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pg_stat_statements: Fix potential use-after-free of PlannedStmt

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pgss_ProcessUtility() included a reference to a portion of a PlannedStmt
after the point where this data's structure could have been freed,
causing an incorrect memory access.  There was a comment documenting
this requirement, missed in 3357471cf9.

This commit includes a test able to make valgrind complain with a
PlannedStmt freed by an internal ROLLBACK query.  Similarly to what is
mentioned in 495e73c207, this can be triggered by using the extended
query protocol, something that can be now tested thanks to the recent
meta-command additions in psql.  This commit mentions potential other
cases, but as far as I can see the extended protocol case with an
internal ROLLBACK is the only problematic pattern reachable in practice.

Issue introduced by 3357471cf9, gone unnoticed due to a lack of test
coverage.  The fix is authored by Chao, my contribution being the new
test.

Author: Chao Li <li.evan.chao@gmail.com>
Co-authored-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/2F91906A-F2B5-4A6B-9695-D136957D4545@gmail.com
This commit is contained in:
Michael Paquier 2026-05-12 13:36:38 +09:00
parent 8974a7c433
commit 8268e41aca
3 changed files with 59 additions and 1 deletions
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38
contrib/pg_stat_statements/expected/plancache.out
View file

@ -216,6 +216,44 @@ SELECT calls, generic_plan_calls, custom_plan_calls, toplevel, query FROM pg_sta
RESET pg_stat_statements.track;
--
-- Procedure with internal ROLLBACK and the extended query protocol.
-- The PlannedStmt used in pgss_ProcessUtility() is freed by the internal
-- ROLLBACK.
--
CREATE OR REPLACE PROCEDURE rollback_proc(a INOUT int) AS $$
BEGIN
ROLLBACK;
END;
$$ LANGUAGE plpgsql;
SELECT pg_stat_statements_reset() IS NOT NULL AS t;
t
---
t
(1 row)
CALL rollback_proc($1) \parse stmt_rollback
\bind_named stmt_rollback 1 \g
a
---
1
(1 row)
\bind_named stmt_rollback 2 \g
a
---
2
(1 row)
SELECT calls, query FROM pg_stat_statements
WHERE query LIKE '%rollback_proc%'
ORDER BY query COLLATE "C";
calls | query
-------+------------------------
2 | CALL rollback_proc($1)
(1 row)
DROP PROCEDURE rollback_proc;
--
-- Cleanup
--
DROP FUNCTION select_one_func(int);

3
contrib/pg_stat_statements/pg_stat_statements.c
View file

@ -1099,6 +1099,7 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
int64 saved_queryId = pstmt->queryId;
int saved_stmt_location = pstmt->stmt_location;
int saved_stmt_len = pstmt->stmt_len;
PlannedStmtOrigin saved_planOrigin = pstmt->planOrigin;
bool enabled = pgss_track_utility && pgss_enabled(nesting_level);
/*
@ -1210,7 +1211,7 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
NULL,
0,
0,
pstmt->planOrigin);
saved_planOrigin);
}
else
{

19
contrib/pg_stat_statements/sql/plancache.sql
View file

@ -87,6 +87,25 @@ SELECT calls, generic_plan_calls, custom_plan_calls, toplevel, query FROM pg_sta
RESET pg_stat_statements.track;
--
-- Procedure with internal ROLLBACK and the extended query protocol.
-- The PlannedStmt used in pgss_ProcessUtility() is freed by the internal
-- ROLLBACK.
--
CREATE OR REPLACE PROCEDURE rollback_proc(a INOUT int) AS $$
BEGIN
ROLLBACK;
END;
$$ LANGUAGE plpgsql;
SELECT pg_stat_statements_reset() IS NOT NULL AS t;
CALL rollback_proc($1) \parse stmt_rollback
\bind_named stmt_rollback 1 \g
\bind_named stmt_rollback 2 \g
SELECT calls, query FROM pg_stat_statements
WHERE query LIKE '%rollback_proc%'
ORDER BY query COLLATE "C";
DROP PROCEDURE rollback_proc;
--
-- Cleanup
--