postgres.git / summary / log / commit / refs

commit    ba80489c66cf721da04dc5b230b3592f97f6be4c
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Jan 18 23:32:30 2021 +0000
First released in: 14.0, 9.5.25, 9.6.21, 10.16, 11.11, 12.6, 13.2

    Avoid crash with WHERE CURRENT OF and a custom scan plan.
    
    execCurrent.c's search_plan_tree() assumed that ForeignScanStates
    and CustomScanStates necessarily have a valid ss_currentRelation.
    This is demonstrably untrue for postgres_fdw's remote join and
    remote aggregation plans, and non-leaf custom scans might not have
    an identifiable scan relation either.  Avoid crashing by ignoring
    such nodes when the field is null.
    
    This solution will lead to errors like 'cursor "foo" is not a
    simply updatable scan of table "bar"' in cases where maybe we
    could have allowed WHERE CURRENT OF to work.  That's not an issue
    for postgres_fdw's usages, since joins or aggregations would render
    WHERE CURRENT OF invalid anyway.  But an otherwise-transparent
    upper level custom scan node might find this annoying.  When and if
    someone cares to expend work on such a scenario, we could invent a
    custom-scan-provider callback to determine what's safe.
    
    Report and patch by David Geier, commentary by me.  It's been like
    this for awhile, so back-patch to all supported branches.
    
    Discussion: https://postgr.es/m/0253344d-9bdd-11c4-7f0d-d88c02cd7991@swarm64.com


 src/backend/executor/execCurrent.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/backend/executor/execCurrent.c b/src/backend/executor/execCurrent.c
index c7f909241b4..bf2c660a778 100644
--- a/src/backend/executor/execCurrent.c
+++ b/src/backend/executor/execCurrent.c
@@ -317,7 +317,12 @@ search_plan_tree(PlanState *node, Oid table_oid,
 	switch (nodeTag(node))
 	{
 			/*
-			 * Relation scan nodes can all be treated alike
+			 * Relation scan nodes can all be treated alike.  Note that
+			 * ForeignScan and CustomScan might not have a currentRelation, in
+			 * which case we just ignore them.  (We dare not descend to any
+			 * child plan nodes they might have, since we do not know the
+			 * relationship of such a node's current output tuple to the
+			 * children's current outputs.)
 			 */
 		case T_SeqScanState:
 		case T_SampleScanState:
@@ -330,7 +335,8 @@ search_plan_tree(PlanState *node, Oid table_oid,
 			{
 				ScanState  *sstate = (ScanState *) node;
 
-				if (RelationGetRelid(sstate->ss_currentRelation) == table_oid)
+				if (sstate->ss_currentRelation &&
+					RelationGetRelid(sstate->ss_currentRelation) == table_oid)
 					result = sstate;
 				break;
 			}


[parent: a0d31b1c9414]