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Fix jsonb_object_agg crash after eliminating null-valued pairs.

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In commit b61aa76e4 I added an assumption in jsonb_object_agg_finalfn
that it'd be okay to apply uniqueifyJsonbObject repeatedly to a
JsonbValue.  I should have studied that code more closely first,
because in skip_nulls mode it removed leading nulls by changing the
"pairs" array start pointer.  This broke the data structure's
invariants in two ways: pairs no longer references a repalloc-able
chunk, and the distance from pairs to the end of its array is less
than parseState->size.  So any subsequent addition of more pairs is
at high risk of clobbering memory and/or causing repalloc to crash.
Unfortunately, adding more pairs is exactly what will happen when the
aggregate is being used as a window function.

Fix by rewriting uniqueifyJsonbObject to not do that.  The prior
coding had little to recommend it anyway.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/ec5e96fb-ee49-4e5f-8a09-3f72b4780538@gmail.com
This commit is contained in:
Tom Lane
2025-12-13 16:18:23 -05:00
parent 315342ffed
commit ef5f559b95
4 changed files with 64 additions and 32 deletions
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7
src/backend/utils/adt/jsonb.c
View File

@@ -1755,8 +1755,11 @@ jsonb_object_agg_finalfn(PG_FUNCTION_ARGS)
* the stored JsonbValue data structure. Fortunately, the WJB_END_OBJECT
* action will only destructively change fields in the JsonbInState struct
* itself, so we can simply invoke pushJsonbValue on a local copy of that.
* (This technique results in running uniqueifyJsonbObject each time, but
* for now we won't bother trying to avoid that.)
* Note that this will run uniqueifyJsonbObject each time; that's hard to
* avoid, since duplicate pairs may have been added since the previous
* finalization. We assume uniqueifyJsonbObject can be applied repeatedly
* (with the same unique_keys/skip_nulls options) without damaging the
* data structure.
*/
result = arg->pstate;

49
src/backend/utils/adt/jsonb_util.c
View File

@@ -2069,12 +2069,14 @@ lengthCompareJsonbPair(const void *a, const void *b, void *binequal)
static void
uniqueifyJsonbObject(JsonbValue *object, bool unique_keys, bool skip_nulls)
{
JsonbPair *pairs = object->val.object.pairs;
int nPairs = object->val.object.nPairs;
bool hasNonUniq = false;
Assert(object->type == jbvObject);
if (object->val.object.nPairs > 1)
qsort_arg(object->val.object.pairs, object->val.object.nPairs, sizeof(JsonbPair),
if (nPairs > 1)
qsort_arg(pairs, nPairs, sizeof(JsonbPair),
lengthCompareJsonbPair, &hasNonUniq);
if (hasNonUniq && unique_keys)
@@ -2084,36 +2086,25 @@ uniqueifyJsonbObject(JsonbValue *object, bool unique_keys, bool skip_nulls)
if (hasNonUniq || skip_nulls)
{
JsonbPair *ptr,
*res;
int nNewPairs = 0;
while (skip_nulls && object->val.object.nPairs > 0 &&
object->val.object.pairs->value.type == jbvNull)
for (int i = 0; i < nPairs; i++)
{
/* If skip_nulls is true, remove leading items with null */
object->val.object.pairs++;
object->val.object.nPairs--;
}
JsonbPair *ptr = pairs + i;
if (object->val.object.nPairs > 0)
{
ptr = object->val.object.pairs + 1;
res = object->val.object.pairs;
while (ptr - object->val.object.pairs < object->val.object.nPairs)
{
/* Avoid copying over duplicate or null */
if (lengthCompareJsonbStringValue(ptr, res) != 0 &&
(!skip_nulls || ptr->value.type != jbvNull))
{
res++;
if (ptr != res)
memcpy(res, ptr, sizeof(JsonbPair));
}
ptr++;
}
object->val.object.nPairs = res + 1 - object->val.object.pairs;
/* Skip duplicate keys */
if (nNewPairs > 0 &&
lengthCompareJsonbStringValue(&pairs[nNewPairs - 1].key,
&ptr->key) == 0)
continue;
/* Skip null values, if told to */
if (skip_nulls && ptr->value.type == jbvNull)
continue;
/* Emit this pair, but avoid no-op copy */
if (i > nNewPairs)
pairs[nNewPairs] = *ptr;
nNewPairs++;
}
object->val.object.nPairs = nNewPairs;
}
}

32
src/test/regress/expected/jsonb.out
View File

@@ -1582,6 +1582,38 @@ SELECT jsonb_object_agg(1, NULL::jsonb);
SELECT jsonb_object_agg(NULL, '{"a":1}');
ERROR: field name must not be null
SELECT jsonb_object_agg_unique(i, null) OVER (ORDER BY i)
FROM generate_series(1, 10) g(i);
jsonb_object_agg_unique
-----------------------------------------------------------------------------------------------------------------
{"1": null}
{"1": null, "2": null}
{"1": null, "2": null, "3": null}
{"1": null, "2": null, "3": null, "4": null}
{"1": null, "2": null, "3": null, "4": null, "5": null}
{"1": null, "2": null, "3": null, "4": null, "5": null, "6": null}
{"1": null, "2": null, "3": null, "4": null, "5": null, "6": null, "7": null}
{"1": null, "2": null, "3": null, "4": null, "5": null, "6": null, "7": null, "8": null}
{"1": null, "2": null, "3": null, "4": null, "5": null, "6": null, "7": null, "8": null, "9": null}
{"1": null, "2": null, "3": null, "4": null, "5": null, "6": null, "7": null, "8": null, "9": null, "10": null}
(10 rows)
SELECT jsonb_object_agg_unique_strict(i, null) OVER (ORDER BY i)
FROM generate_series(1, 10) g(i);
jsonb_object_agg_unique_strict
--------------------------------
{}
{}
{}
{}
{}
{}
{}
{}
{}
{}
(10 rows)
CREATE TEMP TABLE foo (serial_num int, name text, type text);
INSERT INTO foo VALUES (847001,'t15','GE1043');
INSERT INTO foo VALUES (847002,'t16','GE1043');

6
src/test/regress/sql/jsonb.sql
View File

@@ -402,6 +402,12 @@ SELECT jsonb_build_object('{1,2,3}'::int[], 3);
SELECT jsonb_object_agg(1, NULL::jsonb);
SELECT jsonb_object_agg(NULL, '{"a":1}');
SELECT jsonb_object_agg_unique(i, null) OVER (ORDER BY i)
FROM generate_series(1, 10) g(i);
SELECT jsonb_object_agg_unique_strict(i, null) OVER (ORDER BY i)
FROM generate_series(1, 10) g(i);
CREATE TEMP TABLE foo (serial_num int, name text, type text);
INSERT INTO foo VALUES (847001,'t15','GE1043');
INSERT INTO foo VALUES (847002,'t16','GE1043');