Fix mishandling of resjunk columns in ON CONFLICT ... UPDATE tlists.

It's unusual to have any resjunk columns in an ON CONFLICT ... UPDATE
list, but it can happen when MULTIEXPR_SUBLINK SubPlans are present.
If it happens, the ON CONFLICT UPDATE code path would end up storing
tuples that include the values of the extra resjunk columns.  That's
fairly harmless in the short run, but if new columns are added to
the table then the values would become accessible, possibly leading
to malfunctions if they don't match the datatypes of the new columns.

This had escaped notice through a confluence of missing sanity checks,
including

* There's no cross-check that a tuple presented to heap_insert or
heap_update matches the table rowtype.  While it's difficult to
check that fully at reasonable cost, we can easily add assertions
that there aren't too many columns.

* The output-column-assignment cases in execExprInterp.c lacked
any sanity checks on the output column numbers, which seems like
an oversight considering there are plenty of assertion checks on
input column numbers.  Add assertions there too.

* We failed to apply nodeModifyTable's ExecCheckPlanOutput() to
the ON CONFLICT UPDATE tlist.  That wouldn't have caught this
specific error, since that function is chartered to ignore resjunk
columns; but it sure seems like a bad omission now that we've seen
this bug.

In HEAD, the right way to fix this is to make the processing of
ON CONFLICT UPDATE tlists work the same as regular UPDATE tlists
now do, that is don't add "SET x = x" entries, and use
ExecBuildUpdateProjection to evaluate the tlist and combine it with
old values of the not-set columns.  This adds a little complication
to ExecBuildUpdateProjection, but allows removal of a comparable
amount of now-dead code from the planner.

In the back branches, the most expedient solution seems to be to
(a) use an output slot for the ON CONFLICT UPDATE projection that
actually matches the target table, and then (b) invent a variant of
ExecBuildProjectionInfo that can be told to not store values resulting
from resjunk columns, so it doesn't try to store into nonexistent
columns of the output slot.  (We can't simply ignore the resjunk columns
altogether; they have to be evaluated for MULTIEXPR_SUBLINK to work.)
This works back to v10.  In 9.6, projections work much differently and
we can't cheaply give them such an option.  The 9.6 version of this
patch works by inserting a JunkFilter when it's necessary to get rid
of resjunk columns.

In addition, v11 and up have the reverse problem when trying to
perform ON CONFLICT UPDATE on a partitioned table.  Through a
further oversight, adjust_partition_tlist() discarded resjunk columns
when re-ordering the ON CONFLICT UPDATE tlist to match a partition.
This accidentally prevented the storing-bogus-tuples problem, but
at the cost that MULTIEXPR_SUBLINK cases didn't work, typically
crashing if more than one row has to be updated.  Fix by preserving
resjunk columns in that routine.  (I failed to resist the temptation
to add more assertions there too, and to do some minor code
beautification.)

Per report from Andres Freund.  Back-patch to all supported branches.

Security: CVE-2021-32028

2 files changed, 63 insertions, 9 deletions

diff --git a/src/test/regress/expected/update.out b/src/test/regress/expected/update.out
index bbf6705b656..c809f88f546 100644
--- a/src/test/regress/expected/update.out
+++ b/src/test/regress/expected/update.out
@@ -199,7 +199,7 @@ SELECT a, b, char_length(c) FROM update_test;
 (4 rows)
 
 -- Test ON CONFLICT DO UPDATE
-INSERT INTO upsert_test VALUES(1, 'Boo');
+INSERT INTO upsert_test VALUES(1, 'Boo'), (3, 'Zoo');
 -- uncorrelated  sub-select:
 WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
   VALUES (1, 'Bar') ON CONFLICT(a)
@@ -210,22 +210,24 @@ WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
 (1 row)
 
 -- correlated sub-select:
-INSERT INTO upsert_test VALUES (1, 'Baz') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Baz'), (3, 'Zaz') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Correlated', a from upsert_test i WHERE i.a = upsert_test.a)
   RETURNING *;
  a |        b        
 ---+-----------------
  1 | Foo, Correlated
-(1 row)
+ 3 | Zoo, Correlated
+(2 rows)
 
 -- correlated sub-select (EXCLUDED.* alias):
-INSERT INTO upsert_test VALUES (1, 'Bat') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Bat'), (3, 'Zot') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Excluded', a from upsert_test i WHERE i.a = excluded.a)
   RETURNING *;
  a |             b             
 ---+---------------------------
  1 | Foo, Correlated, Excluded
-(1 row)
+ 3 | Zoo, Correlated, Excluded
+(2 rows)
 
 -- ON CONFLICT using system attributes in RETURNING, testing both the
 -- inserting and updating paths. See bug report at:
@@ -250,6 +252,35 @@ INSERT INTO upsert_test VALUES (2, 'Brox') ON CONFLICT(a)
 
 DROP TABLE update_test;
 DROP TABLE upsert_test;
+-- Test ON CONFLICT DO UPDATE with partitioned table and non-identical children
+CREATE TABLE upsert_test (
+    a   INT PRIMARY KEY,
+    b   TEXT
+) PARTITION BY LIST (a);
+CREATE TABLE upsert_test_1 PARTITION OF upsert_test FOR VALUES IN (1);
+CREATE TABLE upsert_test_2 (b TEXT, a INT PRIMARY KEY);
+ALTER TABLE upsert_test ATTACH PARTITION upsert_test_2 FOR VALUES IN (2);
+INSERT INTO upsert_test VALUES(1, 'Boo'), (2, 'Zoo');
+-- uncorrelated sub-select:
+WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
+  VALUES (1, 'Bar') ON CONFLICT(a)
+  DO UPDATE SET (b, a) = (SELECT b, a FROM aaa) RETURNING *;
+ a |  b  
+---+-----
+ 1 | Foo
+(1 row)
+
+-- correlated sub-select:
+WITH aaa AS (SELECT 1 AS ctea, ' Foo' AS cteb) INSERT INTO upsert_test
+  VALUES (1, 'Bar'), (2, 'Baz') ON CONFLICT(a)
+  DO UPDATE SET (b, a) = (SELECT upsert_test.b||cteb, upsert_test.a FROM aaa) RETURNING *;
+ a |    b    
+---+---------
+ 1 | Foo Foo
+ 2 | Zoo Foo
+(2 rows)
+
+DROP TABLE upsert_test;
 ---------------------------
 -- UPDATE with row movement
 ---------------------------
diff --git a/src/test/regress/sql/update.sql b/src/test/regress/sql/update.sql
index d0bc8e9228b..7a7bee77b92 100644
--- a/src/test/regress/sql/update.sql
+++ b/src/test/regress/sql/update.sql
@@ -100,17 +100,18 @@ UPDATE update_test t
 SELECT a, b, char_length(c) FROM update_test;
 
 -- Test ON CONFLICT DO UPDATE
-INSERT INTO upsert_test VALUES(1, 'Boo');
+
+INSERT INTO upsert_test VALUES(1, 'Boo'), (3, 'Zoo');
 -- uncorrelated  sub-select:
 WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
   VALUES (1, 'Bar') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b, a FROM aaa) RETURNING *;
 -- correlated sub-select:
-INSERT INTO upsert_test VALUES (1, 'Baz') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Baz'), (3, 'Zaz') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Correlated', a from upsert_test i WHERE i.a = upsert_test.a)
   RETURNING *;
 -- correlated sub-select (EXCLUDED.* alias):
-INSERT INTO upsert_test VALUES (1, 'Bat') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Bat'), (3, 'Zot') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Excluded', a from upsert_test i WHERE i.a = excluded.a)
   RETURNING *;
 
@@ -126,10 +127,32 @@ INSERT INTO upsert_test VALUES (2, 'Brox') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Excluded', a from upsert_test i WHERE i.a = excluded.a)
   RETURNING tableoid::regclass, xmin = pg_current_xact_id()::xid AS xmin_correct, xmax = pg_current_xact_id()::xid AS xmax_correct;
 
-
 DROP TABLE update_test;
 DROP TABLE upsert_test;
 
+-- Test ON CONFLICT DO UPDATE with partitioned table and non-identical children
+
+CREATE TABLE upsert_test (
+    a   INT PRIMARY KEY,
+    b   TEXT
+) PARTITION BY LIST (a);
+
+CREATE TABLE upsert_test_1 PARTITION OF upsert_test FOR VALUES IN (1);
+CREATE TABLE upsert_test_2 (b TEXT, a INT PRIMARY KEY);
+ALTER TABLE upsert_test ATTACH PARTITION upsert_test_2 FOR VALUES IN (2);
+
+INSERT INTO upsert_test VALUES(1, 'Boo'), (2, 'Zoo');
+-- uncorrelated sub-select:
+WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
+  VALUES (1, 'Bar') ON CONFLICT(a)
+  DO UPDATE SET (b, a) = (SELECT b, a FROM aaa) RETURNING *;
+-- correlated sub-select:
+WITH aaa AS (SELECT 1 AS ctea, ' Foo' AS cteb) INSERT INTO upsert_test
+  VALUES (1, 'Bar'), (2, 'Baz') ON CONFLICT(a)
+  DO UPDATE SET (b, a) = (SELECT upsert_test.b||cteb, upsert_test.a FROM aaa) RETURNING *;
+
+DROP TABLE upsert_test;
+
 
 ---------------------------
 -- UPDATE with row movement