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 3bc78331e45b5c6bbf41a08c3986d97fdac29c8d..9c5d6e66a2e3dad1595ed83f8e0dd0f3bf676435 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -3570,6 +3570,11 @@ 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;