Repair misbehavior with duplicate entries in FK SET column lists.

Since v15 we've had an option to apply a foreign key constraint's
ON DELETE SET DEFAULT or SET NULL action to just some of the
referencing columns.  There was not a check for duplicate entries in
the list of columns-to-set, though.  That caused a potential memory
stomp in CreateConstraintEntry(), which incautiously assumed that
the list of columns-to-set couldn't be longer than the number of key
columns.  Even after fixing that, the case doesn't work because you
get an error like "multiple assignments to same column" from the SQL
command that is generated to do the update.

We could either raise an error for duplicate columns or silently
suppress the dups, and after a bit of thought I chose to do the
latter.  This is motivated by the fact that duplicates in the FK
column list are legal, so it's not real clear why duplicates
in the columns-to-set list shouldn't be.  Of course there's no
need to actually set the column more than once.

I left in the fix in CreateConstraintEntry() too, just because
it didn't seem like such low-level code ought to be making
assumptions about what it's handed.

Bug: #18879
Reported-by: Yu Liang <[email protected]>
Author: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/18879-259fc59d072bd4d7@postgresql.org
Backpatch-through: 15

diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index 4002317f7050244833c1110f12bba6b6435bee65..59565b9d88107cfc69ebbe263c43375d30df410b 100644 (file)
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -120,8 +120,9 @@ CreateConstraintEntry(const char *constraintName,
    if (foreignNKeys > 0)
    {
        Datum      *fkdatums;
+       int         nkeys = Max(foreignNKeys, numFkDeleteSetCols);
 
-       fkdatums = (Datum *) palloc(foreignNKeys * sizeof(Datum));
+       fkdatums = (Datum *) palloc(nkeys * sizeof(Datum));
        for (i = 0; i < foreignNKeys; i++)
            fkdatums[i] = Int16GetDatum(foreignKey[i]);
        confkeyArray = construct_array_builtin(fkdatums, foreignNKeys, INT2OID);

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 40fe7685239492129d82bd272ec10b75079df741..b4c0a61587347f8c4bb6712bd62ec2bfdf0fe074 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -498,8 +498,8 @@ static ObjectAddress ATAddForeignKeyConstraint(List **wqueue, AlteredTableInfo *
                                               Relation rel, Constraint *fkconstraint,
                                               bool recurse, bool recursing,
                                               LOCKMODE lockmode);
-static void validateFkOnDeleteSetColumns(int numfks, const int16 *fkattnums,
-                                        int numfksetcols, const int16 *fksetcolsattnums,
+static int validateFkOnDeleteSetColumns(int numfks, const int16 *fkattnums,
+                                        int numfksetcols, int16 *fksetcolsattnums,
                                         List *fksetcols);
 static ObjectAddress addFkConstraint(addFkConstraintSides fkside,
                                     char *constraintname,
@@ -9340,9 +9340,10 @@ ATAddForeignKeyConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
    numfkdelsetcols = transformColumnNameList(RelationGetRelid(rel),
                                              fkconstraint->fk_del_set_cols,
                                              fkdelsetcols, NULL);
-   validateFkOnDeleteSetColumns(numfks, fkattnum,
-                                numfkdelsetcols, fkdelsetcols,
-                                fkconstraint->fk_del_set_cols);
+   numfkdelsetcols = validateFkOnDeleteSetColumns(numfks, fkattnum,
+                                                  numfkdelsetcols,
+                                                  fkdelsetcols,
+                                                  fkconstraint->fk_del_set_cols);
 
    /*
     * If the attribute list for the referenced table was omitted, lookup the
@@ -9663,17 +9664,23 @@ ATAddForeignKeyConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
  * validateFkOnDeleteSetColumns
  *     Verifies that columns used in ON DELETE SET NULL/DEFAULT (...)
  *     column lists are valid.
+ *
+ * If there are duplicates in the fksetcolsattnums[] array, this silently
+ * removes the dups.  The new count of numfksetcols is returned.
  */
-void
+static int
 validateFkOnDeleteSetColumns(int numfks, const int16 *fkattnums,
-                            int numfksetcols, const int16 *fksetcolsattnums,
+                            int numfksetcols, int16 *fksetcolsattnums,
                             List *fksetcols)
 {
+   int         numcolsout = 0;
+
    for (int i = 0; i < numfksetcols; i++)
    {
        int16       setcol_attnum = fksetcolsattnums[i];
        bool        seen = false;
 
+       /* Make sure it's in fkattnums[] */
        for (int j = 0; j < numfks; j++)
        {
            if (fkattnums[j] == setcol_attnum)
@@ -9691,7 +9698,21 @@ validateFkOnDeleteSetColumns(int numfks, const int16 *fkattnums,
                    (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                     errmsg("column \"%s\" referenced in ON DELETE SET action must be part of foreign key", col)));
        }
+
+       /* Now check for dups */
+       seen = false;
+       for (int j = 0; j < numcolsout; j++)
+       {
+           if (fksetcolsattnums[j] == setcol_attnum)
+           {
+               seen = true;
+               break;
+           }
+       }
+       if (!seen)
+           fksetcolsattnums[numcolsout++] = setcol_attnum;
    }
+   return numcolsout;
 }
 
 /*

diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index 9f3cd3e1d32a972f7ee1c3f288a76d35ff09e4a9..19398fe2b4a327ddeb21e3499e3a67bf4a192518 100644 (file)
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -772,7 +772,8 @@ CREATE TABLE FKTABLE (
   fk_id_del_set_null int,
   fk_id_del_set_default int DEFAULT 0,
   FOREIGN KEY (tid, fk_id_del_set_null) REFERENCES PKTABLE ON DELETE SET NULL (fk_id_del_set_null),
-  FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES PKTABLE ON DELETE SET DEFAULT (fk_id_del_set_default)
+  -- this tests handling of duplicate entries in SET DEFAULT column list
+  FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES PKTABLE ON DELETE SET DEFAULT (fk_id_del_set_default, fk_id_del_set_default)
 );
 SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conrelid = 'fktable'::regclass::oid ORDER BY oid;
                                                 pg_get_constraintdef                                                

diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index 3078f7d45c2a02359b47bfe18ceaad20a113b121..1b0c04aa8fe2660ed70862bd08af0d871d8c33cd 100644 (file)
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -473,7 +473,8 @@ CREATE TABLE FKTABLE (
   fk_id_del_set_null int,
   fk_id_del_set_default int DEFAULT 0,
   FOREIGN KEY (tid, fk_id_del_set_null) REFERENCES PKTABLE ON DELETE SET NULL (fk_id_del_set_null),
-  FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES PKTABLE ON DELETE SET DEFAULT (fk_id_del_set_default)
+  -- this tests handling of duplicate entries in SET DEFAULT column list
+  FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES PKTABLE ON DELETE SET DEFAULT (fk_id_del_set_default, fk_id_del_set_default)
 );
 
 SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conrelid = 'fktable'::regclass::oid ORDER BY oid;