Fix bug #76047

Unlink the current stack frame before freeing CVs or extra args.
This means it will no longer show up in back traces that are
generated during CV destruction.

We already did this prior to destructing the object/closure,
presumably for the same reason.

5 files changed, 81 insertions, 12 deletions

diff --git a/NEWS b/NEWS
index b5ac3d6878..be9592d193 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,8 @@ PHP                                                                        NEWS
     supported). (Nikita)
   . Fixed bug ##79146 (cscript can fail to run on some systems). (clarodeus)
   . Fixed bug #78323 (Code 0 is returned on invalid options). (Ivan Mikheykin)
+  . Fixed bug #76047 (Use-after-free when accessing already destructed
+    backtrace arguments). (Nikita)
 
 - CURL:
   . Fixed bug #79078 (Hypothetical use-after-free in curl_multi_add_handle()).
diff --git a/Zend/tests/bug52361.phpt b/Zend/tests/bug52361.phpt
index 74ed8a8d17..5ffe569e4a 100644
--- a/Zend/tests/bug52361.phpt
+++ b/Zend/tests/bug52361.phpt
@@ -25,9 +25,8 @@ try {
 --EXPECTF--
 1. Exception: aaa in %sbug52361.php:5
 Stack trace:
-#0 %sbug52361.php(13): aaa->__destruct()
-#1 %sbug52361.php(16): bbb()
-#2 {main}
+#0 %sbug52361.php(16): aaa->__destruct()
+#1 {main}
 2. Exception: bbb in %sbug52361.php:13
 Stack trace:
 #0 %sbug52361.php(16): bbb()
diff --git a/Zend/tests/bug76047.phpt b/Zend/tests/bug76047.phpt
new file mode 100644
index 0000000000..f0f743ee3d
--- /dev/null
+++ b/Zend/tests/bug76047.phpt
@@ -0,0 +1,68 @@
+--TEST--
+Bug #76047: Use-after-free when accessing already destructed backtrace arguments
+--FILE--
+<?php
+
+class Vuln {
+    public $a;
+    public function __destruct() {
+        unset($this->a);
+        $backtrace = (new Exception)->getTrace();
+        var_dump($backtrace);
+    }
+}
+
+function test($arg) {
+    $arg = str_shuffle(str_repeat('A', 79));
+    $vuln = new Vuln();
+    $vuln->a = $arg;
+}
+
+function test2($arg) {
+    $$arg = 1; // Trigger symbol table
+    $arg = str_shuffle(str_repeat('A', 79));
+    $vuln = new Vuln();
+    $vuln->a = $arg;
+}
+
+test('x');
+test2('x');
+
+?>
+--EXPECTF--
+array(1) {
+  [0]=>
+  array(6) {
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(%d)
+    ["function"]=>
+    string(10) "__destruct"
+    ["class"]=>
+    string(4) "Vuln"
+    ["type"]=>
+    string(2) "->"
+    ["args"]=>
+    array(0) {
+    }
+  }
+}
+array(1) {
+  [0]=>
+  array(6) {
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(%d)
+    ["function"]=>
+    string(10) "__destruct"
+    ["class"]=>
+    string(4) "Vuln"
+    ["type"]=>
+    string(2) "->"
+    ["args"]=>
+    array(0) {
+    }
+  }
+}
diff --git a/Zend/zend_vm_def.h b/Zend/zend_vm_def.h
index 62a9ad8bed..fbd79019e7 100644
--- a/Zend/zend_vm_def.h
+++ b/Zend/zend_vm_def.h
@@ -2398,9 +2398,9 @@ ZEND_VM_HOT_HELPER(zend_leave_helper, ANY, ANY)
 	uint32_t call_info = EX_CALL_INFO();
 
 	if (EXPECTED((call_info & (ZEND_CALL_CODE|ZEND_CALL_TOP|ZEND_CALL_HAS_SYMBOL_TABLE|ZEND_CALL_FREE_EXTRA_ARGS|ZEND_CALL_ALLOCATED)) == 0)) {
+		EG(current_execute_data) = EX(prev_execute_data);
 		i_free_compiled_variables(execute_data);
 
-		EG(current_execute_data) = EX(prev_execute_data);
 		if (UNEXPECTED(call_info & ZEND_CALL_RELEASE_THIS)) {
 			zend_object *object = Z_OBJ(execute_data->This);
 #if 0
@@ -2426,12 +2426,12 @@ ZEND_VM_HOT_HELPER(zend_leave_helper, ANY, ANY)
 		LOAD_NEXT_OPLINE();
 		ZEND_VM_LEAVE();
 	} else if (EXPECTED((call_info & (ZEND_CALL_CODE|ZEND_CALL_TOP)) == 0)) {
+		EG(current_execute_data) = EX(prev_execute_data);
 		i_free_compiled_variables(execute_data);
 
 		if (UNEXPECTED(call_info & ZEND_CALL_HAS_SYMBOL_TABLE)) {
 			zend_clean_and_cache_symbol_table(EX(symbol_table));
 		}
-		EG(current_execute_data) = EX(prev_execute_data);
 
 		/* Free extra args before releasing the closure,
 		 * as that may free the op_array. */
@@ -2481,6 +2481,7 @@ ZEND_VM_HOT_HELPER(zend_leave_helper, ANY, ANY)
 		ZEND_VM_LEAVE();
 	} else {
 		if (EXPECTED((call_info & ZEND_CALL_CODE) == 0)) {
+			EG(current_execute_data) = EX(prev_execute_data);
 			i_free_compiled_variables(execute_data);
 			if (UNEXPECTED(call_info & (ZEND_CALL_HAS_SYMBOL_TABLE|ZEND_CALL_FREE_EXTRA_ARGS))) {
 				if (UNEXPECTED(call_info & ZEND_CALL_HAS_SYMBOL_TABLE)) {
@@ -2488,7 +2489,6 @@ ZEND_VM_HOT_HELPER(zend_leave_helper, ANY, ANY)
 				}
 				zend_vm_stack_free_extra_args_ex(call_info, execute_data);
 			}
-			EG(current_execute_data) = EX(prev_execute_data);
 			if (UNEXPECTED(call_info & ZEND_CALL_CLOSURE)) {
 				OBJ_RELEASE(ZEND_CLOSURE_OBJECT(EX(func)));
 			}
diff --git a/Zend/zend_vm_execute.h b/Zend/zend_vm_execute.h
index e893e35b6d..33518478c3 100644
--- a/Zend/zend_vm_execute.h
+++ b/Zend/zend_vm_execute.h
@@ -507,9 +507,9 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL zend_leave_helper_SPEC(ZEND_OPCODE_
 	uint32_t call_info = EX_CALL_INFO();
 
 	if (EXPECTED((call_info & (ZEND_CALL_CODE|ZEND_CALL_TOP|ZEND_CALL_HAS_SYMBOL_TABLE|ZEND_CALL_FREE_EXTRA_ARGS|ZEND_CALL_ALLOCATED)) == 0)) {
+		EG(current_execute_data) = EX(prev_execute_data);
 		i_free_compiled_variables(execute_data);
 
-		EG(current_execute_data) = EX(prev_execute_data);
 		if (UNEXPECTED(call_info & ZEND_CALL_RELEASE_THIS)) {
 			zend_object *object = Z_OBJ(execute_data->This);
 #if 0
@@ -535,12 +535,12 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL zend_leave_helper_SPEC(ZEND_OPCODE_
 		LOAD_NEXT_OPLINE();
 		ZEND_VM_LEAVE();
 	} else if (EXPECTED((call_info & (ZEND_CALL_CODE|ZEND_CALL_TOP)) == 0)) {
+		EG(current_execute_data) = EX(prev_execute_data);
 		i_free_compiled_variables(execute_data);
 
 		if (UNEXPECTED(call_info & ZEND_CALL_HAS_SYMBOL_TABLE)) {
 			zend_clean_and_cache_symbol_table(EX(symbol_table));
 		}
-		EG(current_execute_data) = EX(prev_execute_data);
 
 		/* Free extra args before releasing the closure,
 		 * as that may free the op_array. */
@@ -590,6 +590,7 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL zend_leave_helper_SPEC(ZEND_OPCODE_
 		ZEND_VM_LEAVE();
 	} else {
 		if (EXPECTED((call_info & ZEND_CALL_CODE) == 0)) {
+			EG(current_execute_data) = EX(prev_execute_data);
 			i_free_compiled_variables(execute_data);
 			if (UNEXPECTED(call_info & (ZEND_CALL_HAS_SYMBOL_TABLE|ZEND_CALL_FREE_EXTRA_ARGS))) {
 				if (UNEXPECTED(call_info & ZEND_CALL_HAS_SYMBOL_TABLE)) {
@@ -597,7 +598,6 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL zend_leave_helper_SPEC(ZEND_OPCODE_
 				}
 				zend_vm_stack_free_extra_args_ex(call_info, execute_data);
 			}
-			EG(current_execute_data) = EX(prev_execute_data);
 			if (UNEXPECTED(call_info & ZEND_CALL_CLOSURE)) {
 				OBJ_RELEASE(ZEND_CLOSURE_OBJECT(EX(func)));
 			}
@@ -55379,9 +55379,9 @@ zend_leave_helper_SPEC_LABEL:
 	uint32_t call_info = EX_CALL_INFO();
 
 	if (EXPECTED((call_info & (ZEND_CALL_CODE|ZEND_CALL_TOP|ZEND_CALL_HAS_SYMBOL_TABLE|ZEND_CALL_FREE_EXTRA_ARGS|ZEND_CALL_ALLOCATED)) == 0)) {
+		EG(current_execute_data) = EX(prev_execute_data);
 		i_free_compiled_variables(execute_data);
 
-		EG(current_execute_data) = EX(prev_execute_data);
 		if (UNEXPECTED(call_info & ZEND_CALL_RELEASE_THIS)) {
 			zend_object *object = Z_OBJ(execute_data->This);
 #if 0
@@ -55407,12 +55407,12 @@ zend_leave_helper_SPEC_LABEL:
 		LOAD_NEXT_OPLINE();
 		ZEND_VM_LEAVE();
 	} else if (EXPECTED((call_info & (ZEND_CALL_CODE|ZEND_CALL_TOP)) == 0)) {
+		EG(current_execute_data) = EX(prev_execute_data);
 		i_free_compiled_variables(execute_data);
 
 		if (UNEXPECTED(call_info & ZEND_CALL_HAS_SYMBOL_TABLE)) {
 			zend_clean_and_cache_symbol_table(EX(symbol_table));
 		}
-		EG(current_execute_data) = EX(prev_execute_data);
 
 		/* Free extra args before releasing the closure,
 		 * as that may free the op_array. */
@@ -55462,6 +55462,7 @@ zend_leave_helper_SPEC_LABEL:
 		ZEND_VM_LEAVE();
 	} else {
 		if (EXPECTED((call_info & ZEND_CALL_CODE) == 0)) {
+			EG(current_execute_data) = EX(prev_execute_data);
 			i_free_compiled_variables(execute_data);
 			if (UNEXPECTED(call_info & (ZEND_CALL_HAS_SYMBOL_TABLE|ZEND_CALL_FREE_EXTRA_ARGS))) {
 				if (UNEXPECTED(call_info & ZEND_CALL_HAS_SYMBOL_TABLE)) {
@@ -55469,7 +55470,6 @@ zend_leave_helper_SPEC_LABEL:
 				}
 				zend_vm_stack_free_extra_args_ex(call_info, execute_data);
 			}
-			EG(current_execute_data) = EX(prev_execute_data);
 			if (UNEXPECTED(call_info & ZEND_CALL_CLOSURE)) {
 				OBJ_RELEASE(ZEND_CLOSURE_OBJECT(EX(func)));
 			}