence.
---
 src/backend/utils/adt/arrayfuncs.c   | 2 +-
 src/test/regress/expected/arrays.out | 2 ++
 src/test/regress/sql/arrays.sql      | 1 +
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index fb167f226a..0342ebf4fd 100644
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -6839,7 +6839,7 @@ trim_array(PG_FUNCTION_ARGS)
 {
 	ArrayType  *v = PG_GETARG_ARRAYTYPE_P(0);
 	int			n = PG_GETARG_INT32(1);
-	int			array_length = ARR_DIMS(v)[0];
+	int			array_length = (ARR_NDIM(v) > 0) ? ARR_DIMS(v)[0] : 0;
 	int16		elmlen;
 	bool		elmbyval;
 	char		elmalign;
diff --git a/src/test/regress/expected/arrays.out b/src/test/regress/expected/arrays.out
index ce6f3a65f9..97920f38c2 100644
--- a/src/test/regress/expected/arrays.out
+++ b/src/test/regress/expected/arrays.out
@@ -2445,3 +2445,5 @@ SELECT trim_array(ARRAY[1, 2, 3], -1); -- fail
 ERROR:  number of elements to trim must be between 0 and 3
 SELECT trim_array(ARRAY[1, 2, 3], 10); -- fail
 ERROR:  number of elements to trim must be between 0 and 3
+SELECT trim_array(ARRAY[]::int[], 1); -- fail
+ERROR:  number of elements to trim must be between 0 and 0
diff --git a/src/test/regress/sql/arrays.sql b/src/test/regress/sql/arrays.sql
index f774faf856..791af5c0ce 100644
--- a/src/test/regress/sql/arrays.sql
+++ b/src/test/regress/sql/arrays.sql
@@ -754,3 +754,4 @@ FROM
 
 SELECT trim_array(ARRAY[1, 2, 3], -1); -- fail
 SELECT trim_array(ARRAY[1, 2, 3], 10); -- fail
+SELECT trim_array(ARRAY[]::int[], 1); -- fail
-- 
2.37.1