[2.6] MOD-6599: Remove double free in IntersectIterator_Free() (#4543)

* Avoid double free of bestIt

* Revert "Avoid double free of bestIt"

This reverts commit b0988be.

* Avoid double free of bestIt, without line ending changes.

src/index.c

@@ -1,9 +1,9 @@
-/*
- * Copyright Redis Ltd. 2016 - present
- * Licensed under your choice of the Redis Source Available License 2.0 (RSALv2) or
- * the Server Side Public License v1 (SSPLv1).
- */
-
+/*
+ * Copyright Redis Ltd. 2016 - present
+ * Licensed under your choice of the Redis Source Available License 2.0 (RSALv2) or
+ * the Server Side Public License v1 (SSPLv1).
+ */
+
 #include "forward_index.h"
 #include "index.h"
 #include "varint.h"
@@ -652,6 +652,9 @@ void IntersectIterator_Free(IndexIterator *it) {
   IntersectIterator *ui = it->ctx;
   for (int i = 0; i < ui->num; i++) {
     if (ui->its[i] != NULL) {
+      if(ui->its[i] == ui->bestIt) {
+        ui->bestIt = NULL;
+      }
       ui->its[i]->Free(ui->its[i]);
     }
     // IndexResult_Free(&ui->currentHits[i]);

tests/pytests/test_issues.py

@@ -5,6 +5,7 @@
 
 from common import *
 from RLTest import Env
+from random import randint
 
 def test_1282(env):
   conn = getConnectionByEnv(env)
@@ -1018,3 +1019,21 @@ def expect_error(cmd):
   # Test Lua
   for cmd in cmds:
     env.expect('EVAL', f'return redis.call{cmd}', '0').error().contains(expect_error(cmd))
+
+def test_mod_6599_query(env):
+    docs = 1000
+    for i in range(docs):
+        key = "{doc}:" + str(i)
+        numstr = '' . join([str(randint(0,9)) for _ in range(11)])
+        env.cmd("HSET", key, "id", "docum" + numstr, "gender", i%2)
+
+    env.cmd('FT.CREATE idx ON HASH SCHEMA id TEXT gender NUMERIC')
+    waitForIndex(env, 'idx')
+
+    # Test that the query is not crashing if run multiple times
+    for i in range(12):
+        res = env.cmd("FT.SEARCH", "idx",
+                      "(@id: ~doc* ) | (@id: ~docum*)",
+                      "LIMIT", "0", "50", "NOCONTENT",
+                      "FILTER", "gender", "1", "1")
+        env.assertEqual(res[0], docs/2)