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

1 files changed, 25 insertions, 11 deletions

diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index 18e7b9c8798..3a36a83b3c6 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -2607,26 +2607,37 @@ 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;
@@ -2670,6 +2681,9 @@ 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;