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[email protected]

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index addb030b6b501631f898e1d25fb9dcf4a01a9ab3..46c29ed81ea50f14aab036d79ba11f0e7519a027 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -222,6 +222,9 @@ create_plan_recurse(PlannerInfo *root, Path *best_path)
 {
    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 0b9842baefcbea98611d1d8d69bc3836155f3dc6..0741a41181d9f4ab229f353b996eced0d574f7b1 100644 (file)
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -220,6 +220,9 @@ recurse_set_operations(Node *setOp, PlannerInfo *root,
                       int flag, List *refnames_tlist,
                       List **sortClauses, double *pNumGroups)
 {
+   /* Guard against stack overflow due to overly complex setop nests */
+   check_stack_depth();
+
    if (IsA(setOp, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) setOp;