Avoid leakage of zero-length arrays in partition_bounds_copy().

If ndatums is zero, the code would allocate zero-length boundKinds
and boundDatums chunks, which would have nothing pointing to them,
leading to Valgrind complaints.  Rearrange the code to avoid the
useless pallocs, and also to not bother computing byval/typlen when
they aren't used.

I'm unsure why I didn't see this in my Valgrind testing back in May.
This code hasn't changed since then, but maybe we added a regression
test that reaches this edge case.  Or possibly I just failed to
notice the reports, which do say "0 bytes lost".

Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/285483.1746756246@sss.pgh.pa.us

diff --git a/src/backend/partitioning/partbounds.c b/src/backend/partitioning/partbounds.c
index 4bdc2941efb21e7bd120365deabfcd27770fd09c..822cf4ec451a4287a55f60e8d2d52b5f1bc64500 100644 (file)
--- a/src/backend/partitioning/partbounds.c
+++ b/src/backend/partitioning/partbounds.c
@@ -1007,9 +1007,6 @@ partition_bounds_copy(PartitionBoundInfo src,
        int                     ndatums;
        int                     nindexes;
        int                     partnatts;
-       bool            hash_part;
-       int                     natts;
-       Datum      *boundDatums;
 
        dest = (PartitionBoundInfo) palloc(sizeof(PartitionBoundInfoData));
 
@@ -1023,7 +1020,7 @@ partition_bounds_copy(PartitionBoundInfo src,
 
        dest->datums = (Datum **) palloc(sizeof(Datum *) * ndatums);
 
-       if (src->kind != NULL)
+       if (src->kind != NULL && ndatums > 0)
        {
                PartitionRangeDatumKind *boundKinds;
 
@@ -1058,36 +1055,40 @@ partition_bounds_copy(PartitionBoundInfo src,
         * For hash partitioning, datums array will have two elements - modulus
         * and remainder.
         */
-       hash_part = (key->strategy == PARTITION_STRATEGY_HASH);
-       natts = hash_part ? 2 : partnatts;
-       boundDatums = palloc(ndatums * natts * sizeof(Datum));
-
-       for (i = 0; i < ndatums; i++)
+       if (ndatums > 0)
        {
-               int                     j;
-
-               dest->datums[i] = &boundDatums[i * natts];
+               bool            hash_part = (key->strategy == PARTITION_STRATEGY_HASH);
+               int                     natts = hash_part ? 2 : partnatts;
+               Datum      *boundDatums = palloc(ndatums * natts * sizeof(Datum));
 
-               for (j = 0; j < natts; j++)
+               for (i = 0; i < ndatums; i++)
                {
-                       bool            byval;
-                       int                     typlen;
+                       int                     j;
 
-                       if (hash_part)
-                       {
-                               typlen = sizeof(int32); /* Always int4 */
-                               byval = true;   /* int4 is pass-by-value */
-                       }
-                       else
+                       dest->datums[i] = &boundDatums[i * natts];
+
+                       for (j = 0; j < natts; j++)
                        {
-                               byval = key->parttypbyval[j];
-                               typlen = key->parttyplen[j];
-                       }
+                               if (dest->kind == NULL ||
+                                       dest->kind[i][j] == PARTITION_RANGE_DATUM_VALUE)
+                               {
+                                       bool            byval;
+                                       int                     typlen;
 
-                       if (dest->kind == NULL ||
-                               dest->kind[i][j] == PARTITION_RANGE_DATUM_VALUE)
-                               dest->datums[i][j] = datumCopy(src->datums[i][j],
-                                                                                          byval, typlen);
+                                       if (hash_part)
+                                       {
+                                               typlen = sizeof(int32); /* Always int4 */
+                                               byval = true;   /* int4 is pass-by-value */
+                                       }
+                                       else
+                                       {
+                                               byval = key->parttypbyval[j];
+                                               typlen = key->parttyplen[j];
+                                       }
+                                       dest->datums[i][j] = datumCopy(src->datums[i][j],
+                                                                                                  byval, typlen);
+                               }
+                       }
                }
        }