Make json{b}_populate_recordset() use the right tuple descriptor.

json{b}_populate_recordset() used the tuple descriptor created from the
query-level AS clause without worrying about whether it matched the actual
input record type.  If it didn't, that would usually result in a crash,
though disclosure of server memory contents seems possible as well, for a
skilled attacker capable of issuing crafted SQL commands.  Instead, use
the query-supplied descriptor only when there is no input tuple to look at,
and otherwise get a tuple descriptor based on the input tuple's own type
marking.  The core code will detect any type mismatch in the latter case.

Michael Paquier and Tom Lane, per a report from David Rowley.
Back-patch to 9.3 where this functionality was introduced.

Security: CVE-2017-15098

src/backend/utils/adt/jsonfuncs.c

@@ -2695,26 +2695,37 @@ populate_recordset_worker(FunctionCallInfo fcinfo, const char *funcname,
 
 	rsi->returnMode = SFRM_Materialize;
 
-	/*
-	 * get the tupdesc from the result set info - it must be a record type
-	 * because we already checked that arg1 is a record type, or we're in a
-	 * to_record function which returns a setof record.
-	 */
-	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("function returning record called in context "
-						"that cannot accept type record")));
-
 	/* if the json is null send back an empty set */
 	if (PG_ARGISNULL(json_arg_num))
 		PG_RETURN_NULL();
 
 	if (!have_record_arg || PG_ARGISNULL(0))
+	{
 		rec = NULL;
+
+		/*
+		 * get the tupdesc from the result set info - it must be a record type
+		 * because we already checked that arg1 is a record type, or we're in
+		 * a to_record function which returns a setof record.
+		 */
+		if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("function returning record called in context "
+							"that cannot accept type record")));
+	}
 	else
+	{
 		rec = PG_GETARG_HEAPTUPLEHEADER(0);
 
+		/*
+		 * use the input record's own type marking to find a tupdesc for it.
+		 */
+		tupType = HeapTupleHeaderGetTypeId(rec);
+		tupTypmod = HeapTupleHeaderGetTypMod(rec);
+		tupdesc = lookup_rowtype_tupdesc(tupType, tupTypmod);
+	}
+
 	tupType = tupdesc->tdtypeid;
 	tupTypmod = tupdesc->tdtypmod;
 	ncolumns = tupdesc->natts;
@@ -2758,6 +2769,9 @@ populate_recordset_worker(FunctionCallInfo fcinfo, const char *funcname,
 											   false, work_mem);
 	MemoryContextSwitchTo(old_cxt);
 
+	/* unnecessary, but harmless, if tupdesc came from get_call_result_type: */
+	ReleaseTupleDesc(tupdesc);
+
 	state->function_name = funcname;
 	state->my_extra = my_extra;
 	state->rec = rec;

src/test/regress/expected/json.out

@@ -1408,6 +1408,19 @@ select * from json_populate_recordset(row('def',99,null)::jpop,'[{"a":[100,200,3
  {"z":true}    |  3 | Fri Jan 20 10:42:53 2012
 (2 rows)
 
+-- negative cases where the wrong record type is supplied
+select * from json_populate_recordset(row(0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned row contains 1 attribute, but query expects 2.
+select * from json_populate_recordset(row(0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned type integer at ordinal position 1, but query expects text.
+select * from json_populate_recordset(row(0::int,0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned row contains 3 attributes, but query expects 2.
+select * from json_populate_recordset(row(1000000000::int,50::int),'[{"b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned type integer at ordinal position 1, but query expects text.
 --json_typeof() function
 select value, json_typeof(value)
   from (values (json '123.4'),

src/test/regress/expected/jsonb.out

@@ -2090,6 +2090,19 @@ SELECT * FROM jsonb_populate_recordset(row('def',99,NULL)::jbpop,'[{"a":[100,200
  {"z": true}     |  3 | Fri Jan 20 10:42:53 2012
 (2 rows)
 
+-- negative cases where the wrong record type is supplied
+select * from jsonb_populate_recordset(row(0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned row contains 1 attribute, but query expects 2.
+select * from jsonb_populate_recordset(row(0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned type integer at ordinal position 1, but query expects text.
+select * from jsonb_populate_recordset(row(0::int,0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned row contains 3 attributes, but query expects 2.
+select * from jsonb_populate_recordset(row(1000000000::int,50::int),'[{"b":"2"},{"a":"3"}]') q (a text, b text);
+ERROR:  function return row and query-specified return row do not match
+DETAIL:  Returned type integer at ordinal position 1, but query expects text.
 -- jsonb_to_record and jsonb_to_recordset
 select * from jsonb_to_record('{"a":1,"b":"foo","c":"bar"}')
     as x(a int, b text, d text);

src/test/regress/sql/json.sql

@@ -404,6 +404,12 @@ select * from json_populate_recordset(null::jpop,'[{"a":"blurfl","x":43.2},{"b":
 select * from json_populate_recordset(row('def',99,null)::jpop,'[{"a":"blurfl","x":43.2},{"b":3,"c":"2012-01-20 10:42:53"}]') q;
 select * from json_populate_recordset(row('def',99,null)::jpop,'[{"a":[100,200,300],"x":43.2},{"a":{"z":true},"b":3,"c":"2012-01-20 10:42:53"}]') q;
 
+-- negative cases where the wrong record type is supplied
+select * from json_populate_recordset(row(0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+select * from json_populate_recordset(row(0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+select * from json_populate_recordset(row(0::int,0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+select * from json_populate_recordset(row(1000000000::int,50::int),'[{"b":"2"},{"a":"3"}]') q (a text, b text);
+
 --json_typeof() function
 select value, json_typeof(value)
   from (values (json '123.4'),

src/test/regress/sql/jsonb.sql

@@ -520,6 +520,12 @@ SELECT * FROM jsonb_populate_recordset(NULL::jbpop,'[{"a":"blurfl","x":43.2},{"b
 SELECT * FROM jsonb_populate_recordset(row('def',99,NULL)::jbpop,'[{"a":"blurfl","x":43.2},{"b":3,"c":"2012-01-20 10:42:53"}]') q;
 SELECT * FROM jsonb_populate_recordset(row('def',99,NULL)::jbpop,'[{"a":[100,200,300],"x":43.2},{"a":{"z":true},"b":3,"c":"2012-01-20 10:42:53"}]') q;
 
+-- negative cases where the wrong record type is supplied
+select * from jsonb_populate_recordset(row(0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+select * from jsonb_populate_recordset(row(0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+select * from jsonb_populate_recordset(row(0::int,0::int,0::int),'[{"a":"1","b":"2"},{"a":"3"}]') q (a text, b text);
+select * from jsonb_populate_recordset(row(1000000000::int,50::int),'[{"b":"2"},{"a":"3"}]') q (a text, b text);
+
 -- jsonb_to_record and jsonb_to_recordset
 
 select * from jsonb_to_record('{"a":1,"b":"foo","c":"bar"}')