Bug 315787 – [Site Isolation] File URL approval not propagated to new process across PSON for navigations with file iframes

• Component: New Bugs
• Status: RESOLVED FIXED

[Basuke Suzuki]

When a navigation triggers a process swap (PSON) into a fresh WebContent
process under Site Isolation, the new process inherits the page's
back/forward list but its WebProcessProxy::m_previouslyApprovedFilePaths
set is empty. After commit, the new process can surface child-frame
history items via BackForwardUpdateItem IPC. The per-process file URL
approval gate at Source/WebKit/UIProcess/WebBackForwardList.cpp:768
(MESSAGE_CHECK(process, !itemURL.protocolIsFile() ||
process->wasPreviouslyApprovedFileURL(itemURL))) then trips because the
new process was only seeded with the top-level navigation URL — not with
iframe URLs from the target back/forward item's frame-state tree.

Repro: 6 of 7 sample layout tests crash UIProcess with EXC_BREAKPOINT
(MESSAGE_CHECK trap) when SiteIsolationEnabled is on by default:
 - fast/events/pageshow-pagehide-on-back-cached-with-frames.html
 - fast/history/go-back-then-navigate-subframe.html
 - fast/history/go-back-to-object-subframe.html
 - fast/history/history-back-initial-vs-final-url.html
 - fast/loader/form-state-restore-with-frames.html
 - fast/scrolling/iframe-scrollable-after-back.html

Fix: walk navigation.targetItem() and currentItem()'s frame-state trees
via copyMainFrameStateWithChildren() (mainFrameState() returns a
FrameState with cleared children — children live on
WebBackForwardListFrameItem::m_children) recursively in
continueNavigationInNewProcess. Approve both urlString and
originalURLString file URLs on newProcess before any IPC referencing them.

[Basuke Suzuki]

<rdar://problem/178185140>

[Basuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/65930

[EWS]

Committed 314518@main (ceb4d817be51): <https://commits.webkit.org/314518@main>

Reviewed commits have been landed. Closing PR #65930 and removing active labels.