Fix use after free when WeakMap is modified during field write

(When a value's destructor triggers a resizing or rehashing of the WeakMap)

Closes GH-7671

Zend/tests/weakrefs/weakrefs_006.phpt

@@ -0,0 +1,116 @@
+--TEST--
+WeakReference overwriting existing value
+--FILE--
+<?php
+
+class HasDtor {
+    public function __destruct() {
+        echo "In destruct\n";
+        global $w, $all;
+        for ($i = 0; $i < 10; $i++) {
+            $v = new stdClass();
+            $all[] = $v;
+            $w[$v] = $i;
+        }
+    }
+}
+$all = [];
+$w = new WeakMap();
+$o = new stdClass();
+
+$w[$o] = new HasDtor();
+$w[$o] = 123;
+var_dump($w);
+?>
+--EXPECT--
+In destruct
+object(WeakMap)#1 (11) {
+  [0]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#2 (0) {
+    }
+    ["value"]=>
+    int(123)
+  }
+  [1]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#4 (0) {
+    }
+    ["value"]=>
+    int(0)
+  }
+  [2]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#5 (0) {
+    }
+    ["value"]=>
+    int(1)
+  }
+  [3]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#6 (0) {
+    }
+    ["value"]=>
+    int(2)
+  }
+  [4]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#7 (0) {
+    }
+    ["value"]=>
+    int(3)
+  }
+  [5]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#8 (0) {
+    }
+    ["value"]=>
+    int(4)
+  }
+  [6]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#9 (0) {
+    }
+    ["value"]=>
+    int(5)
+  }
+  [7]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#10 (0) {
+    }
+    ["value"]=>
+    int(6)
+  }
+  [8]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#11 (0) {
+    }
+    ["value"]=>
+    int(7)
+  }
+  [9]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#12 (0) {
+    }
+    ["value"]=>
+    int(8)
+  }
+  [10]=>
+  array(2) {
+    ["key"]=>
+    object(stdClass)#13 (0) {
+    }
+    ["value"]=>
+    int(9)
+  }
+}

Zend/zend_weakrefs.c

@@ -351,8 +351,12 @@ static void zend_weakmap_write_dimension(zend_object *object, zval *offset, zval
 
 	zval *zv = zend_hash_index_find(&wm->ht, (zend_ulong) obj_key);
 	if (zv) {
-		zval_ptr_dtor(zv);
+		/* Because the destructors can have side effects such as resizing or rehashing the WeakMap storage,
+		 * free the zval only after overwriting the original value. */
+		zval zv_orig;
+		ZVAL_COPY_VALUE(&zv_orig, zv);
 		ZVAL_COPY_VALUE(zv, value);
+		zval_ptr_dtor(&zv_orig);
 		return;
 	}