Avoid treating nonrequired nbtree keys as required.

petergeoghegan · petergeoghegan · commit 0f08df406822 · 2025-05-02T17:50:58.000-04:00
Consistently prevent nbtree array advancement from treating a scankey as required when operating in pstate.forcenonrequired mode. Otherwise, we risk a NULL pointer dereference. This was possible in the path where _bt_check_compare is called to recheck a tuple that advanced all of the scan's arrays to matching values: its continuescan=false handling expects _bt_advance_array_keys to have been called with a valid pstate, but it'll always be NULL during sktrig_required=false calls (which is how _bt_advance_array_keys must be called when pstate.forcenonrequired). Oversight in commit 8a51027, which optimized nbtree search scan key comparisons. Author: Peter Geoghegan <pg@bowt.ie> Reported-By: Mark Dilger <mark.dilger@enterprisedb.com> Discussion: https://postgr.es/m/CAHgHdKsn2W=gPBmj7p6MjQFvxB+zZDBkwTSg0o3f5Hh8rkRrsA@mail.gmail.com Discussion: https://postgr.es/m/CAH2-WzmodSE+gpTd1CRGU9ez8ytyyDS+Kns2r9NzgUp1s56kpw@mail.gmail.com
diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c
@@ -1826,7 +1826,7 @@ _bt_advance_array_keys(IndexScanDesc scan, BTReadPageState *pstate,
 
 		/* Recheck _bt_check_compare on behalf of caller */
 		if (_bt_check_compare(scan, dir, tuple, tupnatts, tupdesc, false,
-							  false, &continuescan,
+							  !sktrig_required, &continuescan,
 							  &nsktrig) &&
 			!so->scanBehind)
 		{
@@ -2799,8 +2799,6 @@ _bt_check_compare(IndexScanDesc scan, ScanDirection dir,
 {
 	BTScanOpaque so = (BTScanOpaque) scan->opaque;
 
-	Assert(!forcenonrequired || advancenonrequired);
-
 	*continuescan = true;		/* default assumption */
 
 	for (; *ikey < so->numberOfKeys; (*ikey)++)

Original file line number	Diff line number	Diff line change
`@@ -1826,7 +1826,7 @@ _bt_advance_array_keys(IndexScanDesc scan, BTReadPageState *pstate,`
`1826`	`1826`
`1827`	`1827`	`/* Recheck _bt_check_compare on behalf of caller */`
`1828`	`1828`	`if (_bt_check_compare(scan, dir, tuple, tupnatts, tupdesc, false,`
`1829`		`- false, &continuescan,`
	`1829`	`+ !sktrig_required, &continuescan,`
`1830`	`1830`	`&nsktrig) &&`
`1831`	`1831`	`!so->scanBehind)`
`1832`	`1832`	`{`
`@@ -2799,8 +2799,6 @@ _bt_check_compare(IndexScanDesc scan, ScanDirection dir,`
`2799`	`2799`	`{`
`2800`	`2800`	`BTScanOpaque so = (BTScanOpaque) scan->opaque;`
`2801`	`2801`
`2802`		`- Assert(!forcenonrequired \|\| advancenonrequired);`
`2803`		`-`
`2804`	`2802`	`continuescan = true; / default assumption */`
`2805`	`2803`
`2806`	`2804`	`for (; ikey < so->numberOfKeys; (ikey)++)`