Add stack-overflow guards in set-operation planning.

create_plan_recurse lacked any stack depth check.  This is not per
our normal coding rules, but I'd supposed it was safe because earlier
planner processing is more complex and presumably should eat more
stack.  But bug #15033 from Andrew Grossman shows this isn't true,
at least not for queries having the form of a many-thousand-way
INTERSECT stack.

Further testing showed that recurse_set_operations is also capable
of being crashed in this way, since it likewise will recurse to the
bottom of a parsetree before calling any support functions that
might themselves contain any stack checks.  However, its stack
consumption is only perhaps a third of create_plan_recurse's.

It's possible that this particular problem with create_plan_recurse can
only manifest in 9.6 and later, since before that we didn't build a Path
tree for set operations.  But having seen this example, I now have no
faith in the proposition that create_plan_recurse doesn't need a stack
check, so back-patch to all supported branches.

Discussion: https://postgr.es/m/20180127050845.28812.58244@wrigleys.postgresql.org

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 78a1503b9f99961f8687ad2e0920b3fc7b0459f2..a786490d1e2cb3ec54bb69bd634f50ec322315a6 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -355,6 +355,9 @@ create_plan_recurse(PlannerInfo *root, Path *best_path, int flags)
 {
        Plan       *plan;
 
+       /* Guard against stack overflow due to overly complex plans */
+       check_stack_depth();
+
        switch (best_path->pathtype)
        {
                case T_SeqScan:

diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 1d9b1a4c9c7139c5e5556aa5437bbfaa8a6be84d..d83608eab414e6e2fd8fe969878eea512b73d7a5 100644 (file)
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -252,6 +252,9 @@ recurse_set_operations(Node *setOp, PlannerInfo *root,
                                           List **pTargetList,
                                           double *pNumGroups)
 {
+       /* Guard against stack overflow due to overly complex setop nests */
+       check_stack_depth();
+
        if (IsA(setOp, RangeTblRef))
        {
                RangeTblRef *rtr = (RangeTblRef *) setOp;