Avoid reference to nonexistent array element in ExecInitAgg().

When considering an empty grouping set, we fetched
phasedata->eqfunctions[-1].  Because the eqfunctions array is
palloc'd, that would always be an aset pointer in released versions,
and thus the code accidentally failed to malfunction (since it would
do nothing unless it found a null pointer).  Nonetheless this seems
like trouble waiting to happen, so add a check for length == 0.

It's depressing that our valgrind testing did not catch this.
Maybe we should reconsider the choice to not mark that word NOACCESS?

Richard Guo

Discussion: https://postgr.es/m/CAMbWs4-vZuuPOZsKOYnSAaPYGKhmacxhki+vpOKk0O7rymccXQ@mail.gmail.com

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index f2bb5502b2198228b0c8b12251058bb36f10294e..9175f35c6b6988836b1c5c41cd526c59a7fe06c8 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2377,6 +2377,11 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
                                {
                                        int                     length = phasedata->gset_lengths[i];
 
+                                       /* nothing to do for empty grouping set */
+                                       if (length == 0)
+                                               continue;
+
+                                       /* if we already had one of this length, it'll do */
                                        if (phasedata->eqfunctions[length - 1] != NULL)
                                                continue;