Bug 314129 – Only update page main frame's process in ProvisionalPageProxy::didCommitLoadForFrame when committing the main frame itself

• Component: New Bugs
• Status: RESOLVED FIXED

[Basuke Suzuki]

In ProvisionalPageProxy::didCommitLoadForFrame, the code assigns the provisional page's FrameProcess to the underlying page's main frame when the frame process has changed:

    bool frameProcessChanged = m_frameProcess.ptr() != pageMainFrameProcess.ptr();
    if (frameProcessChanged)
        pageMainFrame->setProcess(m_frameProcess);

This assignment is only correct when the provisional commit is for the page's main frame itself. Under Site Isolation, a provisional page may commit for a different frame (e.g., during a multi-process BFCache restoration), in which case overwriting the page main frame's FrameProcess with the provisional's FrameProcess is incorrect — it leaves the real main frame pointing to the wrong process.

Guard the setProcess call with 'pageMainFrame == m_mainFrame' so we only update the process when the provisional owns the page main frame. In paths where the provisional is for the main frame (the common case), this is a no-op.

Prep patch for rdar://173743733 (multi-process BFCache restoration under Site Isolation).

[Basuke Suzuki]

<rdar://problem/176305054>

[Basuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/64310

[EWS]

Committed 312737@main (64bbad66316c): <https://commits.webkit.org/312737@main>

Reviewed commits have been landed. Closing PR #64310 and removing active labels.