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 e230329a45248a60f136335736c024f749ec64d0..5de9235f5ddb79339d2efcee20dcb1eb91cf2425 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -343,6 +343,9 @@ 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 266ee4db5e87c2ca3f26e8a31870733ba8bd8ae9..1d61a0d616fd29dbaba2f59cd4f19c551524a4c3 100644 (file)
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -253,6 +253,9 @@ 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;