Fix RelationBuildPartitionKey's processing of partition key expressions.

Failure to advance the list pointer while reading partition expressions
from a list results in invoking an input function with inappropriate data,
possibly leading to crashes or, with carefully crafted input, disclosure
of arbitrary backend memory.

Bug discovered independently by Álvaro Herrera and David Rowley.
This patch is by Álvaro but owes something to David's proposed fix.
Back-patch to v10 where the issue was introduced.

Security: CVE-2018-1052

src/backend/utils/cache/relcache.c

@@ -983,9 +983,14 @@ RelationBuildPartitionKey(Relation relation)
 		}
 		else
 		{
+			if (partexprs_item == NULL)
+				elog(ERROR, "wrong number of partition key expressions");
+
 			key->parttypid[i] = exprType(lfirst(partexprs_item));
 			key->parttypmod[i] = exprTypmod(lfirst(partexprs_item));
 			key->parttypcoll[i] = exprCollation(lfirst(partexprs_item));
+
+			partexprs_item = lnext(partexprs_item);
 		}
 		get_typlenbyvalalign(key->parttypid[i],
 							 &key->parttyplen[i],

src/test/regress/expected/create_table.out

@@ -419,8 +419,9 @@ DETAIL:  table partitioned depends on function plusone(integer)
 HINT:  Use DROP ... CASCADE to drop the dependent objects too.
 -- partitioned table cannot participate in regular inheritance
 CREATE TABLE partitioned2 (
-	a int
-) PARTITION BY LIST ((a+1));
+	a int,
+	b text
+) PARTITION BY RANGE ((a+1), substr(b, 1, 5));
 CREATE TABLE fail () INHERITS (partitioned2);
 ERROR:  cannot inherit from partitioned table "partitioned2"
 -- Partition key in describe output
@@ -436,13 +437,27 @@ Partition key: RANGE (a oid_ops, plusone(b), c, d COLLATE "C")
 Number of partitions: 0
 
 \d+ partitioned2
-                               Table "public.partitioned2"
- Column |  Type   | Collation | Nullable | Default | Storage | Stats target | Description 
---------+---------+-----------+----------+---------+---------+--------------+-------------
- a      | integer |           |          |         | plain   |              | 
-Partition key: LIST (((a + 1)))
+                                Table "public.partitioned2"
+ Column |  Type   | Collation | Nullable | Default | Storage  | Stats target | Description 
+--------+---------+-----------+----------+---------+----------+--------------+-------------
+ a      | integer |           |          |         | plain    |              | 
+ b      | text    |           |          |         | extended |              | 
+Partition key: RANGE (((a + 1)), substr(b, 1, 5))
 Number of partitions: 0
 
+INSERT INTO partitioned2 VALUES (1, 'hello');
+ERROR:  no partition of relation "partitioned2" found for row
+DETAIL:  Partition key of the failing row contains ((a + 1), substr(b, 1, 5)) = (2, hello).
+CREATE TABLE part2_1 PARTITION OF partitioned2 FOR VALUES FROM (-1, 'aaaaa') TO (100, 'ccccc');
+\d+ part2_1
+                                  Table "public.part2_1"
+ Column |  Type   | Collation | Nullable | Default | Storage  | Stats target | Description 
+--------+---------+-----------+----------+---------+----------+--------------+-------------
+ a      | integer |           |          |         | plain    |              | 
+ b      | text    |           |          |         | extended |              | 
+Partition of: partitioned2 FOR VALUES FROM ('-1', 'aaaaa') TO (100, 'ccccc')
+Partition constraint: (((a + 1) IS NOT NULL) AND (substr(b, 1, 5) IS NOT NULL) AND (((a + 1) > '-1'::integer) OR (((a + 1) = '-1'::integer) AND (substr(b, 1, 5) >= 'aaaaa'::text))) AND (((a + 1) < 100) OR (((a + 1) = 100) AND (substr(b, 1, 5) < 'ccccc'::text))))
+
 DROP TABLE partitioned, partitioned2;
 --
 -- Partitions

src/test/regress/sql/create_table.sql

@@ -419,14 +419,19 @@ DROP FUNCTION plusone(int);
 
 -- partitioned table cannot participate in regular inheritance
 CREATE TABLE partitioned2 (
-	a int
-) PARTITION BY LIST ((a+1));
+	a int,
+	b text
+) PARTITION BY RANGE ((a+1), substr(b, 1, 5));
 CREATE TABLE fail () INHERITS (partitioned2);
 
 -- Partition key in describe output
 \d partitioned
 \d+ partitioned2
 
+INSERT INTO partitioned2 VALUES (1, 'hello');
+CREATE TABLE part2_1 PARTITION OF partitioned2 FOR VALUES FROM (-1, 'aaaaa') TO (100, 'ccccc');
+\d+ part2_1
+
 DROP TABLE partitioned, partitioned2;
 
 --