Fix phpGH-11028 (Heap Buffer Overflow in zval_undefined_cv.)

For analysis see php#11028 (comment)

Author: ndossche

Zend/tests/generators/gh11028_1.phpt

@@ -0,0 +1,35 @@
+--TEST--
+GH-11028 (Heap Buffer Overflow in zval_undefined_cv with generators) - other types variant
+--FILE--
+<?php
+function generator($x) {
+    try {
+        yield $x => 0;
+    } finally {
+        return [];
+    }
+}
+
+function test($msg, $x) {
+    echo "yield $msg\n";
+    try {
+        var_dump([...generator($x)]);
+    } catch (Throwable $e) {
+        echo $e->getMessage(), "\n";
+    }
+}
+
+test("null", null);
+test("false", false);
+test("true", true);
+test("object", new stdClass);
+?>
+--EXPECT--
+yield null
+Keys must be of type int|string during array unpacking
+yield false
+Keys must be of type int|string during array unpacking
+yield true
+Keys must be of type int|string during array unpacking
+yield object
+Keys must be of type int|string during array unpacking

Zend/tests/generators/gh11028_2.phpt

@@ -0,0 +1,24 @@
+--TEST--
+GH-11028 (Heap Buffer Overflow in zval_undefined_cv with generators) - original variant
+--FILE--
+<?php
+$c = (function () {
+    [
+        ...($r = (function () {
+            try {
+                yield $a => 0;
+            } finally {
+                return [];
+            }
+        })()),
+    ];
+})()[0];
+?>
+--EXPECTF--
+Warning: Undefined variable $a in %s on line %d
+
+Fatal error: Uncaught Error: Keys must be of type int|string during array unpacking in %s:%d
+Stack trace:
+#0 %s(%d): {closure}()
+#1 {main}
+  thrown in %s on line %d

Zend/tests/generators/gh11028_3.phpt

@@ -0,0 +1,21 @@
+--TEST--
+GH-11028 (Heap Buffer Overflow in zval_undefined_cv with generators) - throw in finally variant
+--FILE--
+<?php
+function generator() {
+    try {
+        yield null => 0;
+    } finally {
+        throw new Exception("exception");
+        return [];
+    }
+}
+
+try {
+    var_dump([...generator()]);
+} catch (Throwable $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+exception

Zend/zend_generators.c

@@ -279,14 +279,25 @@ static void zend_generator_dtor_storage(zend_object *object) /* {{{ */
 				ZEND_CALL_VAR(ex, ex->func->op_array.opcodes[try_catch->finally_end].op1.var);
 
 			zend_generator_cleanup_unfinished_execution(generator, ex, try_catch->finally_op);
-			Z_OBJ_P(fast_call) = EG(exception);
+			zend_object *old_exception = EG(exception);
+			const zend_op *old_opline_before_exception = EG(opline_before_exception);
 			EG(exception) = NULL;
+			Z_OBJ_P(fast_call) = NULL;
 			Z_OPLINE_NUM_P(fast_call) = (uint32_t)-1;
 
 			ex->opline = &ex->func->op_array.opcodes[try_catch->finally_op];
 			generator->flags |= ZEND_GENERATOR_FORCED_CLOSE;
 			zend_generator_resume(generator);
 
+			if (old_exception) {
+				EG(opline_before_exception) = old_opline_before_exception;
+				if (EG(exception)) {
+					zend_exception_set_previous(EG(exception), old_exception);
+				} else {
+					EG(exception) = old_exception;
+				}
+			}
+
 			/* TODO: If we hit another yield inside try/finally,
 			 * should we also jump to the next finally block? */
 			break;