Fix memory overrun when querying pg_stat_slru

michaelpq · michaelpq · commit a45ed975c58f · 2021-11-12T21:49:21.000+09:00
pg_stat_get_slru() in pgstatfuncs.c would point to one element after the end of the array PgStat_SLRUStats when finishing to scan its entries. This had no direct consequences as no data from the extra memory area was read, but static analyzers would rightfully complain here. So let's be clean. While on it, this adds one regression test in the area reserved for system views. Reported-by: Alexander Kozhemyakin, via AddressSanitizer Author: Kyotaro Horiguchi Discussion: https://postgr.es/m/17280-37da556e86032070@postgresql.org Backpatch-through: 13
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
@@ -1911,14 +1911,15 @@ pg_stat_get_slru(PG_FUNCTION_ARGS)
 		/* for each row */
 		Datum		values[PG_STAT_GET_SLRU_COLS];
 		bool		nulls[PG_STAT_GET_SLRU_COLS];
-		PgStat_SLRUStats stat = stats[i];
+		PgStat_SLRUStats stat;
 		const char *name;
 
 		name = pgstat_slru_name(i);
 
 		if (!name)
 			break;
 
+		stat = stats[i];
 		MemSet(values, 0, sizeof(values));
 		MemSet(nulls, 0, sizeof(nulls));
 
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
@@ -76,6 +76,13 @@ select count(*) >= 0 as ok from pg_prepared_xacts;
  t
 (1 row)
 
+-- There will surely be at least one SLRU cache
+select count(*) > 0 as ok from pg_stat_slru;
+ ok 
+----
+ t
+(1 row)
+
 -- There must be only one record
 select count(*) = 1 as ok from pg_stat_wal;
  ok 
diff --git a/src/test/regress/sql/sysviews.sql b/src/test/regress/sql/sysviews.sql
@@ -37,6 +37,9 @@ select count(*) = 0 as ok from pg_prepared_statements;
 -- See also prepared_xacts.sql
 select count(*) >= 0 as ok from pg_prepared_xacts;
 
+-- There will surely be at least one SLRU cache
+select count(*) > 0 as ok from pg_stat_slru;
+
 -- There must be only one record
 select count(*) = 1 as ok from pg_stat_wal;
 
