Null pointer dereference in g_markup_parse_context_end_parse()

Submitted by Jin @JsHuang

Link to original bug (#795147)

Description

Created attachment 370763 simple test case to reproduce the bug

Function g_markup_parse_context_end_parse() dosen't call current_element() function carefully. and can cause null pointer dereference error while parsing an malformed input.

The definition of function current_element() is as below:

static inline const gchar* current_element (GMarkupParseContext *context) { return context->tag_stack->data; // context->tag_stack may be NULL; }

This bug resides in gmarkup.c ,near line 1837, in case "STATE_AFTER_CLOSE_TAG_NAME":

1834 case STATE_AFTER_CLOSE_TAG_NAME: 1835 set_error (context, error, G_MARKUP_ERROR_PARSE, 1836 _("Document ended unexpectedly inside the close tag for " 1837 "element '%s'"), current_element (context)); 1838 break;

here set_error is called and use the return value of "current_element (context)" as it's parameter, without checking whether "context->tag_stack" is NULL or not. Parsing invalid data may lead to null pointer dereference.

I think this bug may exits in other place where current_element() is not carefully called, a good way to fix it is to add an assertion in current_element().

The attachment is a simple test case to reproduce it.

credit: ADLab of Venustech

Attachment 370763, "simple test case to reproduce the bug":
current_element.c

Version: 2.56.x