xen/evtchn: avoid WARN() when unbinding an event channel

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: xen/evtchn: avoid WARN() when unbinding an event channel When unbinding a user event channel, the related handler might be called a last time in case the kernel was built with CONFIG_DEBUG_SHIRQ. This might cause a WARN() in the handler. Avoid that by adding an "unbinding" flag to struct user_event which will short circuit the handler.

References

• https://git.kernel.org/stable/c/99e425032c6ec13584d3cd33846e0c7307501b47
• https://git.kernel.org/stable/c/35485dad6e28f9b17884764d4692b1655cb848d0
• https://git.kernel.org/stable/c/9e2d4b58c1da48a32905802aaeadba7084b46895
• https://git.kernel.org/stable/c/51c23bd691c0f1fb95b29731c356c6fd69925d17